Pseudotrichonympha grassii numbers in dealate hindguts was determined. In addition, Illumina 16S rRNA gene sequencing and the QIIME2 pipeline were used to determine the impact of those three factors on gut bacteria diversity of dealates. Here we report that pairing status was significantly affected by weight and total protozoa numbers, but not by P. grassii numbers and bacteria diversity. Weight and total protozoa numbers were higher in paired compared to single dealates. Males contained significantly higher P. grassii numbers and bacteria richness and marginally higher phylogenetic diversity despite having lower weights than females. In conclusion, this study showed that dealates with high body weight and protozoa numbers are more likely to pair and become colony founders, probably because of competitive advantage. The combined nutritional resources provided by body weight and protozoa symbionts of the parents are important for successful colony foundation and development.New colonies of Formosan subterranean termites are founded by monogamous pairs. During swarming season, alates (winged reproductives) leave their parental colony. After swarming, they drop to the ground, shed their wings, and male and female dealates find suitable nesting sites where they mate and become kings and queens of new colonies. The first generation of offspring is entirely dependent on the nutritional resources of the founder pair consisting of the fat and protein reserves of the dealates and their microbiota, which include the cellulose-digesting protozoa and diverse bacteria. Since termite kings and queens can live for decades, mate for life and colony success is linked to those initial resources, we hypothesized that gut microbiota of founders affect pair formation. To test this hypothesis, we collected pairs found in nest chambers and single male and female dealates from four swarm populations. The association of three factors  with dealate weights, total protozoa, and protozoa  Coptotermes formosanus Shiraki (Blattodea: Rhinotermitidae), is a species in the family Rhinotermitidae, which belongs to the so-called lower termites . It is one of the most destructive and invasive termite species in the world, causing billions of dollars of damage to structures and crops globally each year [C. formosanus colonies consume only lignocellulose material, mainly in the form of wood [The Formosan subterranean termite, ach year , 2. Like of wood . Cellulo of wood , 5. All  of wood . Protozo of wood –9 and pr of wood  to compl of wood . Bacteri of wood –14. In a of wood , 16.C. formosanus workers [C. formosanus workers harbor three genera of protozoa; however, the number of species was increased to five [Initially, three protozoa species and genera were described from the guts of  workers –19. A re to five .C. formosanus workers have functional niches. Members of the largest gut protozoa species, Pseudotrichonympha grassii (Trichonymphidae), consume wood particles via phagocytosis and degrade them [The protozoa species in the guts of ade them , 21, 22,ade them , 18, 23.In addition to the five protozoa species, at least 213 different bacterial species were identified in Formosan subterranean termite workers via clone-based 16S rRNA gene sequencing , 24, 25 While extensive research has been conducted on eukaryotic and prokaryotic symbionts in the worker caste of termites, limited knowledge exists regarding symbionts associated with the reproductive caste. Given the importance of termite gut symbionts in colony nutrition, protozoa and/or bacteria are likely to play a crucial role in the establishment of new termite colonies.Subterranean termite colonies are founded by a pair of winged reproductives  during swarming season. These alates carry essential microbes acquired from their natal colony , 34 as tNumerous studies have investigated what factors impact the successful survival and growth of incipient colonies, including environmental conditions –50 and cGiven the important dual role of the microbial symbionts in incipient colony nutrition, it is surprising that the potential impact of gut symbionts on pair formation of dealates at the earliest stage of colony initiation has not yet been explored. So far, it has been shown that size, weight and genetic diversity of dealates play a role in pair formation via competitive advantage and/or mate choice, depending on the species of termite , 45, 60,C. formosanus founder pairs and dealates that remained single using 16S rRNA gene sequencing to test whether there is a difference in weight, protozoa numbers and/or bacterial diversity between paired and unpaired and male and female dealates from different populations.In this study, we hypothesized that the founder pair carries a core microbiota consisting not only of the obligate protozoan symbionts, but also essential bacteria, and that pair formation is influenced by the body weight as well as by the composition of protozoa and/or bacteria. In contrast to previous studies that used tandem running pairs, which might still change partners, we investigated pairs that had sealed themselves in incipient nest chambers and, thus, represented the final founder pair. We determined weight and protozoa numbers and described the diversity of bacterial taxa in the guts of Coptotermes formosanus alates were collected in May 2021 from different locations in Louisiana separated by at least 4 km, which exceeds the swarming distance [Four populations of distance , 61. Thedistance .Pseudotrichonympha grassii, were counted in 10 μl of the solution using a Leica DM750 microscope. Protozoa counts were replicated three times and multiplied by 100 to determine the protozoa number per gut. The percentage of P. grassii  was also calculated. Protozoa numbers of the population BG were counted before the decision was made to count P. grassii separately; therefore, no P. grassii numbers or percentages were available for this population. Following confirmation of normal distribution of the data we assessed the effects of pairing status, sex of the dealates, and population on weight, total protozoa number, P. grassii number and percentage of P. grassii. We first performed univariate tests, i.e., two-tailed, unpaired t-tests with Welch’s correction  for the factors pairing status and sex, and a one-way ANOVA for the population factor significances. Interactions of the factors were further tested with multivariate analysis of variance (MANOVA). A factor was only considered to be significant when both MANOVA and univariate tests showed significance (P < 0.05). Box-and-whisker plots were created using GraphPad Prism version 8.0.0 . To determine whether there was a correlation between body weight and protozoa numbers, we conducted Spearman correlation tests in R [Eighty dealates were selected for the study consisting of twenty paired and unpaired male and female dealates from the four populations . Prior tsts in R . The Spe™, life technologies™, CA). Aliquots of 10 μl containing 25 ng of extracted DNA from each sample were sent to University of New Hampshire Hubbard Center for Genome Studies for next-generation sequencing.The remaining gut content was homogenized with a sterile pestle and total DNA was extracted using the Dneasy Blood and Tissue kit . The concentration of extracted DNA was confirmed using an Invitrogen Qubit 4 Fluorometer  with the Qubit dsDNA BR Assay kit  as described in previous studies . The ampBioinformatics was performed using QIIME2 (version 2022.2) , followiThe total sequence depth (number of reads) usually varies widely between samples. In order to test for sufficient sequencing depth and compare samples at the same sequencing depth for diversity analysis, alpha rarefaction implemented in QIIME2 was used to subsample sequence reads without replacement to the common sequencing depth that was equal to the sample with the lowest sequencing depth . The qiiThe ASVs were taxonomically classified by comparing them to bacterial 16S rRNA sequences in the SILVA 138 database using BLAST . All eukP. grassii numbers and percentages were correlated to bacterial ASV richness (number of ASVs) and abundances based on the rarefied number of sequence reads of ASVs using the Spearman’s rank correlation test in R (version 4.2.2). Similarly, the number of rarefied reads of highly abundant bacteria in our dataset that were identified by previous studies as putative protozoa symbionts were correlated to protozoa numbers to test for associations.To evaluate alpha diversity  of all bacterial ASVs, both incidence-based measures (ASV richness and Faith’s PD), and abundance-based indices (Pielou’s evenness and Shannon diversity) were employed. The ASV richness metric quantifies the number of distinct taxa or genetic variants present in a sample and provides a measure of taxonomic diversity . Faith’sBeta diversity  was evaluated using four indices for creating distance matrices consisting of two incidence-based measures, Jaccard  and UnweP. grassii, and the percentage of P. grassii, is available in The raw data, including information on termite dealates such as weight, total protozoa number, number of Body weight varied significantly with pairing status and sex of the dealates. Paired dealates and females had higher body weights . The significant interaction between pairing status and population  and SG (P = 0.0005) populations but not in the BB population (P = 0.7423). Number of total protozoa, P. grassii and percentage of P. grassii were not correlated between paired males and their female partner . Although males were found to carry more total protozoa than females  as opposed to MANOVA (P = 0.032).Male dealates had significantly higher P. grassii numbers or percentages ; P = 0.0093 (BB vs BG); P = 0.035 (BB vs SG)), but not in centages . The MANP. grassii counts, and percentage of P. grassii , but the extrapolated portions of the richness curves continued to increase with additional samples. However, the curves for the effective diversity of the Shannon and Simpson inverse indices only minimally increased with doubling the sample size, which indicates that all common ASVs within the dealates’ gut bacterial community were collected  generated in this study, 624 ASVs  were bacteria that matched to references in SILVA with ≥ 97% similarity. The rest of the ASVs were filtered out because they were either assigned to Eukaryotes  or remained unassigned  due to the absence of close references in the SILVA database.The 624 identified bacterial ASVs belonged to 19 bacterial phyla across all dealate gut samples . The topAt the order level, a total of 67 bacterial orders were identified. Bacteroidales was the most dominant order, accounting for 50.25% of the total bacterial abundance, followed by Spirochaetales (11.42%), Lactobacillales (9.30%), Burkholderiales (9.06%), Pseudomonadales (7.33%), Rickettsiales (4.03%), Desulfovibrionales (1.41%), Peptostreptococcales-Tissierellales (1.12%) and RsaHf231 (1.19%) of the Firmicutes. These top 9 orders, each with > 1% abundance, contained over 95% of identified bacterial reads .Candidatus Azobacteroides, Candidatus Armantifilum, Treponema uncultured Spirochaetes, Pilibacter termitis, Candidatus Vestibaculum, Termite Treponema cluster, Pseudomonas sp., RsaHf231 uncultured bacterium, Acinetobacter pittii, Ralstonia sp., and Enterobacter sp.  did not have Ca. Azobacteroides. Almost twice the number of dealates without Ca. Azobacteroides were found among the unpaired dealates  as compared to paired samples. In almost all pairs, both partners (in 36 pairs) or at least one of the partners (in 3 pairs) carried Ca. Azobacteroides. There was only one pair of dealates from the SG population where both partners lacked Ca. Azobacteroides. The abundance of Ca. Azobacteroides was positively correlated with the numbers of its host protozoa P. grassii , and also with total protozoa number .The most abundant genus, Ca. Armantifilum numbers were not correlated with P. grassii numbers , its abundance was correlated to total protozoa number ; however, Ca. Vestibaculum abundance was not correlated to either measure of protozoa abundance (P > 0.2260) indicating that this ASV was not associated with protozoa.We further tested if there is a correlation between protozoa number and the abundance of other dominant bacteria previously identified as putative protozoa symbionts  from the Ca. Armantifilum (Acc. No. FN377751-FN377758) and Ca. Vestibaculum (AY540335) reference sequences of NCBI; however, they matched to several termite-related uncultured Bacteroidetes bacteria. For example, the Ca. Armantifilum ASVs matched with ≥98% to GQ502508.1 and GQ502483.1 in C. formosanus and KP690878.1 in C. curvignathus; the Ca. Vestibaculum ASVs matched 100% to GQ502489.1 and 98% to GQ502490.1 sequences of C. formosanus in the NCBI database.While BLAST analysis against NCBI reference database confirmed most SILVA taxonomic assignments, our Treponema spirochetes and P. termitis, environmental bacteria, e.g., Pseudomonas, Ralstonia and Enterobacter species, were less abundant overall and largely restricted to specific populations and individual samples.Unlike the termite-specific bacterial symbionts, including the candidate genera, Pairing status had no significant effect on the bacterial richness, diversity, or phylogenetic distance among ASVs of the dealate samples , but both ASV metrics were not correlated to dealates’ weight and percentage of P. grassii. Moreover, Shannon diversity, Pielou’s evenness and Faith’s PD of bacteria communities were not correlated to any of the protozoa counts or delalate weight  and number of ASVs, i.e., bacteria richness, was significantly correlated to Both multiple-factor ADONIS analysis  and marginal differentiation when phylogenetic distance was taken into account ; however, this difference was not observed when considering the relative abundance of bacteria (P ≥ 0.294 for Bray-Curtis and Weighted Unifrac indices)  and Pilibacter  have been previously recognized as dominant bacteria in the worker caste [C. formosanus workers previously collected from Louisiana [Treponema is the most abundant spirochete genus in subterranean termite guts [Treponema are known for H2-CO2 acetogenesis [Treponema is thought to support cellulose digestion in protozoa [Other dominant bacteria in dealates, such as the genera er caste , 28, 105ouisiana  and Trepite guts . Membersogenesis  and nitrogenesis . The ferprotozoa .Pilibacter termitis , a species cultured and described from C. formosanus workers [C. formosanus worker guts [Pilibacter species by sequence identity [Pilibacter and Treponema species were reported at high abundance as free-living bacteria in C. gestroi workers [ workers  was highker guts , 25 wereidentity , 109 aft workers .The presence of core bacteria in dealates and their similarity to the worker caste is expected for two reasons. Firstly, alates obtain their symbionts, i.e., protozoa and bacteria, after their molt to imago from the workers of the natal colony via proctodeal trophallaxis , 34. SecP. grassii protozoa counts in male compared to female guts. Higher protozoa numbers may result in more niches for bacteria in male guts, which is supported by the observed correlation of bacteria richness and abundance with P. grassi and total protozoa numbers, respectively. This especially pertains to the protozoa associated bacterial symbionts, whose numbers correlated with the numbers of their putative protozoa host. Moreover, the explanations for higher P. grassii numbers in males also apply to the increased bacteria diversity and abundance, including male-biased nutrition contributions [The significantly higher bacterial richness, marginally higher phylogenetic diversity in male dealates and differentiation in beta diversity between the sexes based on presence/absence of bacterial taxa might be explained by the higher ibutions , 82, 86.ibutions , colony In contrast to weight and protozoa numbers, neither bacterial alpha nor beta diversity had any effect on pair formation. This suggests that the bacteria community at the time of colony initiation is of less nutritional importance than the proteins and lipids provided by protozoa and the alates’ fat body. Nevertheless, our study showed that the core phyla and expected dominant taxa were present in dealates as “starter package” to inoculate the first brood, regardless of bacterial diversity. Follow-up studies are currently underway to investigate how bacterial communities in founder pairs change over the course of early colony development and if their dynamics is associated with observed spikes in protozoa numbers .The observed differences in weight and protozoa numbers between paired and unpaired delates raise the question of whether active mate choice is at play and how dealates could recognize these differences in potential partners. Alternatively, high weight and protozoa numbers could confer competitive advantage for getting access to partners which would not necessarily require partner assessment.C. formosanus dealates, since no correlation was observed between weight and protozoa numbers or between weight and bacteria diversity. Similar to the results for weight, protozoa numbers and P. grassii percentage were also higher in paired dealates with no correlation among partners.Weight can be easily assessed visually or by antennation during tandem-running and some studies have reported a positive correlation in size and/or weight between partners , 85. HowC. formosanus and C. gestroi males occasionally mate with females of the opposite species might also indicate that there is a lack of diligent partner assessment [C. gestroi males increased their movement speed when searching for a partner in the presence of competition. Faster movement requires higher energy expenditure and, therefore, more fat and protein reserves.The lack of correlation of the respective weights and protozoa numbers between partners suggests that the observed prevalence of dealates with larger weight and protozoa numbers in pairs might not be caused by stringent mutual mate choice, i.e., weight–and symbiont-biased assessment of potential partners. Moreover, predators and environmental pressures likely select for rapid pair formation with limited opportunity to carefully assess and change partners , 50. Thesessment . Insteadsessment  study shS1 File(XLSX)Click here for additional data file.S2 File(XLSX)Click here for additional data file.S3 FileCoptotermes formosanus alate collection in the field and paired dealate collection from corrugated cardboard nest chambers. S2 Fig. Sequence-based rarefaction curves of the bacterial diversity of each sample measured by ASV richness, Faith’s PD and Shannon indices. S3 Fig. Sample- and coverage-based rarefaction curves across all dealate samples.(DOCX)Click here for additional data file.S4 FileP. grassii number and percentage of P. grassii separated by pairing status, sex, and population. S2 Table. Spearman’s rank correlations for dealate weights and protozoa counts. S3 Table. Nineteen bacterial phyla detected across all dealate samples. S4 Table. Correlation analysis (Spearman’s rank test) of protozoa abundance in C. formosanus dealates with rarefied number of reads of previously reported putative symbiotic bacteria of protozoa in termites. S5 Table. Impact of pairing status, sex, and population on alpha diversity of dealate gut bacterial communities. S6 Table. Correlation of dealates’ weight, total protozoa number, P. grassii number, and percentage of P. grassii protozoa to bacterial alpha diversity metrics. S7 Table. Effects of pairing status, sex and population on bacterial beta diversity of dealates. S8 Table. Single factor beta diversity analyses using PERMANOVA (999 permutations) and PERMDISP (1000 permutations).Dealates’ weight, total protozoa number, (DOCX)Click here for additional data file.


In the context of the coronavirus pandemic, countless face-to-face events as well as medical trainings were cancelled or moved to online courses, which resulted in increased digitalization in many areas. In the context of medical education, videos provide tremendous benefit for visualizing skills before they are practised.Based on a previous investigation of video material addressing epidural catheterization available on the YouTube platform, we aimed to investigate new content produced in the context of the pandemic. Thus, a video search was conducted in May 2022.We identified twelve new videos since the pandemic with a significant improvement in the new content in terms of procedural items (p = 0.03) compared to the prepandemic video content. Video content released in the course of the COVID-19 pandemic was more often created by private content creators and were significantly shorter in total runtime than those from university and medical societies (p = 0.04).The profound changes in the learning and teaching of health care education in relation to the pandemic are largely unclear. We reveal improved procedural quality of predominantly privately uploaded content despite a shortened runtime compared to the prepandemic period. This might indicate that technical and financial hurdles to producing instructional videos by discipline experts have decreased. In addition to the teaching difficulties caused by the pandemic, this change is likely to be due to validated manuals on how to create such content. The awareness that medical education needs to be improved has grown, so platforms offer specialized sublevels for high-quality medical videos.The online version contains supplementary material available at 10.1186/s12909-023-04409-8. We found that new educational videos created during the pandemic were improved in terms of procedural quality even though they mostly came from private content creators. However, it remains unclear to what extent this extent this trend was maintained. Platforms containing prior review mechanisms seem promising.The training of medical students is in a constant state of transformation . This isThe COVID-19 pandemic was a caesura in many areas of life. To prevent the spread of infections, many governments worldwide decided to impose far-reaching restrictions on freedom of assembly. In addition to restrictions on sports and recreational events, which were prominently discussed in public, corresponding regulations also applied to medical training and teaching events in attendance , 15. In In modern anaesthesiology, neuroaxial procedures are among the established and most frequently used methods of peripartum and procedural analgesia. Discovered at the turn of the century by August Bier, this extraordinarily effective technique for reducing birth pain has become indispensable . Recent Based on a preliminary investigation of the quantity and quality of available video material on the public video platform YouTube regarding epidural catheterization, we aimed to investigate the current pandemic video material . Within The study was conducted according to the ethical principles of the Helsinki Declaration  . Since thttps://www.youtube.com), a search was conducted analogous to the previous investigation in May 2022 in the German and English languages using the same search terms. The terms “epidural” and “peridural” were collected individually and in combination with the keywords “birth”; “obstetrics”; “delivery”; “catheter”; “anesthesia” and “anaesthesia”. Over 500 videos were examined by independent investigators regarding their suitability to demonstrate peridural anaesthesia. Twelve videos were acquired for study purposes . For each video, the uploader/producers, date of upload, and runtime were recorded for analysis purposes. In addition, the videos were categorized according to the content creators. For this purpose, a consensus was reached among the investigators to categorize the creators of the content into one of three groups: university/ medical association, clinic/ medical business provider, and private content creator.To find suitable newly published video material on the YouTube Platform  with a total of 20 items ordinally scaled from 0 (inapplicable) through 1 (incorrect) to 2 (fully met). A second didactic checklist section with 4 subcategories and a total of 21 items using a five-point Likert scale completed the assessment. The differentiated questionnaire development as well as structure and validation process have already been published and can be accessed open access (10.3390/jcm11061726) .Data were collected using Windows Excel . A statistical analysis plan was designed prior to the study. Data analysis was conducted using SPSS . Data with continuous scales are presented as mean (± standard deviation), and data with categorical scales are presented as frequencies and percentages. Interrater reliability was analyzed using a intraclass correlation coefficient. Correlations were examined with a Spearman’s rho test, as well as a Mann-Whitney U test. A p-value of < 0.05 was considered statistically significant.We found that twelve new videos were published during the study period. The video characteristics in terms of the fulfilment of the procedural and didactic requirements for items of the established questionnaire are shown in Fig. The comparison of the content of the video material produced with regard to didactic aspects showed no significant improvement overall in the content produced in the context of the pandemic (p = 0.837). The analysis of the individual items showed that there was a partly significant improvement with regard to the subject-related items. Similarly, a few significant improvements as well as deteriorations in the didactic section could be found. A list of trends and significant changes in the individual items can be found in Table The statistical evaluation of the correlation coefficient showed no difference in the still very good interrater reliability (prepandemic p = 0.975 vs. pandemic and after p = 0.974) , 28.We were able to identify twelve new videos regarding peridural catheterization over the course of the pandemic. Although the runtime of the videos was decreased, there was a tendency towards an improvement in quality. In addition, there was a marked increase in the amount of private content created and uploaded over the course of the pandemic. The fact that the COVID-19 pandemic profoundly changed learning and teaching worldwide is unquestioned. However, it is largely unclear what long-term changes in education will arise from this fact . In the By comparison, the video content we analysed in the pandemic context showed a decreased average running time, which may be attributed to the increased representation of private content creators. Thus, the increased procedural quality of the videos seems interesting. Prepandemic videos showed a significant correlation between longer runtimes and the quality of the content as well as the didactic quality. However, experts agree that a video should not be too long since the limit of expected working memory capacity is only approximately ten minutes . In the We were able to demonstrate a significant improvement in the procedural content quality of the newly created video material that could not be shown for the didactic questionnaire section. While significant improvements or trends could be found in the majority of items, a deterioration was revealed with regard to the procedural item of “postinterventional vital monitoring” (p = 0.059) and the didactic items “abbreviations avoided or explained” (p = 0.011) and “referencing background information” (p = 0.029). The cause of this deterioration remains largely unclear. The focus of the predominantly private content creators may be more towards their followers and thus a specialized audience, so the increasing use of medical terms and abbreviations could be explained. In this case, suitable referencing would also be appropriate; however, this also significantly decreased. Considering only the improved procedural content quality, it appears that awareness of the need for online-based learning has grown, but training in the creation of more professional instructional videos is still lagging. There are now several validated manuals for creating high-quality instructional video material as well as corresponding public resources ) . Not to It is becoming increasingly apparent that in addition to the quantity of available information and video material, the quality of both content and didactic aspects is of increasing importance. In this regard, in addition to the questionnaires we used, the open educational resource movement has determined important points of presentation, especially for public video material . Regardihttps://health.youtube/), which aims to provide a platform on which high-quality medical knowledge can be shared via video. Under the claim “We are working on ways to expand eligibility to our health features on YouTube to better connect users with health sources”, the program is an attempt by the company to cooperate with large, respected organizations such as the American Heart Association, the New England Journal of Medicine, the World Health Organization (WHO) and many others [The awareness that the visibility of professional medical training material in terms of quality and reliability needs to be improved has grown beyond the world of medical educational experts. One of the most exciting projects is the decision of the Alphabet consortium to expand the YouTube platform to add YouTube Health (y others . It willy others , 37.The findings of our analysis are limited because the search was conducted exclusively for videos related to a single medical skill. Although epidural catheters are a common topic of video content, there are few videos on teaching catheter placement, so our study could only include twelve new videos. In addition, only material available at the time of the study could be considered, and the extent of projects currently producing new educational videos could not be taken into account.We found that within the pandemic situation, twelve new videos were uploaded on YouTube regarding epidural catheter placement. These videos were significantly improved in terms of the procedural item section when compared using a validated questionnaire, although the majority of the new videos were uploaded by private content creators. However, it remains unknown to what extent there is a trend towards increasingly privately created educational content with equally high quality. Adequate control mechanisms based on prior review processes seem to be promising with regard to specific subplatforms.Below is the link to the electronic supplementary material.Supplementary Material 1


Materials appended with primary,secondary-diamines featuring bulky substituents,in particular, exhibit excellent stabilities and CO2 adsorptionproperties. However, these frameworks display double-step adsorptionbehavior arising from steric repulsion between ammonium carbamates,which ultimately results in increased regeneration energies. Herein,we report frameworks of the type diamine–Mg2(olz)(olz4– = (E)-5,5′-bis(2-oxidobenzoate))that feature diverse diamines with bulky substituents and displaydesirable single-step CO2 adsorption across a wide rangeof pressures and temperatures. Analysis of CO2 adsorptiondata reveals that the basicity of the pore-dwelling amine—inaddition to its steric bulk—is an important factor influencingadsorption step pressure; furthermore, the amine steric bulk is foundto be inversely correlated with the degree of cooperativity in CO2 uptake. One material, ee-2–Mg2(olz) , adsorbs>90% of the CO2 from a simulated coal flue stream andexhibitsexceptional thermal and oxidative stability over the course of extensiveadsorption/desorption cycling, placing it among top-performing adsorbentsto date for CO2 capture from a coal flue gas. Spectroscopiccharacterization and van der Waals-corrected density functional theorycalculations indicate that diamine–Mg2(olz) materialscapture CO2 via the formation of ammonium carbamate chains.These results point more broadly to the opportunity for fundamentallyadvancing materials in this class through judicious design.Diamine-appended Mg Approximately 60–70% of the total cost of CCSis associated with CO2 capture,7 resulting in an urgent need for novel CO2 capture materialswith high CO2 selectivities, large separation working capacities,and low regeneration energies. Target gas streams for carbon capturealso contain different concentrations of CO2 dependingon the point source. For example, a typical flue gas composition froma coal-fired power station contains 15–16% CO2,while natural gas combined cycle power plants produce flue gas witha lower CO2 concentration of ∼4%.9 Beyondthe power sector, upgrading crude biogas to biomethane requires captureof CO2 at higher concentrations (30–60%) from CH4, and the cement industry produces waste gas streams with∼30% CO2.11Anthropogenic carbon dioxide emissionsare largely responsiblefor the deleterious global warming measured to date above preindustriallevels, and this warming is rapidly approaching the 1.5 °C increasethat is predicted to cause a global climate crisis.2 capture, and these operateby selectively absorbing CO2 to form ammonium carbamateand bicarbonate species.12 However, suchsolutions exhibit low working capacities and high regeneration energies,are susceptible to oxidative and thermal degradation,15 and can cause significant carbon steel corrosion.16 Porous materials including activated carbons and zeoliteshave been investigated as alternatives for CO2 separations,owing to their large internal surface areas, high adsorption capacities,robust structures, and relatively low regeneration energies.23 However, most porous materials are not suitable for industrial separationsdue to the fact that water vapor in flue gas outcompetes CO2 at the material binding sites.23 To address this issue, amine-functionalized silicas28 and metal–organic frameworks (MOFs)30 have been developed as promising alternatives. Analogous to theselective chemisorption of CO2 in aqueous amine solutions,in these materials, the appended amines selectively react with CO2 to form ammonium carbamate and/or bicarbonate species, evenin the presence of water vapor.29Aqueous aminesolutions represent the current state-of-the-arttechnology for postcombustion CO2(dobpdc) 42 exhibit exceptional selectivities and capacities for CO2, arising from a unique cooperative adsorption mechanism whereinCO2 molecules insert into the framework metal–aminebonds to form ammonium carbamate chains that propagate down the one-dimensionalchannels  materials that are remarkablystable even to steam regeneration.43 Todate, the most prevalent strategy for tuning the threshold for CO2 adsorption in diamine–Mg2(dobpdc) materialshas been to vary the diamine, and the CO2 adsorption propertiesof Mg2(dobpdc) appended with primary,secondary -, primary,tertiary -, and secondary,secondary -diamines have beenstudied in detail. Materials featuring 1°,2°-diamines haveemerged as frontrunners for applications in CO2 capturefrom coal  flue gas, given their thermal stabilitiesand low CO2 adsorption pressures under isothermal conditions.38Among such materials,alkyldiamine-functionalized frameworks ofthe type diamine–Mgchannels 1a.32 Thi2(dobpdc) materials,increasing the steric bulk of the pore-dwelling secondary amine hasbeen shown to further enhance stability to adsorption/desorption cycling.38 However, these frameworks exhibit CO2 adsorption profiles with two steps rather than one, which has beenattributed to steric conflict between adjacent ammonium carbamatechains in the ab crystal plane due to the asymmetricpore structure. This phenomenon limits the overall CO2 capacityunder a given set of conditions and leads to higher regeneration energies.38 Changing the base framework from Mg2(dobpdc) to Mg2(pc-dobpdc) or Mg2(dotpdc) alleviates the steric conflict, giving rise to materials that exhibitsingle-step CO2 adsorption profiles.38 However, as a result of the larger size of the dotpdc4– linker, diamine–Mg2(dotpdc) materialsdisplay gravimetric capacities lower than diamine–Mg2(dobpdc) materials. Furthermore, an expensive palladium catalystis required for the synthesis of H4pc-dobpdc and H4dotpdc linkers, rendering the corresponding amine-appendedframeworks impractical for large-scale use.For 1°,2°-diamine-appended Mg2(dobpdc) materials,we were interested in identifying a MOF that, when appended with diamines,would exhibit robust, tunable single-step CO2 adsorptionunperturbed by changes to the steric bulk of the pore-dwelling amine.We chose to investigate Mg2(olz)  previously developedas a biocompatible platform for drug delivery.44 Of note, the olz4– linker is slightlylonger than dobpdc4– but shorter than dotpdc4–, and its synthesis does not require the use of anexpensive precious metal catalyst. Herein, we report a family of diamine–Mg2(olz) frameworks that exhibit cooperative CO2 uptakefor a range of 1°,1°-, 1°,2°-, and 1°,3°-diamines,as well as higher volumetric capacities than related materials preparedwith Mg2(dotpdc).38 Importantly,all the diamine–Mg2(olz) materials exhibit single-steppedadsorption behavior, including those appended with bulky 1°,2°-diamines,in contrast to previously reported diamine–Mg2(dobpdc)analogues.35 Further, by tuning the diaminesteric bulk and the basicity of the pore-dwelling amine, it is possibleto tune the CO2 step pressure of diamine–Mg2(olz) over three orders of magnitude, and as such these materialsexhibit unparalleled versatility for CO2 capture from numeroustarget emission streams. The variant ee-2–Mg2(olz)in particular exhibits exceptional CO2 adsorption propertiesrelevant to carbon capture from coal flue gas.Seeking to overcomethe aforementioned limitations of the bulky1°,2°-diamine-appended Mg2(olz) was prepared via a modified versionof the previously reported synthesis .44 Diamine grafting was accomplishedby soaking methanol-solvated Mg2(olz) with the diamineof choice in toluene for several hours. We selected one 1°,1°-diamine,1,2-diamino-2-methylpropane (dmen),36 and eight1°,2°- and 1°,3°-diamines featuring variouslysubstituted secondary or tertiary amines (2(olz) frameworks for CO2 capture and the impact of diamine structure on CO2 adsorptionperformance. We adopt a previously described shorthand33 for each diamine that first specifies the alkylsubstituent(s) on the pore-dwelling amine, the number of carbons inthe alkyl bridge, and the substituent on the metal-bound amine (asrelevant). For example, the shorthand for the 1°,2°-diamine N,N-dimethylethylenediamine is mm-2. Previousanalysis of the structures of several diamine–Zn2(dobpdc) variants using single-crystal X-ray diffraction revealedthat 1°,2°- and 1°,3°-diamines typically bindto the framework metal sites via the primary amine,33 and this is presumed to be the case for diamine–Mg2(olz) as well. Langmuir surface areas were calculated from77 K N2 adsorption data, and diamine loadings were confirmedby 1H NMR spectroscopy analysis of digested framework samples. The materialsform as microcrystalline solids  with decomposition temperatures exceeding 200 °C .The framework Mgy amines 1 to rigo2 adsorption isobarsand CO2 adsorption isotherms were collected for the diamine–Mg2(olz) compounds under an atmosphere of pure CO2. All variants exhibit step-shaped CO2 uptake under isobaricand isothermal conditions , consistentwith cooperative adsorption and ammonium carbamate chain formation.38 The frameworks also retain their crystallinity and underlying structureupon pure CO2 adsorption, as determined from insitu powder X-ray diffraction analysis . For each material, the CO2 uptake underisobaric conditions begins to plateau near the theoretical capacityof one CO2 molecule per diamine  frameworks exhibit single-step adsorption profiles,regardless of the size of the alkyl substituent on the pore-dwellingamine . In contrast,prior work has shown that p-2-, i-2-, 3-pent-2-, and dmen-appendedMg2(dobpdc) exhibit double-stepped adsorption behavior,36 and CO2 adsorptionto full capacity (one CO2 per diamine) in the case of dmen–Mg2(dobpdc) is also kinetically limited,36 which is not the case for dmen–Mg2(olz). We attributethe single-step behavior for these diamine–Mg2(olz)materials to the absence of steric hindrance between neighboring ammoniumcarbamate chains formed upon CO2 uptake.Thermogravimetric COnditions S8, consi2 adsorption step temperaturesfor diamine–Mg2(olz) range from 35 to 135 °C(2(dobpdc) counterparts exhibiting two-stepped adsorption, itis challenging to make any direct comparisons. However, the relativestep positions for diamine–Mg2(olz) trend with thefirst adsorption step positions for the corresponding diamine–Mg2(dobpdc) materials. In the case of p-2– and i-2–Mg2(olz), adsorption occurs at a slightly higher temperaturethan initial adsorption in p-2– and i-2–Mg2(dobpdc),38 while the opposite is truefor 3-pent-2–38 and dmen–Mg2(olz).36 Relative to diamine–Mg2(dobpdc) variants exhibiting single-stepped adsorption , the corresponding diamine–Mg2(olz) variants again generally exhibit consistent trends—1°,2°-diamine-appendedvariants adsorb CO2 with step temperatures above 120 °C,while 1°,3°-diamine-appended variants adsorb CO2 with step positions below 70 °C.33 Finally, for diamine–Mg2(olz), the step pressureat 40 °C can be tuned over three orders of magnitude, from 0.2to 200 mbar  exhibit step pressures below 150mbar, and as such, they are all potential candidates for CO2 capture from a coal flue gas.The COo 135 °C2a. Given200 mbar 2b. Signi2(olz) variants featuring1°,2°-diamines, increasing the secondary amine alkyl chainlength from one carbon (m-2) to three carbons (p-2) has little effecton the CO2 step pressure (defined here as the inflectionpoint of the adsorption step), which changes from 10.2 to 13.9 mbarat 85 °C  to 52.6 mbar for 3-pent-2–Mg2(olz)(2 uptake(discussed further below).45 Overall, theincreasing step pressure in the adsorption isotherms  with increasing substituent size is consistent with weakerammonium carbamate ion pairing as the secondary amines become moresterically encumbered.37In the case of diamine–Mgat 85 °C 3a. In coMg2(olz)3b. Along2(olz) materials, there is not a consistent correlation betweentheCO2 step pressure and the steric bulk of the tertiary aminesubstituent (2(olz) is higher than that of mm-2–Mg2(olz) (174versus 38.7 mbar) at 25 °C, as might be expected based on sterics,the step pressure for ee-2–Mg2(olz) is lower thanthat of mm-2–Mg2(olz) (13.8 versus 38.7 mbar), eventhough ee-2 features bulkier alkyl groups. It is also interestingto compare the isothermal (40 °C) step pressures for e-2–,dmen–, and mm-2–Mg2(olz), which feature diamineswith the same overall number of carbon atoms but differing degreesof steric bulk. Based on steric hindrance alone, we might expect thatdmen–Mg2(olz) would exhibit the lowest step pressure;however, its step pressure (10.2 mbar) is intermediate between thoseof e-2– and mm-2–Mg2(olz) .Interestingly, for 1°,3°-diamine–Mgstituent 3c. Indee2 adsorption properties of diamine–Mg2(olz), although these aspects alone do not fully explain thetrends observed. Another important factor is the basicity of the pore-dwellingamine, which abstracts a proton from the metal-bound amine concomitantwith CO2 insertion.32 We thereforesought to investigate whether there is any correlation between thebasicity of the free amine and the observed step pressure or temperaturefor CO2 adsorption. To this end, we generated a seriesof monoamines to represent the pore-dwelling primary, secondary, ortertiary amine (Table S3) by replacingthe metal-bound primary amine with a proton . We found experimentalpKa values only for a select few of thecorresponding ammonium cations,46 and thereforecalculated pKa values were also generatedfor all the representative ammonium cations using SciFinder.47 The calculated pKa values were found to be very similar to the available experimentalvalues (Table S3). Below, we compare experimentaldata when they are available for all amines under consideration, andotherwise calculated values are discussed.It isclear that the structures and steric bulk of the pore-dwellingamine impact the COKa values for the representative ammonium cationsrange from 10.8(1) to 10.8(2); Table S3). As such, for m-2–, e-2–, and p-2–Mg2(olz), steric hindrance appears to be the primary factor influencingthe  differences in their adsorption step positions. Interestingly,the tertiary amines in ee-2 and ii-2 are both expected to be morebasic than the tertiary amine in mm-2 ,11.0(3), and 9.8(3), respectively). The greater basicity of the tertiaryamine in ee-2 could explain why ee-2–Mg2(olz) exhibitsa lower step pressure (more favorable CO2 uptake) thanmm-2–Mg2(olz), despite having a more stericallyencumbered free amine. However, the step pressure of ii-2–Mg2(olz) is the highest of all three materials, even though itstertiary amine is predicted to be the most basic. This result suggeststhat significant steric bulk can counteract basicity as a drivingforce for CO2 binding. Finally, for e-2–, dmen–,and mm-2–Mg2(olz), the CO2 step pressureseems to directly correlate with the basicity of the representativepore-dwelling amine , although sterics cannot be ruled out as amitigating factor.For the secondaryamines with straight chain alkyl groups, increasingthe length of the linear alkyl group from one to three carbons doesnot significantly change the basicity of the amine  or low pressures . However, branching alkyl groups can counteract the effectof basicity by destabilizing the ammonium carbamate chain phase, andas such, the size of the alkyl substituent should also be taken intoaccount.In all, these results suggest that when designingdiamine-appendedframeworks for CO2(olz) leads to a decrease in the sharpness of the CO2 adsorption step  isothermdata collected at various temperatures using the Hill equation (seeSection 2 of the Supporting Information for details).45 The Hill coefficientobtained for each material can be viewed as an approximation of thenumber of CO2 molecules involved in cooperative ammoniumcarbamate chain formation. While this analysis does not allow foran absolute description of the cooperativity of CO2 bindingin a given framework, it is useful to establish overall trends, aspreviously demonstrated for N,N′-dimethylethylenediamine-appendedM2(dobpdc) .32As notedabove, we observed that increasing the steric bulk of the secondaryor tertiary amine in 1°,2°- and 1°,3°-amine-appendedMgion step 3b,d, whi2(olz) materials, neither the Hill coefficient nor the slopeof the CO2 isotherm was found to change significantly withan increase in temperature (Table S4).Thus, for a given framework, the degree of cooperativity in CO2 uptake is relatively insensitive to the temperature overthe examined range. However, a comparison of diamines within the samefamily  reveals thatthe sharpness of the step is dependent on the diamine structure. Form-2–Mg2(olz) and e-2–Mg2(olz),the estimated Hill coefficients (n) are both 11(4),whereas increasing the alkyl chain length to three carbons in p-2–Mg2(olz) results in a decrease of n to 6(2).For frameworks appended with branching 1°,2°- or 1°,3°-diamines, n decreases with increasing steric bulk from 11(4) to 7(1)to 6(2) for e-2–Mg2(olz), i-2–Mg2(olz), and 3-pent-2–Mg2(olz), respectively, andfrom 9(1) to 4.9(6) to 3.0(1) for mm-2–Mg2(olz),ee-2–Mg2(olz), and ii-2–Mg2(olz),respectively. Interestingly, even though the CO2 adsorptionstep temperature of ee-2–Mg2(olz) is higher thanthat of mm-2–Mg2(olz), and therefore the initialCO2 uptake is more thermodynamically favorable in ee-2–Mg2(olz), CO2 adsorption in mm-2–Mg2(olz) is more cooperative. Altogether, these results suggest thatthe diamine structure is a dominant factor influencing the degreeof cooperativity in CO2 uptake in these materials.For each of the diamine–Mg2(olz) are all candidates for the removal of CO2 from a coal flue gas, owing to their CO2 step pressuresbelow 150 mbar at 40 °C. Of these materials, ee-2–Mg2(olz) exhibits the lowest desorption temperature of 85 °C,which prompted us to examine its temperature-dependent CO2 adsorption properties in more detail. Accordingly, CO2 adsorption and desorption isotherms were collected at temperaturesranging from 30 to 85 °C. The material exhibits step-shaped adsorptionat temperatures ≤75 °C, and the step pressure increaseswith increasing temperature , the CO2 isotherm for ee-2–Mg2(olz) at 85 °C is nearly flat up to a pressure of 1 bar. Based on single-componentisotherm data collected for ee-2–Mg2(olz), adsorptionof CO2 at 150 mbar and 40 °C and desorption under1 bar of CO2 at 85 °C would yield a high working capacityof 3.53 mmol/g or 15.5 wt % (2(olz) (0.744 g/cm3) (Table S8), this corresponds to an approximatevolumetric working capacity of 2.63 mmol/cm3 (59 v/v).Based on adsorption isotherm data, ee-2–,dmen–, 3-pent-2–, i-2–, and e-2–Mgperature 4. Consisperature S10, the 2 adsorptionin ee-2–Mg2(olz) as a function of loading from linearinterpolation of the CO2 adsorption isotherms using theClausius–Clapeyron relationship , the differentialenthalpy of CO2 adsorption (Δhads) is −69.9 ± 0.8 kJ/mol. Using the low reversibleheat capacity (2.02 J/g·°C) of ee-2–Mg2(olz) measured by differential scanning calorimetry (DSC) , we calculated an approximate regenerationenergy of 2.15 MJ/kg of CO2 (see Section 3.3 of the Supporting Information for details). Significantly,this value is 40% lower than that for monoethanolamine (3.6 MJ/kgCO2)49 and 15% less than theregeneration energy associated with the framework dmpn–Mg2(dobpdc) ,the leading diamine-appended Mg2(dobpdc) framework forCO2 capture from a coal flue gas.34 Additionally, monoethanolamine and dmpn–Mg2(dobpdc)must be heated to significantly higher temperatures (100–130°C) than ee-2–Mg2(olz) to fully desorb CO2 and would therefore require the use of high-value steam forregeneration.We calculated the differential enthalpy of CO see the .48 At a 2 adsorption performance of ee-2–Mg2(olz)under more realistic multicomponent conditions. To this end, we carriedout thermogravimetric analysis (TGA) experiments wherein a sampleof the framework was exposed to a humidified (∼1.5% H2O) stream containing 15% CO2 in N2 (see the 2 or humidified N2 (∼1.5% H2Oin each case) to enable a qualitative assessment of the adsorptionperformance under a simulated humid flue gas (2(olz) dosed with humid N2 (2(olz) adsorbs negligible N2 under dry isothermaland isobaric conditions , the adsorbed mass under humid N2 can be attributedto uptake of water only (approximately 0.47 molecules of water adsorbedper diamine).We next sought to evaluate the COflue gas 5a. Isoba2 underisobaric conditions, ee-2–Mg2(olz) exhibits step-shapedgas uptake with a step temperature of ∼65 °C and adsorbs15.5 g/100 g (3.53 mmol/g) at 40 °C (2 per diamine (15.2 g/100g or 3.45 mmol/g). When exposed to a stream of humid (∼1.5%H2O) CO2, ee-2–Mg2(olz) alsoexhibits step-shaped gas uptake, albeit with a higher onset temperatureof 80 °C. This result suggests that water promotes CO2 uptake in ee-2–Mg2(olz), a phenomenon observedpreviously for diamine-appended Mg2(dobpdc) materials42 that may be due to stabilizationof the CO2-adsorbed phase through hydrogen bonding withwater.34 The overall gas uptake in ee-2–Mg2(olz) under humid CO2 is 19.6 g/100 g at 40 °C,slightly higher than that under dry conditions and reflecting thepresence of co-adsorbed water (2 in N2 (2(olz) again exhibitsstepped gas adsorption but with a slightly lower onset temperatureof 60 °C relative to that under dry and humid CO2 streams.Altogether, these results indicate that the capture of CO2 in ee-2–Mg2(olz) occurs readily under simulatedcoal flue gas conditions. Of note, ee-2–Mg2(olz)exhibits step-shaped CO2 adsorption at even lower CO2 concentrations of 10 and 5% in humid N2 . Following adsorption of humid 15%CO2 in N2, ee-2–Mg2(olz) canbe fully regenerated upon heating to 85 °C under pure CO2  under simulated coal flue gas CO2 capture conditions using a custom-built breakthrough apparatus(see Section 3 of the Supporting Information for details). In brief, a gram-scale fixed bed was filled with compressed,binder-free ee-2–Mg2(olz) pellets (∼350–700μm diameter) and presaturated with water using a stream of humidifiedHe gas. A gas stream containing humid 15% CO2 in N2 (∼2.3% H2O) was flowed through the columnat 40 °C and atmospheric pressure, and the outlet compositionand flow rate were tracked as a function of time. Rapid breakthroughof N2 occurred first, followed by breakthrough of CO2 much later to humid CO2 exposure under yet more realistic conditions,we evaluated the performance of ee-2–Mg2(olz) overthe course of 1000 TGA adsorption  and desorption (∼2.3% H2O in CO2 at 85 °C and 1 atm) cycles. Notably, the short adsorption (5min) and desorption (1 min) intervals used throughout the course ofthe experiment highlight the rapid CO2/H2O adsorptionand desorption kinetics in ee-2–Mg2(olz). Afteran initial equilibration period, the CO2/H2Ocycling capacity remained relatively unchanged at ∼15.5 g/100g during the last 300 cycles .If the entirety of the adsorbed mass is presumed to be CO2, this capacity would correspond to an uptake of ∼3.52 mmol/g.Based on powder X-ray diffraction analysis and 1H NMR spectroscopydigestion experiments, respectively, ee-2–Mg2(olz)also retained crystallinity  and a high diamine loading of 99% after cycling, highlighting therobustness of the material to thermal and oxidative degradation inthe presence of CO2, O2, and water. Overall,these data suggest that ee-2–Mg2(olz) is an exceptionalcandidate for CO2 capture from coal flue gas.To probe the long-term stability of ee-2–Mg2 adsorptionin diamine–Mg2(olz), with ee-2–Mg2(olz) selected as the representative material. Diagnostic peaks forcarbamate (ν(C–O) = 1630–1690 cm–1 and ν(C–N) = ∼1320 cm–1) werepresent in the IR spectrum collected for ee-2–Mg2(olz) dosed in situ with dry CO2 , supporting ammonium carbamate formation.Infrared (IR) spectroscopy,solid-state magic angle spinning NMR spectroscopy, and van der Waals(vdW)-corrected density functional theory (DFT) calculations wereused to investigate the mechanism of cooperative CO13C NMR spectrum of ee-2–Mg2(olz)dosed with 1 bar of 13CO2 at room temperaturefeatures a resonance at 162.4 ppm, with a shoulder at approximately161.7 ppm (2 speciesand are consistent with those reported previously for carbamate formedin diamine-appended Mg2(dobpdc) upon CO2 uptake.For example, the resonance for the carbamate species formed upon CO2 adsorption in ee-2–Mg2(dobpdc) appearsat 162.5 ppm.50 The presence of more thanone resonance in the case of ee-2–Mg2(olz) is indicativeof slightly different carbamate environments, which could arise becausethe larger pore size of Mg2(olz) can tolerate more conformationsthan Mg2(dobpdc). The two-dimensional (2D) 1H → 13C heteronuclear correlation (HETCOR) spectrumobtained for 13CO2-dosed ee-2–Mg2(olz) features strong correlations at 5.1 and 13.9 ppm, whichare assigned to the presence of NHRCO2– and NHR3+ species, respectively (50 further supporting ammonium carbamate chain formation.50 We note that the 2D 1H → 13C HETCOR spectrum for 13CO2-dosed ee-2–Mg2(dobpdc) is very similar to correlations at 4.7 and 13.7 ppm;this result suggests similar hydrogen bond strengths in the ammoniumcarbamate chains formed in each compound .The 61.7 ppm 7a. Both ectively 7b,50 fur2-dosed structures of ee-2–Mg2(olz) (2 binding energies (ΔEads) and NMR chemical shifts were calculatedto compare with the experimental values (Tables S5–S7). At full capacity, the calculated CO2 binding energy of ee-2–Mg2(olz) is −66.4kJ/mol, which is comparable to the experimental differential adsorptionenthalpy of −69.9 ± 0.8 kJ/mol. The framework e-2–Mg2(olz) was also modeled by using the same method, which yieldedΔEads = −88.6 kJ/mol. Thisenergy agrees well with the experimental differential adsorption enthalpyof −87.1 ± 0.4 kJ/mol  and supports ammonium carbamate formationas the mechanism of CO2 uptake in diamine–Mg2(olz). Analogous calculations were carried out for ee-2–Mg2(dobpdc) and e-2–Mg2(dobpdc), and the resultingCO2 binding energies are within ±5 kJ/mol of the correspondingexperimental Δhads values (Table S5).50 In addition,the calculated carbamate 13C NMR chemical shift in CO2–ee-2–Mg2(olz) at full capacity  is 164.8 ppm, close to the experimentalvalue of 162.4 ppm (Table S7). Similarly,the calculated ammonium and carbamate 1H NMR shifts of3.8 and 13.4 ppm, respectively, are in good agreement with the experiment(Table S7). Taken together, the spectroscopicand computational results support the formation of ammonium carbamatechains upon adsorption of CO2 in diamine-functionalizedMg2(olz) variants.To further confirm the ammonium carbamate chainformation mechanism,we used vdW-corrected DFT to simulate geometry-optimized structuresfor activated and fully COMg2(olz) 8. Using 2 adsorbents, diamine–Mg2(olz), that exhibit single-stepCO2 uptake for various 1°,1°-, 1°,2°-,and 1°,3°-diamines. As a result, smaller temperature swingscan be used to access the full CO2 capacity of these materialsrelative to isoreticular diamine–Mg2(dobpdc) frameworksthat exhibit two-step CO2 adsorption. For diamine–Mg2(olz) compounds featuring diamines with branching alkyl substituents,both diamine sterics and the basicity of the pore-dwelling amine areimportant factors to consider in tuning the CO2 adsorptionstep pressure or temperature. Additionally, within a given class ofdiamines , our results demonstratethat increasing the steric bulk of the pore-dwelling amine gives riseto less sharp CO2 uptake, indicating a lower degree ofcooperativity in adsorption.We have developed a new class of robustcooperative CO2(olz), standsout as a particularly promising candidate for the capture of CO2 from coal flue gas. For example, the thermodynamics of CO2 adsorption in this material (Δhads = −69.9 ± 0.8 kJ/mol and Δsads = −198 ± 2 J/mol·K) are such thatit can capture more than 90% of the CO2 present in a simulatedcoal flue gas stream (humid 15% CO2 in N2).Adsorption of CO2 at 40 °C and regeneration at 85°C under 1 bar of CO2 under fixed-bed multicomponentconditions are associated with a high working capacity of 3.9 mmol/gand a low regeneration energy of 2.15 MJ/kg CO2. In addition,ee-2–Mg2(olz) also maintains excellent performanceover the course of long-term cycling under simulated coal flue gasconditions with less than 1% diamine loss over 1000 cycles and a stableoperating capacity of 15.5 g/100 g. Solid-state NMR spectroscopy and in situ IR spectroscopy data, supported by vdW-correctedDFT calculations, indicate that ee-2–Mg2(olz) capturesCO2 via the formation of ammonium carbamate chains. Basedon the promising performance of ee-2–Mg2(olz) forCO2 capture from simulated coal flue gas, we envision thatother amine-functionalized Mg2(olz) materials can be readilyoptimized for CO2 removal from a variety of other processand emission streams.One variant studied here, ee-2–Mg2), 10%, 5%, and 1.5% CO2 in N2 were purchased from Praxair. The solution-phase 1H nuclear magnetic resonance (NMR) spectra of digested frameworksamples were collected on a Bruker AMX 300 or 400 MHz NMR spectrometerand referenced to residual dimethyl sulfoxide (δ = 2.50 ppm)or chloroform (δ = 7.26 ppm). The attenuated total reflectanceIR spectra were collected on a PerkinElmer Spectrum 400 Fourier transformIR spectrometer. The linker H4olz was prepared followingto the reported procedure.44All synthetic manipulations werecarried out in air, unless noted otherwise. All reagents and solventswere purchased from commercial suppliers at reagent-grade purity orhigher and used without further purification. Custom gas blends of15% (with and without 4% O2(olz) was synthesized employing a modified version of thepreviously reported procedure.44 Usingsonication, the H4olz ligand  andMg(NO3)2·6H2O  were dissolved in a 55:45 (v:v) mixture of methanol and N,N-dimethylformamide (DMF) with a totalvolume of 200 mL. The solution was then filtered to remove any undissolvedparticles and transferred to a 350 mL glass pressure vessel with aTeflon-coated magnetic stir bar. The glass vessel was sealed witha Teflon cap and heated in a silicone oil bath at 120 °C for20 h with stirring, after which time a yellow powder had formed. Thecrude product was vacuum filtered to isolate it from the synthesissolvent and subsequently soaked in 300 mL of DMF at 120 °C fora minimum of 3 h. The solid was again collected by vacuum filtration,and this soaking process was repeated two more times. After the finalsoak, the solid was isolated using vacuum filtration, and the powderwas subsequently soaked in 300 mL of methanol at 60 °C for aminimum of 3 h. The methanol-soaked solid was isolated by vacuum filtration,and this soaking process was repeated two more times. After the finalsoak, the resulting yellow methanol-solvated material was isolatedby using vacuum filtration and stored under fresh methanol when notin use. The methanol-solvated framework was desolvated under flowingN2 for 12 h at 180 °C to yield fully desolvated Mg2(olz) as a bright yellow powder. The powder X-ray diffractionpattern obtained for this material  and the calculated Langmuir surface area of 5070 m2/g  areconsistent with that previously reported for Mg2(olz).44The framework Mg2(olz) frameworks were prepared ina manner similar to that previously reported for diamine–Mg2(dobpdc).34 Methanol-solvated Mg2(olz) (∼150 mg) was filtered using a Büchnerfunnel and added to a 5 mL solution consisting of 20% (v:v) diaminein toluene. After being soaked for 14 h, the solid was filtered andwashed three times with 10 mL of toluene to remove excess diaminein the framework pores prior to activation. The materials were thenactivated under flowing N2 for 30 min at temperatures rangingfrom 120 to 160 °C before analysis of their CO2 adsorptionproperties. The specific activation temperature for each materialwas determined based on the results of thermogravimetric decompositionanalysis (Table S2). Diamine loadings weredetermined from analysis of the 1H NMR spectra collectedfor digested MOF samples, which were prepared by dissolving ∼2mg of material in a solution containing 0.5 mL of dimethyl sulfoxide-d6 and 100 μL of deuterium chloride solution. Surface areas,powder X-ray diffraction patterns, decomposition profiles, IR spectra,and representative diamine loadings obtained from the 1H NMR spectra are presented in Figures S5–S7 and S15 and in Tables S1 and S2, respectively.Diamine–Mg2 TGA experiments were conducted using a TA InstrumentsTGA Q50 instrument where the inlet gas stream was humidified throughtwo room-temperature water bubblers before entering the furnace. Masseswere not corrected for buoyancy effects. Thermogravimetric decompositionexperiments were carried out under 100% N2 with a temperatureramp rate of 2 °C/min from 30 to 600 °C . For isobaric measurements, samples weremeasured at ambient pressure by using a gas flow rate of 25 mL/min.Samples were first activated under flowing N2 at 120–160°C for 30 min, after which time the temperature was rapidly increasedto the highest plotted temperature for each adsorption (cooling) isobar.The gas was then switched to 100% CO2 (or a CO2/N2 blend) and held isothermally for 30 min to allow thegas to completely purge the system. Data were collected while coolingthe sample to 30 °C at a rate of 1 °C/min. The materialwas then reheated to 130–170 °C at a rate of 1 °C/min.For ii-2–Mg2(olz) only, the sample was held isothermallyfor 1 h at 30 °C prior to switching from adsorption to desorptionto allow for complete CO2 uptake due to the slow adsorptionkinetics of the material. Adsorption isobar step temperatures weredetermined as the inflection points of the isobars based on the peakof the temperature derivative. Desorption isobar step temperatureswere determined as the point of closure of the hysteresis loop.Dry TGA experiments wereconducted using a TA Instruments TGA Q5000 or Discovery TGA, whilehumid CO2(olz)was first activated at 130 °C for 30 min under a flowing humidgas stream containing 15% of the dissolved CO2 in N2. The temperature was then rapidly decreased to 40 °Cat a rate of 10 °C/min and held isothermally for 5 min. Afterthe adsorption, the gas was switched to pure CO2 and thetemperature was rapidly changed to 85 °C at a rate of 10 °C/minand held isothermally for 1 min. This adsorption–desorptionprocess was repeated for 1000 cycles.For cycling experiments, a sample of ee-2–Mg2 for 30 minto determine the activated sample mass before being transferred tothe instrument and then reactivated at 130 °C under flowing Hefor 30 min prior to DSC measurements.DSC experiments wereconducted using a TA Instruments Q200 DSC. Samples were analyzed underambient pressure of He using a gas flow rate of 25 mL/min. Sampleswere activated at 130 °C under flowing NKα radiation(λ = 1.5418 Å), with samples placed on a zero-backgroundsample holder. Synchrotron powder X-ray diffraction data were collectedon Beamline 17-BM-B at the Advanced Photon Source at Argonne NationalLaboratory, with an average wavelength of λ = 0.45399 Å.desolvated samples were packed into borosilicate glass capillaries(1.0 mm in diameter) under a N2 atmosphere before beingattached to a custom-designed gas-dosing cell equipped with a gasvalve. These cells were then mounted on the goniometer head and connectedto a gas-dosing manifold for in situ diffractionmeasurements. The sample temperature was controlled using an OxfordCryoSystems Cryostream 800. Samples were briefly heated to 120 °Cunder dynamic vacuum and then cooled to 298 K for data collection.The gas-dosing manifold was used to dose the framework with 1 barof CO2 at 25 °C. Diffraction patterns were recordedusing a PerkinElmer a-Si Flat Panel detector  and were monitored to confirm that the sampleshad reached equilibrium under gas-dosing conditions. Precise unitcell parameters were obtained using structureless Pawley refinements,which were performed in TOPAS-Academic 4.151 (Tables S8 and S9).Laboratory powderX-ray diffraction patterns were collected on a Bruker AXS D8 Advancediffractometer using Cu 2 adsorption isotherms were collected on a MicromeriticsASAP 2420 instrument. All gases were 99.998% purity or higher. Thetemperature was controlled by an oil bath or liquid nitrogen. Approximately40–60 mg of diamine-functionalized MOF was added to a glassadsorption tube equipped with a Micromeritics Transeal for adsorption analysis. Samples were regenerated at 100 °Cunder dynamic vacuum (<10 μbar) for 6 h between isotherms.The isotherm data points were considered equilibrated after <0.01%pressure change occurred over 11 consecutive equilibration time intervals(15 s).Carbon dioxide adsorptionisotherms were collected on a Micromeritics 3Flex gas adsorption analyzer,and Nhads) of CO2 adsorption for each diamine–Mg2(olz) framework was calculated using the Clausius–Clapeyronrelationship  corresponding to constant 1 mmol/g of CO2 loadings (q) were determined at different temperatures (T) by plotting ln(pq)versus 1/T at constant values of q. The y-intercepts of these linear trendlines areequal to – Δsads/R at each loading (with p0 =1 bar), and the slopes were used to determine the corresponding differentialenthalpies of adsorption. Further details are provided in Figures S13 and S14 and Table S5.From the isotherm fits,the exact pressures (2(olz) was activated underflowing N2 at 130 °C for 30 min and subsequently packedinto a 3.2 mm zirconia NMR rotor inside a nitrogen-filled glove bag.The rotor was then evacuated inside a custom-built gas-dosing manifoldfor 10 min. Subsequently, 13CO2 gas  was dosed intothe sample, and a 30 min period was allowed for equilibration. Therotor was then capped inside the manifold using a moveable plunger(see our previous work for details on this apparatus50). The final 13CO2 pressure was 1bar. Dosing was performed at room temperature.A sample of ee-2–Mg13C NMR spectra were acquired by cross-polarization from 1H with a contact time of 1 ms and with continuous-wave decouplingduring acquisition. The 2D HETCOR experiments also employed magnetizationtransfer by cross-polarization with a short contact time of 100 μsused to selectively show short-range correlations. The 1H and 13C chemical shifts were referenced to 1.8 ppm (adamantane)and 38.5 ppm ,respectively.Solid-state NMRexperiments were performed at 16.4 T by using a 3.2 mm Bruker MASprobe. A MAS rate of 15 kHz was used for all experiments. The


What patient characteristics are associated with being offered or choosing telephone vs video visits?In this survey study of 4691 Medicare beneficiaries (representing 27 887 642 Medicare beneficiaries), 17% receiving care from practices offering both video and telephone visits reported that they were personally offered telephone visits only; 43% of those who were personally offered both video and telephone visits chose telephone visits. Being offered and choosing telephone visits were associated with less technology access and lack of video experience; those with Hispanic ethnicity or limited English proficiency were more likely to be offered telephone visits but not more likely to choose them.This study found that many patients reported choosing telephone visits when given the option, suggesting the need to support telephone visits when appropriate while addressing multilevel barriers to video use . After the rapid expansion of telemedicine during the COVID-19 pandemic, there is debate about the role and reimbursement of telephone vs video visits. Missing is an understanding of what type of virtual visits clinicians may offer or patients may choose when given the option.To evaluate characteristics of Medicare beneficiaries associated with practices and clinicians offering telephone visits only and patients receiving telephone visits only, when both telephone and video were available.This survey study used 2019-2020 nationally representative Medicare Current Beneficiary Survey data. Participants included community-dwelling Medicare beneficiaries with a usual source of medical care who attended a practice offering telemedicine. Data were analyzed from May 3 to August 23, 2022.Multivariable regression analysis was used to identify patient sociodemographic , clinical , and technology (technology access and prior use of video visits) factors associated with respondents’ report of (1) practices offering telephone virtual visits only, (2) being offered telephone visits only when both video and telephone visits were available, and (3) receiving telephone visits only when both video and telephone visits were offered.Of 4691 respondents  reporting that their practice offered telemedicine, 1234 (23.3% weighted) reported that their practices offered telephone virtual visits only; factors associated with being in a practice offering telephone only included older age , male sex , Hispanic ethnicity , lower income , poor self-rated health , and less technology access . Of the 1593 patients in practices offering both video and telephone visits, 297 (16.7% weighted) were themselves offered telephone visits only; factors associated with being offered telephone only included Hispanic ethnicity , limited English proficiency , and less technology access . Finally, of the 711 respondents who were themselves offered both video and telephone visits, 304 (43.1% weighted) had a telephone visit; factors associated with receiving telephone visits only were older age  and less technology access . Among those who used video calls in other settings and were offered a choice, 122  chose telephone visits.In this survey study of Medicare beneficiaries, respondents often reported being offered or choosing telephone visits even when video visits were available. Study findings suggest that policy makers and clinical leaders should support the use of telephone visits to the extent that telephone is appropriate, while addressing both practice-level and patient-level barriers to video visits. This survey study of Medicare beneficiaries evaluates patient characteristics associated with practices and clinicians offering telephone visits only and patients receiving telephone visits only, when both telephone and video were available. On the one hand, compared with video visits, telephone visits do not allow for visual patient examination or eye contact and may be more prone to overuse and fraud.6 On the other hand, for some patients and in some scenarios, telephone visits may be clinically equivalent to video and may represent the only option  or the preferred option .5After the rapid expansion of virtual visits via both video and telephone during the COVID-19 pandemic,5 This includes evidence, predominantly from single-site studies of clinics and health systems, of differences by sociodemographic characteristics in the receipt of video vs telephone visits. Specifically, these studies show that telephone visits are more often used by patients who are older,16 are of minoritized race17 or Hispanic ethnicity,16 have limited English proficiency,17 are enrolled in Medicaid or otherwise identified as having low incomes,9 have less education,10 live in rural areas,7 or live in areas with less broadband internet access.9 What has received less attention is the role that clinicians play in driving these differences. Some practices or clinicians may not offer video visits or may only offer video visits to a subset of their patients; 1 study of a large health system found that variation in visit modality was explained more by practices and clinicians than by patients.9 Similarly, the role of patient choice in telephone visits remains unclear—for example, how often do patients choose telephone visits when given both options, and what might drive this choice?Based on evidence to date, policy makers and clinical leaders have largely assumed that the use of telephone visits is due to patients lacking access to video technology .Understanding how the use of telephone visits may be influenced by practice availability, clinician offerings, and patient choice would inform policies and implementation strategies to ensure that patients have access to telemedicine that meets their needs, whether these visits are by video or telephone. To this end, we used nationally representative 2019-2020 Medicare Current Beneficiary Survey (MCBS) data to assess patient sociodemographic, clinical, and technology factors associated with the decision to offer or choose video vs telephone visits at each stage of the decision-making process—from the practice’s decision to offer telephone or video visits, in general, to a clinical team member’s decision to offer a telephone vs video visit to a given patient, and to the final choice of modality.STROBE) reporting guideline.The MCBS is a longitudinal survey with a rotating panel design of a representative national sample of traditional Medicare and Medicare Advantage beneficiaries. This survey is conducted in English and Spanish and enriched for Hispanic and older adult populations. We used the 2019 survey and the COVID-19 fall 2020 supplement  to sample beneficiaries who were continuously enrolled in Medicare from the start of 2020 through fall 2020. Responses to the 2 surveys are linked by an encrypted identifier. The Mass General Brigham institutional review board considered this study exempt from review and from the requirement for informed consent per 45 CFR 46.101(b). The study followed the Strengthening the Reporting of Observational Studies in Epidemiology  who had been recently offered a virtual visit . For group 2, the outcome of interest was the patient being offered telephone visits only (vs video visits only or both).Group 3 was the subset of group 2 composed of respondents who were offered both telephone and video visits since July 1, 2020  and had received a virtual visit . For group 3, the outcome of interest was the patient receiving a telephone visit only (vs a video visit only or both).5Based on literature review and clinical experience, we chose sociodemographic, clinical, and technology variables that may be associated with patient or clinician propensity to choose a given telemedicine modality.Sociodemographic variables collected included age , sex , race , Hispanic ethnicity (yes or no), educational level , income , limited English proficiency , housing type , and number of people living in home .Clinical variables collected included dementia (Alzheimer disease or any type of dementia other than Alzheimer disease), mental illness , poor self-rated health , hearing impairment (yes or no), and vision impairment (yes or no).18 was defined as the following: high access (has internet access and has a smartphone or tablet); moderate access (has a smartphone but no internet access or has internet access and a computer but no smartphone or tablet); or low access . The second variable was use of internet-based video or voice calls .There were 2 technology variables. The first, technology access group (created by the authors based on 5 survey items in the COVID-19 supplement),Statistical analysis was conducted from May 3 to August 23, 2022. For each of our 3 outcomes, we calculated the proportion of eligible survey respondents who had the outcome. We then used multivariable logistic regression to assess sociodemographic, clinical, and technology factors associated with choice of telephone visit at each stage: (1) what the practice offered (group 1), (2) what the respondent was personally offered (group 2), and (3) what the respondent received (group 3). To explore the third stage further, we performed an additional analysis; because the number of people in one’s household may differentially motivate one’s choice of telephone vs video visit for residents of more vs less restrictive housing situations , we added an interaction term for number of people in the household and housing type in this model.20 We considered 2-tailed P values significant at P < .05 and addressed missingness using complete case analysis. To evaluate differences between respondents and nonrespondents, we computed standardized mean differences. Data were analyzed using SAS, version 9.4 (SAS Institute Inc).We applied MCBS sampling weights throughout to construct national estimates and used balanced repeated replication weights for variance estimation.We assessed results from 5440 respondents  who reported that their practice offered telehealth . CompareOf 4691 respondents  who responded regarding modalities offered (group 1), 1234 (23.3% weighted) reported that their practices offered telephone only, 298 (6.6% weighted) reported that their practices offered video only, and 3159 (70.1% weighted) reported that their practices offered both . In multOf the 1593 respondents who reported that their practices offered both and were offered virtual visits (group 2), 297 (16.7% weighted) were personally offered telephone visits only . In multFinally, of the 711 respondents who reported that they were offered both telephone and video visits and had a telemedicine visit (group 3), 304 (43.1% weighted) reported receiving a telephone visit . In mult21 and policymakers and clinicians should address both practice-level and patient-level barriers to video visit use over the longer term.In this study, Medicare beneficiaries commonly reported that clinicians offered them telephone visits or that beneficiaries chose telephone visits, even when both telephone and video visit options were reportedly available. These results suggest the need to expand the current policy debate beyond patients lacking video technology access, to consider the roles of practice availability, clinician offering, and patient preferences in the use of telephone visits. In light of these findings, telephone visits should remain available to patients to the extent that they facilitate access to care,24 In further support of potential use cases for telephone visits, an analysis of video and telephone visits at 2 geriatrics clinics found that telephone visits were shorter than video yet included discussion of more diagnoses and were equally likely to include advance care planning.17Our finding that 43.1% of patients chose telephone visits when given the option between telephone and video visits underscores the often-overlooked idea that patients may prefer telephone visits in some cases. Telephone visits may also be clinically reasonable for certain scenarios, such as in the treatment of mental health conditions.16 have lower incomes,8 are of Hispanic ethnicity,16 or have limited English proficiency.17 Although we found that Hispanic adults and those with limited English proficiency were substantially more likely to be offered only a telephone visit, they were not more likely to choose a telephone visit when given the option between telephone and video visits—in fact, they had lower odds of choosing a telephone visit, although these results were not statistically significant. These results suggest the possibility of implicit biases or assumptions on the part of clinicians or staff members offering visits . There may also be pragmatic concerns .At the same time, given the likely advantages associated with video visits, we were concerned to find lower rates of video visits being offered and received among historically marginalized groups, consistent with prior studies finding fewer video visits among patients who are older,These findings also support the association of technology access with choice of modality. At each stage examined, patients without access to both internet and a smartphone or tablet were more likely to report being offered or receiving only telephone visits. Respondents who used video calls in other settings were consistently and markedly less likely to report telephone-only access or use. These findings support the possibility that, as use of video technology increases over time in settings outside of health care , adults may be more amenable to choosing video visits in health care settings if given the option.25 this finding may reflect that more well-resourced practices are more likely both to diagnose dementia and to offer video visits. We also found that patients with lower educational levels were less likely to choose telephone visits, contrasting with results from an online US Census Bureau survey that was not specific to Medicare beneficiaries and found the opposite.10 Similar to another study,17 we did not note any associations between visit modality and vision or hearing impairment.We found an inverse association between dementia diagnosis and report of telephone-only offering—given the known underdiagnosis of dementia,23 In parallel, efforts to expand technology access are critical, especially those directed to key populations. For example, Silva et al26 described a culturally tailored program to engage Latinx patients in telehealth use. Finally, attention to user-friendly design is critical5 . Future research should further clarify patient preferences, examine health and health care use outcomes linked to telephone vs video visits, and clarify optimal use cases for each modality.Given the common use of telephone visits and that nearly half of Medicare beneficiaries reported choosing telephone visits when given the option, it may be important for policy makers to extend pandemic-era reimbursement of telephone visits as a modality that likely facilitates access to care in the short term and may be suitable in certain scenarios. At the same time, given the potential benefits associated with video visits, our results argue for the need to target practice-level, clinician-level, and patient-level barriers to video visit use over time. For example, to ensure that all practices offer video visits, new policies can offer financial support to practices for the needed infrastructure as well as regulatory incentives to motivate adoption of video visits. To encourage clinicians to offer video visits to all patients, payers might reimburse for telephone visits only if clinicians certify in their notes that they offered a video visit and the patient asked for a telephone visit instead—Medicare recently implemented this strategy for mental health telemedicine.27 Second, the survey was conducted earlier in the COVID-19 pandemic, and use of telephone visits may have evolved during the pandemic. Third, survey items are subject to recall bias and interpretation. For example, patients may inaccurately report what modalities their practice offers; responses indicating that one’s practice offered only telephone visits may in some cases reflect practice staff or clinicians withholding the video visit option for that respondent or patients with less technology access being less aware of the video visit option. Despite these limitations of patient report, it is important to understand patient perceptions of care access. Moreover, claims-based analysis of telephone vs video visits has its own substantial limitations.28 In addition, while these survey data are nationally representative, our results may not be generalizable to all Medicare beneficiaries, due to nonresponse. Fourth, in some cases, sample sizes may have been too small to establish statistical significance; in those cases, the effect estimates allow interpretation of the clinical significance of an association. Fifth, while these survey data allowed us to isolate patients’ actual  choice of telephone visits when given both options and to use rich sociodemographic, clinical, and technology data to unpack factors that may explain this choice, we could not capture privacy preferences or other factors that may have helped to explain this choice.This observational study does not allow causal inference and should be assessed in the context of its limitations. First, while our study is limited to use of virtual visits in the context of one’s usual source of care, most telehealth visits for older adults do take place within established clinician-patient relationships.In this survey, Medicare beneficiaries reported that clinicians commonly offer, and that these beneficiaries commonly choose, telephone visits even when video visits are available. These results suggest the need to ensure access to telephone visits to the extent that these visits facilitate access to care in the short term while addressing practice-level, clinician-level, and patient-level barriers to video visit use in the longer term.