Engineering lanthanide complexes with controlled water exchange rates for magnetic resonance imaging
The control of the rate of water exchange in lanthanide complexes is critical to their future development as contrast agents in magnetic resonance imaging. In traditional T/sub 1/ shortening agents an optimal water residence lifetime (/spl tau//sub M/) of around 25 ns is required if the highest relaxivities are to be achieved. In contrast the newer PARACEST agents require that water exchange is much slower with /spl tau//sub M/ on the order of microseconds. It is now possible to rationally design complexes that exhibit water exchange rates that are ideal for their intended use. The selection of appropriate ligating groups allow a broad control mechanism. Anionic ligating groups such as carboxylates favour faster exchange whereas neutral ligands such as amides favour slower exchange. By altering the steric hindrance around the water coordination site water exchange rates can be fine tuned. The steric hindrance can be altered by controlling the coordination environment of the lanthanide ion and optimal water exchanges rates so achieved.
Gadolinium(III) Chelates as MRI Contrast Agents: Structure, Dynamics, and Applications.
A. Water Exchange 2326 B. Proton Exchange 2327 C. Electronic Relaxation 2327 D. Relaxivity 2331 E. Outerand Second-Sphere Relaxivity 2334 F. Methods of Improving Relaxivity 2336 V. Macromolecular Conjugates 2336 A. Introduction 2336 B. General Conjugation Methods 2336 C. Synthetic Linear Polymers 2336 D. Synthetic Dendrimer-Based Agents 2338 E. Naturally Occurring Polymers (Proteins, Polysaccharides, and Nucleic Acids) 2339
The Categorical Stability of Gambling Motives Among Community-Recruited Gamblers: A Longitudinal Assessment
Over the past decade, several motivational models have been proposed to explain the role of motives in gambling disorder. In the model captured by the four-factor Gambling Motives Questionnaire Financial (GMQ-F), gamblers are described as being primarily motivated to gamble for ‘coping’, ‘enhancement’, ‘social’, and ‘financial’ reasons. Although this model has received significant empirical support; to date, research assessing the role of motives in gambling disorder has been primarily cross-sectional in nature. Thus, the extent to which gambling motives remain stable over time has yet to be explored. In the current study, the stability versus fluidity of self-assessed gambling motives was investigated using the Quinte Longitudinal Study, a longitudinal dataset of gambling behaviour collected over 5 years. Gambling motives of 2795 gamblers were examined over all five annual assessments. The total proportion of gamblers who stayed in the same primary motive category across each of the 5 consecutive assessments was 22%, indicating substantial fluidity in category membership. Substantial movement between categories was seen for each GMQ-F group, as well as an additional group of non-classified motives. Logistic regression analyses suggest that greater resistance to gambling fallacies significantly predicted stability between the baseline assessment and a follow-up 1 year later, but gambling severity did not. Potential limitations in the study design and opportunities for future research are discussed.