Host-guest assembly of ligand systems for metal ion complexation. Synergistic solvent extraction of copper(II) and silver(I) by 1,4,8,11-tetrabenzyl-1,4,8,11-tetraazacyclodecane in combination with carboxylic acids.
Host-guest formation between 1,4,8,11-tetrabenzyl-1,4,8,11-tetraazacyclodecane (1) and lipophilic organic carboxylic acids in chloroform has been investigated and the effect of such ligand assembly on the solvent extraction of copper(II) and silver(I) has been probed. NMR titration experiments in the absence of a metal ion confirm the formation of weak 1:1 and 1:2 (macrocycle:carboxylic acid) assemblies in CDCl(3) between 1 and palmitic (hexadecanoic) acid or 4-tert-butylbenzoic acid while difunctional salicylic acid showed a 1 [ratio] 2 interaction that is somewhat stronger. The interaction between the former two acids and the tetra-N-benzylated macrocycle is significantly less than that reported previously for its non-substituted parent, cyclam; a result that likely reflects the presence of the less-basic, more sterically hindered tertiary nitrogens in 1 relative to the secondary nitrogens present in cyclam. Carboxylic acid-containing assemblies of this type have been used as extractants in a series of solvent extraction (water/chloroform) experiments. From both previous observations as well as from entropy considerations, it was anticipated that the use of a host-guest assembly of the above type for metal-ion complexation might contribute to enhanced metal ion binding (and concomitant enhanced metal ion extraction). Such behaviour is postulated to arise from the components of the coordination sphere being, at least in part, assembled for complex formation. In accord with this, the use of the ligand assembly involving palmitic acid/macrocycle 1 was found to lead to enhanced (synergistic) extraction of copper(II) at a metal ion concentration of 10(-3) mol dm(-3) while, for silver(I), synergism was somewhat marginal at this concentration but was clearly apparent under related conditions when the silver concentration was reduced to 10(-4) mol dm(-3). Similar behaviour towards silver was also observed when 4-tert-butylbenzoic acid was substituted for palmitic acid, while the use of salicylic acid resulted in enhanced (synergistic) extraction at both metal ion concentrations.
Solution chemistry of macrocycles. Part 1. Basicity constants of 1,4,8,11-tetra-azacyclotetradecane, 1,4,8,12-tetra-azacyclopentadecane, and 1,4,8,11-tetramethyl-1,4,8,11-tetra-azacyclotetradecane
The four protonation constants of the macrocyclic tetra-amines 1,4,8,11-tetra-azacyclotetradecane ([14]aneN4), 1,4,8,12-tetra-azacyclopentadecane ([15]aneN4), and 1,4,8,11-tetramethyl-1,4,8,11-tetra-azacyclotetradecane (Me4[14]aneN4) have been determined in 0.5M-KNO3 at 25 °C. Glass and silver/silver chloride electrodes were employed and the experimental e.m.f. values have been corrected for the liquid junction potential. The computer program MINIQUAD has been used for the calculation of the equilibrium constants. The values obtained are: [14]aneN4, log K1= 11.59, log K2= 10.62, log K3= 1.61, log K4= 2.42; [15]aneN4, log K1= 11.08, log K2= 10.38, log K3= 5.28, log K4= 3.60; Me4[14]aneN4, log K1= 9.70, log K2= 9.31, log K3= 3.09, log K4= 2.64. For the first two protonation steps the macrocyclic tetra-amines are more basic than the corresponding open-chain tetra-amines, even if the former exhibit a lower overall basicity.
Phytochemical and FT-IR Spectral Analysis of Certain Bamboo Species of SouthIndia
Bamboo with its varied uses has historically been an integral part of livelihoods and lifestyles in India. The present study was carried out to characterize the bioactive constituents present in the leaf extracts of certain bamboo species using Fourier transform infrared spectroscopic analysis (FT-IR). The various solvent extracts of various bamboo leaves subjected to qualitative analysis showed the availability of phytoconstituents including alkaloids, phenolic compounds, flavonoids, saponins, glycosides, terpenoids, steroids, coumarins and phytosterols. Quinones were completely absent in all the five bamboo species. The FT-IR spectrum confirmed the presence of sulphides (SS), phenols (C-O), aromatic compounds, thiols (S-H), aliphatic compounds (C-Cl) and amines (NH) in different bamboo species. The present investigation has also opened avenues for further research into the development of potent phytomedicines from different bamboo species.