A variety of metal ions and complex ions exist in living organisms and are involved in various biological processes. In addition to physiological and molecular biological methods, quantitative research from the viewpoint of material science is important to understand the mechanism of their uptake from the exterior environment and their function in the body. We focused on the contribution of diffusion to the mechanism of iron uptake via the iron scavenger mugineic acid in grasses: studied the interfacial properties of polyprotic iron complexes, the effect of coexisting ions, and the pH dependence of the interaction between iron complexes and membranes using model–independent interfacial thermodynamics.
The aqueous solutions of hydrochloric acid−tetraethylene glycol monooctyl ether (C8E4) and sodium chloride−C8E4 mixtures were investigated to examine the interaction between inorganic ions and nonionic surfactants both in the adsorbed film and micelle. Their surface tension was measured as a function of the total molality of the inorganic electrolyte and C8E4 mixture and the composition of C8E4. The results of surface tension measurement were analyzed by our thermodynamic procedure, and the phase diagrams of adsorption and micelle formation were drawn. By comparing the phase diagrams of these systems, it was been that the Na+ ions do but Cl- ions do not interact with the ethylene oxide group of the C8E4 molecule. This finding leads us to the conclusion that the attractive interaction observed in the dodecylammonium chloride−C8E4 system reported previously is caused by ion−dipole interaction or hydrogen bonding between the dodecylammonium ion and oxygen atom of the ethylene oxide group of the C8E4 molecule.
We have investigated how the dynamics of surfactant molecules changes with the vesicle-micelle transition by (1)H NMR relaxation studies on the sodium decyl sulfate (SDeS)-decyltrimethylammonium bromide (DeTAB)-deuterium oxide system. The study has been planned with reference to the phase diagram of the SDeS-DeTAB-water system deduced from thermodynamic analysis of the surface tension data. The spin-lattice relaxation time (T(1)) and the spin-spin relaxation time (T(2)) are measured at 90 and 400 MHz at various total molalities, m, and compositions, X(2), of the surfactants. The data were analyzed according to the "two-step" model developed by Wennerström et al. and molecular dynamics of the surfactant is discussed from the viewpoint of correlation time tau(f) associated with the local fast motion of the surfactant molecule, correlation time tau(s) associated with the slow overall motions of the aggregate and surfactant molecules within it, and local order parameter S. We find tau(s) of vesicles is an order of magnitude larger than that of micelles signifying that the tumbling of vesicle particles and surfactant diffusion over the vesicle are much slower than those for micelle. Tau(f) and S for vesicles are also larger than those for micelles. Molecular environments of the surfactant are also discussed from the dependence of the chemical shifts on m at constant X(2) or from that on X(2) at constant m. When the chemical shifts in vesicle and micelle are compared at constant m, the chemical shifts in vesicle are displaced to a lower magnetic field than those in micelle, which implies that the surfactant molecules are arranged more closely to each other in the vesicle than in the micelle.
Mycobacterial mycolic acid (MA) are long chain 2-alkyl branched, 3-hydroxy fatty acid with two intra-chain groups in the so-called meromycolate chain. On the basis of the nature of the functional groups in the meromycolate chains, MAs are categorized into three major groups: α-MA with no oxygen-containing intra-chain groups, methoxy-MA (MeO-MA) in which the distal group has a methoxy gorup and Keto-MA in which the distal group has a carbonyl group (Fig. 1) (Watanabe et al., 2001; 2002). MAs are characteristic components of mycobacterial cell envelopes, where a major proportion are covalently bonded to the underlying cell wall arabinogalactan (Goren & Brennan, 1979; McNeil et al., 1991; Minnikin, 1982).
The oxygenated long-chain mycolic acids from many mycobacteria are characterized by the presence of mid-chain cyclopropane groups, which can have either cis-configuration or trans-configuration with an adjacent methyl branch. To determine the effect of these functional groups on mycolic acid conformation, surface pressure (π) versus mean molecular area isotherms of methoxy- (MeO-) mycolic acids (MAs) from Mycobacterium kansasii, Mycobacterium tuberculosis (Mtb) Canetti and Mtb H37Ra, and of keto-MAs from Mycobacterium avium-intracellulare complex (MAC) and Mtb H37Ra were recorded and analysed. The MeO- and keto-MAs from Mtb H37Ra, containing scarcely any trans-cyclopropyl groups, apparently took no fully folded 'W-form' conformations. Keto-MA from MAC, whose trans-cyclopropyl group content is nearly 90 %, showed a very solid W-form conformation. MeO-MAs from M. kansasii and Mtb Canetti gave stable W-form conformations at lower temperatures and surface pressures and extended conformations at higher temperatures and surface pressures; their W-form conformation was not as stable as expected from their cis-cyclopropyl group content, probably because they had a wide range of constituent homologues. Energy level calculations of cis- or α-methyl trans-cyclopropane-containing model molecules and computer simulation studies confirmed the superior folding properties of the latter functional unit. The present results were compared with those of MeO- and keto-MAs from Mtb and from M. bovis Bacillus Calmette-Guérin (BCG) reported previously. Among the oxygenated MAs, those having higher trans-cyclopropane content tended to take W-form conformations more firmly, implying that the meromycolate proximal intra-chain α-methyl trans-cyclopropane groups facilitated MA folding more than cis-cyclopropane groups.
I. INTRODUCTION The performance of surfactant molecules at the interfaces depends strongly not only on the chemical structure of them and the nature of the interfaces but also on the environmental conditions such as temperature, pressure, pH, the added materials, and so on. In the previous version of this series [1], the structure performance of adsorption properties has been summarized on the emphasis of the experimental results of the surface and interfacial tensions and their analysis according to the fundamental thermodynamic equations, effects of chemical structures of the hydrophobic and hydrophilic groups, effects of circumstances, and the structure of adsorbed films from the scattering techniques. Basically the review itself is still quite useful to understand various interfacial and colloid chemistries.
