A study of the structure of lecithin organic gels by Fourier transform IR spectroscopy

The interaction of water with the polar moiety of the lecithin molecule was studied by Fourier-transform IR spectroscopy. This interaction was respons ible for the transformation of spherical reverse micelles into polymer-like micelles during gradual addition of a polar solvent to a nonaqueous soluti on of lecithin; this process was accompanied by the formation of an organic gel. The water added (whose concentration n was varied from 0 to 5 water m olecules per lecithin molecule) was found to exist in a bound state. Most o f the water added is accumulated near the phosphate groups due to hydrogen bonding. It was demonstrated that, at the initial stage of the process, cor responding to the growth of linear micelles, the spectral parameters of the system change with n practically linearly (at n > 2, the saturation of the phosphate groups by hydrogen bonds was observed). It was assumed that, in the presence of an excess of water, additional sites of growth arise on mic elles, initiating a branching of micelles and leading to a change in the me chanism of their growth; besides, a part of excess water (at n > 3) goes to carbonyl groups of aliphatic acid residues and adds to them by hydrogen bo nds. Preliminary results suggest that the conformation of the phosphorylcho line residue of the lecithin molecule changes during the rearrangement of p olymer-like micelles. The results obtained were used to refine the model de scribing polymer-like micelle aggregates and changes they experience at all stages of the formation of organic gels.