RAMAN AND INFRARED MICROSPECTROMETRIC STR UCTURAL-ANALYSIS OF MYELIN FORMS FROM THE SYSTEM 2-G-OCTADECENOIC ACID PLUS HYDRAZINE 5M SOLUTIONAND THE SYSTEM CHOLESTEROL MONOHYDRATE PLUS SODIUM OLEATE SATURATED SOLUTION

Myelin forms, i.e. multilayer structures (Lalpha) grown in tubular fas hion, prepared from pure Z-9 octadecenoic acid and hydrazine 5M aqueou s solution (system I) and from solid monohydrated cholesterol and sodi um oleate saturated aqueous solution (system II) have been studied by means of Raman and infrared microspectrometry. In both systems, signif icant spectroscopic evidences show that numerous hydrogen bonds occur in the interfacial zone, which contribute to the stability of the lipi dic sheets, i.e. to the decrease of their permeability. In the system I, the structural molecular unit is formed by one oleic acid molecule and one oleate ion linked by acid salt type asymmetric hydrogen bond; in the system II, the hydrogen bonding occurs between the cholesterol 3beta-hydroxyl functions and the oleate carboxylate groups. In both sy stems, the hydrophilic zone is surrounded by a water belt arising from hydration of the amphiphilic molecules polar groups; in addition to t hese interactions, in the system I water layers, the hydrazinium ions are self-associated into more or less long chains cross-linked by seve ral kinds of NH . . . O bonds with the carboxylic or carboxylate oxyge n atoms. As for the lipid bilayers, left-handed structures existence i s showed by the ill-defined Raman line observed near 1090 cm-1 (no ind ication of preferred defect localization in the chain) and circa 800-9 00 cm-1 (end-chain defects). This random disorder, lower in the system II because of the rigid polycyclic part of the cholesterol molecule, leads to a significant weakening of lateral packing forces, allowing t he molecules more room to move. The consequence, i.e. the marked fluid ity of the Lalpha structure explains the telescopic growth of the myel in tubes.