FOURIER-TRANSFORM INFRARED-SPECTRA AND MOLECULAR-ORIENTATION OF BLACKLIPID FILMS IN AIR INTERACTING WITH METAL-IONS

Polarized Fourier transform infrared spectra of black lipid films in a ir withdrawn from aqueous dispersions of dimyristoylphosphatidylcholin e (DMPC) have been recorded at various electrolyte concentrations. The spectra revealed that monovalent cations gave little effect, whereas polyvalent cations except Mg2+ gave remarkable effects on vibrational wavenumbers of both the acyl chain and phosphate ester group of DMPC i n black lipid films. In the case of Mg2+, the effect was discerned onl y for the phosphate ester group. By use of thin film optics, molecular orientation of DMPC in the black lipid film in air was quantitatively evaluated as a function of electrolyte concentration. In the case of monovalent and Mg2+ cations, the orientation angle of the acyl chain a xes from the surface normal was little affected by the electrolyte add ition. On the other hand, the other polyvalent cations caused decrease of the average orientation angle from ca. 40 degrees to 30 degrees. T he affinity of the cations for the DMPC lipid films in air are in the order of Zn2+ > La3+ similar to Ca2+ similar to Pb2+ > Mg2+ > Na+ simi lar to Li+.