OPTICAL ABSORPTION, ELECTRON SPIN RESONANCE, AND ELECTRON SPIN ECHO STUDIES OF THE PHOTOIONIZATION OF TETRAMETHYLBENZIDINE IN CATIONIC AND ANIONIC SYNTHETIC VESICLES: COMPARISON WITH ANALOGOUS MICELLAR SYSTEMS.

Article abstract of DOI:10.1021/ja00356a008

The photoionization of N,N,N prime ,N prime -tetramethylbenzidine (TMB) in dihexadecylphosphate anionic vesicles and in dioctadecyldimethylammonium chloride cationic vesicles has been studied by optical absorption and electron spin resonance in liquid and frozen solutions. The TMB cation has been observed to be stabilized in both types of vesicles. The photoionization efficiency is about twofold greater in the cationic vesicles compared to the anionic vesicles. Shifts in the optical absorption maximum between micellar and vesicle solutions indicate that TMB is in a less polar environment in the vesicle systems. Electron spin echo modulation spectrometry has been used to detect TMB cation-water interactions that are found to be weaker than in previously studied micellar solutions. This is consistent with the optical absorption results and with an asymmetric solubilization site for TMB and TMB** plus within the vesicular structure. A new absorption in the photoionized vesicles is assigned to a nonparamagnetic diamine-diimine charge-transfer complex between two TMB cations in the same vesicle. This complex is not formed in micellar systems.