Comparative electron spin resonance and electron spin echo modulation studies of the photoionization of positively and negatively charged and neutral alkylphenothiazines in cationic dioctadecyldimethylammonium chloride, neutral dipalmitoylphosphatidylcholine, and anionic dihexadecyl phosphate vesicles at 77 K

Positively charged phenothiazine N-alkyltrimethylammonium bromides (PC[sub n]TAB) and negatively charged sodium phenothiazine-N-alkanesulfonates (PC[sub n]S) were synthesized and photoionized in cationic dioctadecyldimethylammonium chloride (DODAC), neutral dipalmitoylphosphatidylcholine (DPPC), and anionic dihexadecyl phosphate (DHP) vesicles. The photoproduced radicals were identified and quantitated with electron spin resonance. The microenvironments of the various photoproduced PC[sub n]S and PC[sub n]TAB cation radicals in frozen D[sub 2]O solutions were investigated with electron spin echo modulation (ESEM). These results are compared with those of neutral N-alkylphenolthiazines (PC[sub n]) in the same vesicles. The effects of the pendent alkyl chain length on the photoyields of PC[sub n]S and PC[sub n]TAB are similar. For short alkyl chains (n = 2 or 3), a large deuteron modulation depth is observed, which correlates with a high photoyield. Good correlation is shown between the photoyields of three series of alkylphenothiazines, PC[sub n]S, PC[sub n]TAB, and PC[sub n], in anionic DHP, neutral DPPC, and cationic DODAC vesicles with their relative positions relative to the vesicle interfaces measured by ESEM methods. The dependences on alkyl chain length of the photoionizable molecule seem well understood. The smaller differences between the PC[sub n]S, PC[sub n]TAB, and PC[sub n] compounds for the same alkyl chain length in amore » single vesicle system also show good correlation between photoyields and relative location measured by ESEM deuteron modulation depths. However, photoionization of a given alkylphenothiazine in the three different vesicles shows an anticorrelation between photoyield and deuteron modulation depth. This means that the photoionization yield is determined more by the vesicle interface charge than the distance of the photoionizable molecule from the interface. 43 refs., 11 figs.« less