Photoionization of Alkylphenothiazines in Vesicles: Effects of the Alkyl Chain Length and the Vesicle Surface Charge

Article abstract of DOI:10.1021/j100365a067

The photoionization of alkylphenothiazine (AP=alkylphenothiazine) in vesicles were observed by electron spin resonance (ESR) and electron spin echo modulation (ESEM) methods.Alkylphenothiazine derivatives including sodium 10-methylphenothiazinesulfonate (C1PSO3Na), sodium 10-dodecylphenothiazinesulfonate (C12PSO3Na), sodium 3-(10'-phenothiazinyl)propane-1-sulfonate (PC3SO3Na), sodium 6-(10'-phenothiazinyl)hexane-1-sulfonate (PC6SO3Na), and sodium 12-(10'-phenothiazinyl)dodecane-1-sulfonate (PC12SO3Na) were synthesized and used to study the effects of the alkyl chain length, the position of the sulfonate group, and the vesicle surface charge on the photoionization.A singlet ESR spectrum due to the alkylphenothiazine cation radicals (AP(+)) was observed from rapidly frozen AP in dioctadecyldimethylammoniumchloride (DODAC) or dihexadecyl phosphate (DHP) vesicles photoirradiated for 10 min with λ>300 nm.In DODAC vesicles with a positive surface charge, the photoionization yield of PC12SO3Na with a sulfonate group at the dodecyl chain end is higher than that of C12PSO3Na with a sulfonate group on the phenothiazine ring.The photoionization yields of AP having the sulfonate group at the alkyl chain end in DODAC vesicles increase with decreasing alkyl chain length.The ESEM data support a correlation between the distance of PCnSO3Na (n= 3, 6, and 12) from the vesicle surface and the photoionization yield.The highest photoionization yield was obtained from PC3SO3Na, which has the shortest alkyl chain in this study and has the sulfonate group at the end of the propyl chain.The photoionization yield of AP in DHP vesicles with a negative surface charge was not changed by added alkyl chains or the position of the sulfonate group in AP.The results are discussed in terms of the alkyl chain length, the position of the sulfonate group, and the vesicle surface charge.