Light-induced electron transfer from a lipid-soluble zinc(II) porphyrin to various electron acceptors in frozen vesicle solutions: effects of cholesterol on the solubilization sites and radical yields

Article abstract of DOI:10.1021/j100350a047

The photoionization of zinc tetraphenylporphyrin (ZnTPP) has been studied by electron spin resonance (ESR) at 77 K in rapidly frozen dipalmitoylphosphatidylcholine (DPPC) vesicle solutions, and in the presence of various electron acceptors like tetrachloro- and tetrabromobenzoquinone (TCBQ and TBBQ) and potassium ferricyanide (K₃Fe(CN)₆). The photoproduced ZnTPP⁺ yield was found to increase, and photoinduced anion formation was also detected for added tetrahalobenzoquinones. Incorporation of cholesterol in these systems altered the ZnTPP⁺ radical yields via two main structural changes: (1) ZnTPP-water contact increased due to intercalation of cholesterol between the surfactant headgroups, and (2) TCBQ moved deeper into the vesicle bilayer because of increased bilayer fluidity.