Photoinduced electron transfer in crystal violet (CV+)-bovine serum albumin (BSA) system:: evaluation of reaction paths and radical intermediates

Photoinduced electron transfer (PET) from excited probes attached to proteins is of considerable current interest. Photochemical processes following 532 nm excitation of triphenyl methane dye, crystal violet (CV+) bound to a protein, bovine serum albumin (BSA), have been investigated in picosecond (ps) to microseconds (mus) time scales by flash photolysis technique. The excited singlet state lifetime of CV+ is found to be increased to similar to130 ps as compared to similar to1-5 ps for the unbound dye in low viscosity solvents. From flash photolysis studies in microsecond region, transient absorption in the region similar to650 nm is observed which is attributed to the dication radical CV.2+ formed by electron transfer from (CV+)-C-3* to B SA, contrary to electron transfer from B SA to the excited dye as proposed in a recent report. Supporting spectral evidence for the electron transfer from 3CV(+)* to BSA is obtained from pulse radiolysis studies. (C) 2002 Elsevier Science B.V. All rights reserved.