title: Effect of self-association and protein binding on the photochemical reactivity of triarylmethanes. Implications of noncovalent interactions on the competition between photosensitization mechanisms type I and type II.
abstract: We have explored the photochemical behavior of cationic triarylmethane dye monomers and dimers free in solution and noncovalently bound to bovine serum albumin (BSA) and examined how self-association and the formation of host-guest complexes involving biopolymers and photosensitizers affect the competition between the photosensitization type I and type II mechanisms. Our results have clearly indicated that tri-para-substituted triarylmethane dyes bind efficiently to albumin as monomers and dimers and, interestingly, that the formation of dye aggregates in aqueous solutions is actually assisted by the protein. Protein-assisted dye aggregation takes place under conditions of high biopolymer loading (high [dye]/[protein] ratios), as attested by the appearance of a hypsochromically shifted absorption band (H-band) that overlaps with the spectral shoulder of the respective dye monomer. As predicted by the molecular exciton theory, the intersystem crossing efficiency in H-type dimers is expected to be higher than in the respective dye monomers, and photoinduced electron transfer events are intrinsically favored in dye aggregates as a result of the physical contact between donor and acceptor. We have found that when triarylmethanes are noncovalently bound to BSA their photoreactivity undergoes a remarkable enhancement, and that the photooxidation mechanism type I is particularly favored in the macromolecular environment. A comparative examination of the behavior of triarylmethane dyes with that of methylene blue have shown that in the case of methylene blue the binding phenomenon also favor the type I mechanism.
authors.affiliation: School of Pharmacy, University of Wisconsin, Madison 53706-1515, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Bartlett
authors.forename: G L
authors.initials: GL
authors.lastname: Indig
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002417:Cattle; D004396:Coloring Agents / Q000737:chemistry* / Q000528:radiation effects*; D005840:Gentian Violet / Q000737:chemistry / Q000528:radiation effects; D066298:In Vitro Techniques; D009930:Organic Chemicals; D010777:Photochemistry; D011485:Protein Binding; D012394:Rosaniline Dyes / Q000737:chemistry / Q000528:radiation effects; D012710:Serum Albumin, Bovine
chemical_list: D004396:Coloring Agents; D009930:Organic Chemicals; D012394:Rosaniline Dyes; D012710:Serum Albumin, Bovine; C041370:victoria blue; C034887:ethyl violet; D005840:Gentian Violet