Photoinduced Coupled Proton and Electron Transfers. 1. 6-Hydroxyquinoline

Association of 6- and 8-Hydroxyquinolines with Aerosol-OT in Heptane: Competition with Dimerization of 8-Hydroxyquinoline

“…The corresponding spectrum (not shown) peaked at 374 nm and the maximum intensity was reduced only by a factor of 4 compared to the emission for W ϭ 0.7. In bulk water the maximum wavelength of the spectrum of 6-HQ is at Ϸ380 nm and the maximum intensity is about twentyfold smaller than in the swollen micelles (14). This shows that, in swollen reverse micelles, 6-HQ is far from behaving similarly as in bulk water.…”

“…It is then interesting to consider this fluorescence behavior in regard to the excited-state tautomerization phenomenon. 6-HQ has been shown to undergo, in dilute aqueous solutions, a very efficient photoinduced tautomerization leading to a poorly fluorescent tautomer (as 8-HQ does) (14). In particular in pure water, the quantum yield of the neutral form of 6-HQ is lower than 1.5 ϫ 10 Ϫ3 , with an emission maximum located at about 380 nm (14).…”

“…6-HQ has been shown to undergo, in dilute aqueous solutions, a very efficient photoinduced tautomerization leading to a poorly fluorescent tautomer (as 8-HQ does) (14). In particular in pure water, the quantum yield of the neutral form of 6-HQ is lower than 1.5 ϫ 10 Ϫ3 , with an emission maximum located at about 380 nm (14). In the present study, on the contrary, bound 6-HQ molecules in the polar micellar interface show an enhancement in their fluorescence quantum yield as compared to neat heptane.…”

Anomalous Acid-Base Equilibria in Biologically Relevant Water Nanopools

“…[5][6][7][8][9][10][11][12][13] For example, the dielectric constant of a water nanopool has been reported to be much lower than that of bulk water (ε = 78. 5) 17 but similar to that of an alcohol (ε = [30][31][32][33][34][35][36][37][38][39][40]. 18,19 On the other hand, biological processes often take place based on proton relay along a hydrogen (H)-bonded chain, [1][2][3][4][20][21][22][23][24] and the dynamics of biological proton relay is determined by the size, the structure, and the motion of a water cluster which is the prime agent in most of biological systems.…”

“…[13][14][15][16][35][36][37][38][39][40][41][42][43][44] On one hand, a 7-hydroxyquinoline molecule can form a cyclically H-bonded complex with two protic solvent molecules such as water and alcohols, so that proton relay from the enolic group to the imino group of 7-hydroxyquinoline occurs along a H-bonded solvent chain in a concerted fashion. 15,16,[42][43][44] On the other hand, those two prototropic groups of 6-hydroxyquinoline (6HQ) are too far from each other to form a cyclic complex with solvent molecules, so that proton transfer from the enolic group to the imino group of 6HQ takes place in a stepwise manner via accumulating cationic or anionic intermediate species.…”