The larger photobiological activity of visnagin (VI) versus khellin (KH) toward several living organisms, including fungi, viruses, yeasts and bacteria, induced a detailed investigation of the photophysical properties of these naturally-occurring furanochromones, using laser-flash-photolysis, photoacoustic calorimetry skid fluorescence (steady-state and time-resolved) techniques in solvents with different polarity and content of water, including micelles and vesicles. The results have shown that the magnitude of all the three rate constants oat of S-1 (radiative, k(f); internal conversion, k(ic) and intersystem crossing, k(isc) for VI and KH strongly depend on the solvent, namely on its hydrogen bonding ability and polarity. The changes of k(f) and k(isc) are due to the solvent-assisted mixing and/or inversion of the two first singlet excited states ((1)n,pi* and (1) pi,pi*), while k(ic), increases with a decrease of the S-0-S-1 energy gap, As a consequence, the quantum yield of triplet formation (phi(T)) strongly decreases horn values of similar to 0.8 in dioxane to (0.05 in water for both compounds. The magnitude of solvent polarity/hydrogen bonding ability required, at which the state order is inverted and phi(T) starts to decrease, is greater for VI than for KH and consequently phi(T) (VI) >> phi(T), ((KH) over a broad range of water content including that appropriate to the environment of the compounds in a living system, These bets account for the larger photobiological activity of VI with respect to KH, regarding both the fungus Fusarium culmorum L. and the wild strain of Escherichia coli, studied by us.
Photophysical properties and photobiological activity of the furanochromones visnagin and khellin
LATTERINI, Loredana;ELISEI, Fausto;
1998
Abstract
The larger photobiological activity of visnagin (VI) versus khellin (KH) toward several living organisms, including fungi, viruses, yeasts and bacteria, induced a detailed investigation of the photophysical properties of these naturally-occurring furanochromones, using laser-flash-photolysis, photoacoustic calorimetry skid fluorescence (steady-state and time-resolved) techniques in solvents with different polarity and content of water, including micelles and vesicles. The results have shown that the magnitude of all the three rate constants oat of S-1 (radiative, k(f); internal conversion, k(ic) and intersystem crossing, k(isc) for VI and KH strongly depend on the solvent, namely on its hydrogen bonding ability and polarity. The changes of k(f) and k(isc) are due to the solvent-assisted mixing and/or inversion of the two first singlet excited states ((1)n,pi* and (1) pi,pi*), while k(ic), increases with a decrease of the S-0-S-1 energy gap, As a consequence, the quantum yield of triplet formation (phi(T)) strongly decreases horn values of similar to 0.8 in dioxane to (0.05 in water for both compounds. The magnitude of solvent polarity/hydrogen bonding ability required, at which the state order is inverted and phi(T) starts to decrease, is greater for VI than for KH and consequently phi(T) (VI) >> phi(T), ((KH) over a broad range of water content including that appropriate to the environment of the compounds in a living system, These bets account for the larger photobiological activity of VI with respect to KH, regarding both the fungus Fusarium culmorum L. and the wild strain of Escherichia coli, studied by us.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
