Proton transfer dynamics in substituted 3-hydroxyflavones: Solvent polarization effects

Swinney, T. C.; Kelley, David F.

doi:10.1063/1.465799

Cited by 162 publications

(150 citation statements)

References 28 publications

Supporting

Mentioning

135

Contrasting

Order By: Relevance

“…From data presented in Fig. 2 and published in the literature (34)(35)(36), it is easy to see that, for the flavonol derivatives studied, the position of the PT tautomer fluorescence band is relatively independent of environmental polarity. This is in contrast to the normal tautomer fluorescence bands of fisetin and DHF, which exhibit dramatic solvent dependences indicating a strong CT character of the SI states.…”

Section: Resultsmentioning

confidence: 97%

Interplay between excited-state intramolecular proton transfer and charge transfer in flavonols and their use as protein-binding-site fluorescence probes.

Sytnik

Gormin

Kasha

1994

Proc. Natl. Acad. Sci. U.S.A.

225

148

View full text Add to dashboard Cite

A comparative study is presented of competitive fluorescences of three flavonols, 3-hydroxyflavone, 3,3',4',7-tetrahydroxyflavone (fisetin), and 4'-diethylamino-3-hydroxyflavone (DEIF). The normal fluorescence Si -* So (400-nm region) is largely replaced by the proton-transfer tautomer fluorescence S' --S' in the 550-nm region for all three of the flavonols in aprotic solvents at room temperature. For DHF in polar solvents the normal fluorescence becomes a charge-transfer fluorescence (460-500 nm) which competes strongly with the still dominant proton-transfer fluorescence (at 570 nm). In protic solvents, and at 77 K, the interference with intramolecular hydrogen bonding gives rise to greatly enhanced normal fluorescence, lowering the quantum yield of proton-transfer fluorescence. The utility of DHF as a discriminating fluorescence probe for protein binding sites is suggested by the strong dependence of the charge-transfer fluorescence on polarity of the environment and by various static and dynamic parameters of the charge-transfer and protontransfer fluorescence which can be determined.The purpose of this paper is to explore the application of molecular fluorescence as probes for protein binding sites. The competition between proton-transfer (PT) fluorescence (1, 2) (i.e., excited-state intramolecular proton transfer, ESIPT) and charge-transfer (CT) fluorescence, and the application of solvent polarity studies, is presented for three hydroxyflavones selected as fluorescence probes. The model compounds chosen are 3-hydroxyflavone (3-HF) and its derivatives 3,3',4',7-tetrahydroxyflavone (fisetin) and 4'-diethylamino-3-hydroxyflavone (DHF). In the first two, PT tautomer fluorescence (Amax 529 nm and 540 nm, respectively) is predominant in aprotic solvents at 298 K, the normal tautomer fluorescence being observed only very weakly. The third molecule (DHF) emits both a PT fluorescence at Amos 570 nm and a prominent CT fluorescence at Amass 460 nm.3-HF has been the object of extensive photophysical studies (1-33). Fisetin has not been studied extensively (29) and attracted our attention again recently because of its extraordinary performance as a lasing material (unpublished work). DHF is a newly synthesized molecule (34-36) which we explore as a protein fluorescence probe.The spectroscopic behavior of these three hydroxyflavones offers some contrasting properties which, for these cases, permit a discrimination between normal fluorescence, strong CT fluorescence, and PT fluorescence and indicate the utility of the latter two as fluorescence probe phenomena. MATERIALS AND METHODSSpectroscopic Measurements. Absorption spectra were measured on a Shimadzu UV-2100 spectrophotometer. The fluorescence spectra were recorded with a SPEX Fluoromax spectrofluorimeter (Spex Industries, Edison, NJ).Chemicals. 3-HF and fisetin were from Aldrich. tDHF and 4'-diethylamino-3-methoxyflavone were synthesized in the laboratory of Pi-Tai Chou (University of South Carolina, Columbia). All solvents were of spectrograde quality and...

show abstract

Section: Resultsmentioning

confidence: 97%

Interplay between excited-state intramolecular proton transfer and charge transfer in flavonols and their use as protein-binding-site fluorescence probes.

Sytnik

Gormin

Kasha

1994

Proc. Natl. Acad. Sci. U.S.A.

225

148

View full text Add to dashboard Cite

show abstract

“…[25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] Direct evidence for the coupling of excited-state proton transfer with excited-state electron transfer has been reported for salicylic acid, 40 imidazopyridines, 41 aminosalicylates 42,43 and amine-substituted flavones. [44][45][46] The nature of the ground state at the ESIPT equilibrium nuclear configuration (i.e., at the geometry of T*) also has been an open question of whether T is a metastable intermediate (represented by a resonance form such as IV or V) in equilibrium with the normal (N) phenolic ground state (closed form I) or whether the proton undergoes rapid, barrierless back-transfer on the ground-state surface following fluorescence. [47][48][49] For example, equilibria in the ground and excited states are controlling parameters for proposed lasing action of ESIPT compounds.…”

Section: Introductionmentioning

confidence: 99%

Ground-State Proton-Transfer Tautomer of the Salicylate Anion

et al. 1999

View full text Add to dashboard Cite

Solutions of sodium salicylate in anhydrous polar solvents exhibit a weak, temperature-dependent absorption band (λ max ≈ 325 nm) lying in the Stokes gap between the main absorption (296 nm) and the fluorescence band (396 nm, acetonitrile). This weak, longer wavelength absorption band is hardly observable in aqueous solution, but its intensity increases with temperature and increases with polarity in anhydrous organic solvents in the order of ethanol < acetonitrile < dimethyl sulfoxide at room temperature. After correction for solvent thermal contraction, the temperature-dependent absorption spectrum of salicylate in acetonitrile solutions reveals a clear isosbestic point ( 310 ) 2000 M -1 cm -1 ) characteristic of an equilibrium between two salicylate species with band-maximum extinction coefficients of 325 ) 3400 M -1 cm -1 and 296 ) 3586 M -1 cm -1 . In acetonitrile at room temperature (298 K) the concentration equilibrium constant (minor/major) for the interconversion reaction between the two species is K 298 ) 0.11, with ∆H ) 1.6 kcal mol -1 and ∆S ) 0.97 cal‚mol -1 K -1 . The fluorescence lifetime (4.8 ns in acetonitrile) and the shape of the fluorescence spectrum are independent of excitation wavelength. The fluorescence quantum yield for excitation in the long-wavelength shoulder (340 nm) is approximately 60% larger than the yield for excitation in the main band at 296 nm ( 340 ) 0.29, 296 ) 0.18) in acetonitrile at room temperature. These results are consistent with assignment of the shoulder band to the proton-transfer tautomer of the salicylate anion. Electronic structure calculations support assignment of the 325 nm absorption band to the ground-state tautomer (phenoxide anion form) of the salicylate anion. Absorption transition moments for both the normal and tautomer forms are parallel to the emission transition moment, are electronically allowed, and are consistent with 1 L b assignment for both absorbing and emitting transitions. The static dipole moments are in the order of µ(N*) g µ(N) > µ(T*) > µ(T) for the normal (N) and tautomer (T) ground and electronic excited states.

show abstract

“…When joined in one molecular system, excited-state events can compete dynamically. An example of such competition is the mutual exclusion of intramolecular electron and PT in 4Ј-diethylamino-3-hydroxyflavone (16)(17)(18)(19). Proper pairing of excited-state transformations can be a source of structural͞dynamical information about the molecules possessing these transformations, the excited-state transformations themselves, and the medium where the coupling takes place.…”

mentioning

confidence: 99%

Energy transfer to a proton-transfer fluorescence probe: Tryptophan to a flavonol in human serum albumin

Sytnik

Litvinyuk

1996

Proc. Natl. Acad. Sci. U.S.A.

171

View full text Add to dashboard Cite

A protein f luorescence probe system, coupling excited-state intermolecular Förster energy transfer and intramolecular proton transfer (PT), is presented. As an energy donor for this system, we used tryptophan, which transfers its excitation energy to 3-hydroxyf lavone (3-HF) as a f lavonol prototype, an acceptor exhibiting excited-state intramolecular PT. We demonstrate such a coupling in human serum albumin-3-HF complexes, excited via the single intrinsic tryptophan (Trp-214). Besides the PT tautomer f luorescence ( max ‫؍‬ 526 nm), these protein-probe complexes exhibit a 3-HF anion emission ( max ‫؍‬ 500 nm). Analysis of spectroscopic data leads to the conclusion that two binding sites are involved in the human serum albumin-3-HF interaction. The 3-HF molecule bound in the higher affinity binding site, located in the IIIA subdomain, has the association constant (k 1 ) of 7.2 ؋ 10 5 M ؊1 and predominantly exists as an anion. The lower affinity site (k 2 ‫؍‬ 2.5 ؋ 10 5 M ؊1 ), situated in the IIA subdomain, is occupied by the neutral form of 3-HF (normal tautomer). Since Trp-214 is situated in the immediate vicinity of the 3-HF normal tautomer bound in the IIA subdomain, the intermolecular energy transfer for this donor͞ acceptor pair has a 100% efficiency and is followed by the PT tautomer f luorescence. Intermolecular energy transfer from the Trp-214 to the 3-HF anion bound in the IIIA subdomain is less efficient and has the rate of 1.61 ؋ 10 8 s ؊1 , thus giving for the donor͞acceptor distance a value of 25.5 Å.Excitation by light may initiate both intramolecular and intermolecular transformations of a molecule. Among excited-state intramolecular processes, the most important are electron transfer (1-4), proton transfer (PT; refs. 5 and 6), and conformational transformation (e.g., twisting, torsion, and isomerization; refs. 7-9). The most conspicuous intermolecular events are electron, proton, and energy transfer (10, 11). Excited-state transformations can be coupled with each other and with the surrounding medium. Dependence of the excitedstate intramolecular electron transfer on environmental relaxation (2, 3) and the twisting of solute groups in response to the excited-state charge transfer (12-15) are well-established phenomena. When joined in one molecular system, excited-state events can compete dynamically. An example of such competition is the mutual exclusion of intramolecular electron and PT in 4Ј-diethylamino-3-hydroxyflavone (16-19). Proper pairing of excited-state transformations can be a source of structural͞dynamical information about the molecules possessing these transformations, the excited-state transformations themselves, and the medium where the coupling takes place.The present paper focuses on the coupling between the Förster intermolecular energy transfer (11,20,21) and intramolecular PT (refs. 6 and 22; Fig. 1). The first step of such a coupling is the R Ϫ6 -dependent (R is the intermolecular distance) dipole-dipole intermolecular energy transfer from excited donor to unexcite...

show abstract

Proton transfer dynamics in substituted 3-hydroxyflavones: Solvent polarization effects

Cited by 162 publications

References 28 publications

Interplay between excited-state intramolecular proton transfer and charge transfer in flavonols and their use as protein-binding-site fluorescence probes.

Interplay between excited-state intramolecular proton transfer and charge transfer in flavonols and their use as protein-binding-site fluorescence probes.

Ground-State Proton-Transfer Tautomer of the Salicylate Anion

Energy transfer to a proton-transfer fluorescence probe: Tryptophan to a flavonol in human serum albumin

Contact Info

Product

Resources

About