Excited State Proton Transfer

Electroabsorption is used to determine the difference dipole moment, N D m N , and the difference polarizability, D a ,o f . HBT and HBO, two molecules that undergo excited-state intramolecular proton transfer ESIPT . These measurements are ) . . compared to ab initio 6-31G and semi-empirical INDO1rs calculations. Good agreement is obtained between ab initio and experimental N D m N values. However, the negative D a values obtained experimentally for both molecules are in disagreement with the calculated D a values which are positive. The absorption maxima, measured as a function of solvent polarity, support the electroabsorption results. Agreement between the observed and calulated shift requires that D a for both molecules be negative. q 1998 Elsevier Science B.V. All rights reserved.

Excited-state intramolecular proton transfer (ESIPT) and dual luminescence behaviour of 3-hydroxyflavone (3-HF) have been utilized to monitor its binding to liposomal membranes prepared from egg yolk phosphatydilcholine (EYPC). Additionally, absorption spectrophotometric assay has been performed to evaluate the antioxidant activity of 3-HF against lipid peroxidation in this membrane system. When 3-HF molecules are partitioned into EYPC liposomes, a weak long-wavelength absorption band with λ ∼410 nm appears in addition to the principal absorption at ∼λ = 345 nm. Selective excitation of the 410 nm band produces the characteristic emission (λ∼460 nm) of the ground-state anionic species, whereas excitation at the higher energy absorption band leads to dual emission with predominatly ESIPT tautomer fluorescence (λ = 528 nm). Both ESIPT tautomer and the anionic species exhibit fairly high fluorescence anisotropy (r) values (r = 0.122 and 0.180, respectively). Biexponential fluorescence decay kinetics are observed for the ESIPT tautomer as well as the ground-state anionic forms, indicating heterogeneity in the microenvironments of the corresponding emitting species. Furthermore, we demonstrate that lipid peroxidation of EYPC liposomes is significantly inhibited upon 3-HF binding, suggesting that 3-HF can be potentially useful as an inhibitor of peroxidative damage of cell membranes. Copyright © 2008 John Wiley & Sons, Ltd.

... CHEMICAL PHYSICS LETTERS 12Apr11 1991 Volume 179, number 1,2 Munna Sarkar and Pradeep K. Sengupta Saha Institute of Nuclear Physics, 1 AF, Bidhannagar, Calcutta 700 064, India Received 1 November 1990; in final ... [2] A. Nag and K. Bhattacharyya, J. Photochem. ...

The phototropins constitute an important class of plant photoreceptor kinases that control a range of physiological responses, including phototropism, light-directed chloroplast movement, and light-induced stomatal opening. The LOV2 domain of phototropin binds a molecule of ...

The structure and electronic spectra of 2-methylamino-6-methyl-4-nitropyridine N-oxide (2M6M) were investigated. The X-ray structure of 2M6M molecule shows that it crystallizes in the monoclinic system of the P21/n space group and forms internally hydrogen-bonded [N

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

We report investigations of resonance energy transfer in the green fluorescent protein and calmodulin-based fluorescent indicator constructs for Ca(2+) called cameleons using steady-state and time-resolved spectroscopy of the full construct and of the component green fluorescent protein mutants, namely ECFP (donor) and EYFP (acceptor). EYFP displays a complicated photophysical behavior including protonated and deprotonated species involved in an excited-state proton transfer. When EYFP is excited in the absorption band of the protonated species, a fast nonradiative deactivation occurs involving almost 97% of the excited protonated population and leading to a low efficiency of excited-state proton transfer to the deprotonated species. ECFP displays a multiexponential fluorescence decay with a major contributing component of 3.2 ns. The time-resolved fluorescence data obtained upon excitation at 420 nm of Ca(2+)-free and Ca(2+)-bound YC3.1 cameleon constructs point to the existence of...

A theoretical and experimental study on the absorption and fluorescence properties of a newly synthesized compound 3,6-bis(4,5-dihydroxyoxazo-2-yl)benzene-1,2-diol in ethanol is reported. Evidence suggesting
intramolecular proton transfer in the excited singlet state is presented. All possible tautomeric forms are studied by means of TDDFT B3LYP/6-31G(d,p) in both the ground and the first excited singlet state. On the basis of the results obtained excited state double proton transfer in the title compound is proposed.

Photophysical and photochemical dynamics of ground state and excited state proton transfer reaction is reported for Pyrrole 2-Carboxyldehyde (PCL). Steady state absorption and emission measurements are conducted in PCL. The theoretical investigation is done by using different quantum mechanical methods (e.g. Hartree Fock, DFT, MP2, CCSD etc.). The reaction pathway and two dimensional potential energy surfaces are computed in various level of theory. A transition state is also reported in gas phase and reaction filed calculation. It is established that PCL forms different emitting species in different media. A large Stokes shifted emission band, which is attributed to species undergoing excited state intramolecular proton transfer, is observed in hydrocarbon solvent. Intermolecular proton transfer is observed in hydroxylic polar solvent. Experimental observations yield all possible signatures of intramolecular and intermolecular proton transfer in excited state of PCL. The origins of these signatures have been explained successfully using corresponding quantum mechanical theories.

We obtain an accurate long time solution for the diffusive kinetics of an excited geminate pair dissociating reversibly in solution, where the excited-state lifetimes of the bound and unbound states may be non-equal. We analyze the long-time asymptotic behavior, finding a transition between two types of behaviors. In region A, the excited bound pair decays as t -3/2 exp(-t /t'0), where t'0 is the lifetime of the unbound state. In region AB, the decay is a pure exponential. At the critical value of the parameters where the transition occurs, we find a  t -1/2 exp(-t /t'0) decay. These predictions are tested against an exact numerical solution of the corresponding coupled partial differential equations. For region A, we supply an experimental example involving time-resolved excited-state proton transfer from 5-cyano-2-naphthol to dimethyl sulfoxide.