Dynamics proton transfer

Seminal studies on the dynamics of proton transfer in the triplet manifold have been performed on HBO [109]. It was found that in the triplet states of HBO, the proton transfer between the enol and keto tautomers is reversible because the two (enol and keto) triplet states are accidentally isoenergetic. In addition, the rate constant is as slow as milliseconds at 100 K. The results of much slower proton transfer dynamics in the triplet manifold are consistent with the earlier summarization of ESIPT molecules. Based on the steady-state absorption and emission spectroscopy, the changes of pKa between the ground and excited states, and hence the thermodynamics of ESIPT, can be deduced by a Forster cycle [65]. Accordingly, compared to the pKa in the ground state, the decrease of pKa in the... 

Wang H, Zhang H, Abou-Zied OK et al (2003) Femtosecond fluorescence upconversion studies of excited-state proton-transfer dynamics in 2-(20-hydroxyphenyl)benzoxazole (HBO) in liquid solution and DNA. Chem Phys Lett 367 599-608... 

Parsapour F, Kelley DF (1996) Torsional and proton transfer dynamics in substituted 3-hydroxyflavones. J Phys Chem 100 2791-2798... 

Swinney TC, Kelley DF (1993) Proton transfer dynamics in substituted 3-hydroxyflavones solvent polarization effects. J Chem Phys 99 211-221... 

Matzke, M. and Matzke, A.J.M. (2003). RNA extends its reach. Science, 301, 1060-1061 Mulkidjanian, A.Y., Cherepanar, D.A., Heberle, J. and Junge, W. (2005). Proton transfer dynamics at membrane/water interface and the mechanism of biological energy conversion. Biochem. (Moscow), 70, 251-256... 

Excited-state proton transfer dynamics of 6-hydroxyquinoline in acidic and alkaline aqueous solutions... 

We have demonstrated that the novel antitumor agent 10-hydroxycamptothecin has remarkable excited-state acidity. In contrast to simple 6-hydroxyquinoline, no tautomerization is observed. The implications for the use of proton transfer dynamics in studying the microenvironment of cells remains to be demonstrated. 

In conclusion, a typical time of 300 fs has been found for the excited-state intramolecular double proton transfer in TAB and DAC. The proton transfer dynamics is not influenced by aggregation. In addition, a vibronic cooling time of 20 ps has been measured for the probe molecules in the molecular and stacked configurations. Finally, aggregation is found to almost completely hamper the rotational diffusion motions of the molecules during the fluorescence state lifetime of 4 ns. 

The signature of proton transfer in solution is the red-shifted fluorescence of the deprotonated chromophore [4-7], From the transition frequencies of absorption and emission and the ground-state dissociation constant, the dissociation constant in the excited state can be calculated [4-7], The time scales of proton transfer processes generally are very short, of the order of picoseconds or below [7], Only recently has it become possible to detect the photoinduced proton transfer dynamics in solution in real time [9,10],... 

An interesting interpretation of temperature dependent lineshapes based on population changes as a function of temperature has been proposed recently [208]. In particular, variable temperature 15N CP MAS NMR has been employed to investigate proton transfer dynamics and N-H bond lengthening in N-H - -N hydrogen bonds. 

Kearley, G. J., Fillaux, F., Baron, M.-Fl., Bennington, S., andTomkinson, J.,A new look at proton transfer dynamics along the hydrogen bonds in amides and peptides. Science 264, 1285-1289 (1994). 

Tanaka, M., Fujiwara, M., Xu, Q., Ando, H., Raeker, T. J. Influence of Conformation and Proton-Transfer Dynamics in the Dibenzyl s-Complex on Regioselectivity in Gattermann-Koch Formylation via Intracomplex Reaction. J. Org. Chem. 1998, 63,4408-4412. 

In particular, in Ref. 78 the proton transfer dynamics of hydrogen bonds in the vicinity of the guest molecules has been studied by using a field-cyclic nuclear magnetic relaxometry (spin-lattice relaxometry). It has been revealed that the spin lattice relaxation incorporates the two major members ... 

Proton transfer dynamics in polar liquids can be monitored by the solvent polarization, AE R), [36,37]... 

In conclusion to this section, band-shape analysis of vibrational spectra and ground state splitting observed with INS demonstrate that proton transfer dynamics are quantal in nature, even at room temperature. Semiclassical models are not relevant. The dramatic failure of quantum chemistry to account for the observed dynamics should be regarded as one of the major unsolved theoretical problems at the present time. 

F. Fillaux J. Tomkinson (1992). J. Mol Struct., 270, 339-349. Proton transfer dynamics in the hydrogen bond. Inelastic neutron scattering spectra of Na, Rb and Cs hydrogen carbonates at low temperature. 

F. Fillaux, J.P. Fontaine, M.H. Baron, N. Leygue, G.J. Kearley J. Tomkinson (1994). Biophysical Chemistry, 53, 155-168. Inelastic neutron-scattering study of the proton transfer dynamics in polyglycine I at 20K. 

Proton transfer dynamics of photoacids to the solvent have thus, being reversible in nature, been modelled using the Debye-von Smoluchowski equation for diffusion-assisted reaction dynamics in a large body of experimental work on HPTS [84—87] and naphthols [88-92], with additional studies on the temperature dependence [93-98], and the pressure dependence [99-101], as well as the effects of special media such as reverse micelles [102] or chiral environments [103]. Moreover, results modelled with the Debye-von Smoluchowski approach have also been reported for proton acceptors triggered by optical excitation (photobases) [104, 105], and for molecular compounds with both photoacid and photobase functionalities, such as lO-hydroxycamptothecin [106] and coumarin 4 [107]. It can be expected that proton diffusion also plays a role in hydroxyquinoline compounds [108-112]. Finally, proton diffusion has been suggested in the long time dynamics of green fluorescent protein [113], where the chromophore functions as a photoacid [23,114], with an initial proton release on a 3-20 ps time scale [115,116]. 

Mavri, J., Grdadolnik, J., Proton transfer dynamics in acetylacetone A mixed quantum-classical simulation of... 

Another aspect of the intermembranal water phase that can be elucidated by the time-resolved proton transfer dynamics is the intensity of the electrostatic forces. The thin layer of a high dielectric fluid sandwiched between the low dielectric lipid plates, each covered by positive and negative charges, forms a very complex medium for calculation of electrostatic interaction (24, 25). 

At this point, we do not know which of several approaches is most promising. Thus, our membrane development efforts involve (1) a full-fledged effort to explore approaches involving polymer synthesis and development, as well as implementation of new carrier media to replace the function of water in Nafion, and (2) a study of proton transfer dynamics. We are using theoretical approaches to explore specific possibilities for new acid group types or for... 

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