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51.
52.
Presiado I Karton-Lifshin N Erez Y Gepshtein R Shabat D Huppert D 《The journal of physical chemistry. A》2012,116(27):7353-7363
Steady-state and time-resolved emission techniques were used to study the photoprotolytic properties of three recently synthesized strong quinone cyanine photoacids (QCy7 and its sulfonated derivatives). The rate coefficient of the excited-state proton transfer (ESPT), k(PT), of the three dyes is roughly 1.5 × 10(12) s(-1), a high value that is comparable to the solvation dynamics rate of large polar organic molecules in H(2)O and D(2)O. It is twice as fast as the proton transfer rate between two adjacent water molecules in liquid water. We found that, as expected, two of the sulfonated photoacids geminately recombines with the proton at an elevated rate. The accelerated geminate recombination process of the sulfonated derivatives is different from a simple diffusion process of protons. The ESPT rate coefficient of these molecules is the highest recorded thus far. 相似文献
53.
Proton antenna effect of the gamma-cyclodextrin outer surface, measured by excited state proton transfer 总被引:2,自引:0,他引:2
Gepshtein R Leiderman P Huppert D Project E Nachliel E Gutman M 《The journal of physical chemistry. B》2006,110(51):26354-26364
The reversible proton dissociation and geminate recombination of the common photoacid, 8-hydroxypyrene-1,3,6-trisulfonate (pyranine), either in dilute aqueous solution or when forming a complex with gamma-cyclodextrin (gamma-CD), has been studied by time-resolved fluorescence spectroscopy and supplemented by molecular modeling and dynamics simulations. We find that the dissociation rate of the proton from the excited molecule was decreased to about approximately 50% of its value in water, while the rate of recombination was doubled. These observations were evaluated by molecular modeling of the reactants at atomic resolution. The combination of the two methodologies indicates that the pyranine in the complex can assume more than one level of interaction with the solvent. The polysugar torus surrounding the pyranine perturbs the hydrogen bond in the dye's immediate vicinity and deforms the electrostatic potential inside the Coulomb cage, causing major deviations from a simple spheric symmetry. These observations can account for the special kinetic features measured for the complex. We suggest that this system can be used as a basic model for evaluating the mechanism of proton transfer in non-homogeneous systems, such as the surface of proteins or biomembranes. 相似文献
54.
Leiderman P Gepshtein R Uritski A Genosar L Huppert D 《The journal of physical chemistry. A》2006,110(29):9039-9050
The reversible proton dissociation and geminate recombination of a photoacid is studied as a function of temperature in water electrolyte solutions and binary water-methanol mixtures, containing 0.1 and 0.2 mole fractions of methanol. 8-Hydroxypyrene-1,3,6-trisulfonate trisodium salt (HPTS) is used as the photoacid. The experimental data are analyzed by the reversible geminate recombination model. We found that the slope of the logarithm of the proton-transfer rate constant as a function of the inverse of temperature (Arrhenius plot) in the liquid phase of these samples are temperature-dependent, while in the solid phase, the slope is nearly constant. The slope of the Arrhenius plot in frozen electrolyte solution is larger than that of the water-methanol mixtures, which is about the same as in pure water. Careful examination of the time-resolved emission in ice samples shows that the fit quality using the geminate recombination model is rather poor at relatively short times. We were able to get a better fit using an inhomogeneous kinetics model assuming the proton-transfer rate consists of a distribution of rates. The model is consistent with an inhomogeneous frozen water distribution next to the photoacid. 相似文献
55.
Time-resolved emission was used to measure the photoprotolytic cycle of an excited photoacid as a function of temperature, both in liquid water and in ice, in the presence of an inert salt. The inert salt affects the geminate recombination between the transferred proton with the conjugate base of the photoacid. We used the Debye-Hückel theory to express the screening of the Coulomb electrical potential by the inert salt. We find that in the liquid phase the measured screening effect is small and the Debye-Hückel expression slightly overestimates the experimental effect. In ice, the screening effect is rather large and the Debye-Hückel expression under estimates the measured effect. We explain the large screening in ice by the "salting-out" effect in ice that tends to concentrate the impurities to confined volumes to minimize the ice crystal energy. 相似文献
56.
Dr. Luís Pinto da Silva Dr. Ron Simkovitch Prof. Dr. Dan Huppert Prof. Dr. Joaquim C. G. Esteves da Silva 《Chemphyschem》2013,14(15):3441-3446
The oxyluciferin family of fluorophores has been receiving much attention from the research community and several systematic studies have been performed in order to gain more insight regarding their photophysical properties and photoprotolytic cycles. In this minireview, we summarize the knowledge obtained so far and define several possible lines for future research. More importantly, we analyze the impact of the discoveries on the firefly bioluminescence phenomenon made so far and explain how they re‐open again the discussion regarding the identity (keto or enol species) of the bioluminophore. 相似文献
57.
Solntsev KM Sullivan EN Tolbert LM Ashkenazi S Leiderman P Huppert D 《Journal of the American Chemical Society》2004,126(39):12701-12708
Time-resolved and steady-state emission characterization of 10-hydroxycamptothecin reveals a rich but less complex proton-transfer behavior than its parent hydroxyquinoline. The electronic effect of the additional electron-withdrawing ring makes the excited-state both less basic and more acidic than the parent and adds to the class of high-acidity excited-state proton donors in photochemistry and photobiology. 相似文献
58.
We report time-resolved fluorescence data for the anion of p-hydroxybenzylidene dimethylimidazolinone (p-HBDI), a model chromophore of the green fluorescence protein, in viscous glycerol-water mixtures over a range of temperatures, T. The markedly nonexponential decay of the excited electronic state is interpreted with the aid of an inhomogeneous model possessing a Gaussian coordinate-dependent sink term. A nonlinear least-squares fitting routine enables us to achieve quantitative fits by adjusting a single activation parameter, which is found to depend linearly on 1/T. We derive an analytic expression for the absolute quantum yield, which is compared with the integrated steady-state fluorescence spectra. The microscopic origins of the model are discussed in terms of two-dimensional dynamics, coupling the phenyl-ring rotation to a swinging mode that brings this flexible molecule to the proximity of a conical intersection on its multidimensional potential energy surface. 相似文献
59.
Bertram Huppert 《Archiv der Mathematik》1980,35(1):164-176
Ohne Zusammenfassung
Wolfgang Gaschütz zum 60. Geburtstag 相似文献
60.
Results are presented of a series of experiments in which hyper-eutectic aqueous solutions of NH4Cl and NH4Br contaminated by small amounts of CuSO4 are cooled from below. The experiments with NH4Cl indicate that beyond a contamination of 0.3 wt%, the well-known chimney structure that is associated with solidification from a pure aqueous solution of NH4Cl disappears. Subsidiary experiments indicate that at approximately the same level of contamination, the branched dendritic morphology that is usually associated with crystalline NH4Cl is suppressed. It is suggested that the macroscopic chimney-driven compositional convection that results from cooling hyper-eutectic aqueous solutions of NH4Cl is rather sensitive to the microscopic details of the crystal growth. Solidification experiments with pure hyper-eutectic aqueous solutions of NH4Br display a similar chimney-driven convective pattern; however, this is effectively unchanged even in the presence of contaminations of up to 1 wt% of CuSO4. 相似文献