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60 results on '"Chemerisov, S."'

51. H-Atom Electron-Spin Polarization in Irradiated Water and Ice Confined in the Nanopores of Vycor Glass

Author

Tarasov, V. F., Chemerisov, S. D., and Trifunac, A. D.

Abstract

Chemically Induced Dynamic Electron-spin Polarization (CIDEP) in radiolytically generated H atoms in water-saturated Vycor glass is observed at different temperatures (+29 to −94 °C) by time-resolved pulsed EPR spectroscopy. The kinetics of polarization is investigated by means of the numerical solution of the stochastic Liouville equation (SLE) as applied to a two-site kinetic model. The experimental results are quantitatively simulated assuming that the H atom is one of the partners of the random (or triplet geminate) radical pairs and that the Heisenberg spin−spin exchange interaction is the only inter-radical interaction in such pairs. The recombination of H atoms with radical pair partners is a spin-selective reaction with activation parameters close to those of H-atom diffusion. It is shown that the rate of longitudinal spin relaxation of the partner, the rate of encounters, and the rate of the spin-selective recombination of the H atom with a partner are the most important kinetic parameters defining the observed time evolution of CIDEP. The kinetics of the CIDEP is defined mostly by the polarization generated in random pairs. The contribution of CIDEP from the geminate triplet radical pairs is important only at short times.

Published
2003

55. A Multinuclear NMR Study on the Structure and Dynamics of Lanthanide(III) Complexes of the Poly(amino carboxylate) EGTA4- in Aqueous Solution

Author

Aime, S., Barge, A., Borel, A., Mauro Botta, Chemerisov, S., Merbach, A. E., Müller, U., and Pubanz, D.

Abstract

The structures and intramolecular dynamics of [Ln(EGTA)(H2O)]- (Ln = La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+, Lu3+ and EGTA4- = 3,12-bis(carboxymethyl)-6,9-dioxa-3,12-diazatetradecanedioate(4-)) in aqueous solution have been investigated by variable temperature 1H and 13C NMR. The quantitative analysis of the proton hyperfine shifts and considerations about the stereochemical nonrigidity indicate the occurrence of a structural change along the lanthanide series with the crossover between Sm and Eu. Changes of coordination number from 10 to 9 to 8 are proposed to occur across the series. The experimental data from 17O NMR, EPR and NMRD studies for the Gd3+ complex are treated using a self-consistent theoretical model in a simultaneous multiple parameter least-squares fitting procedure (Powell, D. H.; Ni Dhubhghaill, O. M.; Pubanz, D.; Helm, L.; Lebedev, Y. S.; Schlaepfer, W.; Merbach, A. E. J. Am. Chem. Soc. 1996, 118, 9333). An intermolecular dipole-dipole electronic relaxation mechanism that has very recently been described for Gd3+ complexes (Powell et al., op. cit.) is included in the data treatment. The high water exchange rate of [Gd(EGTA)(H2O)]- of kex298= (3.1 ± 0.2) × 107 s-1 is explained in terms of a limiting dissociative exchange mechanism (DV* = +10.5 ± 1.0 cm3mol-1), favored by the steric constraints on the water binding site that are revealed by the study on the solution structure.

59. Manipulation of spatiotemporal photon distribution via chromatic aberration.

Author

Li Y and Chemerisov S

Abstract

We demonstrate a spatiotemporal laser-pulse-shaping scheme that exploits the chromatic aberration in a dispersive lens. This normally harmful effect transforms the phase modulation into a beam-size modulation at the focal plane. In combination with the intricate diffraction effect via beam apodization, this method provides a spatiotemporal control of photon distribution with an accuracy of diffraction limit on a time scale of femtoseconds.

Published
2008
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60. Proton transfer at helium temperatures during dioxygen activation by heme monooxygenases.

Author

Davydov R, Chemerisov S, Werst DE, Rajh T, Matsui T, Ikeda-Saito M, and Hoffman BM

Subjects
Camphor 5-Monooxygenase chemistry, Camphor 5-Monooxygenase metabolism, Cold Temperature, Electron Spin Resonance Spectroscopy methods, Heme Oxygenase (Decyclizing) chemistry, Myoglobin chemistry, Myoglobin metabolism, Oxidation-Reduction, Oxygen chemistry, Oxyhemoglobins chemistry, Oxyhemoglobins metabolism, Heme Oxygenase (Decyclizing) metabolism, Oxygen metabolism
Abstract

In the first measurement of enzymatic proton transfer at liquid helium temperatures, we examine protonation of the peroxo-ferriheme state of heme oxygenase (HO) produced by in situ radiolytic cryoreduction of oxy-HO in H2O and D2O solvents at ca. 4 K and above, and compare these findings with analogous measurements for oxy-P450cam and for oxy-Mb. Proton transfer in HO occurs at helium temperatures in both solvents; it occurs in P450cam at approximately 50 K and higher; in Mb it does not occur until T > 170 K. For Mb, this transfer at 180 K is biphasic, and the majority phase shows a solvent kinetic isotope effect of 3.8. We discuss these results in the context of the picture of environmentally coupled tunneling, which links proton transfer to two classes of protein motions: environmental reorganization (lambda in Marcus-like equations) and protein fluctuations ("active dynamics"; gating) which modulate the distance of proton transfer.

Published
2004
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