Rotational mechanism for vibrational relaxation in rigid media. Interaction potentials

Using the assumption of pairwise additive forces we derive the interaction potential acting upon a substantial impurity in a crystalline lattice. The angle dependent parts of the force on the impurity internal vibrations are represented in the form of a Fourier series. Numerical calculations of the Fourier coefficients of the force are presented for a model system employing empirical argon—argon interactions. The higher Foutier coefficients are shown to decrease rapidly in conformity with the simple model potential used to describe the vibrational relaxation in a preceding paper.     

Separation of naphthalene-2,3-dicarboxaldehyde-derivatized-substance P and its metabolites by micellar electrokinetic chromatography

This paper describes the development of analytical methodology for the separation of naphthalene-2,3-dicarboxaldehyde (NDA)-derivatized substance P (CBI-SP) and five lysine-containing metabolites by micellar electrokinetic chromatography (MEKC). The effect of surfactant composition and organic modifiers on the separation was investigated. The final separation buffer consisted of 80 mM sodium cholate in 50 mM N-tris (hydroxymethyl)methyl-2-aminoethanesulfonic acid (TES), pH 7. All six lysine-containing peptides were separated under these conditions.     

Nonradiative decay processes in benzene

We investigate the behavior of single vibronic level nonradiative decay rates in benzene and benzene-d₆. The effects of excitation in a promoting mode which undergoes frequency and geometry changes in the S₁ relaxation (to T₁ or S₀) are considered in detail. Calculated relative nonradiative decay rates are compared with experimental values and are used to assign triplet state vibrational frequencies to the ν_s, ν₁₀ and ν₁₆ vibrations. This comparison also indicates that none of these modes, nor the modes ν₁ and ν6, are likely to be the dominant promoting modes for the S₁ → T₁ decay. Some simple expressions are given which provide good estimates of the vibronic state dependence of the non-radiative decay rates. In conjuction with experimental decay rate data, these estimates can aid in guiding spectral assignments of vibronic bands. Simple but general theoretical criteria are derived which are useful in determining those vibrations which are poor (or good) accepting modes. Our previous theory is generalized to consider absolute nonradiative decay rates. The results are used to suggest a possible mechanism for the “channel three” decay process observed by Callomon . Although the numerical applications presented here are to benzene electronic relaxation processes, the theoretical developments also apply to and the calcultions illustrate general features of nonradiative decay in the statistical limit.     

The analysis of elliptic families. I. Metrics and connections on determinant bundles

In this paper, we construct the Quillen metric on the determinant bundle associated with a family of elliptic first order differential operators. We also introduce a unitary connection on and calculate its curvature. Our results will be applied to the case of Dirac operators in a forthcoming paper.     

Parametrization, molecular dynamics simulation, and calculation of electron spin resonance spectra of a nitroxide spin label on a polyalanine alpha-helix

The nitroxide spin label 1-oxyl-2,2,5,5-tetramethylpyrroline-3-methyl-methanethiosulfonate (MTSSL), commonly used in site-directed spin labeling of proteins, is studied with molecular dynamics (MD) simulations. After developing force field parameters for the nitroxide moiety and the spin label linker, we simulate MTSSL attached to a polyalanine alpha-helix in explicit solvent to elucidate the factors affecting its conformational dynamics. Electron spin resonance spectra at 9 and 250 GHz are simulated in the time domain using the MD trajectories and including global rotational diffusion appropriate for the tumbling of T4 Lysozyme in solution. Analysis of the MD simulations reveals the presence of significant hydrophobic interactions of the spin label with the alanine side chains.     

Solvation effect on conformations of 1,2:dimethoxyethane: charge-dependent nonlinear response in implicit solvent models

The physical content of and, in particular, the nonlinear contributions from the Langevin-Debye model are illustrated using two applications. First, we provide an improvement in the Langevin-Debye model currently used in some implicit solvent models for computer simulations of solvation free energies of small organic molecules, as well as of biomolecular folding and binding. The analysis is based on the implementation of a charge-dependent Langevin-Debye (qLD) model that is modified by subsequent corrections due to Onsager and Kirkwood. Second, the physical content of the model is elucidated by discussing the general treatment within the LD model of the self-energy of a charge submerged in a dielectric medium for three different limiting conditions and by considering the nonlinear response of the medium. The modified qLD model is used to refine an implicit solvent model (previously applied to protein dynamics). The predictions of the modified implicit solvent model are compared with those from explicit solvent molecular dynamics simulations for the equilibrium conformational populations of 1,2-dimethoxyethane (DME), which is the shortest ether molecule to reproduce the local conformational properties of polyethylene oxide, a polymer with tremendous technological importance and a wide variety of applications. Because the conformational population preferences of DME change dramatically upon solvation, DME is a good test case to validate our modified qLD model. The present analysis of the modified qLD model provides the motivation and tools for studying a wide variety of other interesting systems with heterogeneous dielectric properties and spatial anisotropy.     

EPR distance measurements support a model for long-range radical initiation in E. coli ribonucleotide reductase

The class I E. coli ribonucleotide reductase, composed of homodimers of R1 and R2, catalyzes the conversion of nucleoside diphosphates to deoxynucleoside diphosphates. The reduction process involves the tyrosyl radical on R2 that generates a transient thiyl radical on R1 over a proposed distance of 35 A. A mechanism-based inhibitor, 2'-azido-2'-deoxyuridine-5'-diphosphate, that reduces the tyrosyl radical on R2 and forms a nitrogen-centered radical on R1 has provided a method to measure the diagonal distance between the two subunits. PELDOR and DQC paramagnetic resonance methods give rise to a distance of 48 A, similar to that calculated from a docking model of the R1 and R2 structures.     

International Conference dedicated to the bicentenary of the publication of the first theory of electrolysis by Theodor Grotthuss (1785–1822)

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International Conference dedicated to the bicentenary of the publication of the first theory of electrolysis by Theodor Grotthuss (1785–1822)     

Green's function semiclassical quantization of non-closed quasiperiodic classical trajectories

A semiclassical quantization procedure is introduced within the Green's function formalism for non-closed quasiperiodic trajectories which have previously defied quantization with this formalism. The results are interpreted in terms of the uncertainty principle and lead to conjectures concerning the semiclassical quantization of ergodic trajectories.