Search results for "Effects"
showing 10 items of 2634 documents
Amino Acid Chemistry in Solution: Structural Study and Vibrational Dynamics of Glutamine in Solution. An ab Initio Reaction Field Model
1998
The self-consistent reaction field (SCRF) theory was used to study structural and vibrational features of the amino acid L-glutamine in solution. Raman and infrared spectra of this molecule in solutions of H 2O and D2O were recorded and measured. The bands were firstly assigned on the basis of the isotopic shifts. An ab initio quadratic force field at the 6-31 +G* level was achieved. The calculation simulated a polar solvent by placing the molecule in an ellipsoidal cavity surrounded by a continuum dielectric. The theoretical results, in terms of structural parameters, vibrational frequencies and descriptions, and infrared intensities, were in satisfactory agreement with the experimental da…
Amino acid chemistry in solution: structural properties and vibrational dynamics of serine using density functional theory and a continuum solvent mo…
2004
A structural and vibrational study of amino acid serine in aqueous solution has been carried out using Fourier transform spectroscopies and quantum mechanical calculations. FT-IR and FT-Raman spectra of serine in H2O and D2O solutions were recorded and a general assignment of the observed bands was proposed on the basis of a zwitterionic structure for serine. Main criteria were the observed wavenumber shifts upon deuteration and previous assignments for other amino acids. A quadratic force field was computed using ab initio methodology at the 6-31+G** level and the hybrid functional B3LYP. The solvent effect was simulated by placing the serine molecule into an ellipsoidal cavity surrounded …
Determination of the relative quantum yields of the conformational species of autoassociating polypeptide gramicidin A in organic solvent using combi…
1987
Abstract A simple, novel method is proposed for the accurate determination of the relative quantum yields of each of the interconverting conformational species of the autoassociating polypeptide gramicidin A in organic solution. The method is based on fitting the experimental results obtained independently from fluorescence emission spectroscopy and high performance liquid chromatography. The fluorescence parameters obtained are discussed in terms of the structural features of the individual conformational species. The advantages of this approach and its possible application to other different organic solvents or to other autoassociating polypeptides are also considered.
Intermolecular coupling influence on conformations of molecules in solution
1994
Abstract The influence of non-specific intermolecular interactions on conformational equilibria of organic molecules is investigated with the help of the London-Debye-Keesom pair coupling potentials. It is shown that in a series of apolar solvents equilibrium constant logarithms are proportional to ζα ≡ Z αs/ R 6s,d, and in a series of polar solvents equilibrium constants logarithms are proportional to ζμ ≡ Z μ2s/ R 6s,d, where Z is the average number of neighbours of a solute molecule in the first coordination sphere, αs is the polarizability, μs the dipole moment of solvent molecules, and R s,d = R s + R d is the sum of the radii of spherical volumes per molecule of solvent (s) and dissol…
Stability of thin polymer films: influence of solvents.
2004
The interface and surface properties and the wetting behavior of polymer-solvent mixtures are investigated using Monte Carlo simulations and self-consistent field calculations. We carry out Monte Carlo simulations in the framework of a coarse-grained bead-spring model using short chains (oligomers) of N(P)=5 beads and a monomeric solvent, N(S)=1. The self-consistent field calculations are based on a simple phenomenological equation of state for compressible binary mixtures and we employ Gaussian chain model. The bulk behavior of the polymer-solvent mixture belongs to type III in the classification of van Konynenburg and Scott [Phil. Trans. R. Soc. London, Ser. A 298, 495 (1980)]. It is char…
Fluctuation theorems for non-Markovian quantum processes
2013
Exploiting previous results on Markovian dynamics and fluctuation theorems, we study the consequences of memory effects on single realizations of nonequilibrium processes within an open system approach. The entropy production along single trajectories for forward and backward processes is obtained with the help of a recently proposed classical-like non-Markovian stochastic unravelling, which is demonstrated to lead to a correction of the standard entropic fluctuation theorem. This correction is interpreted as resulting from the interplay between the information extracted from the system through measurements and the flow of information from the environment to the open system: Due to memory e…
Hidden entanglement, system-environment information flow and non-Markovianity
2014
It is known that entanglement dynamics of two noninteracting qubits, locally subjected to classical environments, may exhibit revivals. A simple explanation of this phenomenon may be provided by using the concept of hidden entanglement, which signals the presence of entanglement that may be recovered without the help of nonlocal operations. Here we discuss the link between hidden entanglement and the (non-Markovian) flow of classical information between the system and the environment.
Memory Effects in High-Dimensional Systems Faithfully Identified by Hilbert–Schmidt Speed-Based Witness
2022
A witness of non-Markovianity based on the Hilbert–Schmidt speed (HSS), a special type of quantum statistical speed, has been recently introduced for low-dimensional quantum systems. Such a non-Markovianity witness is particularly useful, being easily computable since no diagonalization of the system density matrix is required. We investigate the sensitivity of this HSS-based witness to detect non-Markovianity in various high-dimensional and multipartite open quantum systems with finite Hilbert spaces. We find that the time behaviors of the HSS-based witness are always in agreement with those of quantum negativity or quantum correlation measure. These results show that the HSS-based witness…
Improved stability of solid state light emitting electrochemical cells consisting of ruthenium and iridium complexes
2006
ABSTRACTTwo charged organometallic complexes containing bulky hydrophobic ligands based on ruthenium (II) and iridium (III) were synthesized and their performance in solid state light emitting electrochemical cells is described. The complexes were chosen as due to their large ligands a diminished susceptibility towards the formation of destructive complexes during device operation is expected. The LEC device performances reveal the longest living devices reported so far under dc bias. Quantum chemical calculations confirm that the major effect of the bulky diphenylphenanthroline ligands is of steric origin and not related with changes in the molecular electronic structure of the complexes.
Low-energy couplings of QCD from topological zero-mode wave functions
2003
By matching 1/m^2 divergences in finite-volume two-point correlation functions of the scalar or pseudoscalar densities with those obtained in chiral perturbation theory, we derive a relation between the Dirac operator zero-mode eigenfunctions at fixed non-trivial topology and the low-energy constants of QCD. We investigate the feasibility of using this relation to extract the pion decay constant, by computing the zero-mode correlation functions on the lattice in the quenched approximation and comparing them with the corresponding expressions in quenched chiral perturbation theory.