Effects of the Bead‐Solvent Interaction on the Dynamics of Macromolecules, 1

Summary: Hamiltonian dynamics and a chain model are used to study the dynamics of macromolecules immersed in a solution. From the Hamiltonian of the overall system, “macromolecule + solvent,” a master and a Fokker‐Planck equation are then derived for the phase‐space distribution of the macromolecule. In the Fokker‐Planck equation, all the information about the interaction among the beads of the macromolecule as well as the effects of the surrounding solvent is described by friction tensors, which are expressed in terms of the bead‐solvent interaction and the dynamic structure factor of the solvent. To explore the influence of the bead‐solvent potential on the dynamics of macromolecules, the friction tensors are calculated for a dumbbell molecule and for three choices of the interaction (Yukawa, Born‐Mayer, and Lennard‐Jones). Expressions are derived, in particular, for the friction tensor coefficients of the center‐of‐mass and the relative coordinates of the dumbbell. For the long‐term behaviour of the internal momentum autocorrelation function, moreover, an “algebraic decay” is found, in contrast to the (unphysical) exponential decay as known from phenomenological theory.

Yukawa, Born‐Mayer and Lennard‐Jones bead‐solvent interaction potentials.     

Electron correlation and the compton profile of atomic neon

The radial momentum distribution I_o(p) and the Compton profile J_o(q) are determined for atomic neon from several restrictid Hartree-Fock (RHF) wavefunctions and two configuration interaction (CI) wavefunctions. The CI functions are the well correlated (full“second-order”) function of Viers, Schaeffer and Harris, and the Ahlrichs-Hinze multi-configuration Hartree-Fock (MCHF) function which includes only L-shell correlation. It is found for this completely closed shell system that the effects of electron correlation are quite small. This contrasts with the results for systems such as Be(²S) and B(²P) where the semi-internal and internal correlation effects were responsible for significant discrepancies between the RHF and CI results. These results indicate that a wavefunction which carefully includes the semi-internal, orbital polarization, and internal correlations beyond the RHF wavefunction (i.e., a “first-order” or “charge-density” function), should account for the principal correlation effects on the Compton profiles and momentum distributions.     

DWBA predicted relative product rotational state distribution for H + D2 → HD + D

Relative product rotational state distributions for H + D₂ → HD + D are reported based on the DWBA of Suck Salk, and are shown to agree reasonably well with observations. The rotational peak positions are found to have good correlation with computed “semiclassical” angular momentum.     

Recursion formula for electron repulsion integrals over Hermite polynomials

A method for computing electron repulsion integrals over contracted Gaussian functions is described in which intermediate integrals over Hermite polynomials are generated by a “pre‐Hermite” recursion (PHR) step before the conversion to regular integrals. This greatly reduces the floating‐point operation counts inside the contraction loops, where only simple “scaling”‐type operations are required, making the method efficient for contracted Gaussians, particularly of high angular momentum. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Struktur-Reaktivitäts-Beziehungen bei koordinativ-ungesättigten Chelatkomplexen. VI. Synthese,Adduktbildung, Redoxpotentiale und photochrome lodderivate von Eisen(II)-Komplexen Schiffscher Basen mit elektronenziehenden Substituenten

Structure Reactivity Correlations in Coordinatively Unsaturated Chelate Complexes. VI. Synthesis, Adduct Formation, Redox Potentials, and Photochromic Iodine Derivatives of Iron(II) Complexes with Schiff Base Ligands Possessing Electron-Withdrawing Substituents Iron(II) complexes of the type 1 have been prepared by different synthetic methods. In contrast to similar chelates of the “saloph” and “salen” types, the high-spin complexes 1 form stable high-spin diadducts ( 1a – 1d ) and an unusual triadduct ( 1e ) with pyridine. The oxidation potentials of the Fe^II/Fe^III couple as measured by cyclic voltammetry are dependent on the solvent as well as the equatorial ligand substituents. The potentials are more positive in pyridine than in DMF, indicating a stabilization of Fe^II by pyridine. The redox potentials are discussed with respect to those of other metals in the same ligand environment. The complexes form iodine derivatives which show photochromic behaviour in THF solution. The rate of the reaction with dioxygen in the solid state as well as in pyridine solution decreases in the order 1f > 1a ≈ 1b > 1c ≈ 1d > 1e and correlates with the increasing oxidation potentials.     

Looking at atomic orbitals through fourier and wavelet transforms

Solutions of Hartree–Fock equations expressed as Gaussian functions are studied in various spaces: position, momentum, and position–momentum spaces. The use of the wavelet transform allows one to visualize position and momentum characteristics of atomic orbitals on the same drawing. A complementary viewpoint is then obtained on top of usual position and momentum representations. Applications to Gaussian “atomic” orbitals modeled as one-dimensional functions are performed. © 1993 John Wiley & Sons, Inc.     

Electro-Deprotection—Electrochemical Removal of Protecting Groups

The reactions of electrochemical splitting may be successfully used for removal of protecting groups. Theoretical and preparative aspects of the method of electro-deprotection are discussed, and examples of its use are given. The removal often requires high potentials. The use of modified protecting groups (“inner activation”) or of catalysts (electron carriers) which facilitate electron transfer against the standard potential gradient (“external activation”), can greatly increase the scope of the electrochemical method.     

环己烯分子2b和3a轨道的电子动量谱学研究

The electron momentum profile for inner valence orbitals 2b and 3a of cyclohexene (C6H10) was firstly studied by the binary (e,2e) electron momentum spectroscopy (EMS), at the impact energy of 1200 eV plus binding energy using symmetric non-coplanar kinematics. The complete valence shell binding energy spectrum of C6H10 was also obtained. The experimental momentum profile of the summed orbitals was compared with Hartree Fock (HF) and density functional theory (DFT) methods with various basis sets. The experimental measurement was well described by the HF and DFT calculations except for the low-p region (p<0.25 a.u.). Experimental small “turn-up” effects of momentum profile in the low-p region could be due to the distorted wave effects.     

Dynamical model for the “translational excitation features” in the atom—diatom reaction cross section

A collision model for the kinetic energy dependence of the reaction cross section has been obtained by considering total angular momentum limitation at the entrance (reactants) or exit (products) reactive channel in the atom—diatom scheme. The model provides a satisfactory representation of the main “translational cross section features” (i.e., Arrhenius like behaviour near threshold, maximum, post-maximum decline and minimum) found in the reaction cross section by molecular beam experiments. Maximum and minimum explanations, including some predictions as well as a comparison with previous theoretical treatments are reported. Also an approximate method to obtain dissociation energies of the product diatom from the cross-section data is presented with relative success.     

New bounds for the atomic charge and momentum densities at the origin

The “Stieltjes moment problem” technique together with the positivity and monotonic decreasing properties of the electronic density of an atom is used to find new and more accurate lower bounds for the charge density at the nucleus and the momentum density at the origin, in terms of radial and momentum expectation values, respectively. Bounds depending on two and three expectation values are given explicitly and a Hartree-Fock study of their quality is carried out. Also, the behavior of the new bounds at largeZ's is discussed. The Stieltjes technique allows to find lower bounds of better accuracy by including expectation values of higher order.     

The electronic structure of the BrF3 and BrF5 molecules

Ionization potentials of the BrF₃ and BrF₅ molecules have been calculated by the SCF DV Xα method. The calculations hale been carried out in numerical Hartree-Fock basis sets, or, to be more specific, in bases that are extensions of these bases since “virtual” bromine 4d-functions are added to the numerical HF bases. The results are used for the interpretation of the experimental PDS of these compounds.     

Nodal structure of the electronic Wigner function of many-electron atoms and molecules

On the example of several atomic and small molecular systems, the regular behavior of nodal patterns in the electronic one-particle reduced Wigner function is demonstrated. An expression found earlier relates the nodal pattern solely to the dot-product of the position and the momentum vector, if both arguments are large. An argument analogous to the “bond-oscillatory principle” for momentum densities links the nuclear framework in a molecule to an additional oscillatory term in momenta parallel to bonds. It is shown that these are visible in the Wigner function in terms of characteristic nodes. © 1996 John Wiley & Sons, Inc.     

A general efficient implementation of the BSSE-free SCF and MP2 methods based on the chemical Hamiltonian approach

We describe some details related to a new, general, and efficient implementation of the BSSE‐free SCF and second‐order Møller–Plesset perturbation theories of intermolecular interactions, based on the “Chemical Hamiltonian Approach” (CHA). The program is applicable for both open‐shell and closed‐shell systems and for an arbitrary number of interacting subsystems. With the new program the CHA method is faster than the usual “counterpoise correction” scheme for single point calculations, especially for clusters consisting of several molecules. The numerical results provided by these conceptually different schemes, however, have again found to be very close to each other. The CHA scheme is particularly good for providing truly BSSE‐free MP2 data for intermolecular potentials. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1505–1516, 2006     

Characterization of the anodic growth and dissolution of oxide films on valve metals

Chemical dissolution processes coupled to anodic oxide growth taking place by a “high-field” conduction mechanism, are considered. The equation for the steady-state current density obtained during potentiodynamic polarization measurements is derived and the effect of the oxide dissolution rate on the overall potentiodynamic behaviour by applying repetitive scans with either fixed or increasing anodic switching potentials is discussed. The procedure for obtaining the current dissolution as well as the parameters that characterize the high-field growth is discussed.     

Illustration of chemical reaction on the flow of viscous fluid in a deformable permeable layer: A numerical approach

In this article, analysis is carried out for the flow of viscous liquid in a deformable permeable layer. Influence of chemical reaction is considered that will affect the flow behavior. The governing equation describes the coupling between the solid deformation, fluid movement and concentration in the porous layer. However, these complex transformed designed problems are numerically examined retaining “Runge-Kutta fourth-order” in coordination with shooting method. Computational results for the numerous parameters on the flow phenomena such as solid displacement profiles are presented graphically. Moreover, the significant finding of the results is; increasing viscous drag retards the momentum within the permeable stratum whereas increasing particle concentration has opposite impact on the solid displacement within the domain.     

Interprétation des mesures potentiométriques au moyen des courbes de polarisation

The observed experimental results of the potentiometric determinations can be explained by means of the polarisation curves. Thus explanations are given of the following phenomena: Electro-activity and non-electro-activity of ions. Nature of the potential taken by an electrode. Time required to establish a stable potential. Significance of the limiting potentials and the limiting concentrations. Influence of oxygen on the value of the measured potentials and on the limit of electro-activity of the oxidants. Significance of the “irreversible” potentials. Formulas giving the potentials in the presence of oxygen. Utility of removing the oxygen from the solution in view of potentiometric determinations. It appears that for all the “slow” redox systems, which are very numerous in inorganic and organic chemistry, the knowledge of the polarisation curves is fundamental.     

Vibrational levels and Franck–Condon factors of diatomic molecules via Morse potentials in a box

This work deals with two shortcomings in the use of Morse potentials to describe energy spectra and transitions of diatomic molecules: (1) Morse's well-known “exact” solution for purely vibrational states includes the unphysical region – ∞ < r < 0 of the internuclear separation, and (2) Franck-Condon factors are evaluated in harmonic and anharmonic approximations to the Morse potentials. The method of confining the molecule in a spherical box is developed to obtain (1) purely vibrational energy spectra and eigenvectors of Morse potentials in the physical region 0 ? r < ∞, and (2) the corresponding Franck-Condon factors without any additional approximations. The method is applied to Li₂, N₂, CN, and CO molecules. © 1995 John Wiley & Sons, Inc.