Dynamics Of Molecular Motion Research Articles

Molecular motion of ferroelectric liquid crystalline polymers

Abstract Dynamic molecular motions of ferroelectric liquid crystalline polymer are investigated by time resolved FT-IR technique. The absorbance of main chain and that of the mesogenic moiety synchronously change. This suggests the reason the electro-optical response of ferroelectric liquid crystalline polymers is 100 to 1000 times as late as that of low molecular weight ferroelectric liquid crystals.

Structure and dynamics of α-chymotrypsin-N-trifluoroacetyl-4-fluorophenylalanine complexes

Fluorine NMR lineshape, relaxation and Overhauser effect data collected at 282 and 470 MHz have been used to obtain information about the nature of complexes formed between N-trifluoroacetyl-4-fluorophenylalanine and the enzyme chymotrypsin. Systems involving both enantiomers have been examined as well as derivatives of these in which the aromatic ring hydrogens have been replaced by deuterium. The enzyme-induced fluorine chemical shift effects and the dynamics of molecular motions of the fluorophenyl ring at the respective binding sites appear to be similar in both complexes and, where comparable, the results are in agreement with data obtained at lower frequencies that have been reported by other workers. The dynamics of the fluoroaromatic ring in these complexes are significantly different from those observed in a closely related acylated enzyme.

Carbon black filled natural rubber. 1. Structural investigations

The effects of solvent extraction of increasing severity on carbon black filled natural rubber are examined. Collated NMR, DSC, and DMTA methods examine the glass transition and motional cooperation in the filled system. DSC is insensitive to the immobilization of small amounts of tightly bound rubber on the surface of carbon black particles. Also examination of component T 2 intensity data as a function of temperature engenders the notion of a range of binding energies between the rubber and the carbon black. The Carr-Purcell pulse train has been used to glean additional insight into the dynamics of molecular motion, and exchange between heterogeneous sites is explored

ChemInform Abstract: Dynamic Molecular Motions of p‐Methylcinnamic Acid Included into β‐Cyclodextrin Derivatives: A New Type of Free‐Energy Relationship in Complex Formation.

The deuterium quadrupolar relaxation times of (E)-[β,methyl-2H2]-p-methylcinnamic acid (G) included into various β-cyclodextrin derivatives have been measured by line-shape analysis. The association constants for the complexation of host with (G) are largely affected by additional recognition elements substituted into the parent β-cyclodextrin. The correlation times for the molecular motion of G which have been estimated from the corresponding relaxation times are also greatly affected by these additional recognition elements. Thus, the relationship between the association constants and the correlation times of (G) may be described simply in the present case, i.e., the host molecule having the larger association constant restricts the molecular motion of (G) more significantly. One exception is 6,6′-dideoxy-6,6′-di-iodo-β-cyclodextrin (CDI2) which has a large association constant but restricts only slightly the molecular motion of (G). The observed large association constant and the small correlation time for CDI2 are reasonably interpreted in terms of the effect of the large polarizability of iodine. The free-energy relationship between the binding process and the molecular motion of (G) is discussed on the basis of these new observations.

Dynamic molecular motions of p-methylcinnamic acid included into β-cyclodextrin derivatives: a new type of free-energy relationship in complex formation

The deuterium quadrupolar relaxation times of (E)-[β,methyl-2H2]-p-methylcinnamic acid (G) included into various β-cyclodextrin derivatives have been measured by line-shape analysis. The association constants for the complexation of host with (G) are largely affected by additional recognition elements substituted into the parent β-cyclodextrin. The correlation times for the molecular motion of G which have been estimated from the corresponding relaxation times are also greatly affected by these additional recognition elements. Thus, the relationship between the association constants and the correlation times of (G) may be described simply in the present case, i.e., the host molecule having the larger association constant restricts the molecular motion of (G) more significantly. One exception is 6,6′-dideoxy-6,6′-di-iodo-β-cyclodextrin (CDI2) which has a large association constant but restricts only slightly the molecular motion of (G). The observed large association constant and the small correlation time for CDI2 are reasonably interpreted in terms of the effect of the large polarizability of iodine. The free-energy relationship between the binding process and the molecular motion of (G) is discussed on the basis of these new observations.

Dynamic molecular motions of guest molecule included in modified β-cyclodextrins

Upon inclusion in capped β-cyclodextrin, the overall reorientational motion of doubly deuterium labeled p-methylcinnamic acid slows down by a factor of 14 compared with that in an aqueous solution but the internal rotation of the methyl group still remains free.

ChemInform Abstract: Structure and Dynamic Behavior in Solution of Binuclear Nickel(II) Face‐to‐Face Complexes with Bis(cyclidene) Ligands.

AbstractNMR studies of the dinickel(II) complexes (I) with macrocyclic bis(cyclidene) ligands reveal a dynamic molecular motion in solution.

Dynamics of Molecular Motion at Single-Crystal Surfaces

Dramatic advances in our understanding of the motion of individual atoms and molecules at single-crystal surfaces have been made within the past 5 years. Recent experimental and theoretical studies of the interaction of nitric oxide with metal surfaces illustrate the depth of understanding now obtainable. General principles, applicable to a broader range of molecule-surface encounters, have begun to emerge out of the systematic and in-depth analyses of these and related studies.

Model for vibrational dephasing of diatomic molecules in liquids Liquid N2 and O2

The characteristics of spontaneous Raman scattering from solutions of diatomic molecules are reviewed, especially with regard to what they may tell one about the dynamics of molecular motion. In the limit of extreme motional narrowing the polarized component of the Q branch is a lrentzian with a width which depends upon the rate (τ-1) of dephasing of the molecular vibrations. An approximate, closed, quantum-mechanical expression for the contribution of ‘translational-translational’ quasielastic scattering to τ-1, called τph -1(T-T), is derived. The translational states of the liquid are determined by invoking the Lennard-Jones-Devonshire (LJD) cell model. The full LJD cell potential is replaced by an harmonic approximation thereto. The dependence of the τph(T-T) upon thermodynamic variables and microscopic properties is discussed. The derived expression for τph -1 (T-T) is then used to compute upper bounds on τ for liquid N2 and O2, for which experimental data are available. It is concluded that the T-T q...

Dynamic Polarization, Molecular Motion and Solvent Effects in Several Organic Solutions as Studied by Proton-Electron Double Resonance

Abstract Dynamic proton polarization in several free radical solutions has been studied systematically with different radicals at five widely separated magnetic field strengths and at various temperatures. Normally, in organic solutions the dynamic enhancements of the solvent proton resonances decay with increasing field and decreasing temperature. Scalar proton-electron coupling has only been observed in exceptional cases. The spectral intensity functions describing the experimental behaviour are derived from the dipolar interaction whose time dependence is in the first place due to translational diffusion of individual molecules. In addition, a certain solvation effect has to be taken into account. Strong solvation occurs in solutions of hydroxyl containing solvents with nitroxide radicals. In this case, the dynamic proton polarization appears to be quite different. As an example, solutions of tetramethyl piperidineoxyl in acetic acid have been examined in more detail. The results are explained in terms of hydrogen bridged solvates. The important motional mechanism that modulates the proton-electron interaction switches from “translation” to “rotation”, and electron spin density is temporarily transferred to the solvent molecule.