Molecular rotation cooperative

The treatment of electrostatics and dielectric effects in molecular mechanics calculations necessary for redox property calculations can be divided into two issues electronic polarization contributions to the dielectric response and reorientational polarization contributions to the dielectric response. Without reorientation, the electronic polarization contribution to e is 2 for the types of atoms found in biological systems. The reorientational contribution is due to the reorientation of polar groups by charges. In the protein, the reorientation is restricted by the bonding between the polar groups, whereas in water the reorientation is enhanced owing to cooperative effects of the freely rotating solvent molecules. 

The isomerization from 10 to 11 in the crystalUne state requires not only the movements of atoms but also a change in the crystal symmetry and the reconstruction of the hydrogen bond network pattern. In the crystals of these primary ammonium carboxylates, ID ladder-type hydrogen bonds are observed. The isomerization from the ZZ to EE form is associated with the rotation of carbonyl groups and the change in the hydrogen bond structure in this case. The quantitative transformation of 10 to 11 in the crystalUne state suggests that the molecular motion in the crystals occurred cooperatively with the minimum movement of atoms in the crystals via a phase transition from the crystal of 10... 

The molecular basis of site-site cooperativity in ATP synthase still remains unelucidated [46], and the absence of any direct evidence for cooperativity (despite almost three decades of effort) is explained, within the framework of the torsional mechanism, by the fact that site-site cooperativity does not exist in the physiological, steady state mode of functioning. Since, according to the torsional mechanism, no rotation takes place in uni-site or bi-site catalysis... 

Dielectric relaxation study is a powerful technique for obtaining molecular dipolar relaxation as a function of temperature and frequency. By studying the relaxation spectra, the intermolecular cooperative motion and hindered dipolar rotation can be deduced. Due to the presence of an electric field, the composites undergo ionic, interfacial, and dipole polarization, and this polarization mechanism largely depends on the time scales and length scales. As a result, this technique allowed us to shed light on the dynamics of the macromolecular chains of the rubber matrix. The temperature as well as the frequency window can also be varied over a wide... 

Carbon-13 rotating-frame relaxation rate measurements are used to elucidate the mechanism of gas transport in glassy polymers. The nmr relaxation measurements show that antiplasticization-plasticization of a glassy polymer by a low molecular weight additive effects the cooperative main-chain motions of the polymer. The correlation of the diffusion coefficients of gases with the main-chain motions in the polymer-additive blends shows that the diffusion of gases in polymers is controlled by the cooperative motions, thus providing experimental verification of the molecular theory of diffusion. Carbon-13 nmr relaxation... 

In conclusion, the average rotating-frame relaxation rate of the methylene- and methine-carbons correlate with the apparent diffusion coefficients for H2 and CO in PVC when the main-chain molecular motions of the polymer are altered by an additive. (Fig. 2). These results provide experimental evidence that main-chain cooperative motions control the diffusion of gases through polymers. In Section IIB we will show that perturbation of polymeric cooperative motions is not restricted to classical plasticizing additives. 

Thus, specific interactions directly determine the spectroscopic features due to hydrogen bonding of the water molecules, while unspecific interactions arise in all or many polar liquids and are not directly related to the H-bonds. Now it became clear that the basis of four different processes (terms) used in Ref. [17] and mentioned above could rationally be explained on a molecular basis. One may say that specific interactions are more or less cooperative in their nature. They reveal some features of a solid state, while unspecific interactions could be understood in terms of a liquid state of matter, if we consider chaotic gas-like motions of a single polar molecule, namely, rotational motions of a dipole in a dense surroundings of other molecules. The modem aspect of the spectroscopic studies leads us to a conclusion that both gas-like and solid-state-like effects are the characteristic features of water. In this section we will first distinguish between the following two mechanisms of dielectric relaxation ... 

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