Translational Motion Of Solvent Molecules Research Articles

Direct Observation of Electrophoretic Flow of Solvent Molecules with Lithium Ions By NMR Imaging

Lithium ion transport in the organic liquid electrolyte is a key process in conventional lithium ion batteries, where the lithium ion shuttles between the positive and negative electrodes while the charging and discharging process. The translational motion of the lithium ion in the liquid electrolyte is accompanied by the coordinating organic solvent molecules such as EC, DMC etc., which must be detached from the lithium ion at the electrodes by the desolvation process. On the other hand, the counter anions such as PF6 - is thought to move opposite direction, although the local concentration is the same to that of lithium cation in order to keep the electroneutrality condition. Although this picture is based on many evidences by electrochemical measurements, the direct observation of the correlated motion of the lithium ions and solvated molecules has not been reported. In this paper, we first demonstrate the direct observation of the translational motion of solvent molecules (EC,DEC) with the lithium ions by using NMR micro-imaging technique. NMR microimaging is observed by Avance 400 spectrometer equipped with mini-Imaging probe by Bruker Co. The 1H and 19F NMR imaging are observed in this measurement. Model cell is constructed in NMR spectrometer, which is composed by LiMn2O4 cathode, lithium metal anode and liquid electrolyte of EC/DMC+LiPF6. The cell is connected to an electrochemical charge-discharge set-up to operate the cell. Small desolution of Mn2+ from the cathode acts as a contrast agent to enhance the flow image of the cell. Some vertical images of the cell in a charge-discharge process are shown in Fig. 1, where the LiMn2O3 positive electrode is located at the bottom and the lithium metal anode is on the top. Constant current mode of 25 mA is used. While the charging current is set upward from LiMn2O3 cathode to the lithium anode, namely the Li+ cations move upward, then the proton NMR imaging observing the motion of the EC and DMC molecules is confirmed to upward, which is the same direction as that of the Li+ ions. Moreover, the flowing current of the solvent moves toward left and right directions near the lithium anode, where the EC and DMC should release the Li+ to the anode and move aside. This continuous flow generates an electroconvection which can be seen in Fig. 1 as a vortex curling from center to the side wall. On the other hand, when the current is reversed to discharge, the flow of the solvent changes its direction from the top (anode) to the bottom (cathode), which generate the reverse vortex as shown in Fig. 1. Figure 1

Hidden peak of radial distribution function and effective attraction between like-charged proteins caused by translational motion of solvent molecules

To discuss the effective interactions between macroanions, such as acidic proteins, the radial distribution function between macroanions, gMM(r), was calculated using an integral equation theory with a charged hard spheres model under weak coupling conditions. Explicit and implicit solvent models were examined. The gMM(r) for the explicit solvent model indicated a significant peak at the contact distance, which was caused by the translational motion of solvent molecules. In contrast, the gMM(r) for the implicit solvent model did not indicate any significant peak at the distance because of no explicit solvent particles. Although there was a significant difference in the gMM(r) for the explicit and implicit models, the structure factor SMM(k) was nearly the same and the shapes and peak shifts caused by macroanion concentration changes were also similar to the experimental results. To reproduce the first sharp peak in gMM(r), the structure factor SMM(k) provided by scattering experiments was not sufficiently long for standard analyses. This showed that the results provided by conventional small-angle scattering experiments cannot deny the existence of a first sharp peak in gMM(r).

Adsorption of xenon on a protein arising from the translational motion of solvent molecules

A simple method was used to predict binding sites and to calculate the binding free energy for a xenon atom on a protein to determine the importance of the translational motion of water molecules in molecular recognition. We examined xenon bound on myoglobin and on a fragment of ammonium transporter. Despite the simplicity of our method, the predicted binding sites and the experimental results agree very well, and the estimated values of the free energy gain are also reasonable. We discuss the van der Waals picture of molecular recognition between a protein and a small hydrophobic molecule, such as an anesthetic molecule, which gives us a simple physical justification for the idea of a "lock and key" relationship used in conventional structure-based drug design programs.

Interaction between like-charged colloidal particles in aqueous electrolyte solution: Attractive component arising from solvent granularity

The potential of mean force (PMF) between like-charged colloidal particles immersed in aqueous electrolyte solution is studied using the integral equation theory. Solvent molecules are modeled as neutral hard spheres, and ions and colloidal particles are taken to be charged hard spheres. The Coulomb potentials for ion-ion, ioncolloidal particle, and colloidal particle-colloidal particle pairs are divided by the dielectric constant of water. This simple model is employed to account for the effects of solvent granularity neglected in the so-called primitive model. The van der Waals attraction between colloidal particles, which is an essential constituent of conventional DLVO theory, is omitted in the present model. Nevertheless, when the electrolyte concentration is sufficiently high, attractive regions appear in the PMF. I n particular, the interaction at small separations is significantly attractive and the contact of colloidal parti cles is stabilized. This interesting behavior arises from the effects of the translational motion of solvent molecules.

Calorimetry and Macromolecular Interaction Arising from Translational Motion of Solvent Molecules

Calorimetry and Macromolecular Interaction Arising from Translational Motion of Solvent Molecules

Monte Carlo Simulation Study of Free Energy Curves for Electron Transfer Reactions in Polar Solutions by considering the Electronic Polarizability

Abstract We have conducted Monte Carlo simulations of polar solutions with a spherical hard core model by properly taking into account the electronic polarizability of solvent molecules. We have calculated the free energy curve as a function of the reaction coordinate of electron transfer reactions in cases where the reactant is neutral and charged. From the analysis of the free energy curvature ratio between the two cases, we have found that the electronic polarizability contributes to enhance the non-linear response of solvent polarizations and that this enhancement is greatly strengthened if the translational motion of solvent molecules is frozen.