Simulations of guest transport in clathrates of Dianin's compound and hydroquinone

Clathrates have been proposed for use in a variety of applications including gas storage, mixture separation and catalysis due to the potential for controlled guest diffusion through their porous lattices. Here molecular dynamics simulations are employe

Computational study of methyl group dynamics in the hydroquinone clathrate of acetonitrile

We report molecular dynamics simulations of the acetonitrile clathrate of hydroquinone, with a focus on the dynamics of acetonitrile methyl groups. There are three inequivalent acetonitrile molecules in the unit cell, one with its dipole parallel to the c-axis, and the other two antiparallel. Although these three guest molecules have previously been found to exhibit two slightly different frequencies of rotation over a wide range of temperatures, the frequencies could not be assigned to specific methyl groups. Perhaps counterintuitively, our simulations suggest that the molecule with the lower frequency is one of the two molecules oriented the same way, the different dynamical behaviour being due to subtle differences in the environments of the molecules

Microeconomic analysis and policy

The study guide reflects the issues of the formation of microeconomic policy and microeconomic analysis. The main issues of models and the state of markets, firm costs, pricing methods and many others are considered. The guide is addressed to students of the 2nd stage of higher education, specialty 1-25 80 01 "Economics"

Molecular imprisonment: Host response to guest location, orientation, and dynamics in clathrates of Dianin's compound

Single crystal X-ray diffraction data measured at 100 K for Dianin's compound (DC) and 18 of its clathrates formed with a wide range of guest molecules provide considerable insight into the way the host adjusts to accommodate guest molecules. Detailed information is also obtained regarding the location, orientation, and dynamics of the guests in the host cavity. Although all unit cells are closely similar in size, the host undergoes significant change in response to the imprisonment of its various guests. Enclathration typically results in a larger cell and cavity volume, but for the small molecules methanol, ethanol, and nitromethane the host actually shrinks significantly around the guests in the cavity. In most clathrates, there is evidence of close contacts between atoms in the guest and the phenol -OH group and/or ring of the DC host. The series of clathrates formed by benzene, toluene, and the halobenzenes show the orientation of the benzene ring to be progressively modifed by the increasing size of the substituent atom or group on the ring in a systematic manner that reflects functional group contributions to van der Waals volumes. © 2014 American Chemical Society

Bespoke force field for simulating the molecular dynamics of porous organic cages

Most organic molecules pack in such a way to 1 6 minimize free space, therefore exhibit minimal void volume have previously demonstrated the synthesis of porous organic cages that are permanently porous to a variety of gases. However, study of the static structure alone does not adequately explain the porosity of these materials. This is especially evident in CC3, which takes up a large amount of nitrogen experimentally but its porosity is not obvious from consideration of the computed geometric solvent accessible surface area of the static crystal structure obtained from single crystal X-ray diffraction data. In this study, we show that the structure and flexibility of these organic cages is not well represented by "off the shelf" force fields that have been developed in other areas. Hence, we develop and test a bespoke force field (CSFF) for simulating the molecular dynamics of a series of porous organic cage materials. The development of CSFF has unlocked the ability to investigate phenomena that are difficult to study by direct experiments, for example, molecular dynamic analysis of the window diameters in CC3 has helped to rationalize its high N-2 uptake. In the future, there is much scope to use CSFF to understand the uptake of gases and also larger guests such as halogens and solvents within a whole host of different cage systems leading on to the use of MD analysis for in silico screening of cage materials for particular molecular separations. If reliable, this could be faster than the associated sorption experiments

Gas diffusion in a porous organic cage:analysis of dynamic pore connectivity using molecular dynamics simulations

Molecular dynamics simulations were used to investigate the diffusion of six small gas molecules in a crystalline porous organic cage, CC3. A flexible host model was used to simulate transient channel formation, the effects of which are reflected in the calculated diffusion coefficients for the six gases of 5.64 × 10–8, 5.94 × 10–9, 2.60 × 10–9, 9.60 × 10–9, 2.40 × 10–9, and 1.83 × 10–10 m2 s–1, respectively, for H2, N2, CO2, CH4, Kr, and Xe. By contrast, a larger gas molecule, SF6, was predicted to be unable to diffuse in the pores of this material. We introduce a new method—a void space histogram—to analyze dynamic pore topologies and to graphically illustrate the structural factors determining guest diffusion