Atomistic molecular modeling

Over the last 15 years particularly atomistic molecular modeling methods have found widespread application in the investigation of small-molecule permeation [2-15]. 

Atomistic molecular modeling techniques have proven to be a very useful tool for the investigation of the structure and dynamics of dense amorphous membrane polymers and of transport processes in these materials. By utilizing these methods, information can be obtained that is not accessible by experimental means. 

Polymer science has undergone a transition recently. Many of the traditional computational tools used for atomistic molecular modeling are now being used in polymer science. In Chapter 3, Professor Vassilios Galiatsatos provides an account of how these modern computational methods are being implemented and refined by polymer scientists to complement existing theories developed by Flory, DeGennes, and others. The focus here is on homopolymers. 

ATOMISTIC MOLECULAR MODELING OF ELECTRIC FIELD POLING OF NONLINEAR OPTICAL POLYMERS... 

Keywords Atomistic molecular modeling nonlinear optical polymers... 

Atomistic molecular modeling studies of the electtic field poling of nonlinear optical polymers have been studied by at least two groups over tire past few years. Methods for determining the simulation parameters corresponding to appropriate experimental conditions are ongoing. It is important to keep tire simulations rooted in experiments as tlieir applicability is limited if tire simulation parameters keep the simulations far from reality. 

Although no one has yet reproduced the experimental roll-off of the electro-optic coefficient with increased chromophore concentration using the atomistic molecular modeling methods to date, significant progress has been made. We are currently working on integrating the three explicit terms for the dipole-dipole interaction, the dipole-induced dipole interaction, and the induced dipole-induced dipole interaction into the simulation. The results of this work will be published elsewhere. 

From their QSERR they find solute lipophilicity and steric properties as being responsible for analyte retention (k ) while enantioseparation (a) varied mainly with electronic and steric properties. The main difference between the analytes is that the enantioseparation of the esters is correlated with steric parameters that scale linearly with log a while the sulfoxides scale nonlinearly (parabolic), but this may be due to a computational artifact. The 3D-QSERR derived from field analysis revealed that while superpositioning of field maps for both analytes are not exactly the same, a similar balance of physicochemical forces involved in the chiral recognition process are at play for both sets of analyes. This type of atomistic molecular modeling, then, is a powerful adjunct to the type of modeling described earlier in this chapter and will, no doubt, be used more frequently in future studies. 

Most of the aforementioned studies represent quantitative structure-retention relationship studies where a series of analytes are used as probes of enantiodiscrimination. There are, however, a number of atomistic molecular modeling studies where the interactions of chiral guests (analytes) with chiral hosts (CSPs) are explicitly determined. Here guest and host are considered as transient diastereomeric complexes and both liquid and gas chromatographic separations have been modeled. 

D. Hofmaim, L. Fritz, J. Ulbrich, C. Schepers, M. Boehning, Detailed atomistic molecular modeling of small molecule diffusion and solution processes in polymeric membrane materials, Macromol. Theory Simul., 9, 293-327 (2000). 

Gestoso, P. and Brisson, (. (2001) Effect of hydrogen bonds on the amorphous phase of a polymer as determined by atomistic molecular modelling. Comput. Theor. Polym. Sci., 11, 263—271. 

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