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Although the actual structure of the receptor binding site is not known, some theoretical modeling computations based on experimental competitive binding studies support a stacking interaction model (Long, McKinney, and Pedersen 1987 McKinney et al. 1985 McKinney, Long, and Pederson 1984 McKinney and Pederson 1986). In this model, the toxigen is envisioned as being invol ved in a recognition step at a porphine-like binding site (26). For the specific case of TCDD, the most favorable interaction...

Applications of Density Functional Theory to Biological Systems

Tomasz Adam Wesolowski Jacques Weber The term biological systems may be used in reference to a wide class of polyatomic systems. They can be defined as minimal functional units which perform specific biological functions enzymatic reactions, transport across membranes, or photosynthesis. At present, such systems as a whole are not amenable to quantum-chemistry studies because of their large size. The smallest enzymes are built of few thousands of atoms (e.g., lysozyme consists of 129 amino-acid...

X

And F H - < (xjjl vv > for 4> on atom A, 4> on atom B, (j. * v (2.49) In Eq. (2.48), the summation is clearly taken over the orbitals centered on all atoms other than A, and PBB is the total electron density associated with atom B, i.e., the summation is over all AOs on B. The problem is now to derive suitable expressions for the one-electron elements H in a manner consistent with the neglect of orbital overlap. Without detailing the derivation, the diagonal Fock matrix elements take...

Jane S Murray Peter Politzer

The quest for improved methods for elucidating and predicting the reactive behavior of molecules and other chemical species is a continuing theme of theoretical chemistry. This has led to the introduction of a variety of indices of reactivity some are rather arbitrary, while others are more or less directly related to real physical properties. They have been designed and are used to provide some quantitative measure of the chemical activities of various sites and or regions of the molecule. In...

F interaction with electrophiles X F

Our calculated surface electrostatic potentials for CC14 and CBr4 show the anticipated negative regions around the chlorines and bromines, except at the outer ends, which are actually positive Brinck, Murray, and Politzer 1992b . The negative rings around the sides of the CI and Br have surface minima at angles of 102 and 96 with the C-Cl and C-Br axes, respectively. These results are consistent with the observed orientational preferences of both electrophiles and nucleophiles interacting with...