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Molecular electrostatic potentials (MESP) surrounding the pi-region of several substituted ethylenes (CH(2)CHR) have been characterized by locating the most negative-valued point (V(min)) in that region. The substituents have been classified as electron donating and withdrawing on the basis of the increase or decrease in the negative character of V(min) in these systems as compared to ethylene. The values of V(min) show a good linear correlation with the Hammett sigma(p) constants, suggesting that the substituent electronic effects in substituted ethylenes and substituted benzenes are basically similar. With electron-donating substituents, the position of MESP minimum is closer to the unsubstituted carbon facilitating the pi-complex formation of it with HCl at this site. Such a regiospecific pi-complex formation is found to favor the formation of Markovnikov-type transition state for the addition of HCl to CH(2)CHR. For the electron-withdrawing substituents, the V(min) location is almost equidistant and farther from the ethylenic carbon atoms. This and the less negative V(min) values account for the less regiospecific CH(2)CHR...HCl pi-complexes as well as the transition states for the HCl addition to CH(2)CHR when R is an electron-withdrawing group. The interaction energy (E(int)) between CH(2)CHR and HCl for the formation of the CH(2)CHR...HCl pi-complex shows a good linear correlation with the corresponding V(min) value.

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Conformational features of naphthazarin, juglone, and naphthoquinone have been examined via ab initio (Hartree-Fock) SCF calculations at 3-21G level. The results suggest a planar structure for all the three molecules and internally hydrogen-bonded structure for naphthazarin and juglone to be their preferred conformation. The optimized structural features are essentially the same as their crystal geometries. Molecular electrostatic potential (MEP) calculations using ab initio SCF methods ranging from 3-21G to 6-31G levels have been performed to visualize their three-dimensional pharmacophoric patterns and topography. The results indicate that two factors--(i) the depth, extent, and relative location of negative potential around hydroxyl and quinonoid oxygens, and (ii) a gradual loss of negative potential over the molecular plane due to the presence and orientation of the hydroxyl groups in the phenolic part of the molecules--are crucial for recognition interaction of the compounds with their receptors. Aqueous solvation seems to have significant influence on the MEP profiles of the molecules. Although intrinsic nucleophilicity increases for all the compounds, including the different conformers, due to aqueous solvation, the intrinsic electrophilicity shows remarkable decrease for all. It appears that the acidic nature of the hydrogens in these compounds and conformers decreases sharply along with shifts of positions while going from the gas phase to the aqueous phase. These observations may help to explain the mechanism of action(s) of the anthracyclin family of cytotoxic antibiotics.

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A desktop PC-based graphics package, UNIVIS, for visualization of three-dimensional numerical data is described. Apart from routine molecular model visualization, the package provides for a host of other features such as extraction of various surfaces, planar cross-sections of the three-dimensional data, and property texturing. Fast rendering and transparency are the strengths of the present package. These features are comprehensively discussed. The salient features of UNIVIS are presented in the form of visualization of a variety of molecular properties, which are of immense importance in understanding molecular structure and reactivity patterns.

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An algorithm for generation and visualization of a variety of molecular surfaces is described. The algorithm employs center-of-mass or nuclei-centered spherical polar coordinate systems. In the present work, surfaces based on two fundamental molecular scalar fields, viz., the molecular electron density (MED) and the molecular electrostatic potential (MESP), are considered. Four such surfaces are presented: a constant MED surface with rho = 0.002 au; a minimal MESP anionic surface defined recently by Gadre et al.; a molecular covalency surface with a constant MESP value chi (chi being the Mulliken electronegativity value); and the van der Waals (vdW) surface. The MESP is superposed as a "texture" on the first and last surfaces. The color graphics visualization of these surfaces is implemented on a Silicon Graphics IRIS 4D/20 workstation. Several illustrative examples are presented.

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A LOCAL DENSITY FUNCTIONAL THEORY OF THE GROUND ELECTRONIC STATES OF ATOMS AND MOLECULES IS GENERATED FROM THREE ASSUMPTIONS: (i) The energy functional is local. (ii) The chemical potential of a neutral atom is zero. (iii) The energy of a neutral atom of atomic number Z is -0.6127 Z(7/3). The energy functional is shown to have the form [Formula: see text] where A(0)=6.4563 and B(0)=1.0058. The first term represents the electronic kinetic energy, the second term represents the electron-electron repulsion energy for N electrons, and the third term is the nucleus-electron attraction energy. The energy E and the electron density rho are obtained and discussed in detail for atoms; their general properties are described for molecules. For any system the density becomes zero continuously at a finite distance from nuclei, and contours of the density are contours of the bare-nuclear potential v. For an atomic species of fractional charge q = 1 - (N/Z), an energy formula is obtained, [Formula: see text] which fits Hartree-Fock energies of 625 atoms and ions with root-mean-square error of 0.0270. A more general local density functional involving a coefficient B(N) = B(0)N(2/3) + B(1) is briefly considered.