Electrostatic potential surface charge

Molecular surfaces can express various chemical and physical properties, such as electrostatic potential, atomic charges or hydrophobicity, using colored mapping. 

Electrostatic potential-derived charges assign point charges to fit the computed electrostatic potential at a number of points on or near the van der Waals surface. This sort of analysis is commonly used to create input charges for molecular mechanics calculation. 

Chemists also need to know the distribution of electric charge in a molecule, because that distribution affects its physical and chemical properties. To do so, they sometimes use an electrostatic potential surface (an elpot surface), in which the net electric potential is calculated at each point of the density isosurface and depicted by different colors, as in Fig. C.2f. A blue tint at a point indicates that the positive potential at that point due to the positively charged nuclei outweighs the negative potential due to the negatively charged electrons a red tint indicates the opposite. 

Fig. 1-5. Electrostatic potential of charged and noncharged condensed phases = inner potential = outer potential X = surface potential.

Atomic charges on the guest molecules were obtained from first principles Hartree-Fock calculations, fitting the electrostatic potential surface (EPS), then scaled up or down in order to reproduce the experimental dipole moments. Table 2 gives partial charges of typical molecules considered in our work. 

Binding affinity data of thiazoles and thiadiazoles at the hA3 AR have been subjected to QSAR analysis (Bhattacharya et al. 2005). This study disclosed the importance of molecular electrostatic potential surface (Wang-Ford charges) in correspondence of atoms C2, C5, C7, X8 and S9 (Fig. 7.6), the last two playing the most important roles. Furthermore, the A3 binding affinity increases with decrease of lipophilicity of the compounds and in the presence of short alkyl chains (Me or Et) at the R position. 

Special emphasis is placed here on the effect of the presence of adsorbed lead and other cations on the pH-dependency of this adsorption, particularly that which results from the effect of the adsorbed cations on electrostatic potential and charge density at the solution-surface interface. 

The second term in Equation 1, . involves carrying out a Poisson-Boltzmann calculation and evaluating the exposed surface area of all atoms for all the snapshots for C, M, and L. Currently, we use Hartree-Fock (HF)/6-31G restrained electrostatic potential (RESP) charges and PARSE radii for the PB calculation within DELPHI and the program... 

The importance of electrostatics in the interaction of aromatics fluorine with cations and hydrogen bond donors can be visualized using electrostatic potential surfaces (Figure 20.37). In monofluorobenzene, the potential of the fluorine is concentrated on the unique fluorine present, whereas in polyfluorobenzene the negative charge is spread over several fluorine atoms. For this reason, monofluorobenzene may give stronger interactions. 

In 1991 Cioslowski, Mixon, and Reischmann [408] examined the electronic structures of CHFj, CH(CN)3, and CH(N02)3 at the HF/6-31G and HF/6-31-H-G levels in an effort to understand the high acidities of these species. They were unable to find any simple correlations between the gas-phase acidities and properties of these compounds, such as partial atomic charges and C-H bond lengths. At the same time Murray, Brinck. and PoUtzer [409] were able to establish correlations between the aqueous pK s of a set of ten mostly cyclic hydrocarbons and two measures from the molecular electrostatic potential surface, the minimum local ionization energy Ig and the potential minimum V . 

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