Anthony Duben

Stephen F. Austin State University · Department of Chemistry and Biochemistry

The Soave-Redlich-Kwong (SRK-EOS) and Peng-Robinson (PR-EOS) equations of state are used often to describe the behavior of pure substances and mixtures despite difficulties in handling substances, like water, with high polarity and hydrogen bonding. They were employed in studying the binary vapor-liquid equilibria (VLE) of methane + methanol, monoe...

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Bonding in the hypervalent molecules SF4, BrF5, PF5, and SF6 was studied using multicenter bond order indices and examination of the eigenvalues and the eigenvectors of the Fermi holes of the constituent atoms. Diagonalization of the Fermi holes provided quantitative validation of Musher's categorization of hypervalency with SF4 and BrF5 representa...

Bonding in the hypervalent molecules SF4 , BrF5 , PF5 , and SF6 was studied using multicenter bond order indices and examination of the eigenvalues and the eigenvectors of the Fermi holes of the constituent atoms. Diagonalization of the Fermi holes provided quantitative validation of Musher's categorization of hypervalency with SF4 and BrF5 represe...

The conformational statistics of the glycosylated dipeptide N - acetyl - 8 - N - (2 - acetamido - ~ - D - glucopyranosyl) - L - asparaginyl - N' - methyl amide (glcNAc-Asn), a model of N-linked glycopeptides, was determined using umbrella sampling. The use of umbrella sampling allowed the importance sampling algorithm to accept new conformations wi...

The conformational statistics of the glycosylated dipeptide N - acetyl - δ - N - (2 - acetamido - β - D - glucopyranosyl) - L - asparaginyl - N' - methyl amide (glcNAc-Asn), a model of N-linked glycopeptides, was determined using umbrella sampling. The use of umbrella sampling allowed the importance sampling algorithm to accept new conformations wi...

The conformational statistics of the glycosylated dipeptides N acetyl - y - 0 - (2 - acetamido - a - D - galactopyranosyl) - L seryl - N - methyl amide and its threonyl analog (galNAc Ser/Thr) as models of O-linked glycopeptides were determined using umbrella sampling. The use of umbrella sampling allowed the importance sampling algorithm to accept...

The NMR-NOESY specla'um of a previously assigned polypeptide (eraerimicin IV) is compared against simulated spectra using the motional models of a cylinder and a larger rigid sphere in order to determine the effect of motional model in determining conformation. The anisotropic model provides a good fit against the experimental peaks originating wit...

In order to determine the effect of the choice of potential function used in the conformational analysis of a carbohydrate, the NMR spectrum of methyl beta-xylobioside [beta-D-Xyl-(1-->4)-beta-D-Xyl-(1-->O)-Me] was interpreted using calculated J13C-H coupling constants and nuclear Overhauser effects for protons across the anomeric linkage. Conforma...

The behavior of methyl beta-xylobioside has been analysed by 1H-n.m.r. spectroscopy for solutions in water and methanol in the range - 15 degrees to 85 degrees. Experimental n.O.e. values did not change with temperature and solvent in contrast to the inter-glycosidic 3JC,H values. Experimental n.O.e. data accorded with the values calculated from ti...

A detailed theoretical analysis of longitudinal NMR cross-relaxation for a proton pair attached to molecules with a variety of sizes and shapes is presented. The universally applied rigid Isotropic model for calculating cross-relaxation behavior has been extended to treat a rotating proton pair on a spherical molecule and on prolate and oblate elli...

Homonuclear cross relaxation for a proton pair with external relaxation is evaluated theoretically. Results for nuclear Overhauser effect experiments and for two-dimensional NOESY spectra are given. The effects of internal motion are treated. The calculations give insight into experimental results obtained from cross-relaxation studies of proteins...

The bathochromic shift of the longest wavelength band observed when benzene is substituted can be demonstrated theoretically using a simple frontier orbital analysis. Keywords (Audience): Upper-Division Undergraduate

In order to search for probable conformations of the peptide, the amino acid side chain, and the carbohydrate linkage in glycoproteins, conformational energy surfaces of glycopeptide model compounds were studied by Monte Carlo methods using the Metropolis algorithm. The potential energies were composed of empirical energy functions which include no...

The effect of solvent on the barrier to internal rotation of formamide has been studied using an ab initio 4-3IG method coupled with a polarizable continuum model. The trend of increasing rotation barrier with increasing solvent dielectric constant is reproduced. Conformational free energies were calculated by adding dispersion and cavitation terms...

The effect of solvent on the barrier to internal rotation of formamide had been studied using a solvaton method within the CNDO/2 parameterization. The experimental trend of increasing rotational barrier with increasing solvent dielectric constant has been reproduced. A critical examination of the manner in which interactions between solute and sol...

In order to examine the relative ease by which the catalytic hydrodesulfurization of thiophene and the catalytic denitrogenation of pyridine proceed, I have used simple Hueckel molecular orbital theory to study both reactions. In both cases, the description of the catalyst (presumed to have been a typical cobalt-molybdenum catalyst) was kept the sa...

The calculation of reliable electrostatic isopotential maps from CNDO or INDO wavefunctions while preserving the ZDO approximation fails because the individual atoms are treated as if they were spherical charge distributions. The resulting potential maps could be adequately interpreted on the basis of classical electrostatics. Approaches to the det...

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The circular dichroism spectra of carbohydrates vicinally substituted by acetamido groups differ fundamentally from those of the common 2-acetamido-2-deoxy sugars as a result of mutual coupling effects. The calculations presented in this paper follow a method due to Schellman and co-workers which has been widely used in peptide CD calculations and...

The Lipsch and Schuit model for the hydrodesulfurization of thiophene and the monomethylthiophenes is examined using simple Hückel theory. The optimal situation requires that the metal have its two d orbitals which are of proper symmetry to interact with the thiophene π orbitals doubly occupied with electrons. The sequence of reactions in the Lipsc...

Correlation energies were calculated by “Effective Pair Correlation Energy” (EPCE) and minimal basis set configuration interaction (CI) methods for pairs of electrons in the occupied molecular orbitals for the (π 4u ) neutral ground state, (π 3u ) ground state of the positive ion, and (π 4u π g ) ground state of the hypothetical negative ion of ace...

The solution of the time dependent Schrödinger equation, including renormalization of the wave function, is used to obtain quantum mechanical expressions for the optical rotation and the circular dichroism. The use and form of the radiative damping term is examined with respect to its effects in the circular dichroism formula.

Four configuration interaction calculations on the D3h H3+ molecule—ion are reported. Two Gaussian lobe basis sets are used and calculations are made with only doubly substituted configurations and also with both doubly and singly substituted configurations. The best calculation gives an energy of −1.34050 hartree at a fixed internuclear distance o...

Effects of correlation on one‐electron distribution and other properties are calculated for the H3+ molecule ion. Effects due to singly substituted and doubly substituted configurations are essentially additive for this closed shell species. The effect of doubly substituted configurations is to shift charge from the molecular center to nuclear regi...