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See detailBonding patterns of [Ag2-alanine]0,± hybrid complexes and the implementation of Molecular logic gates.
Zhang, Chenggen ULg; Periyasamy, Ganga ULg; Remacle, Françoise ULg

in International Journal of Quantum Chemistry (2010), 110(12), 2237-2246

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See detailThe magic gold cluster AU(20)
Kryachko, Eugène ULg; Remacle, Françoise ULg

in International Journal of Quantum Chemistry (2007), 107(14), 2922-2934

The 20-nanogold cluster Au-20 exhibits a large variety of two- and three-dimensional isomeric forms. Among them is the ground-state isomer Au-20(T-d) representing the stable cluster with a unique ... [more ▼]

The 20-nanogold cluster Au-20 exhibits a large variety of two- and three-dimensional isomeric forms. Among them is the ground-state isomer Au-20(T-d) representing the stable cluster with a unique tetrahedral shape, with all atoms on the surface, and large HOMO-LUMO gap which even slightly exceeds that of the buckyball fullerene C-60. The anionic cluster Au-20(-) (T-d) that holds its parent tetrahedral symmetry features a high catalytic activity. The list of the properties of the 20-nanogold clusters surveyed in the present work ranges from the energetic order of stability of its isomers to the optical absorption and excitation spectra of the Au-20(T-d) cluster. We also report the structures and properties of its doubly charged clusters Au-20(2+) and Au-20(2-) and computationally confirm that Au-20 is indeed stable. The zero-point-energy-corrected adiabatic second electron affinity of Au-20(T-d) amounts to 0.43-0.53 eV that is consistent with the experimental data. In addition, we provide computational evidence of the existence of the novel, hollow cage isomer of Au-20 and analyze its key properties. (C) 2007 Wiley Periodicals, Inc. [less ▲]

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See detailAb initio study of organic mixed valency
Dehareng, Dominique ULg; Dive, Georges ULg; Moradpour, Alec

in International Journal of Quantum Chemistry (2000), 76(4), 552-573

A series of six radical cations of the type (D-L-B)(+) was investigated at the ab initio unrestricted Hartree-Fock level. One localized and one delocalized conformation were systematically searched by ... [more ▼]

A series of six radical cations of the type (D-L-B)(+) was investigated at the ab initio unrestricted Hartree-Fock level. One localized and one delocalized conformation were systematically searched by full geometry optimization At both nuclear arrangements, mostly found as being minima in the symmetry-restrained Hartree-Fock framework, excitation energies were calculated through the expansion of the wave function on single electronic excitations of the Hart ee-Fock fundamental determinant and at the unrestricted Hartree-Fock or at the multiconfigurational self consistent field levels. Few calculations were also performed by taking into account some part of the electronic correlation. Except for N,N,N',N'-tetramethyl p-phenylenediamine, all the studied compounds are localized stable cations, at the symmetry-restrained Hartree-Fock level. However, the reoptimization of their wave function changes this observation since only three of them seem to conserve a localized stable conformation. Most of the studied systems are characterized by one or two excited electronic states very dose to the fundamental one and should thus present an unresolved broadened first absorption band in the near-infrared region These features are in agreement with the available experimental data. Strong Hartree-Fock instabilities are found for the delocalized structure and put in relation with the existence of the large nonadiabatic coupling in this conformational region. The solvent influence is discussed in the Onsager dipolar reaction field framework. (C) 2000 John Wiley & Sons, Inc. [less ▲]

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See detailSerine peptidase catalytic machinery: Cooperative one-step mechanism
Dive, Georges ULg; Dehareng, Dominique ULg

in International Journal of Quantum Chemistry (1999), 73(2), 161-174

The acylation reaction of beta-lactamases by beta-lactam compounds is modeled as a one-step process. Twenty seven transition-state models are investigated at the restricted Hartree-Fock (RHF) level within ... [more ▼]

The acylation reaction of beta-lactamases by beta-lactam compounds is modeled as a one-step process. Twenty seven transition-state models are investigated at the restricted Hartree-Fock (RHF) level within the minimal MINI-1' basis set. These transition states differ by the nature of both the substrate and the amino acids constituting the reactive nucleophile. The intrinsic reactivity of the class-A and class-C beta-lactamases are under concern. Eight transition-state models were docked in a class-A beta-lactamase, TEM1, as optimized with the benzylpenicillin at the molecular mechanics level. In the proposed one-step acylation process, only two amino acids are directly involved, the usual nucleophilic serine, S70 in TEM1, and a close serine or tyrosine, S130 in TEM1, Y150 in P99. The lysine close to these two residues, K73 in TEM1, plays only an indirect role in the process. (C) 1999 John Wiley & Sons, Inc. Int J Quant Chem 73: 161-174, 1999. [less ▲]

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See detailEnergetic and conformational study of four benzylimidazole compounds with alpha 2 agonist profile: The mivazerol and three methylated derivatives
Vancampenhout, Nathalie; Dive, Georges ULg; Dehareng, Dominique ULg

in International Journal of Quantum Chemistry (1996), 60(4), 911-930

The mivazerol and three of its methylated derivatives are studied at the ab initio SCF level within the MINI-1 and 6-31G basis sets. This study aimed at determining some probable conformations, either ... [more ▼]

The mivazerol and three of its methylated derivatives are studied at the ab initio SCF level within the MINI-1 and 6-31G basis sets. This study aimed at determining some probable conformations, either neutral or protonated, that could interact with the alpha 2 adrenoceptors. The solvent effect was also studied within the Onsager's solvent model at the two dielectric constant (epsilon) values of 4 and 80. The interaction with the environment (either solvent or receptor) is schematically studied by positioning either two water molecules or one formamide or/and one formic add near the amide and the imidazole for few isomers. The medium polarization, through epsilon, and the solvation effect, through the interaction with the solvent molecules or the receptor side chains, stabilize the same isomers. Post-SCF calculations are performed at the CISD level, the first excited singlet and triplet states energies are determined, and the question of the wave-function stability is addressed. The results indicate the probability of a spin-orbit coupling with the first excited triplet state, thus opening the question of such a possibility within an enzyme active site. (C) 1996 John Wiley & Sons, Inc. [less ▲]

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See detailProposition for the acylation mechanism of serine proteases: A one-step process?
Dive, Georges ULg; Dehareng, Dominique ULg; Peeters, Daniel

in International Journal of Quantum Chemistry (1996), 58(1), 85-107

This work proposes a very detailed ab initio study of the hypothesis for a one-step serine protease acylation process with one water molecule acting as the main catalyst reactant. For the 11 increasing ... [more ▼]

This work proposes a very detailed ab initio study of the hypothesis for a one-step serine protease acylation process with one water molecule acting as the main catalyst reactant. For the 11 increasing complexity models considered, the minimum and transition state conformations for the reaction are determined by full geometry optimizations at the ab initio self-consistent field (scF) levels within several basis sets, from MINI-1 to 6-31G, and, for the smallest complexes, at the post-SCF MP2 level within the 6-31G** basis set. The related thermodynamical quantities are calculated for all the conformations. The influence of the oxyanion hole stabilizer and of the dyad His57-Asp102 is quantified and a very good agreement is obtained with point mutagenesis. The activation barrier is found in the range 15-18 kcal/mol. (C) 1996 John Wiley & Sons, Inc. [less ▲]

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See detailPolarization correction of the electrostatic potential for aromatic-compounds - Study of the nucleophilic-attack
Dive, Georges ULg; Dehareng, Dominique ULg

in International Journal of Quantum Chemistry (1993), 46(1), 127-136

The electrostatic potential (EP) and the polarization correction (PL) on the EP were calculated for four aromatic compounds: benzene, chlorobenzene, phenol, and benzoic amide, at the ab initio SCF level ... [more ▼]

The electrostatic potential (EP) and the polarization correction (PL) on the EP were calculated for four aromatic compounds: benzene, chlorobenzene, phenol, and benzoic amide, at the ab initio SCF level within two basis sets: 6-31G** and MINI-1. One calculation was performed using the polarized MINI-1** basis set. The quantity total interaction energy (TEH) defined as -EP + PL can be used as an indicator of the nucleophilic attack preferential position. By reference to 6-31G**, MINI-I provides very satisfactory results. Moreover, the MINI-1** results are very similar to the MINI-I ones. It appears that -EP does not provide a reliable tool to study the nucleophilic attack susceptibility, whereas TEH seems to be very well adapted for this kind of approach. [less ▲]

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See detailAnalytical calculation of the electrostatic interaction energy within the CNDO framework
Dehareng, Dominique ULg; Dive, Georges ULg; Ghuysen, Jean-Marie ULg

in International Journal of Quantum Chemistry (1993), 46(6), 711-734

This work analyses the adequacy of an analytical electrostatic energy formulation within the CNDO framework to predict the stable conformations of large molecular complexes. Comparisons are made with ab ... [more ▼]

This work analyses the adequacy of an analytical electrostatic energy formulation within the CNDO framework to predict the stable conformations of large molecular complexes. Comparisons are made with ab initio results for small systems such as water-formamide, methanol-water-imidazole, or guanine-cytosine and with AM1 results for two large systems: a molecular tweezer + the 9-methyladenine complex and a model active site of the alpha-chymotrypsin and its ligand complex. This approach is efficient in providing reliable conformers for large molecular systems in a very fast way. [less ▲]

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