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See detailCoumarinic derivatives as mechanism-based inhibitors of alpha-chymotrypsin and human leukocyte elastase
Pochet, Lionel; Doucet, Caroline; Dive, Georges ULg et al

in Bioorganic & Medicinal Chemistry (2000), 8(6), 1489-1501

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See detailHartree-Fock instabilities and electronic properties
Dehareng, Dominique ULg; Dive, Georges ULg

in Journal of Computational Chemistry (2000), 21(6), 483-504

Hartree-Fock instabilities are investigated for about 80 compounds, from acetylene to mivazerol (27 atoms) and a cluster of 18 water molecules, within a double zeta basis set. For most conjugated systems ... [more ▼]

Hartree-Fock instabilities are investigated for about 80 compounds, from acetylene to mivazerol (27 atoms) and a cluster of 18 water molecules, within a double zeta basis set. For most conjugated systems, the restricted Hartree-Fock wave function of the singlet fundamental state presents an external or so-called triplet instability. This behavior is studied in relation with the electronic correlation, the vicinity of the triplet and singlet excited states, the electronic delocalization linked with resonance, the nature of eventual heteroatoms, and the size of the systems. The case of antiaromatic systems is different, because they may present a very large internal Hartree-Fock instability. Furthermore, the violation of Hund's rule, observed for these compounds, is put in relation with the fact that the high symmetry structure in its singlet state has no feature of a diradical-like species. It appears that the triplet Hartree-Fock instability is directly related with the spin properties of nonnull orbital angular momentum electronic systems. (C) 2000 John Wiley & Sons, Inc. [less ▲]

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See detailStructure-activity relationships on adrenoceptors and imidazoline-preferring binding sites (I(1,2)-PBSs). Part 1: Weak intramolecular H-bond and conformational flexibility in a new I1-PBS-selective imidazoline analogue, trans1-(4',5'-dihydro-1'H-imidazol-2'-yl)methyl-2-hydroxyindane (PMS 952).
Ye, Hai Fen; Dive, Georges ULg; Dehareng, Dominique ULg et al

in Bioorganic & Medicinal Chemistry (2000), 8(8), 1861-9

The highly selective I1-PBS imidazoline analogue PMS 952 has been selected to study the incidence of intramolecular hydrogen bond and molecular flexibility on its biological activity. On one hand, the ... [more ▼]

The highly selective I1-PBS imidazoline analogue PMS 952 has been selected to study the incidence of intramolecular hydrogen bond and molecular flexibility on its biological activity. On one hand, the weak energy difference between three calculated conformers does not support the stabilization of one conformer by an internal hydrogen bond. The 3-D electrostatic map confirms this feature and the solvent effect does not significantly modify the relative energy of these conformers. On the other hand, the conformational spaces of the neutral and ionized forms present a great number of equilibrium structures, in a short energetic range (20 Kcal). The results are representative of an exceptional conformational flexibility due to a cooperative effect between several parts of the molecule. [less ▲]

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See detailCritical points and reaction paths characterization on a potential energy hypersurface
Ramquet, Marie-Noëlle; Dive, Georges ULg; Dehareng, Dominique ULg

in Journal of Chemical Physics (2000), 112(11), 4923-4934

Most of the time, the definitions of minima, saddle points or more generally order p (p=0,...,n) critical points, do not mention the possibility of having zero Hessian eigenvalues. This feature reflects ... [more ▼]

Most of the time, the definitions of minima, saddle points or more generally order p (p=0,...,n) critical points, do not mention the possibility of having zero Hessian eigenvalues. This feature reflects some flatness of the potential energy hypersurface in a special eigendirection which is not often taken into account. Thus, the definitions of critical points are revisited in a more general framework within this context. The concepts of bifurcation points, branching points, and valley ridge inflection points are investigated. New definitions based on the mathematical formulation of the reaction path are given and some of their properties are outlined. (C) 2000 American Institute of Physics. [S0021-9606(00)01110-7]. [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 detailNew acylnitroso compounds for the asymetric oxyamination of dienes
Gouverneur, Véronique; Mc Carthy, S. J.; Mineur, C. et al

in Tetrahedron (1998), 54(35), 10537-10554

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See detailSynthesis and evaluation of RGD peptidomimetics aimed at surface bioderivatization of polymer substrates
Boxus, Thierry; Touillaux, Roland; Dive, Georges ULg et al

in Bioorganic & Medicinal Chemistry (1998), 6(9), 1577-1595

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See detailCatalytic reaction pathways approached by quantum chemistry: a challenge
Dive, Georges ULg; Dehareng, Dominique ULg; Ghosez, Léon

in Cellular and Molecular Life Sciences : CMLS (1998), 54(4), 378-382

This review explores the potential of quantum chemistry to help understand complex biochemical reactions such as enzyme catalysis. Starting from a historical background, the article introduces the reader ... [more ▼]

This review explores the potential of quantum chemistry to help understand complex biochemical reactions such as enzyme catalysis. Starting from a historical background, the article introduces the reader to the great diversity of problems than can be dealt with in the framework of quantum chemistry. [less ▲]

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See detailRésistance bactérienne aux beta-lactamines
Charlier, Paulette ULg; Coyette, Jacques ULg; Dehareng, Dominique ULg et al

in Medecine Sciences : M/S (1998), 14(5), 544-555

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See detailStepwise introduction of pi-electron cross-conjugaison: a possible access to [5] radialenes ?
Geneste, Florence; Moradpour, Alec; Dive, Georges ULg

in Journal of Organic Chemistry (1997), 62(16), 5339-5343

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See detailDesign and modeling of new platelet-activating factor antagonists.2. Synthesis and biological activity of 1,4-bis-(3',4',5'-trimethoxybenzoyl)-2-alkyl and 2-alkoxymethylpiperazines
Tavet, Fabrice; Lamouri, Aazdine; Heymans, Françoise et al

in Journal of Lipid Mediators and Cell Signalling (1996), 15

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See detailDesign and modeling of new platelet-activating factor antagonists.3. Relative importance of hydrophobicity and electronic distribution in piperazinic series
Heymans, Françoise; Dive, Georges ULg; Lamouri, Aazdine et al

in Journal of Lipid Mediators and Cell Signalling (1996), 15(2), 161-173

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See detailStructure-activity relationships in platelet-activating factor (PAF).7. Tetrahydrofuran derivatives as dual PAF antagonists and acetylcholinesterase inhibitors. Synthesis and PAF-antagonist activity
Le Texier, Laurence; Favre, Edith; Redeuilh, Catherine et al

in Journal of Lipid Mediators and Cell Signalling (1996), 13

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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 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 detailINTERVALENCE TRANSITIONS IN MIXED-VALENCE BIS(TETRATHIAFULVALENE) COMPOUNDS
Lahlil, Khalid; Moradpour, Alec; Bowlas, Christopher et al

in Journal of the American Chemical Society (1995), 117(40), 9995-10002

The series of new bis(tetrathiafulvalene) [bis(TTF)] compounds 10-12a,b have been synthetized with the TTF-like synthon 8a,b, previously used to prepare the pyrazine-fused bis(TTF) 7a,b. These compounds ... [more ▼]

The series of new bis(tetrathiafulvalene) [bis(TTF)] compounds 10-12a,b have been synthetized with the TTF-like synthon 8a,b, previously used to prepare the pyrazine-fused bis(TTF) 7a,b. These compounds exhibit four reversible sequential one-electron oxidation steps, on the basis of cyclic voltammetry. For the cation radicals 7b(.+), 10(.+), and 12(.+), generated electrochemically, rather intense and broad bands in the near-IR region, specific of class II mixed valence compounds, were found. Theoretical calculations at the semiempirical AM1 level as well as at the ab-initio level indicated that these cation radicals are charge-distributions localized as related to mixed valence species. These calculations also allowed the low-energy absorption bands to be assigned to intervalence transitions; these transitions imply the existence of multiple low-lying excited states that are non-adiabatically coupled to the ground-state of these open-shell species. [less ▲]

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See detailBiochemistry of the penicilloyl serine transferases
Ghuysen, Jean-Marie ULg; Dive, Georges ULg

in Ghuysen, Jean-Marie; Hackenbeck, Regine (Eds.) Bacterial cell wall (1994)

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