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See detailDynamics of mononuclear cadmium beta-lactamase revealed by the combination of NMR and PAC spectroscopy.
Hemmingsen, L.; Damblon, Christian ULg; Antony, J. et al

in Journal of the American Chemical Society (2001), 123(42), 10329-35

The two metal sites in cadmium substituted beta-lactamase from Bacillus cereus 569/H/9 have been studied by NMR spectroscopy ((1)H, (15)N, and (113)Cd) and PAC spectroscopy ((111m)Cd). Distinct NMR ... [more ▼]

The two metal sites in cadmium substituted beta-lactamase from Bacillus cereus 569/H/9 have been studied by NMR spectroscopy ((1)H, (15)N, and (113)Cd) and PAC spectroscopy ((111m)Cd). Distinct NMR signals from the backbone amides are identified for the apoenzyme and the mononuclear and binuclear cadmium enzymes. For the binuclear cadmium enzyme, two (113)Cd NMR signals (142 and 262 ppm) and two (111m)Cd PAC nuclear quadrupole interactions are observed. Two nuclear quadrupole interactions are also observed, with approximately equal occupancy, in the PAC spectra at cadmium/enzyme ratios < 1; these are different from those derived for the binuclear cadmium enzyme, demonstrating interaction between the two metal ion binding sites. In contrast to the observation from PAC spectroscopy, only one (113)Cd NMR signal (176 ppm) is observed at cadmium/enzyme ratios < 1. The titration of the metal site imidazole (N)H proton signals as a function of cadmium ion-to-enzyme ratio shows that signals characteristic for the binuclear cadmium enzyme appear when the cadmium ion-to-enzyme ratio is between 1 and 2, whereas no signals are observed at stoichiometries less than 1. The simplest explanation consistent with all data is that, at cadmium/enzyme ratios < 1, the single Cd(II) is undergoing exchange between the two metal sites on the enzyme. This exchange must be fast on the (113)Cd NMR time scale and slow on the (111m)Cd PAC time scale and must thus occur in a time regime between 0.1 and 10 micros. [less ▲]

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See detailControlling the electrografting of polymers onto transition metal surfaces through solvent vs monomer adsorption
Crispin, Xavier; Lazzaroni, Roberto; Geskin, Victor et al

in Journal of the American Chemical Society (1999), 121(1), 167-187

Electropolymerization of methacrylic monomers opens the possibility of chemically grafting a wide range of polymers onto transition metal surfaces. In this work, the electropolymerization of ... [more ▼]

Electropolymerization of methacrylic monomers opens the possibility of chemically grafting a wide range of polymers onto transition metal surfaces. In this work, the electropolymerization of polyacrylonitrile and polyethyl acrylate is studied in different solvents; we experimentally confirm that the choice of solvent is a critical parameter for obtaining electrografted polymers. A density-functional theory−based study modeling the interaction of solvent (acetonitrile, dimethylformamide, and pyridine) or monomer (acrylonitrile and ethyl acrylate) molecules with the Ni(100) metal surface provides the means to classify the organic molecules with respect to their ability to interact with the surface. The surface binding-energy difference between monomer and solvent is introduced in a Frumkin-type isotherm. This allows us to rationalize the experimental observations in terms of a competitive adsorption at the metal surface between the monomer and the solvent. The first step in the electrografting mechanism thus appears to be the chemisorption of the monomer at the electrode surface before cathodic polarization is applied; the chemisorbed monomer is therefore the first species reduced, giving rise to an adsorbed reactive intermediate, which is thus able to start the polymerization of a grafted chain. [less ▲]

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See detailH-1-N-15 HMQC for the identification of metal-bound histidines in Cd-113-substituted Bacillus cereus zinc beta-lactamase
Damblon, Christian ULg; Prosperi, Christelle ULg; Lian, L. Y. et al

in Journal of the American Chemical Society (1999), 121(49), 11575-11576

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See detailA novel three-enzyme reaction cycle for the synthesis of N-acetyllactosamine with in situ regeneration of uridine 5'-diphosphate glucose and uridine 5'-diphosphate galactose
Zervosen, Astrid ULg; Elling, Lothar

in Journal of the American Chemical Society (1996), 118(8), 1836-1840

A new three-enzyme reaction cycle consisting of sucrose synthase, UDP glucose 4‘-epimerase, and human β-1,4-galactosyltransferase was established for the synthesis of N-acetyllactosamine (LacNAc) with in ... [more ▼]

A new three-enzyme reaction cycle consisting of sucrose synthase, UDP glucose 4‘-epimerase, and human β-1,4-galactosyltransferase was established for the synthesis of N-acetyllactosamine (LacNAc) with in situ regeneration of UDP galactose. We found that UDP glucose 4‘-epimerase is reductively inactivated in the presence of UMP and acceptor substrates of β-1,4-galactosyltransferase. Reactivation of UDP glucose 4‘-epimerase by the transition state analogues dUDP or dTDP 6-deoxy-d-xylo-4-hexulose in combination with the repetitive batch technique enabled us to use the native enzymes for 11 days in this cycle. With 10 U of sucrose synthase, 5 U of UDP glucose 4‘-epimerase, and 1.25 U of β-1,4-galactosyltransferase, 594 mg of LacNAc could be synthesized. N-Acetyllactosamine was also subsequently converted to Neu5Acα2,6Galβl,4GlcNAc with α-2,6-sialyltransferase and CMP-Neu5Ac. [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 detailDetailed Study of a Molecule in a Molecule N-Acetyl-L-Tryptophanamide in a Active-Site Model of Alpha-Chymotrypsin
Dive, Georges ULg; Dehareng, Dominique ULg; Ghuysen, Jean-Marie ULg

in Journal of the American Chemical Society (1994), 116(6), 2548-2556

Six complexes between a model active site of alpha-chymotrypsin (261 atoms) and N-acetyl-L-tryptophanamide (33 atoms) were optimized at the semiempirical AM1 level. In one of these complexes, a water ... [more ▼]

Six complexes between a model active site of alpha-chymotrypsin (261 atoms) and N-acetyl-L-tryptophanamide (33 atoms) were optimized at the semiempirical AM1 level. In one of these complexes, a water molecule was included. A detailed study at the geometric and energetic levels is presented. The discussion deals with the nature of the interaction, the effect of the environment, the ligand deformation, the backbone relaxation, the water molecule freedom, and the comparison with the molecular mechanics results. [less ▲]

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See detailGeometric control of a pyridoxal-catalyzed aldol condensation
Koh, John T.; Delaude, Lionel ULg; Breslow, Ronald

in Journal of the American Chemical Society (1994), 116(25), 11234-11240

A chiral cyclophane derivative of pyridoxal has been synthesized that has amino groups oriented specifically over one face of the cofactor. The compound catalyzes the formation of threonine and allo ... [more ▼]

A chiral cyclophane derivative of pyridoxal has been synthesized that has amino groups oriented specifically over one face of the cofactor. The compound catalyzes the formation of threonine and allo-threonine from glycine and acetaldehyde with enantioinductions that are a function of pH, reversing the optical selectivity between low pH and high pH. The stereochemical results are compared with those of structurally related pyridoxal cyclophanes that lack titratable catalytic groups. Explanations are advanced for this stereochemical reversal and for the otherwise surprising preference of most of these compounds to react on the more hindered face of the pyridoxal. Models indicate that the transamination intermediate is distorted by the transannular chain, and stereoelectronic arguments predict that this distortion should lead to reaction on the face that carries the chain, as observed. The stereochemical reversal with the attached (dimethylamino)alkyl group, as a function of pH, may reflect catalysis by the protonated form, but metal coordination by the basic form cannot be excluded. [less ▲]

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See detailPolarization-corrected electrostatic potentials of aromatic compounds
Dehareng, Dominique ULg; Dive, Georges ULg; Ghuysen, Jean-Marie ULg

in Journal of the American Chemical Society (1993), 115(15), 6877-6882

The electrostatic potentials (EPS) corrected for polarization (TPS) of the aromatic compounds benzene, aniline, chlorobenzene, nitrobenzene, phenol, benzamide, and N-phenylacetamide have been calculated ... [more ▼]

The electrostatic potentials (EPS) corrected for polarization (TPS) of the aromatic compounds benzene, aniline, chlorobenzene, nitrobenzene, phenol, benzamide, and N-phenylacetamide have been calculated at the ab initio SCF level within three basis sets: 6-31G**, MINI-1, and STO-3G. For chlorobenzene in its MINI-1-optimized geometry, the calculation was also performed within MINI-1**. By reference to 6-31G**, the MINI-1-computed EP is much more satisfactory than the STO-3G-computed EP, whereas the MINI-I and STO-3G basis sets give very similar total potentials corrected for polarization (TPs). The MINI-1** basis set appears to be miscalibrated for computing EPs. It provides qualitative results that differ from those obtained with the 6-31G** basis set. The EP has a negative well above the middle of the benzene ring, while the TP exhibits a negative crown just above the benzene carbon atoms, where electrophilic attack takes place. The TP calculated for the interaction of nitrobenzene with a hydride ion instead of a proton allowed analyzation of the effects of polarization on the positive EP above the N-C bond. [less ▲]

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See detailThe isomerization of oxirane. Stable .CH2OCH2., .CH2CH2O. and :CHOCH3 and Their Counterpart Ions
Wesdemiotis, Chrysostomos; Leyh, Bernard ULg; Fura, Aberra et al

in Journal of the American Chemical Society (1990), 112

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