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At least 73 records · Page 4Linked to original sources
PubMed2006

Bis[bis(methoxycarbimido)amine-kappa2N,N']bis(perchlorato-kappaO)copper(II) bis[bis(methoxycarbimido)amine-kappa2N,N']bis(methanol-kappaO)copper(II) bis(perchlorate) methanol disolvate.

The title compound, [Cu(ClO4)2(C4H9N3O2)2][Cu(C4H9N3O2)2(CH4O)2](ClO4)2.2CH3OH, comprises two independent Cu(II) species lying on different inversion sites. In the Cu complexes, a distorted octahedral geometry arises (from basic square-planar N4 coordination) from the weak coordination of two perchlorate ions (as Cu-O) in one species and two methanol molecules in the other (also as Cu-O). Interactions between the O atoms of the perchlorate anions or methanol groups and the imide or amine NH groups afford an extensive intermolecular hydrogen-bonding network.

Journal Article↗
PubMed1999

Esterification of decanoic acid during supercritical fluid extraction employing either methanol-modified carbon dioxide or a methanol trap.

The methylation of decanoic acid during the supercritical fluid extraction process was investigated. It was found that the majority of the methylation occurred not during the extraction, but during the collection step, in the presence of methanol. Increasing dynamic extraction time (and hence collection time) from 0 to 60 min increased acid to ester conversions from 2% to 4%. The addition of HCl as a catalyst to the reaction increased the reaction rate 10-fold, and resulted in 88% conversion to the methyl ester within 30 min, without any detrimental effects on the chromatographic system. Higher collection temperatures appeared to increase conversion, but decreased methyl ester collection efficiency.

Carbon Dioxide↗
PubMed2003

In silico studies of the mechanism of methanol oxidation by quinoprotein methanol dehydrogenase.

The mechanism of bacterial methanol dehydrogenase involves hydride equivalent transfer from substrate to the ortho-quinone PQQ to provide a C5-reduced intermediate that subsequently rearranges to the hydroquinone PQQH(2). We have studied the PQQ reduction by molecular dynamic (MD) simulations in aqueous solution. Among the five simulated structures, either Asp297 or Glu171 or both are ionized. Reasonable structures are obtained only when both carboxyl groups are ionized. This is not unexpected since the kinetic pH optimum is 9.0. In the structure of the enzyme.PQQ.HOCH(3) complex, the hydrogen bonded Glu171-CO(2)(-).H-OCH(3) is in a position to act as a general base catalyst for hydride equivalent transfer to C5 of PQQ. We thus suggest that Glu171 plays the role of general base catalyst in PQQ reduction rather than Asp297 as previously suggested. The reduction is assisted by Arg324, which hydrogen bonds to the ortho-quinone moiety of PQQ. The rearrangement of the C5-reduced intermediate to provide hydroquinone PQQH(2) is also assisted by proton abstraction by Glu171-CO(2)(-) and the continuous hydrogen bonding of Arg324 throughout the entire reaction. These features as well as the mapping of the channel for substrate and water into the active site entrance are the observations of major importance.

Alcohol Oxidoreductases↗
PubMed2007

Mechanism of methanol oxidation by quinoprotein methanol dehydrogenase.

At neutral pH, oxidation of CH(3)OH --> CH(2)O by an o-quinone requires general-base catalysis and the reaction is endothermic. The active-site -CO(2)(-) groups of Glu-171 and Asp-297 (Glu-171-CO(2)(-) and Asp-297-CO(2)(-)) have been considered as the required general base catalysts in the bacterial o-quinoprotein methanol dehydrogenase (MDH) reaction. Based on quantum mechanics/molecular mechanics (QM/MM) calculations, the free energy for MeOH reduction of o-PQQ when MeOH is hydrogen bonded to Glu-171-CO(2)(-) and the crystal water (Wat1) is hydrogen bonded to Asp-297-CO(2)(-) is DeltaG++ = 11.7 kcal/mol, which is comparable with the experimental value of 8.5 kcal/mol. The calculated DeltaG++ when MeOH is hydrogen bonded to Asp-297-CO(2)(-) is >50 kcal/mol. The Asp-297-CO(2)(-)...Wat1 complex is very stable. Molecular dynamics (MD) simulations on MDH.PQQ.Wat1 complex in TIP3P water for 5 ns does not result in interchange of Asp-297-CO(2)(-) bound Wat1 for a solvent water. Starting with Wat1 removed and MeOH hydrogen bonded to Asp-297-CO(2)(-), we find that MeOH returns to be hydrogen bonded to Glu-171-CO(2)(-) and Asp-297-CO(2)(-) coordinates to Ca(2+) during 3 ns simulation. The Asp-297-CO(2)(-)...Wat1 of reactant complex does play a crucial role in catalysis. By QM/MM calculation DeltaG++ = 1.1 kcal/mol for Asp-297-CO(2)(-) general-base catalysis of Wat1 hydration of the immediate CH(2)==O product --> CH(2)(OH)(2). By this means, the endothermic oxidation-reduction reaction is pulled such that the overall conversion of MeOH to CH(2)(OH)(2) is exothermic.

Alcohol Oxidoreductases↗
PubMed2003

Metal complexes of N-benzamidoporphyrin: (N-benzimido-meso-tetraphenylporphyrinato)(methanol)zinc(II) methanol solvate and (acetato)(N-benzamido-meso-tetraphenylporphyrinato)cadmium(II) benzene solvate.

The crystal structures of N-benzamido-meso-tetraphenylporphyrin (NHCOC(6)H(5)-Htpp; 1), (N-benzimido-meso-tetraphenylporphyrinato)(methanol)zinc(II) [Zn(N-NCOC(6)H(5)-tpp)(MeOH); 2(MeOH)], and (acetato)(N-benzamido-meso-tetraphenylporphyrinato)cadmium(II) [Cd(N-NHCOC(6)H(5)-tpp)(OAc); 3] were established. The coordination sphere around Zn(2+) ion in 2(MeOH) is a distorted trigonal bipyramid with N(2), N(5), and O(2) lying in the equatorial plane, whereas, for Cd(2+) ion in 3, it is a sitting-atop derivative with a distorted trigonal bipyramidal geometry in which the apical site is occupied by atoms N(2) and O(2). Cd in 3 acquires five-coordination with five strong bonds [Cd(1)-N(1) = 2.319(5) A, Cd(1)-N(2) = 2.252(5) A, Cd(1)-N(3) = 2.332(5) A, Cd(1)-O(2) = 2.292(5) A, and Cd(1)-O(3) = 2.317(5) A] and with one secondary intramolecular interaction [Cd(1)...N(4)]. The porphyrin ring in these two complexes is distorted to a large extent. The plane of the three pyrrole nitrogen atoms [i.e., N(1)-N(3)] strongly bonded to Zn(2+) in 2(MeOH) and to Cd(2+) in 3 is adopted as a reference plane 3N. For the Zn(2+) complex, the pyrrole nitrogen bonded to the benzamido (BA) ligand lies in a plane with a dihedral angle of 33.8 degrees with respect to the 3N plane, but for the Cd(2+) complex, this dihedral angle is found to be 31.4 degrees. In the former complex, Zn(2+) and N(5) are located on the different side at -0.08 and 1.39 A from its 3N plane, and in the latter one, Cd(2+) and N(5) are also located on the different side at 1.08 and -1.51 A from its 3N plane. VT NMR ((1)H and (13)C) studies of 3 show that the acetate acts as a bidentate ligand and the OAc(-) exchange does not occur in CD(2)Cl(2). Moreover, the NH proton [i.e., H(5)] of 3 in CD(2)Cl(2) is observed as a sharp singlet at delta = -1.13 ppm with Delta nu(1/2) = 4 Hz at 20 degrees C indicating that the intermolecular proton exchange between water and NH proton is rapid.

Journal Article↗
PubMed2000

Bis(1,10-phenanthroline-N,N')(thiosulfato-O, S)nickel(II)-water-methanol (1/0.92/1.4) and bis(2,2'-bipyridyl-N, N')(thiosulfato-O,S)nickel(II)-water-methanol (1/2/0.55)

The title compounds, [Ni(S(2)O(3))(C(12)H(8)N(2))(2)].0.92H(2)O.1. 4CH(4)O and [Ni(S(2)O(3))(C(10)H(8)N(2))(2)].2H(2)O.0.55CH(4)O, are monomeric, containing nickel(II) in a distorted octahedral coordination environment provided by the four N atoms of two bidentate bipy or phen groups and one S and one O atom from a chelating thiosulfate anion. The crystals are highly unstable outside their mother liquors and are stabilized in solution by a not fully determined number of water and methanol solvate molecules. The phenanthroline structure includes two independent moieties related by a non-crystallographic inversion center. The thiosulfate anions display the usual S-O lengthening found when the anion acts in a bidentate mode.

Journal Article↗
PubMed2004

Bis[tris(1-methyl-1H-imidazol-2-yl)phosphine-kappa3N3]iron(II) tetrachloroferrate(II) methanol tetrasolvate (ca 153 K) and bis[tris(1-methyl-1H-imidazol-2-yl)methanol-kappa3N3]iron(III) bis[tetrachloroferrate(III)] chloride (redetermination, ca 153 K).

The first of the title compounds, [Fe(C12H15N6P)2][FeCl4].4CH4O, is the first homoleptic bis(ligand)iron(II) species reported for this phosphorus bridgehead ligand; interestingly, the complex is isomorphous with its tris(1-methyl-1H-imidazol-2-yl)methanol counterpart, the second of the title compounds, [Fe(C13H16N6O)2][FeCl4]2Cl. In both compounds, the Fe atom of the cation lies on an inversion centre. The structure determinations presented here allow an interesting comparison of iron(II) and iron(III) species in similar coordination environments.

Journal Article↗
PubMed1998

Central role of hemoglobin degradation in mechanisms of action of 4-aminoquinolines, quinoline methanols, and phenanthrene methanols.

We have used a specific inhibitor of the malarial aspartic proteinase plasmepsin I and a nonspecific cysteine proteinase inhibitor to investigate the importance of hemoglobin degradation in the mechanism of action of chloroquine, amodiaquine, quinine, mefloquine (MQ), halofantrine, and primaquine. Both proteinase inhibitors antagonized the antiparasitic activity of all drugs tested with the exception of primaquine. An inhibitor of plasmepsin I, Ro40-4388, reduced the incorporation of radiolabelled chloroquine and quinine into malarial pigment by 95%, while causing a 70% reduction in the incorporation of radiolabelled MQ. Cysteine proteinase inhibitor E64 reduced the incorporation of chloroquine and quinine into malarial pigment by 60 and 40%, respectively. This study provides definitive support for the central role of hemoglobin degradation in the mechanism of action of the 4-aminoquinolines and the quinoline and phenanthrene methanol antimalarials.

Amodiaquine↗