Complexes of vanadium(V) with α-hydroxycarboxylic acids studied by 1H, 13C, and 51V nuclear magnetic resonance spectroscopy

1987 ◽  
Vol 65 (10) ◽  
pp. 2434-2440 ◽  
Author(s):  
M. Madalena Caldeira ◽  
M. Luísa Ramos ◽  
Nuno C. Oliveira ◽  
Victor M. S. Gil
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Magnetic Resonance Spectroscopy ◽  
Relative Stability ◽  
Nuclear Magnetic Resonance Study ◽  
Resonance Spectroscopy ◽  
Magnetic Resonance Study ◽  
Hydroxycarboxylic Acids ◽  
Ph Range ◽  
Nuclear Magnetic

A proton, carbon-13, and vanadium-51 nuclear magnetic resonance study is reported on the number, stoichiometry, geometry, and relative stability of the complexes that form when vanadate(V) solutions are mixed with each one of the following organic α-hydroxyacids in the pH range ~2.5 – ~7: glycolic, lactic, chloro-3- and phenyl-3-lactic, mandelic, glyceric, and malic acids. The predominant complexes have 1:1 composition (almost certainly in a polymeric structure) in contrast with the 1:2 (metal:ligand) stoichiometry of the corresponding Mo(VI) and W(VI) complexes.

Nuclear magnetic resonance study of addition–cyclization involving ethyl thioacetoacetate and α-nucleophiles

1981 ◽  
Vol 59 (3) ◽  
pp. 629-634 ◽  
Author(s):  
Michael Cocivera ◽  
Soumen Basu ◽  
Leslie Copp ◽  
Vincenzo Malatesta
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Magnetic Resonance Spectroscopy ◽  
Nuclear Magnetic Resonance Spectroscopy ◽  
Nuclear Magnetic Resonance Study ◽  
Resonance Spectroscopy ◽  
Magnetic Resonance Study ◽  
Cyclic Product ◽  
Rates Of Decay ◽  
Nuclear Magnetic

Addition of NH2NH2 or NH2OH to ethyl thioacetoacetate to form the corresponding cyclic product, 3-methylpyrazol-5-one or 3-methylisoxazol-5-one proceeds via cyclization of the carbinolamine formed by addition to the β-keto carbon, i.e., cyclization is faster than dehydration of the carbinolamine to form the imine. In contrast the corresponding carbinolamine derived from ethylacetoacetate undergoes dehydration faster than cyclization. By means of 1H nuclear magnetic resonance spectroscopy, it is possible to detect the cyclic carbinolamine as well as another transient and measure their rates of decay. Based on these results, a mechanism is proposed.

scholarly journals Purification and Characterization of Exo-β-d-Glucosaminidase from a Cellulolytic Fungus,Trichoderma reesei PC-3-7

1998 ◽  
Vol 64 (3) ◽  
pp. 890-895 ◽  
Author(s):  
Masahiro Nogawa ◽  
Hiroya Takahashi ◽  
Aya Kashiwagi ◽  
Kenji Ohshima ◽  
Hirofumi Okada ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Magnetic Resonance Spectroscopy ◽  
Nuclear Magnetic Resonance Spectroscopy ◽  
Trichoderma Reesei ◽  
Resonance Spectroscopy ◽  
Product Analysis ◽  
Ph Range ◽  
Layer Chromatography ◽  
Nuclear Magnetic

ABSTRACT Chitosan-degrading activities induced by glucosamine (GlcN) orN-acetylglucosamine (GlcNAc) were found in a culture filtrate of Trichoderma reesei PC-3-7. One of the chitosan-degrading enzymes was purified to homogeneity by precipitation with ammonium sulfate followed by anion-exchange and hydrophobic-interaction chromatographies. The enzyme was monomeric, and its molecular mass was 93 kDa. The optimum pH and temperature of the enzyme were 4.0 and 50°C, respectively. The activity was stable in the pH range 6.0 to 9.0 and at a temperature below 50°C. Reaction product analysis from the viscosimetric assay and thin-layer chromatography and 1H nuclear magnetic resonance spectroscopy clearly indicated that the enzyme was an exo-type chitosanase, exo-β-d-glucosaminidase, that releases GlcN from the nonreducing end of the chitosan chain. 1H nuclear magnetic resonance spectroscopy also showed that the exo-β-d-glucosaminidase produced a β-form of GlcN, demonstrating that the enzyme is a retaining glycanase. Time-dependent liberation of the reducing sugar from partially acetylated chitosan with exo-β-d-glucosaminidase and the partially purified exo-β-d-N-acetylglucosaminidase from T. reesei PC-3-7 suggested that the exo-β-d-glucosaminidase cleaves the glycosidic link of either GlcN-β(1→4)-GlcN or GlcN-β(1→4)-GlcNAc.

Complexes of W(VI) and Mo(VI) with glycolic, lactic, chloro- and phenyl-lactic, mandelic, and glyceric acids studied by 1H and 13C nuclear magnetic resonance spectroscopy

1987 ◽  
Vol 65 (4) ◽  
pp. 827-832 ◽  
Author(s):  
M. Madalena Caldeira ◽  
M. Luisa Ramos ◽  
Victor M. S. Gil
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Sodium Tungstate ◽  
Sodium Molybdate ◽  
Nuclear Magnetic Resonance Study ◽  
Resonance Spectroscopy ◽  
Magnetic Resonance Study ◽  
Ph Values ◽  
13C Nuclear Magnetic Resonance ◽  
Nuclear Magnetic

A proton and carbon-13 nuclear magnetic resonance study is reported on the number, stoichiometry, geometry, and stability of the complexes that form when sodium tungstate or sodium molybdate is mixed with each one of the following α-hydroxyacids in aqueous solution at pH values in the range 3–8: glycolic, lactic, chloro-3- andphenyl-3-lactic, mandelic, and glyceric acids. The predominant complexes have 1:2 composition and pK of formation of the order of −5 to −16.

Quantitative Determination of Sodium Dodecatungstosilicate Speciation by 183W Nuclear Magnetic Resonance Spectroscopy

2002 ◽  
Vol 55 (4) ◽  
pp. 281 ◽  
Author(s):  
B. J. Smith ◽  
V. A. Patrick
Keyword(s):  
Aqueous Solution ◽  
Nuclear Magnetic Resonance ◽  
Nmr Spectroscopy ◽  
Magnetic Resonance ◽  
Magnetic Resonance Spectroscopy ◽  
Resonance Spectroscopy ◽  
High Concentration ◽  
Ph Range ◽  
Nuclear Magnetic

The speciation and equilibria of sodium dodecatungstosilicate has been determined using 183W nuclear magnetic resonance (NMR) spectroscopy over the pH range 3-13.5. The use of NMR allowed the direct observation of polytungstate anions in aqueous solution and at high concentration (0.5 mol L-1). Using this technique, the speciation of α-[SiW12O40]4-, α-[SiW11O39]8-, α-[NaSiW11O39]7-, α-[H2W12O40]6-, [H8W11O40]6-, [H7W11O40]7-, [W7O24]6-, [H2W12O42]10-, and WO42- was quantified as a function of pH. This work has allowed stability constants for α-[SiW12O40]4- (log K 46) and α-[SiW11O39]8- (log K 86) to be estimated.

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