Search results for "Reaction"
showing 10 items of 6134 documents
Modeling for the active site nitrate reductase. Oxidation of the complex [MovO(O2CC(S) CH3Ph)2]− by nitrate and nitrite in methanol
1998
Abstract Under acid conditions the [MoVIO2(O2CC(S)CH1Ph)2]2 reacts with thiols to yield the monomeric [MoVO(O2CC(S)CH3Ph)2] and disulfide. The reduced complex [MoVO(O2CC(S)CH3Ph)2]− can react with NO3− and NO2− in a one-electron step yeilding respectively NO2 and NO and the original molybdenum (VI)-dioxo complex. The experimental pseudo-first-order rate constant with respect to the Mo(V) complex at 25°C was found to be kobs=2.3×10−4s−1 for NO3− and kobs=1.0×10−2 for NO2−. Oxo transfers to and from the substrate have been coupled to produce a catalytic system which turns over the reaction RSH+(No3− or NO2−)+H+a 1 2 [ RS ] 2 +( NO ] 2 or NO )+ H 2 O , in which thiols, NO1− and NO2− serve as a…
Hydrophobically Directed Aldol Reactions: Polystyrene-SupportedL-Proline as a Recyclable Catalyst for Direct Asymmetric Aldol Reactions in the Presen…
2007
The cover picture shows the aldol reaction between ketones and arylaldehydes carried out by using a polystyrene-supported L-proline catalyst. This material furnishes aldol products in high yields and stereoselectivities. Screening of solvents showed that these reactions take place only in the presence of water. This solvent effect, coupled with the high stereoselectivities observed, has been explained by the formation of a hydrophobic core in the inner surface of the resin with the hydrophilic proline moiety in the resin/water interface. Such a microenvironment promotes the aldol reaction and increases the stereoselectivity. Recycling investigations have shown that this material can be reus…
Organocatalytic Enantioselective Friedel-Crafts Alkylation of 1-Naphthol Derivatives and Activated Phenols with Ethyl Trifluoropyruvate
2015
An organocatalytic enantioselective Friedel–Crafts alkylation of a series of substituted 1- naphthol derivatives and activated phenols with ethyl trifluoropyruvate, catalyzed by a quinine-derived squaramide, is presented. Good yields and high to excellent enantioselectivities of the Friedel– Crafts alkylation products were obtained.
Phytophthora species causing crown and root rot of tomato in southern Italy
2000
Phytophthora capsici, Phytophthora cryptogea and Phytophthora nicotianae were isolated from tomato plants with symptoms of crown and root rot in plastic-house crops in Sicilia and Calabria (southern Italy). The species were identified primarily on the basis of morphological and cultural characteristics. The identification was confirmed using molecular methods, polyacrylamide gel electrophoresis (PAGE) of mycelial proteins and polymorphism of DNA sequences amplified by polymerase chain reaction using random primers (RAPD-PCR). P. capsici caused significant losses in tomato crops that had succeeded capsicum crops. P. cryptogea was found to be the most frequent species causing basal stem rot o…
Computational Modeling of Biological Systems: The LDH Story
2010
Lactate dehydrogenases, LDH, catalyzed reaction has been used in this chapter as a conductor wire to present the evolution and difficulties on computing methods to model chemical reactions in enzymes, since the early calculations based at semiempirical level carried out in gas phase to the recent sophisticated simulations based on hybrid Quantum Mechanical/Molecular Mechanics Dynamics (QM/MM MD) schemes. LDH catalyzes the reversible transformation of pyruvate into lactate. The chemical step consists in a hydride and a proton transfer from the cofactor (NADH) and a protonated histidine (His195), respectively. This fact has generated a lot of controversy about the timing of both transfers in …
Dehydrochlorination of Hexachlorocyclohexanes Catalyzed by the LinA Dehydrohalogenase. A QM/MM Study
2015
The elucidation of the catalytic role of LinA dehydrohalogenase in the degradation processes of hexachlorocyclohexane (HCH) isomers is extremely important to further studies on the bioremediation of HCH polluted areas. Herein, QM/MM free energy simulations are employed to provide the details of the dehydrochlorination reaction of two HCH isomers (γ and β). In particular, the role of the protonation state of one of the catalytic residues-His73-is explored. Based on our calculations, two distinct minimum free energy pathways (concerted and stepwise) were found for γ-HCH and β-HCH. The choice of the reaction channel for the dehydrochlorination reactions of γ- and β-HCH was shown to depend on t…
2,2′-[2,3,5,6-Tetramethyl-p-phenylenebis(methylenethio)]bis(pyridineN-oxide)
2008
Mol-ecules of the title compound, C(22)H(24)N(2)O(2)S(2), lie across centres of inversion. The two thio-pyridine N-oxide groups adopt a stepped trans configuration with respect to the benzene ring, by virtue of the symmetry. The oxopyridinium ring forms a dihedral angle of 79.9 (2)° with the benzene ring. The crystal structure is stabilized by a strong π-π inter-action between the pyridinium rings of adjacent mol-ecules [ring centroid-centroid distance = 3.464 (3) Å].
Lactobacillus tucceti sp. nov., a new lactic acid bacterium isolated from sausage
2006
Abstract Following the application of several molecular techniques strain R 19c, isolated from sausage by Reuter in 1970 and deposited at the DSMZ as Lactobacillus sp., has been identified as pertaining to a new species. It showed singular ISR- Dde I and ISR- Hae III profiles that allowed its differentiation from 68 lactic acid bacteria reference strains analyzed. Phylogenetic analysis based on 16S rRNA gene sequences places this strain in the genus Lactobacillus within the Lactobacillus alimentarius group. Species L. versmoldensis is the closest phylogenetic neighbor with 96.3% sequence similarity. DNA–DNA hybridization experiments confirmed the independent status at species level of this …
Cu/P(4-PVP) stereochemistry in tetralin liquid-phase oxidation
2007
Abstract Cu/P(4-PVP) catalyst was used as catalyst for oxidation of tetralin in liquid phase. The catalyst was prepared by reaction of a Cu(II) salt with a 4-vinylpyridine-co-divinylbenzene polymer receptor and characterized by solid 1 H and 13 C NMR, XPS, FTIR, ESR spectroscopies, and by chemical reaction with pure tetralin. That information was used to gain insight into the stereochemistry of the active site needed to orient the reaction toward tetralone production. It was found that the Cu coordination with the pyridine was critical in influencing the peroxy-radical catalytic reaction, and that polyvinylpyridine was able to limit the autothermal oxidation. The active center is postulated…