155 research outputs found
Experimental and theoretical study of the gas-phase interaction between ionized nitrile sulfides and pyridine
AbstractThe gas-phase reactivity of ionized nitrile sulfides, R-CN+-S•, towards neutral pyridine was studied both experimentally (six sector hybrid mass spectrometer) and theoretically (density functional theory and Møller-Plesset ab initio calculations). An ionized sulfur atom transfer and a cycloaddition process respectively yielding ionized pyridine N-thioxide and a thiazolopyridinium cation were observed. Whereas the very efficient S•+ transfer reaction probably involves the intermediacy of several ion-molecule complexes, the thiazolopyridinium ion formation is likely to be initiated by an electrophilic attack of the R-CN+-S• ion on the nitrogen atom of pyridine; the resulting intermediate then undergo an intramolecular substitution of an α-hydrogen atom by the sulfur atom
Chromatographic, Spectrometric and NMR Characterization of a New Set of Glucuronic Acid Esters Synthesized by Lipase
An enzymatic synthesis was developed on a new set of D-glucuronic acid esters and particularly the tetradecyl-D-glucopyranosiduronate also named tetradecyl D-glucuronate. Chromatographic analyses revealed the presence of the ester as a mixture of anomeric forms for carbon chain lengths superior to 12. TOF/MS and MS/MS studies confirmed the synthesis of glucuronic acid ester. The NMR study also confirmed the structure of glucuronic acid esters and clearly revealed an anomeric (α/β) ratio equivalent to 3/
Real-time monitoring of enzymatic DNA hydrolysis by electrospray ionization mass spectrometry
A fast and direct method for the monitoring of enzymatic DNA hydrolysis was developed using electrospray ionization mass spectrometry. We incorporated the use of a robotic chip-based electrospray ionization source for increased reproducibility and throughput. The mass spectrometry method allows the detection of DNA fragments and intact non-covalent protein–DNA complexes in a single experiment. We used the method to monitor in real-time single-stranded (ss) DNA hydrolysis by colicin E9 DNase and to characterize transient non-covalent E9 DNase–DNA complexes present during the hydrolysis reaction. The mass spectra showed that E9 DNase interacts with ssDNA in the absence of a divalent metal ion, but is strictly dependent on Ni(2+) or Co(2+) for ssDNA hydrolysis. We demonstrated that the sequence selectivity of E9 DNase is dependent on the ratio protein:ssDNA or the ssDNA concentration and that only 3′-hydroxy and 5′-phosphate termini are produced. It was also shown that the homologous E7 DNase is reactive with Zn(2+) as transition metal ion and that this DNase displays a different sequence selectivity. The method described is of general use to analyze the reactivity and specificity of nucleases
Malolactic fermentation of wine: study of the influence of some physico-chemical factors by experimental design assays
International audienceThe ability of selected lactic acid bacteria to carry out malolactic fermentation depends on the level of numerous wine characteristics. A Hadamard's experimental matrix was used to determine the main effects of 11 physico-chemical factors on malolactic activity of three Leuconostoc Å“nos strains and one Lactobacillus plantarum strain. Ethanol had the greatest inhibitory effect on the achievement of malolactic fermentation for all Leuc. Å“nos strains. An inhibitory effect of the L-malic acid was also found in the operating conditions. These strains show different degrees of sensitivity to pH. One of these strains was inhibited by SO2. Malolactic activity of the Lact. plantarum strain is mainly affected by a low pH, and this strain is often less efficient than Leuc. Å“nos strains. This methodology could be used for the selection of strains for malolactic starters. Further work is in progress using factorial design in order to determine the interactions between influential factors
Qualitative and Quantitative Saponin Contents in Five Sea Cucumbers from the Indian Ocean
To avoid predation, holothuroids produce feeding-deterrent molecules in their body wall and viscera, the so-called saponins. Five tropical sea cucumber species of the family Holothuriidae were investigated in order to study their saponin content in two different organs, the body wall and the Cuvierian tubules. Mass spectrometry techniques (MALDI- and ESI-MS) were used to detect and analyze saponins. The smallest number of saponins was observed in Holothuria atra, which contained a total of four congeners, followed by Holothuria leucospilota, Pearsonothuria graeffei and Actinopyga echinites with six, eight and ten congeners, respectively. Bohadschia subrubra revealed the highest saponin diversity (19 congeners). Saponin mixtures also varied between the two body compartments within a given animal. A semi-quantitative approach completed these results and showed that a high diversity of saponins is not particularly correlated to a high saponin concentration. Although the complexity of the saponin mixtures described makes the elucidation of their respective biological roles difficult, the comparisons between species and between body compartments give some clues about how these molecules may act as predator repellents
Mass spectrometry of cyclopentadienylideneketene: differentiation of isomeric ion structures by means of ion/molecule reactions
The nature of the m/z 104 ions formed by loss of CO2 or Ph-O-NCO from the molecular ions of phthalic anhydride, N-phenoxyphthalimide, and N-phenoxyisophthalimide was investigated by means of ion/molecule reactions with acetone. This allows a clear-cut differentiation of the so-obtained ions from the isomeric molecular ions of cyclopentadienylideneketene. The different intrinsic chemical reactivities of ionized cyclopentadienylideneketene and its distonoid isomer towards neutral acetone were investigated on a large-scale hybrid mass spectrometer and confirmed by density functional theory calculations
Detrimental Ni(0) Transfer in Kumada Catalyst Transfer Polycondensation of Benzo[2,1-b:3,4-b ']dithiophene
© 2016 Wiley Periodicals, Inc. This article deals with the Kumada Catalyst Transfer Polycondensation (KCTP) of 4,7-dioctylbenzo[2,1-b:3,4-b']dithiophene (BDP-Oct) using Ni(II) catalyst or In/cat combination. A combination of MALDI MS, GPC, and 31P NMR spectroscopy is used to reveal the failure of the KCTP of this particular monomer. Intermolecular transfer reactions to monomer appeared to prevent the formation of polymer. This result is remarkable, since isomeric benzo[1,2-b:4,5-b']dithiophene polymerizes in a controlled way. The presence of a "non-aromatic double bond" in annulated monomers is discussed.status: publishe
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