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991.
992.
F. Gonzalez-Muñoz A. Pérez-Oseguera J. Cassani M. Jiménez-Estrada R. Vazquez-Duhalt A. López-Munguía 《Journal of carbohydrate chemistry》2013,32(3):275-283
ABSTRACT The enzymatic synthesis of ß2-2' and ß2-1'-D- fructopyranosyl glycerol was carried out with levansucrase from Bacillus circulans or B.subtilis, using sucrose as fructosyl donor and glycerol. The specificity and efficiency of the enzyme was modified by controlling both the water and the total substrate concentrations. The products were purified by HPLC and analyzed by 1H, 13C NMR and GC-MS. 相似文献
993.
J. M. Sanz Báñez J. A. Sastre López M. R. Molina Patiño T. Gómez Santacana C. Romero-Ávila García 《Journal of carbohydrate chemistry》2013,32(4):403-417
ABSTRACT The synthesis of several 3-aryl-5-glycosylisoxazole derivatives has been achieved. By condensation of the protected aldehydo-sugars 2,3-O-isopropylidene-D-glyceraldehyde (1), 2,3:4,5-di-O-isopropylidene-aldehydo-D-arabinose (2) and D-xylose (3), and 2,5-anhydro-3,4,5-tri-O-benzoyl-D-mannose (4) with benzoylmethylenetriphenylphosphorane, enulose derivatives were formed, which were later converted into a,ß-unsaturated ketoximes. These ketoximes were oxidatively cyclized with iodine and, after removal of the hydroxyl protecting groups, 3-phenyl-5-glycosylisoxazoles were formed. 相似文献
994.
Rodrigo Casasnovas David Fernández Joaquín Ortega-Castro Juan Frau Josefa Donoso Francisco Muñoz 《Theoretical chemistry accounts》2011,130(1):1-13
CBS-QB3, two simplified and less computationally demanding versions of CBS-QB3, DFT-B3LYP, and HF quantum chemistry methods
have been used in conjunction with the CPCM continuum solvent model to calculate the free energies of proton exchange reactions
in water solution following an isodesmic reaction approach. According to our results, the precision of the predicted pK
a values when compared to experiment is equivalent to that of the thermodynamic cycles that combine gas-phase and solution-phase
calculations. However, in the aqueous isodesmic reaction schema, the accuracy of the results is less sensitive to the presence
of explicit water molecules and to the global charges of the involved species since the free energies of solvation are not
required. In addition, this procedure makes easier the prediction of pK
a values for molecules that undergo large conformational changes in solvation process and makes possible the pK
a prediction of unstable species in gas-phase such as some zwitterionic tautomers. The successive pK
a values of few amino acids corresponding to the ionization of the α-carboxylic acid and α-amine groups, which is one of the
problematic cases for thermodynamic cycles, were successfully calculated by employing the aqueous isodesmic reaction yielding
mean absolute deviations of 0.22 and 0.19 pK
a units for the first and second ionization processes, respectively. 相似文献
995.
Georgina Bassani Pablo Fuciños Guillermo Picó Beatriz Farruggia 《Colloids and surfaces. B, Biointerfaces》2010,75(2):532-537
The interaction between a lipase from Candida rugosa (Lip1) and polyethyleneglycols of different molecular masses was studied using fluorescence and circular dichroism approaches in order to be applied to the analysis of the enzyme partition mechanism in aqueous two-phase systems of polyethyleneglycol–potassium phosphate. The decrease of the partition coefficients with the polyethyleneglycol molecular mass showed that the enzyme partition is driven by the excluded volume effect and not by the enzyme–polymer interaction. The polymer did not affect the secondary and tertiary structure of the enzyme nor its biological activity. The lipase from Candida rugosa lyophilizate was partitioned in favour of the polyethyleneglycol rich phase; PEG 2000 being the system which showed the better enzyme recovery (78.26%) with a purification factor of 2.3. This method could be applied as a first step to isolate the enzyme from a culture medium with good recovery and without modifying the enzymatic capacity and the molecular structure. 相似文献
996.
997.
J. A. López Sastre J. F. Rodríguez Amo J. M. Báñez Sanz J. Molina Molina M. C. Romero-Avila A. Sanz Tejedor 《Journal of carbohydrate chemistry》2013,32(3):291-308
Abstract The reaction of 2,3-O-isopropylidene-D-glyceraldehyde with different dialkyl and diarylthiomethyl sulfoxides occurs with a high selectivity and produces the corresponding 1-alkyl(or l-aryl)-sulfynil-l-alkyl(or 1-aryl) thio-3,4-O-isopropylidene-D-tetroses as pure diastereoisomers. We have determined the absolute configuration of the three chiral centers formed in these reactions. 相似文献
998.
Glycosides of Monoallyl Diethylene Glycol. A New Type of Spacer Group for Synthetic Oligosaccharides
V. Fernandez-santana J. R. Mariño-Albernas V. Verez-bencomo C. S. Perez-martinez 《Journal of carbohydrate chemistry》2013,32(3):531-537
Abstract The preparation of spacer-armed synthetic oligosaccharides, which can be coupled to either proteins or polymers for use respectively as immunogens or immunoadsorbants for affinity chromatography, is today an important field in chemistry. The methoxycarbonyloctyl glycosides developed by Lemieux and coworkers1 are frequently used and remain the most popular. Other glycosides with amide,2 thioether, 3 and ether4 type spacer groups have also been employed. Recently, an alternative to coupling to proteins appeared when copolymerization of allyl glycosides with acrylamide provided excellent immunogens.5 相似文献
999.
A theoretical investigation of the H2O + HCNO reaction, which is carried out by means of CCSD(T)/6‐311G(d,p)//B3LYP/6‐311G(d,p)+ZPVE computational method to determine a set of reasonable pathways, there are seven product pathways, P i with i = 1 , 2 , …, 7 are involved. It is shown that P 1 (H2O + NCOH), P 2 (CO + NH2 + OH), P 4 (HCN + HO2 + H), and P 6 (CO + NH2OH) are the major product channels; and P 7 (HOC + H2 + NO) is the minor product channels, whereas the other channels for P 3 (HNO + HCOH) and P 5 (HNO + H2CO) are very minor, the minor product channels. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献
1000.
Hexachloroosmate(IV) effectively catalyzes the photodecomposition of chloroform in aerated solutions. The decomposition products are consistent with a mechanism in which excited state OsCl62− reduces chloroform, rather than one involving photodissociation of chlorine atoms. Trace amounts of ethanol or water in the chloroform lead to photosubstitution to form OsCl5(EtOH)− or OsCl5(H2O)−, neither of which is photocatalytically active. 相似文献