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1.
Ready detection of small amounts of lactulose in dairy products by thin-layer chromatography 总被引:1,自引:0,他引:1
Summary Ready detection of lactulose in milk and in mixtures with other sugars is achieved by diluting the sample ten times with acetone and successive thin-layer chromatographic separation on silica gel-boric acid, developed with acetonitrile: water 5020. The method allows detection of up to 0.02% lactulose on total carbohydrates and permits a semi-quantitative estimation of lactulose in milk. 相似文献
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Free energy calculations for the transfer of a water molecule from the pure liquid to an interior cavity site in a protein are presented. Two different protein cavities, in bovine pancreatic trypsin inhibitor (BPTI) and in the I76A mutant of barnase, represent very different environments for the water molecule: one which is polar, forming four water-protein hydrogen bonds, and one which is more hydrophobic, forming only one water-protein hydrogen bond. The calculations give very different free energies for the different cavities, with only the polar BPTI cavity predicted to be hydrated. The corresponding entropies for the transfer to the interior cavities are calculated as well and show that the transfer to the polar cavity is significantly entropically unfavorable while the transfer to the nonpolar cavity is entropically favorable. For both proteins an analysis of the fluctuations in the positions of the protein atoms shows that the addition of a water molecule makes the protein more flexible. This increased flexibility appears to be due to an increased length and weakened strength of protein-protein hydrogen bonds near the cavity. 相似文献
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Barluenga J Fernández-Rodríguez MA Aguilar E Fernández-Marí F Salinas A Olano B 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(16):3533-3544
A new procedure for the synthesis of 1,3,4-trisubstituted and 1,4-disubstituted pyrrolidin-2-one derivatives in an enantioselective fashion is reported. The 1,3-dipolar cycloaddition of (+/-)-menthol and (-)-8-phenylmenthol derived Fischer alkoxy alkenyl carbene complexes with in situ generated functionalized azomethine ylides gives the corresponding cycloadducts as chelated tetracarbonyl Fischer carbene complexes. Only one regioisomer is detected in all cases, and the diastereoselectivity of the reaction is very high when (-)-8-phenylmenthol derived carbenes are employed. Oxidation and further transformation of the cycloadducts provide an easy access to pyrrolidin-2-ones. The anti-inflammatory and antidepressant drug (+)-Rolipram is readily prepared in four steps in a 20% overall yield by taking advantage of this newly developed methodology. 相似文献
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Theresa Hague Andrea Petroczi Paul LR Andrews James Barker Declan P Naughton 《Chemistry Central journal》2010,4(1):2
This is a correction to the following paper: Hague T, Petroczi A, Andrews PR, Barker J, Naughton DP: Determination of metal
ion content of beverages and estimation of target hazard quotients: a comparative study. Chem Central J 2008, 2:13. 相似文献
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Moreno FJ Quintanilla-López JE Lebrón-Aguilar R Olano A Sanz ML 《Journal of the American Society for Mass Spectrometry》2008,19(7):927-937
A mass spectrometric study has been carried out to elucidate the structures of glycated peptides obtained after in vitro gastrointestinal digestion of bovine beta-lactoglobulin (beta-LG) glycated with prebiotic galacto-oligosaccharides (GOS). The digests of both native and glycated beta-LG were analyzed by MALDI-MS, LC-ESI-MS, and LC-ESI-MS/MS. MALDI-MS profiles showed marked differences mainly related to the lower intensity of ions corresponding to the digest of glycated beta-LG. Overall, 58 and 23 unglycated peptides covering 97% and 63% of the mature beta-LG sequence could be identified in the digests of native and glycated samples, respectively. The LC-ESI-MS analyses corroborated the MALDI-MS results regarding the unglycated peptides but they also enabled an extensive investigation into the digest of glycated beta-LG. Thus, a total of 19 peptides glycated with GOS from two to seven hexose units could be identified. The tandem mass spectra of glycated peptides were mostly characterized by two neutral losses of 1026/1056, 864/894, 702/732, 540/570, 378/408, and 216/246 u, corresponding to the formation of the furylium ion and its subsequent "CHOH" loss, indicative of the peptide glycation with hepta-, hexa-, penta-, tetra-, tri-, and disaccharides, respectively. Also, other minor ionic species containing the furylium ring linked to different galactose units could be also detected, showing the diversity of the fragmentation pattern of peptides glycated with larger size carbohydrates. Finally, the putative GOS glycation sites could be determined at the NH(2)-terminal Leu residue and at Lys residues located in positions 14, 47, 75, 77, 83, 91, 100, 135, and 138. 相似文献
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Summary A quantitative GC method has been developed which allows determination of mono and disaccharides in enteral formulations.
The method is based on the isolation of the mono and disaccharide fraction on a charcoal-celite column and conversion to trimethylsilylated
oximes (TMS-oximes). The repeatability of the complete method and recovery were acceptable. In the five commercial samples
assayed, maltose was the main sugar (5.24–8.85 gL−1) followed by glucose (1.06–2.41 gL−1) and lactose (0–1.17 gL−1) Low levels of fructose (0–0.18 gL−1) and sucrose (0–0.07 gL−1) were observed and galactose was detected in two of the samples. The presence of maltulose is reported in enteral formulations
for the first time. Maltulose formed from maltose during processing, was present in variable amounts (0.12–1.07 gL−1) and could be a useful indicator for enteral formulation classification. 相似文献
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Moss SJ Carletti I Olano C Sheridan RM Ward M Math V Nur-E-Alam M Braña AF Zhang MQ Leadlay PF Méndez C Salas JA Wilkinson B 《Chemical communications (Cambridge, England)》2006,(22):2341-2343
We report the directed biosynthesis of borrelidin analogues and their selective anti-proliferative activity against human cancer cell lines. 相似文献
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Olano C Wilkinson B Sánchez C Moss SJ Sheridan R Math V Weston AJ Braña AF Martin CJ Oliynyk M Méndez C Leadlay PF Salas JA 《Chemistry & biology》2004,11(1):87-97
The biosynthetic gene cluster for the angiogenesis inhibitor borrelidin has been cloned from Streptomyces parvulus Tü4055. Sequence analysis indicates that the macrolide ring of borrelidin is formed by a modular polyketide synthase (PKS) (borA1-A6), a result that was confirmed by disruption of borA3. The borrelidin PKS is striking because only seven rather than the nine modules expected for a nonaketide product are encoded by borA1-A6. The starter unit of the PKS has been verified as trans-cyclopentane-1,2-dicarboxylic acid (trans-1,2-CPDA), and the genes involved in its biosynthesis identified. Other genes responsible for biosynthesis of the nitrile moiety, regulation, and self-resistance were also identified. 相似文献