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21.
Peroxidase based biosensors for the selective determination of D,L-lactic acid and L-malic acid in wines 总被引:1,自引:0,他引:1
A novel bioelectrochemical method for the direct determination of D(−) L(+) lactic acid and of L(−) malic acid in wines is presented. Multienzymatic biosensors were realized for the selective determination of the three analytes: D(−) and L(+) lactic acid were measured by a trienzymatic biosensor based on the catalytic activities of the enzymes L(+) lactate oxidase (LOD), D(−) lactate dehydrogenase (D-LDH) and horseradish peroxidase (HRP); L(−) malic acid was measured by a bienzymatic electrode, realized by coupling the enzymes L(−) malic dehydrogenase (L-MDH) and horseradish peroxidase (HRP). In both cases the enzymes were immobilized on an oxygen selective Clark electrode.The simultaneous determination of the two organic acids can be accomplished either in batch or in a flow injection analysis apparatus using the same biosensors as detectors. The analytical performance of the method, tested in standard aqueous solutions and on real samples of wines, showing high repeatability, short response times and reduced cost of analysis, suggest that the experimental approach here described could be followed to monitor the progress of malolactic fermentation. 相似文献
22.
Expanded bed adsorption was used to purify a marketable xylanase often used in the kraft pulp bleaching process. Experiments in packed and expanded beds were carried out mainly to study the adsorption of xylanase on to a cationic adsorbent (Streamline SP) in the presence of cells. In order to study the presence of cells, a Bacillus pumilus mass (5% wet mass) was mixed with the enzyme extract and submitted to an expanded bed adsorption system. One xylanase was purified to homogeneity in the packed bed. However, the 5% cell content hampered purification. 相似文献
23.
Franco Gatta Maria Rosaria Del Giudice Luciano Di Simone Guido Settimj 《Journal of heterocyclic chemistry》1980,17(5):865-868
A new synthesis of 7-chloro-2,3-diamino-5-phenyl-3H-1,4-benzodiazepines is described, which allows for the preparation of compounds bearing the same or different substituents at the 2 and 3 positions, starting from 2-amino-7-chloro-3-hydroxy-5-phenyl-3H-1,4-benzodiazepines. 相似文献
24.
Bianchini C Giambastiani G Laschi F Mariani P Vacca A Vizza F Zanello P 《Organic & biomolecular chemistry》2003,1(5):879-886
A new potentially hexadentate tetraazamacrocycle based on the cyclen skeleton has been synthesized and fully characterized. The macrocycle 4,10-dimethyl-1,4,7,10-tetraazacyclododecane-1,7-bis(methanephosphonic acid monoethyl ester) dipotassium salt (Me2DO2PME) contains mutually trans monoethyl ester phosphonate acid substituents on two nitrogen atoms, and trans methyl substituents on the other two nitrogen atoms. The protonation constants of this macrocycle and the stability constants of its complexes with Cu2+, Zn2+, Gd3+ and Ca2+ ions have been determined by pH potentiometric titrations. The protonation sequence of the macrocycle has been studied by 1H, 31P[1H] and 13C[1H] NMR spectroscopy: the first and second protonation steps take place at the methyl-substituted nitrogen atoms, while the third protonation involves one oxygen from a phosphonate group. Upon protonation, all the CH2 ring protons become magnetically inequivalent on the NMR time scale due to a slow conformational rearrangement, most likely occasioned by the formation of multiple hydrogen bonds within the macrocyclic ring. Me2DOPM forms neutral, mononuclear complexes with all the metals investigated. The presence of hydroxo complexes was observed for Ca2+ and Zn2+ at high pH values. Structural information on the neutral complex [Cu(Me2DO2PME)] has been obtained by a solution X-Band EPR study. It is proposed that Me2DO2PME binds Cu2+ in a distorted octahedral structure using all of its donor atoms, i.e. the four nitrogen atoms and the two phosphonate oxygen atoms. The redox chemistry of [Cu(Me2DO2PME)] in dimethyl sulfoxide and water has been studied by electrochemical measurements. Cyclic voltammetry in DMSO shows the complex to undergo a quasireversible one-electron reduction step leading to an unstable CuI species. 相似文献
25.
[(?) (R)-1,2-bis (Diphenylphosphino)-1-phenylethane]nickel (II) chloride was found to catalyze the asymmetric alkylation of some chiral and achiral allylic alcohols with Grignard reagents, leading to the formation of optically active olefins. Enantiomer discrimination of the substrate takes place in the alkylation of chiral allylic alcohols. 相似文献
26.
The bond dissociation enthalpies (BDE) of several phenols containing electron-withdrawing substituents in the para position have been determined by means of the EPR radical equilibration technique. It has been found that CN, NO(2), CHO, COOR, and COOH induce an increase of the BDE value of the O-H bond, thus producing a worsening of the antioxidant activity of phenols, while Cl, Ph, and CH[double bond]CHPh show an opposite effect. The contributions of these substituents for the calculation of the BDE values in polysubstituted phenols by using the group additivity rule have also been derived. It is shown that this rule provides quite reliable predictions of bond strengths, so that the method can be conveniently used to estimate new data on substituted phenols. 相似文献
27.
The pseudo-halide 1, 2, 3, 4-thiatriazol-5-thiolate, in the anion and acid forms, undergoes photochemical decomposition with the formation of sulfur, nitrogen and the thiocyanate anion, with quantum yields (θ313) of 0.13 and 0.26 for the acid and anion forms, respectively. 相似文献
28.
Shaginian A Patel M Li MH Flickinger ST Kim C Cerrina F Belshaw PJ 《Journal of the American Chemical Society》2004,126(51):16704-16705
We describe the development of photolabile protecting groups based on the 3,4,5-trimethoxyphenacyl group (TMP). Orthogonal safety-catches were created by introducing an acid-activatible dimethyl ketal (AA-TMP) and an oxidatively activatible 1,3-dithiane (OA-TMP) into the photolabile TMP group. We demonstrate the application of these protecting groups in light-directed synthesis of small molecule microarrays with diversity elements radially attached to a hydroxyproline scaffold. 相似文献
29.
Angela Lopedota Adriana Trapani Annalisa Cutrignelli Valentino Laquintana Nunzio Denora Massimo Franco Giuseppe Trapani Gaetano Liso 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):425-432
The objective of this work was to develop a novel microparticulate system based on the mucoadhesive polymer Eudragit-RS 100
and cyclodextrins (CDs), potentially useful for the oral administration of Glutathione (γ–glutamylcysteinylglycine, GSH).
For this purpose, an oil-in-oil (O/O) emulsion-solvent evaporation method was used for the preparation of microparticles (MPs)
containing GSH alone or together with one of the following CDs: α-, β-, γ-, methyl-β-(Me-β-), hydroxypropyl-β-(HP-β-) or sulfobutylether-β-cyclodextrin
(SBE7m-β-CD). MPs were obtained by emulsifying a mixture of Eudragit RS 100, GSH, CD and magnesium stearate in acetone or acetonitrile
with a mixture of liquid paraffin and Span 80. Size, encapsulation efficiency, and drug release of the prepared MPs were evaluated.
The results clearly indicated that all the examined properties were dependent on the water-miscible solvents and CD used.
In particular, MPs prepared by using acetone or acetonitrile showed different size distributions with mean diameters in the
ranges 82–350 and 15–22 μm, respectively. Moreover, encapsulation efficiency values were found to be high in all cases (71–99%)
and was significantly affected by the CD type. The GSH release rates were evaluated employing dissolution media with different
pH values (1.2, 6.8 and 7.4) and the following rank order was obtained for MPs prepared using acetone: MPs incorporating Me-β-CD > MPs
without CD > MPs incorporating the remaining CDs. On the other hand, MPs prepared using acetonitrile gave the highest GSH
release rate. Finally, stability of GSH encapsulated in MPs containing HP-β-CD to enzymatic attack by pepsin A, α-chymotrypsin,
and γ-glutamyltranspeptidase was also investigated. 相似文献
30.
Chromium trioxide oxidation of 1-phenylisochroman-4-spiro-1′-cyclopentane (Ia) in acetic acid led to the expected 1-(2-benzoylphenyl)cyclopentanecarboxylic acid (IIa), while its 6,7-dimethoxy analogue Ib and 6,7-dimethoxy-1-phenylisochroman-4-spiro-4′-(1′-methyl)piperidine (Ic) under the same conditions gave a mixture of their related 1-hydroxy derivatives VIIIb and VIIIc and of the p-benzoquinones, 1-benzoyloxymethyl-1-(2,5-dioxo-4-methoxyphenyl)cyclopentane (IXb) and 1-benzoyloxymethyl-1-(2,5-dioxo-4-methoxyphenyl)-1-methylpiperidine (IXc). Cyclization of Ila with hydrazine or monomethylhydrazine led to the 5-spiro-substituted 1-phenyl-3,5-dihydro-4H-2,3-benzodiazepin-4-ones IIIa or XIa. 相似文献