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11.
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
12.
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
13.
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
14.
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
15.
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
16.
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
17.
Mario Bianchi Ugo Matteoli Piero Frediani Gloria Menchi Franco Piacenti 《Journal of organometallic chemistry》1982,236(3):375-380
Hydrogen transfer from racemic alcohols to prochiral ketones in the presence of H4Ru4(CO)8[(?)-DIOP]2 has been examined. The enantiomer-discrimination is influenced by the structure of the reactants, temperature and the excess of phosphine present. 相似文献
18.
Separation of enantiomers: needs, challenges, perspectives 总被引:15,自引:0,他引:15
Chiral drugs, agrochemicals, food additives and fragrances represent classes of compounds with high economic and scientific potential. First the present implications of their chiral nature and necessity of separating enantiomers are summarised in this article. In the following a brief overview of the actual approaches to perform enantioseparations at analytical and preparative scale is given. Challenging aspects of these strategies, such as problems associated with data management, choice of suitable chiral selectors for given enantioseparations and enhanced understanding of the underlying chiral recognition principles, are discussed. Alternatives capable of meeting the requirements of industrial processes, in terms of productivity, cost-effectiveness and environmental issues (e.g., enantioselective membranes) are critically reviewed. The impact of combinatorial methodologies on faster and more effective development and optimisation of novel chiral selectors is outlined. Finally, the merits and limitations of most recent trends in discrimination of enantiomers, including advances in the fields of sensors, microanalysis systems, chiroptical methods and chemical force microscopy are evaluated. 相似文献
19.
Application of the explicit finite-difference simulation method to linear-sweep cyclic voltammetry in the case of non-first-order electrode reactions is described. Reversible, quasi-reversible and totally irreversible electrode reactions with reaction orders > 1 or < 1 are discussed. Simple criteria for evaluating the kinetic parameters are proposed. The accuracy of the proposed method is checked by comparing the results obtained with literature data. 相似文献
20.
The use of the simplex procedure as a non-linear least-squares curve-fitting method is proposed for evaluation of equivalence points in sigmoidal and segmented titration curves. The application of this procedure to theoretical curves affected by different amounts of random noise indicates its effectiveness and accuracy for locating the correct end-point in titrations characterized by very low reaction constants. The relevant results are compared with those obtained by other regression methods as well as by the first-derivative and Gran approaches. 相似文献