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61.
Ramos EL Mata-Gómez MA Rodríguez-Durán LV Belmares RE Rodríguez-Herrera R Aguilar CN 《Applied biochemistry and biotechnology》2011,165(5-6):1141-1151
Tannase is an inducible enzyme with important applications in the food and pharmaceutical industries. This enzyme was produced by the fungus Aspergillus niger GH1 under solid-state fermentation using polyurethane foam as solid support and tannic acid as sole carbon source and tannase inducer. Physicochemical properties of A. niger tannase were characterized, and the kinetic and thermodynamics parameters on methyl gallate hydrolysis were evaluated. The enzyme was stable in a pH range of 2-8 and a functional temperature range of 25-65 °C. The highest k(cat) value was 2,611.10 s(-1) at 65 °C. Tannase had more affinity for methyl gallate at 45 °C with a K(M) value of 1.82 mM and an efficiency of hydrolysis (k(cat)/K(M)) of 330.01 s(-1) mM(-1). The lowest E(a) value was found to be 21.38 kJ/mol at 4.4 mM of methyl gallate. The lowest free energy of Gibbs (ΔG) and enthalpy (ΔH) were found to be 64.86 and 18.56 kJ/mol, respectively. Entropy (ΔS) was -0.22 kJ/mol K. Results suggest that the A. niger GH1 tannase is an attractive enzyme for industrial applications due its catalytic and thermodynamical properties. 相似文献
62.
Brayshaw SK Schiffers S Stevenson AJ Teat SJ Warren MR Bennett RD Sazanovich IV Buckley AR Weinstein JA Raithby PR 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(16):4385-4395
We introduce a new highly efficient photochromic organometallic dithienylethene (DTE) complex, the first instance of a DTE core symmetrically modified by two Pt(II) chromophores [Pt(PEt(3))(2)(C≡C)(DTE)(C≡C)Pt(PEt(3))(2)Ph] (1), which undergoes ring-closure when activated by visible light in solvents of different polarity, in thin films and even in the solid state. Complex 1 has been synthesised and fully photophysically characterised by (resonance) Raman and transient absorption spectroscopy complemented by calculations. The ring-closing photoconversion in a single crystal of 1 has been followed by X-ray crystallography. This process occurs with the extremely high yield of 80%--considerably outperforming the other DTE derivatives. Remarkably, the photocyclisation of 1 occurs even under visible light (>400 nm), which is not absorbed by the non-metallated DTE core HC≡C(DTE)C≡CH (2) itself. This unusual behaviour and the high photocyclisation yields in solution are attributed to the presence of a heavy atom in 1 that enables a triplet-sensitised photocyclisation pathway, elucidated by transient absorption spectroscopy and DFT calculations. The results of resonance Raman investigation confirm the involvement of the alkynyl unit in the frontier orbitals of both closed and open forms of 1 in the photocyclisation process. The changes in the Raman spectra upon cyclisation have permitted the identification of Raman marker bands, which include the acetylide stretching vibration. Importantly, these bands occur in the spectral region unobstructed by other vibrations and can be used for non-destructive monitoring of photocyclisation/photoreversion processes and for optical readout in this type of efficiently photochromic thermally stable systems. This study indicates a strategy for generating efficient solid-state photoswitches in which modification of the Pt(II) units has the potential to tune absorption properties and hence operational wavelength across the visible range. 相似文献
63.
A single-chirality solid phase can be obtained in boiling solutions containing a racemic mixture of left- and right-handed enantiomorphous crystals due to dissolution-crystallization cycles induced by a temperature gradient. This phenomenon provides further insights into asymmetric amplification mechanisms under presumably prebiotic conditions. 相似文献
64.
Buckley BR Patel AP Wijayantha KG 《Chemical communications (Cambridge, England)》2011,47(43):11888-11890
The use of CO(2) for the preparation of value-added compounds has dramatically increased due to increased global warming concerns. We herein report an electrochemical cell containing a copper cathode and a magnesium anode that effectively converts epoxides and carbon dioxide to cyclic carbonates under mild electrochemical conditions at atmospheric pressure. 相似文献
65.
We establish the best possible condition for point singularities to be removable for nonlinear elliptic equations in divergent
form with lower order terms from the non-linear Kato classes.
相似文献
66.
Stochastic programming for nurse assignment 总被引:1,自引:0,他引:1
Prattana Punnakitikashem Jay M. Rosenberger Deborah Buckley Behan 《Computational Optimization and Applications》2008,40(3):321-349
We present a brief overview of four phases of nurse planning. For the last phase, which assigns nurses to patients, a stochastic
integer programming model is developed. A Benders’ decomposition approach is proposed to solve this problem, and a greedy
algorithm is employed to solve the recourse subproblem. To improve the efficiency of the algorithm, we introduce sets of valid
inequalities to strengthen a relaxed master problem. Computational results are provided based upon data from Baylor Regional
Medical Center in Grapevine, Texas. Finally, areas of future research are discussed. 相似文献
67.
68.
Delanson R. Crist Chung-Hua Li Charles F. Hammer Keith A. Nelson Horst G. Adolph 《Journal of heterocyclic chemistry》1994,31(6):1525-1528
The base-promoted addition of glyoxal to 1,1,2,2-tetrakis(ethoxycarbonylamino)ethane in DMF gives a product mixture containing mostly 1,1′,3,3′-tetrakis(ethoxycarbonyl)-4,4′,5,5,'-tetrahydroxy-2,2′-biimidazolidyl. An alternate structure containing a tetraazadecalin system was considered less likely, since the most significant peak in the mass spectrum of this product and a tetraacetate derivative corresponded to half the mass of the parent ion. Two-dimensional nmr spectra on the major hplc fraction are more consistent with the biimidazolidinyl structure (very low Jvic and lack of NOE enhancement). A HETCOSY spectrum on the mixture allowed assignment of 1H nmr shifts. 相似文献
69.
J.J. Buckley 《Fuzzy Sets and Systems》1984,13(1):25-37
This paper investigates the problem of selecting, from a set of issues, those which best satisfy a collection of criteria. A group of judges have fuzzy sets defined over the issues, for each criterion, whose values lie in a finite linearly ordered set . These judges also have fuzzy sets defined over the set of criteria. The paper discusses methods of aggregating all the fuzzy sets into one fuzzy set μ, defined on the issues, so that μA?L gives the final ranking for issue A. 相似文献
70.
Mixtures of AgI and PbI2 form a phase stable at temperatures above 125°C with a substantial solid solubility about the composition 67% AgI, this phase exhibits a high electrical conductivity (~0.1S m-1). A proposal is made for the basic form of the AgI-PbI2 equilibrium diagram below 200°C, and comparison made to the systems AgI-ZnI2 and AgI-CdI2. 相似文献