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991.
Sucrose is determined by its reaction in a packed-bed enzyme reactor containing co-immobilized invertase, mutarotase and glucose oxidase. The hydrogen peroxide produced is measured spectrophotometrically after a chromogenic reaction. Glucose in the samples is decomposed in a pre-reactor containing co-immobilized mutarotase, glucose oxidase and catalase. The response is linear over more than three decades. The detection limit is 0.1 μM sucrose for injection volumes of 80 μl. The sample frequency is 80 h?1 with an r.s.d. of 0.3%. The response for glucose is 0.7% that for sucrose. 相似文献
992.
Mamatkulov SI Khabibullaev PK Netz RR 《Langmuir : the ACS journal of surfaces and colloids》2004,20(11):4756-4763
We studied the water density profile close to spherical and planar hydrophobic objects using molecular dynamics (MD) simulations. For normal pressure and room temperature, the depletion layer thickness of a planar substrate is approximately 2.5 Angstroms. Even for quite large spherical solutes with a radius of R = 18 Angstroms, the depletion layer thickness is reduced by 30%, which shows that substrate curvature and roughness is an experimentally important factor. Rising temperature leads to a substantial increase of the depletion layer thickness. The compressibility of the depletion layer is found to be surprisingly small and only approximately 5 times higher than that of bulk water. A high electrostatic surface potential of 0.5 V is found, which presumably plays an important role in the presence of charged solutes, since it can promote adsorption into the interfacial layer. 相似文献
993.
994.
The salt elimination reaction of the transition carbonyl metal-lates [L(CO)nM](Na/K) (M = Cr, Mo, W, Mn, Re, Fe, Co, Ni; L= CO, n5-C5R5, PR3; n= 1-4; R= alkyl, aryl) with the base-stabilized galliumhalides ClaGaR3 -a(Do) (R = H, alkyl, halide; Do = THF, N(CH3)3, NC7H13) or ClaGa[(CH2)3N-R2](R)2 - a yielded almost quantitatively the transition metal-substituted, gallanes [L(CO)nM]aGaR3 - a(Do) and [L(CO)n-M]aGa[(CH2)3NR2](R)2 - a, respectively. Residual halide functionalities in these complexes were selectively replaced by various other groups. The new compounds were characterized by means of elemental analysis, 1H-, 13C-, 31P-NMR, MS, and lR v(CO) data. The single-crystal X-ray structure analysis of trans-(Ph3P)(CO)3Co-Ga[(CH2) 3N(C2H5)2](R)( 6s : R = Cl, 6t : R= CH3) showed s̀(Co-Ga) lengths of 237.78(4) and 249.5(1) pm, respectively. A short s̀(Fe-Ga) contact of 236.18(3) pm was found for (n5-C5H5)(CO)2Fe-Ga-Cl2[N(CH 3)3] ( 5a ). Low-pressure MOCVD experiments were performed to give thin films of analytically pure CoGa alloy. 相似文献
995.
Paul Pfffli Wolfgang Oppolzer Roland Wenger Hartmut Hauth 《Helvetica chimica acta》1975,58(4):1131-1145
Vincamine ( 13 ) was prepared from the aldehyde 8 in 5 steps using methyl dimethyl-phosphono-methoxy-acetate as a synthon for the pyruvic ester residue. A method to convert apovincamine ( 12 ) into vincamine ( 13 ) has hen worked out. Optically active 8 was synthesized from ethyl-malonaldehydic acid ethyl ester in 9 steps including optical revolution of the acid intermediate 3 by means of salt formation with L-(+)-pseudoephedrine. The two diastereomeric salts were distinguishable by NMR. in carbontetrachloride. 相似文献
996.
The effects of ionic size asymmetry on long-range electrostatic interactions in electrolyte solutions are investigated within the primitive model. Using the formalism of dressed ion theory we analyze correlation functions from Monte Carlo simulations and the hypernetted chain approximation for size asymmetric 1:1 electrolytes. We obtain decay lengths of the screened Coulomb potential, effective charges of ions, and effective permittivity of the solution. It is found that the variation of these quantities with the degree of size asymmetry depends in a quite intricate manner on the interplay between the electrostatic coupling and excluded volume effects. In most cases the magnitude of the effective charge of the small ion species is larger than that of the large species; the difference increases with increasing size asymmetry. The effective charges of both species are larger (in absolute value) than the bare ionic charge, except for high asymmetry where the effective charge of the large ions can become smaller than the bare charge. 相似文献
997.
Huynh HV Schulze-Isfort C Seidel WW Lügger T Fröhlich R Kataeva O Hahn FE 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(6):1327-1335
As a part of a broader study directed towards helical coordination compounds with benzenedithiolate donors, we have synthesized the bis(benzenedithiol) ligands 1,2-bis(2,3-dimercaptobenzamido)ethane (H(4)-1) and 1,2-bis(2,3-dimercaptophenyl)ethane (H(4)-2). Both ligands form dinuclear complexes with Ni(II), Ni(III) and, after air-oxidation, Co(III) ions under equilibrium conditions. Complexes (NEt(4))(4)[Ni(II)(2)(1)(2)] (11 b), (NEt(4))(2)[Ni(III)(2)(1)(2)] (13), and Na(4)[Ni(II)(2)(2)(2)] (14) were characterized by X-ray diffraction. In all complexes, two square-planar [Ni(S(2)C(6)H(3)R)(2)] units are linked in a double-stranded fashion by the carbon backbone and they assume a coplanar arrangement in a stair-like manner. Cyclic voltammetric investigations show a strong dependence of the redox potential on the type of the ligand. The substitution of 1(4-) for 2(4-) on nickel (-785 mV for 11 b versus -1130 mV for 14, relative to ferrocene) affects the redox potential to a similar degree as the substitution of nickel for cobalt (-1160 mV for [Co(2)(1)(2)](2-)/[Co(2)(1)(2)](4-), relative to ferrocene). The redox waves display a markedly less reversible behavior for complexes with the shorter bridged ligand 2(4-) compared to those of 1(4-). 相似文献
998.
W. Bartel P. Duinker J. Olsson P. Steffen J. Heintze G. Heinzelmann R.D. Heuer R. Mundhenke H. Rieseberg B. Schürlein A. Wagner A.H. Walenta 《Physics letters. [Part B]》1976,64(4):483-487
Decays of the J/ψ (3.1) resonance into final states with two charged hadrons and two photons are investigated. Branching ratios for the decays J/ψ → ?π and J/ψ → γη′ are determined to be Upper limits for the same decay modes of ψ′ (3.7) are also determined. 相似文献
999.
1000.
Hansjürgen Mattausch Horst Borrmann Roland Eger R. K. Kremer Arndt Simon 《无机化学与普通化学杂志》1994,620(11):1889-1897
Gd4I6CN: A Carbide Nitride with Chains of Gd6(C2) Octahedra and Gd6N2 Double Tetrahedra The compound α-Gd4I6CN is prepared by reaction of Gd, GdI3, C, and GdN (1:2:1:1 mole ratio) at 1 170 K in sealed Ta tubes. It is obtained as brown red, transparent needles which are air and moisture sensitive. The structure of α-Gd4I6CN contains Gd6 octahedra centered by C2 groups and double tetrahedra centered by N atoms. The units are alternatingly connected via common edges to form chains (Gd2Gd4/2C2) (Gd2/2Gd2/2N)2 parallel [001]. The linear chains are surrounded by I atoms above all free edges of the metal polyhedra and linked according to (Gd2Gd4/2C2) (Gd2Gd4/2N2)I4/2I8I2 in the a – b plane. We also found β-Gd4I6CN, which is formed in a monotropic transition from the α-form. In the structure the chains of Gd octahedra and tetrahedra as described for α-Gd4I6CN are more densely packed. The structure of Y6I9C2N is composed by chains of pairs of Y-octahedra and Y-tetrahedra, respectively. The octahedra are centered by C2 groups, the tetrahedra by N-atoms. We also synthesized the compounds Gd4Br6CN und La4I6CN by tempering at 1 220 K. They are isotypic with α-Gd4I6CN. 相似文献