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991.
Yoon SK Choban ER Kane C Tzedakis T Kenis PJ 《Journal of the American Chemical Society》2005,127(30):10466-10467
One of the long-standing challenges in biocatalysis is the search for methods to continuously regenerate essential cofactors such as NADH that would enable a wide range of enzymes to be used in the more environmentally friendly synthesis of chiral fine chemicals including pharmaceuticals, cosmetics, and food additives. This communication reports a microreactor-based cofactor regeneration method that exploits the microfluidic phenomenon of laminar flow: a reactant stream and a buffer stream are introduced in a microchannel and continue to flow side by side without turbulent mixing between two electrodes that cover opposing channel walls. Adjustment of the flow rate ratio of the two streams in laminar flow enables focusing of the reactant stream close to the cathode, thereby reversing a normally unfavorable reaction equilibrium essential for cofactor regeneration. The absence of a bulk phase in these microreactors prevents the undesired reverse reaction to take place, which has prevented the use of electrochemical cofactor regeneration in macroscale processes. Here, we demonstrate the regeneration of NADH with conversion efficiencies as high as 31%. We also show the subsequent in situ conversion of an achiral substrate, pyruvate, into a chiral product, l-lactate, within this microreactor. 相似文献
992.
The signal amplification technique of peptide nucleic acid (PNA)-based electrochemical DNA sensor was developed in a label-free and one-step method utilizing enzymatic catalysis. Electrochemical detection of DNA hybridization on a PNA-modified electrode is based on the change of surface charge caused by the hybridization of negatively charged DNA molecules. The negatively charged mediator, ferrocenedicarboxylic acid, cannot diffuse to the DNA hybridized electrode surface due to the charge repulsion with the hybridized DNA molecule while it can easily approach the neutral PNA-modified electrode surface without the hybridization. By employing glucose oxidase catalysis on this PNA-based electrochemical system, the oxidized mediator could be immediately reduced leading to greatly increased electrochemical signals. Using the enzymatic strategy, we successfully demonstrated its clinical utility by detecting one of the mutation sequences of the breast cancer susceptibility gene BRCA1 at a sample concentration lower than 10(-9) M. Furthermore, a single base-mismatched sample could be also discriminated from a perfectly matched sample. 相似文献
993.
K. Y. Lee M. K. Yang Y. Y. Yoon S. K. Shim S. Y. Cho B. K. Seo Y. S. Chung J. H. Lee 《Journal of Radioanalytical and Nuclear Chemistry》2004,259(1):69-74
Most elemental concentrations in crops should be related to those in soil and other circumferential environments. In the present study, more than thirty minor and trace elements in soils and crops were determined by the use of ICP, XRF and NAA. Soil and crop samples were collected at eleven abandoned mine regions in Chungnam province located in the middle part of Korea. The elemental concentrations in soils were compared to the crustal mean concentrations in both Chungnam area and worldwide. The concentration ratios of the elements in soils and crop compartments were calculated and the distribution characteristics of each element were investigated between soil and crop compartments. 相似文献
994.
Kinetic modeling of non-thermal plasma chemistry is conducted to investigate hydrocarbon (CH4, C2H4, C3H6, and C3H8) effects on the promotion of NO–NO2 conversion. A reduced plasma chemistry model, in which radical reactions are selectively involved, is validated with experimental data. The higher reactivity of hydrocarbon additive with O radicals, which produces initial radicals, is requisite to initiate hydrocarbon decomposition, thus providing NO–NO2 conversion. Initial radicals by plasma discharge induce continual hydrocarbon decomposition and this self-preserved reaction mechanism greatly contributes to the promotion of energy efficient NO–NO2 conversion. Increase in the conversion extent by ethylene and propylene additives is substantial because of their stronger affinity with O radical. The primary routes of NO–NO2 conversion process differed by hydrocarbon additives are presented and discussed with the assistance of sensitivity analysis. 相似文献
995.
Sang Il Jeon Mu Shik Jhon 《Journal of polymer science. Part A, Polymer chemistry》1984,22(11):3555-3561
Isotactic and syndiotactic poly(2-hydroxyethyl methacrylate) (PHEMA) have been prepared. Intrinsic viscosity–molecular weight relationships were established for the isotactic and syndiotactic PHEMA in N,N-dimethylformamide (DMF) at 25°C by solution viscometry and light scattering. The unperturbed dimensions and interaction parameters were examined in DMF, water, methanol, ethanol, and water–methanol (1:7 by volume) mixture for isotactic PHEMA and in DMF, methanol, and water–methanol (1:7 by volume) mixture for syndiotactic PHEMA using the Stockmayer–Fixman representation. The results suggest that the compact random coil structure for isotactic PHEMA occurs in water solvent and the isotactic PHEMA is more highly extended in polar solvents. 相似文献
996.
997.
998.
l-Cysteine molecules dramatically enhance the photoluminescence of colloidal CdSe/ZnSe quantum dots (i.e., CTAB/TOPOQD). Based on our spectroscopic studies of temporal variations in QD quantum yields as well as the in situ infrared spectral features of QDs, we propose that adsorption and rearrangement of l-cysteine molecules at the QD–water interface induces the observed unusual enhancement of the photoluminescence quantum yield. Upon addition of l-cysteine to the CTAB/TOPOQD solution, the adsorption of l-cysteine to the CTAB/TOPOQD colloidal particles is driven by the formation of a kinetically favorable intermediate species, which is formed by the coordination of thiol groups to the QD surface Cd atoms. The above species then reacts further to form a thermodynamically stable QD species, which probably involves coordination of both the amine and thiol groups of l-cysteine on the QD surface. Additional comparison studies using MPAQD and other small ligands (i.e., l-alanine, l-serine, and MPA) confirmed our proposed mechanism of l-cysteine adsorption at the CTAB/TOPOQD–water interfaces. In addition to these adsorption structures, we also propose that the dramatic enhancement of QY observed in this study is probably induced by the rearrangement and structural organization of l-cysteine and CTAB molecules at the QD–water interface, which improves the homogeneity and self-organization of the interfacial molecules. 相似文献
999.
Bon-Sung Koo Myung-Hyun Jang Haechul Park Satish Kalme Hey-Yeon Park Jin-Wook Han Yun-Soo Yeo Sang-Hong Yoon Soo-Jin Kim Chang-Muk Lee Moon-Young Yoon 《Applied biochemistry and biotechnology》2010,160(1):122-128
There are several conditions which might modulate polymerization to produce polymers having normal lattice structure. In the absence of 1 mM MgCl2 the assembly was reduced by 36% in Capsicum annuum tubulin (CAnm tubulin). There was no significant difference in the final assembly formation in the presence of 5% to 10% glycerol. However, nucleation rate was slow and apparent study state was achieved lately in the presence of 10% glycerol. Taxol at 100 μM concentration increased 23% tubulin assembly. One millimolar CaCl2, ≥1% dimethyl sulfoxide (DMSO) and physiologically low temperature reduced CAnm tubulin assembly. A value of 0.089 mg/ml was obtained as critical concentration for polymerization. Benomyl significantly reduced the number of cysteine residues accessible to 5,5’-dithiobis-(2-nitrobenzoic acid); there were 4.77?±?0.21 and 3.49?±?0.35 residues accessible per tubulin dimer in the presence of 50 and 100 μM benomyl respectively. 相似文献
1000.