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71.
Density functional theory (DFT) was carried out to identify the existence of intermolecular dihydrogen bonds of the 2-pyridone
(2PY)-diethylmethylsilane (DEMS) and 2PY-triethylgermanium (TEGH) clusters in the ground state. The H···H distances of both
clusters are shorter than the sum of their van der Waals radii. Thus, intermolecular dihydrogen bonds N–H•••H–Si and N–H•••H–Ge
exist in the 2PY-DEMS and 2PY-TEGH clusters, respectively. Based on the ground-state conformations, intermolecular dihydrogen
bonds N–H•••H–Si and N–H•••H–Ge in the electronically excited state of the 2PY-DEMS and 2PY-TEGH clusters were also investigated
using time-dependent density functional theory (TDDFT). Electronic transition of the 2PY-DEMS cluster resembles that of the
2PY-TEGH cluster. Their S1 state is a locally excited (LE) state centered on 2PY moiety. The H•••H distances of the 2PY-DEMS and 2PY-TEGH clusters both
stretch in the S1 state compared to those in the ground state. Upon electronic excitation, intermolecular dihydrogen bonding N–H•••H–Si and
N–H•••H–Ge can weaken with decreasing dihydrogen bonding energies. 相似文献
72.
Biotransformation of piceid in Polygonum cuspidatum to resveratrol by Aspergillus oryzae 总被引:1,自引:0,他引:1
Wang H Liu L Guo YX Dong YS Zhang DJ Xiu ZL 《Applied microbiology and biotechnology》2007,75(4):763-768
Biotransformation of piceid in Polygonum cuspidatum to resveratrol by Aspergillus oryzae was investigated in this study. Resveratrol is widely used in medicine, food, and cosmetic because of its pharmacological
properties. However, it has a much lower content in plants compared with its glucoside piceid, which has a much lower bioavailability.
Traditionally, the aglycone is acquired by acid or enzymatic hydrolysis of its glucoside, but the violent condition and the
acid pollution in hydrolytic reaction and the high cost of the enzyme limit their industrial development. In this paper, fermentation
of P. cuspidatum by A. oryzae was successfully performed, during which, piceid was converted to resveratrol with the highest yield of trans-resveratrol 1.35%, 3.6 times higher than that obtained from raw herb by microwave-assisted extraction. Scale-up production
was also performed and the yield of trans-resveratrol was 3.1 times higher after 24 h incubation. Therefore, biotransformation is a better method to increase the yield
of resveratrol because of its high yield and mild conditions. 相似文献
73.
采用类系祖建系的方法 ,对HLA -Ⅱ类基因DRα 和DRB1 0 4 0 1转基因小鼠模型进行了繁育。通过PCR和Southernblot分子杂交的方法 ,检测小鼠尾组织的DNA样品 ,以确定DR基因的整合和复制情况。结果表明 ,HLA -Ⅱ类基因DR已稳定地遗传至第五代(F5) ;共产仔 32 6只 ,PCR检测出阳性小鼠 95只 ,阳性率为 2 9.1 %。PCR—Southern印迹杂交检测 ,发现 68只仔鼠整合有DR基因 ,总有效率为 2 0 9%。经Nothern杂交和RT -PCR检测HLA -DR基因在脾脏和肾脏中均有表达。 相似文献
74.
The knowledge of the mechanism of flux distribution will benefit understanding cell physiology and regulation of metabolism.
In this study, the measured fluxes obtained under steady-state conditions were used to estimate intracellular fluxes and identify
the robustness of branch points of the anaerobic glycerol metabolism in Klebsiella pneumoniae for the production of 1,3-propanediol by metabolic flux analysis. The biomass concentration increased as NADH2/NAD+ decreased at low initial concentration and inversed at high initial glycerol concentration. The flux distribution revealed
that the branch points of glycerol and dihydroxyacetonephosphate were rigid to the environmental conditions. However, the
pyruvate and acetyl coenzyme A metabolisms gave cells the flexibility to regulate the energy and intermediate fluxes under
various environmental conditions. Additionly, it was found that the formation rate of ethanol and the ratio of pyruvate dehydrogenase
to pyruvate formate lyase appeared visible fluctuations at high glycerol uptake rate. 相似文献
75.
Transcriptional regulation of Fcgr2b gene by polymorphic promoter region and its contribution to humoral immune responses 总被引:4,自引:0,他引:4
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78.
A mathematical model has been developed for immobilized enzyme-catalyzed kinetic resolution of racemate in a fixed-bed reactor in which the enzyme-catalyzed reaction (the irreversible uni-uni competitive Michaelis-Menten kinetics is chosen as an example) was coupled with intraparticle diffusion, external mass transfer, and axial dispersion. The effects of mass-transfer limitations, competitive inhibition of substrates, deactivation on the enzyme effective enantioselectivity, and the optical purity and yield of the desired product are examined quantitatively over a wide range of parameters using the orthogonal collocation method. For a first-order reaction, an analytical solution is derived from the mathematical model for slab-, cylindrical-, and spherical-enzyme supports. Based on the analytical solution for the steady-state resolution process, a new concise formulation is presented to predict quantitatively the mass-transfer limitations on enzyme effective enantioselectivity and optical purity and yield of the desired product for a continuous steady-state kinetic resolution process in a fixed-bed reactor. 相似文献
79.
Yuan ZF Liu C Wang HP Sun RX Fu Y Zhang JF Wang LH Chi H Li Y Xiu LY Wang WP He SM 《Proteomics》2012,12(2):226-235
Determining the monoisotopic peak of a precursor is a first step in interpreting mass spectra, which is basic but non-trivial. The reason is that in the isolation window of a precursor, other peaks interfere with the determination of the monoisotopic peak, leading to wrong mass-to-charge ratio or charge state. Here we propose a method, named pParse, to export the most probable monoisotopic peaks for precursors, including co-eluted precursors. We use the relationship between the position of the highest peak and the mass of the first peak to detect candidate clusters. Then, we extract three features to sort the candidate clusters: (i) the sum of the intensity, (ii) the similarity of the experimental and the theoretical isotopic distribution, and (iii) the similarity of elution profiles. We showed that the recall of pParse, MaxQuant, and BioWorks was 98-98.8%, 0.5-17%, and 1.8-36.5% at the same precision, respectively. About 50% of tandem mass spectra are triggered by multiple precursors which are difficult to identify. Then we design a new scoring function to identify the co-eluted precursors. About 26% of all identified peptides were exclusively from co-eluted peptides. Therefore, accurately determining monoisotopic peaks, including co-eluted precursors, can greatly increase peptide identification rate. 相似文献
80.