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941.
Although the tubulysin (tub) biosynthetic gene cluster has been located in two myxobacterial strains, it appears in both cases to be incomplete as obvious candidates for acyl transfer and oxidation functions are lacking. Here, we report the engineering of?a heterologous expression system for the tub biosynthetic pathway from strain Cystobacter sp. SBCb004. The entire tub core cluster was reconstituted from two cosmids using Red/ET recombineering and heterologous expression achieved in strains Pseudomonas putida and Myxococcus xanthus. Availability of the heterologous expression system and the natural producer strain SBCb004 provided a platform for the functional investigation of various biosynthetic genes by targeted inactivation. In addition, BLAST analysis of SBCb004 genome data was?used to identify multiple candidate monooxygenases, whose involvement in tubulysin assembly was evaluated using a combination of knockout mutagenesis and heterologous expression. 相似文献
942.
Jang SI Mok JY Jeon IH Park KH Nguyen TT Park JS Hwang HM Song MS Lee D Chai KY 《Molecules (Basel, Switzerland)》2012,17(3):2992-3007
The aim of this study was to examine the proliferative ability of dibutyryl chitin (DBC) on scratch wounds in HaCaT keratinocytes and to evaluate the effect of nanoporous non-woven mat (DBCNFM) on skin wound healing in hairless mice using the advantages of DBCNFM, such as high porosity and high surface area to volume. The cell spreading activity of DBC was verified through a cell spreading assay in scratched human HaCaT keratinocytes. Scratch wound experiments showed that DBC notably accelerates the spreading rate of HaCaT keratinocytes in a dose dependent manner. The molecular aspects of the healing process were also investigated by hematoxylin & eosin staining of the healed skin, displaying the degrees of reepithelialization and immunostaining on extracellular matrix synthesis and remodeling of the skin. Topical application of DBCNFM significantly reduced skin wound rank scores and increased the skin remodeling of the wounded hairless mice in a dose dependent way. Furthermore, DBCNFM notably increased the expression of the type 1 collagen and filaggrin. These results demonstrate that DBC efficiently accelerates the proliferation of HaCaT keratinocytes and DBCNFM notably increases extracellular matrix synthesis on remodeling of the skin, and these materials are a good candidate for further evaluation as an effective wound healing agent. 相似文献
943.
Dang TT Zhu Y Ghosh SC Chen A Chai CL Seayad AM 《Chemical communications (Cambridge, England)》2012,48(12):1805-1807
An efficient amide synthesis by atmospheric pressure aminocarbonylation using palladium nanoparticles supported on MOF-5 is reported. Interestingly, only 0.5 wt% palladium loading was required to achieve high yields. The catalyst is recyclable and offers negligible palladium leaching. 相似文献
944.
We systematically investigate the possible complex transition origin of electronic excitations of giant molecular systems by using the recently proposed QNTO analysis [J.-H. Li, J.-D. Chai, G. Y. Guo and M. Hayashi, Chem. Phys. Lett., 2011, 514, 362.] combined with long-range corrected TDDFT calculations. Thymine (Thy) related excitations of a B-DNA biomolecule are then studied as examples, where the model systems have been constructed by extracting from the perfect or an X-ray crystal (PDB code 3BSE) B-DNA structure with at least one Thy included. In the first part, we consider the systems composed of a core molecular segment (e.g. Thy, or di-Thy) and a surrounding physical/chemical environment of interest (e.g. backbone, adjacent stacking nucleobases) in gas phase and examine how the excitation properties of the core vary in response to the environment. We find that the orbitals contributed by the DNA backbone and surrounding nucleobases often participate in a transition of Thy-related excitations affecting their composition, absorption energy, and oscillator strength. A vast number of strongly backbone-orbital involved excitations are also found at an absorption wavelength below ~180 nm predicted by TD-ωB97X. In the second part, we take into account geometrically induced variation of the excitation properties of various B-DNA segments, e.g. di-Thy, dTpdT etc., obtained from different sources (ideal and 3BSE). It is found that the transition origin of several Thy-related excitations of these segments is sensitive to slight conformational variations, suggesting that DNA with thermal motions may from time to time exhibit very different photo-induced physical and/or chemical processes. 相似文献
945.
Pan PR Lin YS Tsai MK Kuo JL Chai JD 《Physical chemistry chemical physics : PCCP》2012,14(30):10705-10712
Due to the severe self-interaction errors associated with some density functional approximations, conventional density functionals often fail to dissociate the hemibonded structure of the water dimer radical cation (H(2)O)(2)(+) into the correct fragments: H(2)O and H(2)O(+). Consequently, the binding energy of the hemibonded structure (H(2)O)(2)(+) is not well-defined. For a comprehensive comparison of different functionals for this system, we propose three criteria: (i) the binding energies, (ii) the relative energies between the conformers of the water dimer radical cation, and (iii) the dissociation curves predicted by different functionals. The long-range corrected (LC) double-hybrid functional, ωB97X-2(LP) [J.-D. Chai and M. Head-Gordon, J. Chem. Phys., 2009, 131, 174105], is shown to perform reasonably well based on these three criteria. Reasons that LC hybrid functionals generally work better than conventional density functionals for hemibonded systems are also explained in this work. 相似文献
946.
[RhCp*Cl(2)](2) can catalyze the oxidative coupling of secondary isonicotinamides with activated olefins using Cu(OAc)(2) as an oxidant. The selectivity can be controlled by the solvent. In MeCN, the mono-olefination and two-fold oxidation reaction is the major pathway, while in THF this reaction gave mostly diolefination products. In both cases, the coupled products contain an exocyclic C=C bond. 相似文献
947.
等温吸附曲线在四川威远页岩气区块的应用与表征 总被引:1,自引:1,他引:0
基于四川威远页岩储层条件,在90℃下开展了对四川威远区块页岩气等温吸附实验,分析了影响吸附的主要因素。结合生产实际阐述了吸附气在生产中的变化规律。同时应用吸附势理论,建立不同深度下的吸附模型,对不同深度下的吸附气量进行了预测。研究表明,当地层压力较高时,解吸附气体较少,主要是游离气在贡献,随着地层压力降至10 MPa后,吸附气解析速率逐渐增大直至吸附气起主导作用;黏土含量越高,黏土与有机质的竞争吸附中占主导;吸附气含量越小,而TOC越高,有机质与黏土竞争吸附中占主导;吸附气量越高,另外压力越高、温度越低,吸附气量越高;基于吸附势理论的吸附模型比Langmuir等温吸附模型具有较好的拟合程度,具有较强的适用性;对异常高压的页岩气藏而言,随着深度的增加,吸附气含量逐渐增加,并未出现明显的极值,温度对吸附气量的影响没有压力的影响大,压力对吸附气的含量起主导作用。 相似文献
948.
949.
950.
ABSTRACTMetal-free catalysts have attracted more attention due to their highly active in catalytic oxidation reactions. The electronic structure and catalytic property of BC3 sheet are investigated by using first-principles calculations. It is found that the BC3 sheet as the active surface can effectively regulate the adsorptive stability of reactive gases. Besides, the possible reaction processes for CO oxidation on the BC3 sheet are comparably analysed through different reaction mechanisms, which include the Eley–Rideal (ER), Langmuir–Hinshelwood (LH) and termolecular Eley–Rideal (TER). In the CO oxidation reactions, the decomposition of O2 molecule as the starting state (0.40?eV) is an energetically more favourable process than those of other processes, the Eley–Rideal (ER) reactions (2Oads+2CO→CO2) are more prone to take place with lower energy barriers (0.20?eV) on the BC3 sheet. These results provide an important guidance on exploring the highly efficiency metal-free catalyst for CO oxidation. 相似文献