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991.
Dr. Lichao Wang Dr. Lian Xu Dr. Bingmei Su Prof. Wei Lin Dr. Xinqi Xu Prof. Juan Lin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(37):9654-9660
l -Threonine aldolase from Actinocorallia herbida (AhLTA) is an ideal catalyst for producing l -threo-4-methylsulfonylphenylserine [(2S,3R)- 1 b ], a key chiral precursor for florfenicol and thiamphenicol. The moderate Cβ stereoselectivity is the main obstacle to the industrial application of AhLTA. To address this issue, a combinatorial active-site saturation test (CAST) together with sequence conservatism analysis was applied to engineer the AhLTA toward improved Cβ stereoselectivity. The optical mutant Y314R could asymmetrically synthesize l -threo-4-methylsulfonylphenylserine with 81 % diastereomeric excess (de), which is 23 % higher than wild-type AhLTA. Molecular dynamic (MD) simulations revealed that the mechanism for the improvement in Cβ stereoselectivity of Y314R is due to the acylamino group of residues Arg314 controlling the orientation of substrate 4-methylsulfonyl benzaldehyde ( 1 a ) in the active pocket by directed interaction with the methylsulfonyl group; this leads to asymmetric synthesis of l -threo-4-methylsulfonylphenylserine. The success in this study demonstrates that direct control of substrates in an active pocket is an attract strategy to address the Cβ stereoselectivity problem of LTA and contribute to the industrial application of LTA. 相似文献
992.
Dr. Aipeng Li Ting Wang Qing Tian Dr. Xiaohong Yang Dongming Yin Prof. Yong Qin Prof. Lianbing Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(20):6283-6294
Enzyme stereoselectivity control is still a major challenge. To gain insight into the molecular basis of enzyme stereo-recognition and expand the source of antiPrelog carbonyl reductase toward β-ketoesters, rational enzyme design aiming at stereoselectivity inversion was performed. The designed variant Q139G switched the enzyme stereoselectivity toward β-ketoesters from Prelog to antiPrelog, providing corresponding alcohols in high enantiomeric purity (89.1–99.1 % ee). More importantly, the well-known trade-off between stereoselectivity and activity was not found. Q139G exhibited higher catalytic activity than the wildtype enzyme, the enhancement of the catalytic efficiency (kcat/Km) varied from 1.1- to 27.1-fold. Interestingly, the mutant Q139G did not lead to reversed stereoselectivity toward aromatic ketones. Analysis of enzyme–substrate complexes showed that the structural flexibility of β-ketoesters and a newly formed cave together facilitated the formation of the antiPrelog-preferred conformation. In contrast, the relatively large and rigid structure of the aromatic ketones prevents them from forming the antiPrelog-preferred conformation. 相似文献
993.
Warda Mohamed Altogbia Nor Azah Yusof Zulkarnain Zainal Azni Idris Siti Khadijah Ab Rahman Siti Fatimah Abd Rahman Azizul Isha 《Arabian Journal of Chemistry》2021,14(2):102928
Palm oil mill effluent (POME) is one of the most significant pollutant in the form of wastewater. It could have negative effects on the environment include the emission of biogas and water pollution which comes from discharging the brownish tick POME to the water bodies if not properly managed. Discharge of dark brownish colored of POME directly into water bodies may affect the aquatic life as it will reduce sunlight penetration and suppress the photosynthetic activity. A molecularly imprinted polymer (MIP) for removal of β-carotene from POME has been aimed to develope in this study. The preparation of β-carotene imprinted and non-imprinted polymer (NIP) involves polymerization of β-carotene (or without it) with β-cyclodextrin (β-CD), 9-vinylcarbazole (9VC), tolylene diisocyanate (TDI) and N,N-dimethylformamide (DMF) as the monomer, co-monomer, cross-linker and solvent (porogen), respectively. Analysis from FTIR showed that MIP and NIP have similar characteristic peak with different peaks intensity, indicating the similarity in the backbone structure of polymerization. TGA result displayed high thermal stability with final decomposition at 320 °C for MIP-β-CD-9VC as compared to NIP-β-CD-9VC. The pH study shows that sorption of β-carotene increased with decreasing the pH of POME and the maximum sorption capacities achieved at pH 2 were 10 μg/g and 7 μg/g for MIP-β-CD-9VC and NIP-β-CD-9VC, respectively. The maximum sorption achieved by using 500 mg of MIP as the sorption of β-carotene increased with increasing the dosage of MIP. Kinetic model evaluation has been applied on this prepared materials. The sorption equilibrium data was well described by Freundlich model. The results indicated that the sorption of β-carotene on MIP follows a pseudo–second–order kinetic. 相似文献
994.
Yeon Seo Cho Seulbi Kim Prof. Young-Kwan Kim Prof. Sung Giu Jin Ji Hun Park 《化学:亚洲杂志》2021,16(22):3636-3639
Resveratrol (3,4’,5-trihydroxystilbene) is beneficial to human health due to its diverse biological activities including its anti-inflammatory and anti-oxidative effects as confirmed by pharmacokinetic tests. Despite these clinical merits, resveratrol's limited hydrosolubility and chemical vulnerability remain challenging with regard to developing a controlled delivery system with enhanced bioavailability. In this work, we report a resveratrol-β-lactoglobulin (R-BLG) composite nanocoating through a layer-by-layer assembly with Fe(III)-tannic acid nanofilms. The R-BLG composite nanocoating can be formed in planar and particulate substrates, showing excellent film stability under a broad range of pH values and against enzymatic digestion during a weeklong incubation. We envision that the proteinaceous nanocoating herein could be combined with existing pharmaceutical carrier materials (e. g., microcapsules and nanoparticles) to realize advanced drug delivery systems with an expanded repertoire of hydrophobic drugs. 相似文献
995.
The title compound, 4β,6α,9α-trimethy-2-carboxyltricyclo[6.3.0.0^(4,5)]undec-2-ene, is a sesquiterpene which was first isolated from Ligularia caloxantha and characterized by MS and NMR. In addition, the structure was determined by X-ray single-crystal diffraction. It crystallizes in orthorhombie, space group P212121 with a = 8.197(2), b = 14.876(3), c = 22.281(6) A, α = β = γ = 90°, V = 2716.9(11) ]A^3, Z = 8, C15H22O2, Mr = 234.34, Dc = 1.146 g/cm^3, μ(MoKa) = 0.074 mm^-1, F(000) = 1024, the final R = 0.0384 and wR = 0.0856 for 6200 independent reflections (Rint = 0.066) and 2538 observed ones (I 〉 2σ(I)). In the molecule, there are three fused five-membered rings; while in this crystal form, the asymmetric unit contains two molecules of the same hand and they are linked together by two intermolecular O-H...O hydrogen bonds to form a dimer. 相似文献
996.
Christopher D. Zangmeister 《Journal of solid state chemistry》2007,180(6):1826-1831
The phase transition between the two anhydrous modifications of NaHSO4 (α and β) was studied using Raman spectroscopy and differential scanning calorimetry. These measurements indicate that β-NaHSO4 is a metastable phase and readily undergoes phase transition to thermodynamically stable α-NaHSO4 with an exothermic enthalpy change of 3.5 kJ/mol. Both thermal (temperatures >434 K) and chemical (exposure to H2O) pathways were identified for this transition. The transition is irreversible, and α-NaHSO4 is an intermediate phase between β-NaHSO4 and NaHSO4·H2O. The possible mechanism of the phase transition is discussed. 相似文献
997.
首次应用变温实验方法和13C核自旋弛豫方法研究了抗癌药β-榄香烯小分子的内部运动状况。结果表明β-榄香烯分子的六元环在所研究的温度范围(298~318K)内几乎是刚性的。该分子的整体滚动自扩散活化能为14kJ/mol.其六元环外侧链基团CH2=CCH3-和CH2=CH-的整体内旋转扩散活化能均为19kJ/mol.而与该六元环直接相连的甲基的内旋转扩散活化能为18kJ/mol.这个数值大大高于连在六元环上不同位置的两个侧链基团CH2=CCH3一中甲基的内旋转扩散活化能(其数值分别为了7kJ/mol和2.8KJ/mol).3个不同位置的甲基的内旋转扩散活化能有很大差别可能是由它们所处的分子空间环境不同而引起的。 相似文献
998.
关于(α,β) -度量的S -曲率 总被引:1,自引:0,他引:1
崔宁伟 《数学物理学报(A辑)》2006,26(6):1047
给出(α,β) -度量F=α\phi(β/α)的S -曲率的计算公式. 证得对一般的(α,β) -度量,当β为关于α长度恒定的Killing1 -形式时,S=0.研究了Matsumoto -度量F=α2/(α-β)和(α,α) -度量F=α+εβ+kβ2/α)的S -曲率, 证得S=0当且仅当β为关于α长度恒定的Killing1 -形式.同时还得到这两类度量成为弱Berwald度量的充要条件.其中\phi(s)为光滑函数,α(y)=\sqrt{aij(x)yiyj}为黎曼度量,β(y)=bi(x)yi为非零1 -形式且ε,k≠ 0为常数. 相似文献
999.
β-Cyclodextrin was immobilized on PEGylated Merrifield resin through cross-linking with 1,6-hexamethylene diisocyanate (HMDI) reagent, using conventional and microwave-assisted methodologies. FT-IR analysis of the solid intermediates indicated the attachment of the linker arm to the resin due the appearance of characteristic bands centered at 1716 and 2270 cm−1 and the attachment of cyclodextrin to the resin was accompanied with increased absorption at the OH stretching regions (3330-3400 cm−1). β-Cyclodextrin linked PEGylated resins are water insoluble and can be used to trap volatile organic compounds (VOCs) from water and subsequently be analyzed by headspace HS/GC, after simple filtration and drying steps. 相似文献
1000.
Noriaki Miyake 《Journal of fluorine chemistry》2003,122(2):243-246
The utility of microreactor for the synthesis of α-fluoro-α,β-unsaturated esters, trifluoromethylation and Michael addition reaction, is described. 相似文献