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981.
Complex formation ability and stability of both weak and super-weak acids was studied by mean of in silico determined thermodynamic data of the complexes. While weak acids act like Brønsted acids forming hydrogen bond type Brønsted complexes, super-weak acids form Lewis complexes via van der Waals interaction. Unlike in the former type, upon complexation, C-H distances changes insignificantly, yet the complex formation is energy driven in the terms of zero-point corrected Energies, ΔE zp < 0 kcal mol?1, which supports the Lewis complex formation, with the exception of CH4, an extremely “weak acid”. 相似文献
982.
Xiao-Xu Song Chong-Chen Wang Xue-Yan Xu Huan-Ping Jing Peng Wang Shi-Jie Gao 《Transition Metal Chemistry》2017,42(2):181-191
Four coordination complexes of copper(II) and iron(II), namely [CuCl(phen)2](5-NO2-Hipa)·2H2O (BUC-10), [Cu(phen)(3,4-H2dczpb)(H2O)]·H2O (BUC-11), [Fe(phen)(L)(H2O)]2 (BUC-12), and [Fe(phen)3](3,4-H3dczpb)2·0.6H2O (BUC-13) (phen = 1,10-phenanthroline; 5-NO2-H2ipa = 5-nitroisophthalic acid; 3,4-H4dczpb = 3,4-dicarboxyl-(3′,4′-dicarboxylazophenyl) benzene; L = 6,12-dihydroxy-1,2,6,12-tetrahydroindazolo[2,1-a]indazole-1,7-dicarboxylic acid), have been synthesized under hydrothermal conditions. All four complexes were characterized by single-crystal X-ray diffraction, FTIR, elemental analysis and UV–Vis diffuse reflection spectroscopy. The photocatalytic performances of the complexes for decomposition of methylene blue under UV irradiation were also investigated. 相似文献
983.
Metalloproteins have inspired chemists for many years to synthesize artificial catalysts that mimic native enzymes.As a complementary approach to studying native enzymes or making synthetic models,biosynthetic approach using small and stable proteins to model native enzymes has offered advantages of incorporating non-covalent secondary sphere interactions under physiological conditions.However,most biosynthetic models are restricted to natural amino acids.To overcome this limitation,incorporating unnatural amino acids into the biosynthetic models has shown promises.In this review,we summarize first synthetic,semisynthetic and biological methods of incorporates unnatural amino acids(UAAs)into proteins,followed by progress made in incorporating UAAs into both native metalloproteins and their biosynthetic models to fine-tune functional properties beyond native enzymes or their variants containing natural amino acids,such as reduction potentials of azurin,O_2 reduction rates and percentages of product formation of HCO models in Mb,the rate of radical transport in ribonucleotide reductase(RNR)and the proton and electron transfer pathways in photosystemⅡ(PSⅡ).We also discuss how this endeavour has allowed systematic investigations of precise roles of conserved residues in metalloproteins,such as Metl21 in azurin,Tyr244 that is cross-linked to one of the three His ligands to CuB in HCO,Tyr122,356,730 and 731 in RNR and TyrZ in PSⅡ.These examples have demonstrated that incorporating UAAs has provided a new dimension in our efforts to mimic native enzymes and in providing deeper insights into structural features responsible high enzymatic activity and reaction mechanisms,making it possible to design highly efficient artificial catalysts with similar or even higher activity than native enzymes. 相似文献
984.
Solid phase peptide synthesis (SPPS) based on Fmoc chemistry has become a commonly used technique in peptide chemistry, as it can be easily conducted using automated machine, and not requiring highly toxic HF in comparison to Boc-SPPS. With the fast development in the emerging field of protein chemical synthesis, many efforts have been endeavored aiming to find more efficient methods for preparing peptide fragments required in ligation reactions. This review briefly summarizes recent advances in the engineering and modification of Fmoc-SPPS-derived peptides, which can be used as the N-terminal fragments in a native chemical ligation (NCL) or NCL-type ligation reactions. 相似文献
985.
Ag@C core–shell structure composites were successfully synthesized by hydrothermal method, and then Ag nanoparticles were decorated on the surface of Ag@C by reduction of AgNO3. The morphology, composition and structure of the Ag@C@Ag composites were characterized by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). Cyclic voltammetry and amperometry were used to evaluate the electrocatalytic performance of the Ag@C@Ag/GCE for detection of H2O2. Meanwhile, a new electrochemical method of zero current potentiometry was used for electrochemical detection of H2O2. The linear range and the detection limit were from 0.2 to 10, and 0.07 μM, respectively. 相似文献
986.
Pharmaceuticals, especially fluoroquinolone antibiotics, have received increasing global concern, due to their intensive use in the environment and potential harm to ecological system as well as human health. Degradation of antibiotics, such as oxidative degradation by metal oxides, often plays an important role in the elimination of antibiotics from the environment. The kinetics of oxidation of levofloxacin by water-soluble manganese dioxide has been studied in aqueous acidic medium at 25 °C temperature. The stoichiometry for the reaction indicates that the oxidation of 1 mol of levofloxacin requires 1 mol of manganese dioxide. The reaction is second order, that is first order with respect to manganese dioxide and levofloxacin. The rate of reaction increases with the increasing [H+] ion concentration. A probable reaction mechanism, in agreement with the observed kinetic results, has been proposed and discussed. The energy and enthalpy of activation have been calculated to be 30.54 and 28.07 kJ mol?1, respectively. 相似文献
987.
Five saturated α-branched fatty acids, also known as Guerbet acids, including α-propylhexyl acid (G 1 ), α-butylhexyl acid (G 2 ), α-propyloctyl acid (G 3 ), α-butyloctyl acid (G 4 ), and α-hexyloctyl acid (G 5 ), were synthesized in high yields by four-step reaction. Colorless, almost odorless, and oily products were obtained with high purity, whose structures were confirmed by GC, 1H/13C NMR, and ESI–MS characterization. G 1 , G 3 , and G 4 had pour points lower than ?60 °C, while G 2 and G 5 showed higher pour points (?42 °C and 6 °C, respectively) because of their molecular symmetry. Considering the low-temperature properties, G 1 , G 3 , G 4 , and even G 2 held great potential applications in the lubricant and oilfield. 相似文献
988.
Subin Jung Byeong-Chul Jeong Soon-Kwang Hong Chang-Ro Lee 《Applied biochemistry and biotechnology》2017,181(3):961-971
A novel β-agarase AgaJ11 belonging to the glycoside hydrolase (GH) 16 family was identified from an agar-degrading bacterium Gayadomonas joobiniege G7. AgaJ11 was composed of 317 amino acids (35 kDa), including a 26-amino acid signal peptide, and had the highest similarity (44 % identity) to a putative β-agarase from an agarolytic marine bacterium Agarivorans albus MKT 106. The agarase activity of purified AgaJ11 was confirmed by zymogram analysis. The optimum pH and temperature for AgaJ11 activity were determined to be 4.5 and 40 °C, respectively. Notably, AgaJ11 is an acidic β-agarase that was active only at a narrow pH range from 4 to 5, and less than 30 % of its enzymatic activity was retained at other pH conditions. The K m and V max of AgaJ11 for agarose were 21.42 mg/ml and 25 U/mg, respectively. AgaJ11 did not require metal ions for its activity, but severe inhibition by several metal ions was observed. Thin layer chromatography and agarose-liquefying analyses revealed that AgaJ11 is an endo-type β-agarase that hydrolyzes agarose into neoagarohexaose, neoagarotetraose, and neoagarobiose. Therefore, this study shows that AgaJ11 from G. joobiniege G7 is a novel GH16 β-agarase with an acidic enzymatic feature that may be useful for industrial applications. 相似文献
989.
A sensitive and accurate LC method was developed and further validated for the determination of enantiomeric purity of GSK962040. Before separation, a pre-column derivatization procedure was performed. Baseline separation with a resolution higher than 1.9 was accomplished within 15 min using a Chiralpak AD-H (250 × 4.6 mm; particle size 5 μm) column, with n-hexane: 2-propanol (85:15 v/v) as mobile phase at a flow rate of 1 mL min?1. The eluted analytes were subsequently detected with a UV detector at 260 nm. The effects of mobile phase components and temperature on enantiomeric selectivity as well as resolution of enantiomers were thoroughly investigated. The calibration curves were plotted within the concentration range between 4 and 200 μg mL?1 (n = 8), and recoveries between 98.15 and 101.48% were obtained, with relative standard deviation (RSD) lower than 1.42%. The LOD and LOQ for the Boc-GSK962040 were 1.23 and 4.15 μg mL?1 and for its enantiomer were 1.38 and 4.76 μg mL?1, respectively. The developed method was also evaluated and validated by analyzing bulk samples with different enantiomeric ratios of GSK962040. It was demonstrated that the method was accurate, robust and sensitive, and also had practical utilities for real analysis. 相似文献
990.
To improve the photoproduction of hydrogen (H2) by a green algae-based system, the effect of light/dark regimens on H2 photoproduction regulated by carbonyl cyanide m-chlorophenylhydrazone (CCCP) was investigated. A fuel cell was integrated into a photobioreactor to allow online monitoring of the H2 evolution rate and decrease potential H2 feedback inhibition by consuming the generated H2 in situ. During the first 15 h of H2 evolution, the system was subjected to dark treatment after initial light illumination (L/D = 6/9 h, 9/6 h, and 12/3 h). After the dark period, all systems were again exposed to light illumination until H2 evolution stopped. Two peaks were observed in the H2 evolution rate under all three light/dark regimens. Additionally, a high H2 yield of 126 ± 10 mL L?1 was achieved using a light/dark regimen of L 9 h/D 6 h/L until H2 production ceased, which was 1.6 times higher than that obtained under continuous illumination. H2 production was accompanied by some physiological and morphological changes in the cells. The results indicated that light/dark regimens improved the duration and yield of H2 photoproduction by the CCCP-regulated process of Tetraselmis subcordiformis. 相似文献