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51.
Shamsa Kanwal Qiang Ma Wenchao Dou Guannan Wang 《International journal of environmental analytical chemistry》2013,93(2):210-221
A new sensitive chemiluminescence (CL) method combined with continuous flow injection analysis is described for the determination of Cr(VI). Strong CL signals were generated by Cr(VI)-catalysed oxidation of gallic acid in the presence of potassium permanganate and hydrogen peroxide. Effects of reagent concentrations, temperature, pH, flow rates, mixing coil length and mixing flow sequences on the chemiluminescence intensity were studied. Under the optimised experimental conditions, the relationship between the logarithm of concentration (log?C) of Cr(VI) and the logarithm of intensity (log?I) is linear over the range of 2?×?10?11 – 5?×?10?4?mol?L?1, with the detection limit (3σ) of 4?×?10?12?mol?L?1. Relative standard deviation of ten measurements of 1?×?10?9?mol?L?1 Cr(VI) is 1.7%. This flow injection analysis (FIA) system proved to be able to analyse up to 40 samples h?1. Effects of various interferences possibly present in the water samples were investigated. Most cations and anions, as well as organic compounds, did not interfere with the determination of Cr(VI) in water samples. The experimental results obtained for chromium in reference materials were also in good agreement with the certified values. 相似文献
52.
Retention behavior of a homologous series and positional isomers of aliphatic amino acids in hydrophilic interaction chromatography 下载免费PDF全文
Michal Douša Jan Srbek Zdeněk Stránský Petr Gibala Lucie Nováková 《Journal of separation science》2014,37(7):739-747
The retention behavior of several series of free α‐ and ω‐amino acids and positional isomers of amino pentanoic acid in the hydrophilic interaction chromatography mode (HILIC) was studied. The study was carried out on three stationary phases followed by post‐column derivatization with fluorescence detection in order to describe the retention mechanism of the tested amino acids. The effect of chromatographic conditions including acetonitrile content in the mobile phase, mobile phase pH (ranging from 3.5 to 6.5) and concentration of buffer in the mobile phase was investigated. The effect of the number of carbon atoms (nC) in aliphatic chains of the individual homologue of α‐ and ω‐amino acids and the logarithm of the partition coefficient (logD) on retention was also a part of the presented study. A good correlation (r > 0.98) between the logk and logD values of amino acids or nC, respectively, was observed. The described linear relationships were subsequently applied to predict the retention behavior of individual members of the homologous series of amino acids and to optimize the mobile phase composition in HILIC. The obtained results confirmed that the retention mechanism of α‐amino acids, ω‐amino acids and positional isomers of amino acids was based on the logD values and the number of carbon atoms in the aliphatic chains of amino acids. The elution order of ω‐amino acids and positional isomers of amino pentanoic acid was strongly dependent on the mobile phase pH in the investigated range whereas the retention factors of all α‐amino acids remained essentially unchanged on all tested stationary phases. 相似文献
53.
Servo constraints are used in inverse dynamics simulations of discrete mechanical systems, especially for trajectory tracking control problems [1], whose desired outputs are represented by state variables and treated as servo constraints [2]. Servo constraint problems can be classified into fully actuated and underactuated multibody systems, and the equations of motion take the form of differential algebraic equations (DAEs) including holonomic and servo constraints. For fully actuated systems, control inputs can be solved from the equations by model inversion, as the input distribution matrix is nonsingular and invertible. However, underactuated systems have more degrees of freedom than control inputs. The input distribution matrix is not invertible, and in contrast to passive constraints, the realization of servo constraints with the use of control forces can range from orthogonal to tangential [3]. Therefore, it is challenging for the determination of control inputs which force the underactuated system to realize the partly specified motion. For differentially flat underactuated systems, the differentiation index of DAEs may exceed three. Hence we need to apply specific index reduction techniques, such as the projection approach applied in [3], [4], and [6]. The present work applies index reduction by minimal extension [5] to differentially flat underactuated crane systems and shows that the index can be reduced from five to three and even to one. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
54.
Haotian Pei Wenyu Su Meng Gui Mingjie Dou Yingxin Zhang Cuizhu Wang Dan Lu 《Molecules (Basel, Switzerland)》2021,26(7)
Six parts of lotus (seeds, leaves, plumule, stamens, receptacles and rhizome nodes) are herbal medicines that are listed in the Chinese Pharmacopoeia. Their indications and functions have been confirmed by a long history of clinical practice. To fully understand the material basis of clinical applications, UPLC-QToF-MS combined with the UNIFI platform and multivariate statistical analysis was used in this study. As a result, a total of 171 compounds were detected and characterized from the six parts, and 23 robust biomarkers were discovered. The method can be used as a standard protocol for the direct identification and prediction of the six parts of lotus. Meanwhile, these discoveries are valuable for improving the quality control method of herbal medicines. Most importantly, this was the first time that alkaloids were detected in the stamen, and terpenoids were detected in the cored seed. The stamen is a noteworthy part because it contains the greatest diversity of flavonoids and terpenoids, but research on the stamen is rather limited. 相似文献
55.
San-E Zhu Jian-Hui Zhang Yu Gong Li-Feng Dou Li-Hua Mao Hong-Dian Lu Chun-Xiang Wei Hong Chen Xue-Fei Wang Wei Yang 《Molecules (Basel, Switzerland)》2021,26(5)
A broadband visible light-absorbing [70]fullerene-BODIPY-triphenylamine triad (C70-B-T) has been synthesized and applied as a heavy atom-free organic triplet photosensitizer for photooxidation. By attaching two triphenylmethyl amine units (TPAs) to the π-core of BODIPY via ethynyl linkers, the absorption range of the antenna is extended to 700 nm with a peak at 600 nm. Thus, the absorption spectrum of C70-B-T almost covers the entire UV–visible region (270–700 nm). The photophysical processes are investigated by means of steady-state and transient spectroscopies. Upon photoexcitation at 339 nm, an efficient energy transfer (ET) from TPA to BODIPY occurs both in C70-B-T and B-T, resulting in the appearance of the BODIPY emission at 664 nm. Direct or indirect (via ET) excitation of the BODIPY-part of C70-B-T is followed by photoinduced ET from the antenna to C70, thus the singlet excited state of C70 (1C70*) is populated. Subsequently, the triplet excited state of C70 (3C70*) is produced via the intrinsic intersystem crossing of C70. The photooxidation ability of C70-B-T was studied using 1,5-dihydroxy naphthalene (DHN) as a chemical sensor. The photooxidation efficiency of C70-B-T is higher than that of the individual components of C70-1 and B-T, and even higher than that of methylene blue (MB). The photooxidation rate constant of C70-B-T is 1.47 and 1.51 times as that of C70-1 and MB, respectively. The results indicate that the C70-antenna systems can be used as another structure motif for a heavy atom-free organic triplet photosensitizer. 相似文献
56.
Many gauge theory models on fuzzy complex projective spaces will contain a strong instability in the quantum field theory leading to topology change. This can be thought of as due to the interaction between space–time via its noncommutativity and the fields (matrices) and it is related to the perturbative UV–IR mixing. We work out in detail the example of fuzzy CP2 and discuss at the level of the phase diagram the quantum transitions between the 3 spaces (space–times) CP2, S2 and the 0-dimensional space consisting of a single point {0}. 相似文献
57.
W. W. Zhong You-Ying Di J. M. Dou 《Journal of Thermal Analysis and Calorimetry》2014,115(3):2527-2533
Two novel complexes [Mg(DPC)(H2O)3]·2H2O(s) and Sr2(H2DPC)2(HDPC)2(DPC)(H2O)2(s) were synthesized by the method of liquid phase reflux. X-ray crystallography, chemical analysis, and elemental analysis were applied to characterize the structures and compositions of the two complexes. Low-temperature heat capacities of the complexes were measured over the temperature ranges from 78 to 350 and 78 to 352 K for [Mg(DPC)(H2O)3]·2H2O(s) and Sr2(H2DPC)2(HDPC)2(DPC)(H2O)2(s), respectively. The polynomial regressions as a function of temperature were carried out through least square fitting method according to the experiment points. The polynomial fitted values of the molar heat capacities and the thermodynamic functions relative to the standard reference temperature 298.15 K based on the polynomial equations were derived. In addition, thermal behavior of the two compounds was investigated by thermal analysis techniques, differential scanning calorimetry/thermogravimetric analysis. 相似文献
58.
Dr. Victor Malgras Dr. Priyanka Jood Dr. Ziqi Sun Prof. Shi Xue Dou Prof. Yusuke Yamauchi Prof. Jung Ho Kim 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(33):10451-10455
Porous titanium dioxide synthesized with a bicontinuous surfactant template is a promising method that leads to a high active surface area electrode. The template used is based on a water/isooctane/dioctyl sodium sulfosuccinate salt together with lecithin. Several parameters were varied during the synthesis to understand and optimize channel formation mechanisms. The material is patterned in stacked conical channels, widening towards the centre of the grains. The active surface area increased by 116 % when the concentration of alkoxide precursors was decreased and increased by 241 % when the template formation temperature was decreased to 10 °C. Increasing the oil phase viscosity tends to widen the pore aperture, thus decreasing the overall active surface area. Changing the phase proportions alters the microemulsion integrity and disrupts channel formation. 相似文献
59.
Xiaomei Zhang Guoqiang Xu Hui Li Wenfang Dou Zhenghong Xu 《Applied biochemistry and biotechnology》2014,173(7):1607-1617
The direct fermentative production of l-serine from sugar has attracted increasing attention. Corynebacterium glutamicum SYPS-062 can directly convert sugar to l-serine. In this study, the effects of exogenous and endogenous regulation of cofactor folate on C. glutamicum SYPS-062 growth and l-serine accumulation were investigated. For exogenous regulation, the inhibitor (sulfamethoxazole) or precursor (p-aminobenzoate) of folate biosynthesis was added to the medium, respectively. For endogenous regulation, the gene (pabAB) that encodes the key enzyme of folate biosynthesis was knocked out or overexpressed to obtain the recombinant C. glutamicum SYPS-062 ΔpabAB and SYPS-062(pJC-tac-pabAB), respectively. The results indicated that decreased levels of cofactor folate supported l-serine accumulation, whereas increased levels of cofactor folate aided in cell growth of C. glutamicum SYPS-062. Thus, this study not only elucidated the role of folate in C. glutamicum SYPS-062 growth and l-serine accumulation, but also provided a novel and convenient approach to regulate folate biosynthesis in C. glutamicum. 相似文献
60.
Dr. Guobin Wen Dr. Bohua Ren Dr. Moon G. Park Dr. Jie Yang Dr. Haozhen Dou Dr. Zhen Zhang Dr. Ya-Ping Deng Prof. Zhengyu Bai Prof. Lin Yang Prof. Jeff Gostick Prof. Gianluigi A. Botton Prof. Yongfeng Hu Prof. Zhongwei Chen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(31):12960-12967
Simultaneously improving energy efficiency (EE) and material stability in electrochemical CO2 conversion remains an unsolved challenge. Among a series of ternary Sn-Ti-O electrocatalysts, 3D ordered mesoporous (3DOM) Sn0.3Ti0.7O2 achieves a trade-off between active-site exposure and structural stability, demonstrating up to 71.5 % half-cell EE over 200 hours, and a 94.5 % Faradaic efficiency for CO at an overpotential as low as 430 mV. DFT and X-ray absorption fine structure analyses reveal an electron density reconfiguration in the Sn-Ti-O system. A downshift of the orbital band center of Sn and a charge depletion of Ti collectively facilitate the dissociative adsorption of the desired intermediate COOH* for CO formation. It is also beneficial in maintaining a local alkaline environment to suppress H2 and formate formation, and in stabilizing oxygen atoms to prolong durability. These findings provide a new strategy in materials design for efficient CO2 conversion and beyond. 相似文献