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1.
A commercial cation exchange resin Amberlite 200 has been modified after immersion in solutions of polyethyleneimine (PEI). The kinetic of fixation of the metallic ions have been determined. The modification of the surface of the resin deals with a change in the order of the affinities of the resins towards cations. The retention is the function of the formation and the stability of the complex. The conditions of modification (pH, PEI concentration and time of immersion) have been examined and the modification was confirmed by the determination of the exchange capacities, the distribution coefficient (P) and the selectivity factors (S). The obtained results revealed the effect of PEI on the exchange properties of the resin. The pH range selected (6-8) permitted a good adherence of PEI onto the resin surface. The quantity of the adsorbed PEI was increased by raising the initial concentration and the immersion period. The exchange capacity for copper ion passed from 2.6 mmol g−1, in the case of unmodified resin, to 3.9 mmol g−1 for the modified one. 相似文献
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Leon P. Jenner Mickael V. Cherrier Patricia Amara Luis M. Rubio Yvain Nicolet 《Chemical science》2021,12(14):5269
The nitrogenase MoFe protein contains two different FeS centers, the P-cluster and the iron–molybdenum cofactor (FeMo-co). The former is a [Fe8S7] center responsible for conveying electrons to the latter, a [MoFe7S9C-(R)-homocitrate] species, where N2 reduction takes place. NifB is arguably the key enzyme in FeMo-co assembly as it catalyzes the fusion of two [Fe4S4] clusters and the insertion of carbide and sulfide ions to build NifB-co, a [Fe8S9C] precursor to FeMo-co. Recently, two crystal structures of NifB proteins were reported, one containing two out of three [Fe4S4] clusters coordinated by the protein which is likely to correspond to an early stage of the reaction mechanism. The other one was fully complemented with the three [Fe4S4] clusters (RS, K1 and K2), but was obtained at lower resolution and a satisfactory model was not obtained. Here we report improved processing of this crystallographic data. At odds with what was previously reported, this structure contains a unique [Fe8S8] cluster, likely to be a NifB-co precursor resulting from the fusion of K1- and K2-clusters. Strikingly, this new [Fe8S8] cluster has both a structure and coordination sphere geometry reminiscent of the fully reduced P-cluster (PN-state) with an additional μ2-bridging sulfide ion pointing toward the RS cluster. Comparison of available NifB structures further unveils the plasticity of this protein and suggests how ligand reorganization would accommodate cluster loading and fusion in the time-course of NifB-co synthesis.The K-cluster of NifB as a key intermediate in the synthesis of the nitrogenase active site supports [Fe4S4] cluster fusion occurs before carbide and sulfide insertion and displays ligand spatial arrangement reminiscent to that of the P-cluster. 相似文献
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New hybrid organic-inorganic gels have been obtained by reaction of 1,4-butanediol, on tetramethoxysilane Si(OMe)4 dissolved in CCl4. This reaction does not require water and leads to the formation of polymeric transparent materials.Infrared, 29Si and 13C NMR spectroscopy shows that interchange reactions between OMe groups of alkoxide and -O-(CH2)4-O of 1,4-butanediol occurred, leading to the monolithic transparent gels in which both organic (Si-O-(CH2)4-O-Si) and inorganic (Si-O-Si) bridges are formed. 相似文献
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Determination of the inhibitory effect of green tea extract on glucose‐6‐phosphate dehydrogenase based on multilayer capillary enzyme microreactor
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Mohamed Amara Camara Miaomiao Tian Xiaoxia Liu Xin Liu Yujia Wang Jiqing Yang Li Yang 《Biomedical chromatography : BMC》2016,30(8):1210-1215
Natural herbal medicines are an important source of enzyme inhibitors for the discovery of new drugs. A number of natural extracts such as green tea have been used in prevention and treatment of diseases due to their low‐cost, low toxicity and good performance. The present study reports an online assay of the activity and inhibition of the green tea extract of the Glucose 6‐phosphate dehydrogenase (G6PDH) enzyme using multilayer capillary electrophoresis based immobilized enzyme microreactors (CE‐IMERs). The multilayer CE‐IMERs were produced with layer‐by‐layer electrostatic assembly, which can easily enhance the enzyme loading capacity of the microreactor. The activity of the G6PDH enzyme was determined and the enzyme inhibition by the inhibitors from green tea extract was investigated using online assay of the multilayer CE‐IMERs. The Michaelis constant (Km) of the enzyme, the IC50 and Ki values of the inhibitors were achieved and found to agree with those obtained using offline assays. The results show a competitive inhibition of green tea extract on the G6PDH enzyme. The present study provides an efficient and easy‐to‐operate approach for determining G6PDH enzyme reaction and the inhibition of green tea extract, which may be beneficial in research and the development of natural herbal medicines. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Horváth and Kiss (Proc. Amer. Math. Soc., 2005) proved the upper bound estimate for Dirichlet eigenvalue ratios of the Schrödinger problem ?y′′ + q(x)y = λy with nonnegative and single‐well potential q. In this paper, we prove that if q(x) is a nonpositive, continuous, and single‐barrier potential, then for λn > λm≥ ? 2q?, where . In particular, if q(x) satisfies the additional condition , then λ1 > 0 and for n > m ≥ 1. For this result, we develop a new approach to study the monotonicity of the modified Prüfer angle function. 相似文献
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Sujan Dilly Penchala Jasmini Alagaratnam Elizabeth Challenger Alieu Amara Laura Else Alan Winston Saye Khoo 《Biomedical chromatography : BMC》2020,34(1):e4711
A high-performance liquid chromatography tandem mass spectrometric method was developed and validated for cenicriviroc (CVC) quantification in human plasma and cerebrospinal fluid (CSF). The method involved precipitation with acetonitrile and injecting supernatants onto the column. Separation was achieved on an XBridge C18 column with a gradient elution of 0.1% formic acid in water and acetonitrile. Analyte detection was conducted in positive ion mode using selected reaction monitoring. The m/z transitions were: CVC (697.3 → 574.3) and CVC-d7 (704.4 → 574.3). Calibration curve ranged from 5 to 1000 ng/mL for plasma and from 0.241 to 15.0 ng/mL for CSF. The intra- and inter-day precision and accuracy were <15% for both plasma and CSF across four different concentrations. CVC recovery from plasma and artificial CSF was >90%. The method was utilized for the measurement of patients’ plasma and CSF samples taking a dose of 50, 150 and 300 mg q.d. 相似文献
8.
Polystyrene template microspheres of narrow size distribution were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2-methoxy ethanol. These template particles dispersed in aqueous solution have been used for the entrapment of ferrocene by a swelling process of methylene chloride emulsion droplets containing ferrocene within these particles, followed by evaporation of methylene chloride. The effects of CH2Cl2 volume and the [CH2Cl2]/[FeC10H10] (w/w) ratio on the size and size distribution of the swollen template particles were elucidated. Air-stable Fe3C nanoparticles embedded in amorphous carbon matrix (Fe3C/C) have been prepared by thermal decomposition of the ferrocene-swollen template polystyrene particles at 500 °C for 2 h in a sealed cell. Decomposition of these swollen template particles for 2 h at higher temperatures led to the formation of carbon nanotubes (CNTs) in addition to the Fe3C/C composite nanoparticles. The yield of the CNTs increased as the annealing temperature was raised. An opposite behavior was observed for the diameter of the formed CNTs. The size and size distribution, crystallinity, and magnetic properties of the different Fe3C/C composite nanoparticles have also been controlled by the annealing temperature. 相似文献
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Besma Lajmi Mourad Hidouri Mongi Ben Amara 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(11):i156-i158
The crystal structure of tripotassium pentairon hexaphosphate has been determined by single‐crystal X‐ray diffraction. The structure contains one Fe atom on a center of symmetry, one K, two Fe and two P atoms on twofold axes, and one Fe, two P and one K atom in general positions. The K3Fe5(PO4)6 structure consists of a complex three‐dimensional framework of corner‐sharing between iron polyhedra, and corner‐ and edge‐sharing between PO4 tetrahedra and iron polyhedra (FeO5 and FeO6). This linkage between iron and phosphorus forms intersecting channels containing the K atoms. 相似文献