Tài liệu miễn phí Hoá học
Download Tài liệu học tập miễn phí Hoá học
Partial purification and biochemical characterization of an extremely thermo- and pH-stable esterase with great substrate affinity
Presence of 10% (v/v) acetonitrile in the reaction medium indicated that purified enzyme was strongly inhibited. It was also detected that some metal ions affected enzyme activity at different rates. As a result, it was observed that esterase from Geobacillus sp. DF20 has extreme temperature and pH stabilities. Therefore, the stability and Km value of the enzyme make this study interesting when compared with the literature.
4/5/2023 5:10:15 AM +00:00
Adsorption of the urea molecule on the B12N12 nanocage
The HOMO–LUMO gap of the nanocage does not change significantly upon urea adsorption, while the Fermi level is dramatically changed from −4.27 eV in the pristine nanocage to upper energies upon urea adsorption. The geometric structure, adsorption energy, solvation effect, charge transfer, and frequency analyses of the urea adsorption on the nanocage models showed that the urea molecule could be firmly adsorbed by the nanocage and the nanocage could be a potential efficient adsorbent for the adsorption of urea.
4/5/2023 5:10:07 AM +00:00
Synthesis, spectral characterisation, electrochemical, and fluorescence studies of biologically active novel Schiff base complexes derived from E-4-(2-hydroxy-3- methoxybenzlideneamino)-N-(pyrimidin-2-yl)benzenesulfonamide
The reasonable shifts in FT-IR and NMR spectral signals of the complexes with respect to the free ligand confirm good coordination of the Schiff-base ligand with the metal through imine nitrogen and oxygen atoms of Schiff base moiety. The Schiff-base ligand and the complexes were screened for antimicrobial activity and fluorescent behaviour. From the analytical and spectral data, the stoichiometry was found to be 1:2 for all the complexes. An octahedral structure was proposed. All the complexes were found to be active against bacteria and fungi.
4/5/2023 5:09:59 AM +00:00
In vitro effects of pesticide exposure on the activity of the paraoxonase-1 enzyme from sheep liver microsomes
The organophosphate target enzyme paraoxonase-1 (PON1) has been extensively studied in toxicology. Pesticides are organophosphate compounds that are commonly used in agriculture. They are also used as nerve gases, such as sarin and soman. Therefore, the effects of these compounds on enzymatic activity are well known. In the present study, we investigated the in vitro effects of fenoxaprop-p-ethyl, lambda cyhalothrin, imidacloprid, and dichlorvos pesticides on sheep liver microsomal PON1.
4/5/2023 5:09:53 AM +00:00
Solvent extraction of praseodymium(III) from acidic nitrate medium using Cyanex 921 and Cyanex 923 as extractants in kerosene
On the basis of slope analysis, the compositions of the extracted species were formulated as Pr(NO3)3.2Cyanex 921 and Pr(NO3)3.Cyanex 923. The percentage of extraction of Pr(III) was found to decrease with increases in temperature. The standard enthalpy and entropy changes were negative owing to the complexation with decrease in randomness without a compensatory disruption of the hydration sphere of the metal ion. Mineral acids like hydrochloric acid (0.008 M) and sulfuric acid (0.03/0.02 M) were effective for the stripping of Pr(III) from the loaded organic phase with 0.5 M Cyanex 921/1 M Cyanex 923.
4/5/2023 5:09:46 AM +00:00
Selective oxidation of sulfides and hydrocarbons with H2O2 over manganese catalyst supported on nanoparticles
The synthesized catalyst was characterized by several physico-chemical and spectroscopic methods. This immobilized complex was found to be an efficient heterogeneous catalyst for the oxidation of different sulfides and hydrocarbons using hydrogen peroxide (H2 O2) as an oxidant. The catalyst is readily recovered by simple magnetic decantation and can be recycled several times with no considerable loss of catalytic activity.
4/5/2023 5:09:40 AM +00:00
Spectroscopic investigation and oxidation of the anticholinergic drug atropine sulfate monohydrate by hexacyanoferrate(III) in aqueous alkaline media: a mechanistic approach
The oxidation of the anticholinergic drug atropine sulfate monohydrate by hexacyanoferrate(III) in aqueous alkaline media was investigated spectrophotometrically by monitoring the decrease in absorbance of hexacyanoferrate(III) (HCF(III)). Oxidation products were identified. The oxidation mechanism was proposed from kinetic studies. The reaction constants involved in the different steps of the mechanism were calculated.
4/5/2023 5:09:33 AM +00:00
Facile synthesis of 5-bromotropono[c]-fused pyrazoles and isoxazole
A facile synthesis of a series of new 5-bromotropono[c]pyrazole derivatives (3 and 10–15) as well as 5- bromotropono[c]isoxazole (17) is described, involving a condensation reaction of 3-acetyl-5-bromotropolone (1) with hydrazine monohydrate (2), arylhydrazine hydrochlorides (4–9), and hydroxylamine hydrochloride (16), respectively. All the synthesized compounds were obtained in good yields of 56%–77% and their structures were characterized by spectral data and HRMS.
4/5/2023 5:09:26 AM +00:00
Investigation of the adsorption kinetics of methylene blue onto cotton wastes
Cotton stalk (CS), cotton waste (CW), and cotton dust (CD), which are cotton wastes, were used as adsorbents to study the adsorption kinetics of methylene blue from aqueous solution. Kinetics of the batch adsorption experiment was investigated according to the pseudo-first order, the pseudo-second order, and the intraparticle diffusion models used commonly in the literature. The effects of the initial concentration, solution pH, and temperature on kinetic parameters (adsorption rate constant, initial adsorption rate, equilibrium adsorption capacity, etc.) were studied.
4/5/2023 5:09:19 AM +00:00
Synthesis and phase transition studies of new dimer compounds connected to a 1,3-dimethylbarbituric acid core
A series of dimeric unsymmetrical liquid crystals derived from heterocyclic 1,3-dimethylbarbituric acid exhibiting smectic A and nematic phase are reported. All compounds were prepared by the condensation of 4’-(R-(4- formylphenoxy)butoxy)biphenyl-4-carboxylate with 1,3-dimethylbarbituric acid in ethanol. The mesomorphic properties were investigated by DSC and POM, where the type of phase depends on the length of spacer alkoxy chains and the length of the terminal chain.
4/5/2023 5:09:10 AM +00:00
Novel N-acyl/aroyl-2-(5-phenyl-2H-tetrazol-2-yl)acetohydrazides: synthesis and characterization
A number of novel N-acyl/aroyl-2-(5-phenyl-2H-tetrazol-2-yl)acetohydrazides (4a–j) of biological interest were efficiently synthesized by treating 2-(5-phenyl-2H-tetrazole-2-yl)acetohydrazide (3) with a variety of aroyl/heterocyclyl or alkanoyl chlorides. FTIR, 1H NMR, 13C NMR, GC-MS, and elemental analyses data confirmed the structures assigned to the newly synthesized compounds.
4/5/2023 5:09:04 AM +00:00
Te(II)-induced heterocyclization of 1,2-alkadienephosphonates
The reactivity of some 1,2-alkadienephosphonates towards phenyltelluryl halides was investigated. A plausible mechanism of the reaction is discussed. Consequently, many attempts for their synthesis have been made. One of the easiest and most fruitful methods for the synthesis of these derivatives is electrophile-induced heterocyclization of 1,2-alkadienephosphonates.
4/5/2023 5:08:57 AM +00:00
An efficient synthesis of some new bisbenzimidazoles via microwave technique
2,2’-[1,4(1,3)-Phenylenedi(methylene)]bis-1H-benzimidazole derivatives were obtained from the reaction of 1,4- or (1,3)-bisiminoester hydrochloride and o-phenylenediamine derivatives under microwave irradiation. Ester and hydrazide derivatives were prepared from a free NH group. This practical method revealed good results for yield, reaction time, and quick isolation of products.
4/5/2023 5:08:47 AM +00:00
Deposition and characterization of Cu9S5 nanocrystals from unsymmetrical [(Hex)(Me)NC(S)NC(O)C6H3(NO2)2-3,5]2Cu(II) and [(Et)(Bu)NC(S)NC(O)C6H4-4-NO2]2Cu(II) complexes by colloidal thermolysis method
Cu9S5 nanocrystals were synthesized from unsymmetrical [(Hex)(Me)NC(S)NC(O)C6H3(NO2)2-3,5]2Cu(II) and [(Et)(Bu)NC(S)NC(O)C6H4-4-NO2]2Cu(II) complexes by colloidal thermolysis in the presence of surfactant oleylamine. The unsymmetrical copper complexes were synthesized by the reaction of copper(II) acetate with N-[hexyl(methyl)carbamothioyl]-3,5-dinitrobenzamide and N-[ethyl(butyl)carbamothioyl]-4-nitrobenzamide. The complexes were used as single-source precursors for the preparation of Cu9S5 nanocrsytals. The Cu9S5 nanocrystals were characterized by X-ray powder diffraction and transmission electron microscopy.
4/5/2023 5:08:38 AM +00:00
Crystal growth morphology of magnesium hydroxide
In this paper, the formation process of magnesium hydroxide unit cells, as well as the structural characteristics and growth morphology of magnesium hydroxide, is discussed from the perspective of growth units. The growth process of the hexagonal structure of the magnesium hydroxide is as follows: the growth units are first incorporated into a larger hexagonal dimension unit on the same plane, and then the hexagonal layers connect to each other in the z-axis direction for the hexagonal magnesium hydroxide unit cell.
4/5/2023 5:08:32 AM +00:00
The chemistry concerned with the sonochemical-assisted synthesis of CeO2/poly(amic acid) nanocomposites
Characterization with FTIR, powder X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and atomic force microscopy confirmed the successful synthesis of nanocomposites with good dispersion of nanoparticles in the polymer matrix. Both field emission scanning electron microscope and transmission electron microscope analyses showed that the cerium oxide was well dispersed in the PAA matrix; it was dispersed in the PAA matrix on a nanometer scale. Moreover, the thermal and topological properties of PAA and nanocomposites were also investigated, respectively.
4/5/2023 5:08:22 AM +00:00
Preparation and characterization of nonmetal promoter modified CuZnAl catalysts for higher alcohol from synthesis gas through complete liquid phase method
A complete liquid phase technology and a function regulator were applied to prepare CuZnAl catalysts for higher alcohol synthesis. Characterizations showed that the introduction of the function regulator can change the reduction ability of copper oxides and the surface basicity of catalysts. Activity tests indicated that the selectivity of higher alcohol is high when considerable medium-strong basicity and the synergistic effects of copper ion and metal copper exist on the catalytic surface.
4/5/2023 5:08:15 AM +00:00
PW12-APTES@MCF: effective nanosized mesoporous composites for the oxidation of benzyl alcohols
The surface of mesocellular silica foam (MCF) was modified by grafting 3-aminopropyl-triethoxysilane (APTES) to have a positive charge, and thus to provide sites for the immobilization of H3PW12O40(PW12). This modified nanosized mesoporous silica (PW12-APTES@MCF) was characterized by FTIR, XRD, BET, and TEM. XRD and adsorption–desorption analysis shows that the mesostructure of silica remains intact after various modifications, while the spectral technique shows the successful grafting of the neat PW12 inside the porous silica support.
4/5/2023 5:08:06 AM +00:00
Application of guanidine and its salts in multicomponent reactions
This review gives an overview of the application of guanidine and its salts in multicomponent reactions. It can act as a catalyst or solvent for multicomponent reactions or as a reagent for synthesis of substituted diazines, triazines, and macroheterocycles by multicomponent reactions.
4/5/2023 5:07:59 AM +00:00
Aryl butenoic acid derivatives as a new class of histone deacetylase inhibitors: synthesis, in vitro evaluation, and molecular docking studies
New aryl butenoic acid derivatives have been synthesized by combining hydroxy- or methoxy-substituted phenyl rings as the capping group, with a double bond in the short linker as well as metal binding groups, enoic ester, and salts bearing either methyl or morpholine. These compounds have been shown to possess promising histone deacetylase inhibition activities via in vitro fluorometric assay and molecular docking studies.
4/5/2023 5:07:48 AM +00:00
Spectrophotometric determination of molybdenum using surfactant-mediated liquid–liquid extraction
A new spectrophotometric method has been developed for determination of molybdenum using surfactantmediated liquid–liquid extraction. Molybdenum(V) obtained by ascorbic acid reduction in 2.5 M H2 SO4 reacted spontaneously with thiocyanate and cetyl trimethyl ammonium bromide (CTAB), forming an intense orange yellow complex that was extracted quantitatively into 1,2-dichloroethane and absorbed at 460 nm. The absorbance of the extract was found to be stable for more than 24 h.
4/5/2023 5:07:41 AM +00:00
Synthesis and characterization of new metallophthalocyanines containing O4S2 mixed-donor substituted macrocyclic group
New phthalocyanine compounds containing mixed-donor substituted macrocyclic groups were synthesized. The complexes of metal phthalocyanines 3–5 were prepared by the reaction of 2 to get dinitrile derivative complexes by means of the corresponding anhydrous metal salts. Structures of the new compounds were characterized by IR, 1H NMR, 13C NMR, elemental analysis, and MS spectral data.
4/5/2023 5:07:33 AM +00:00
Platinum or nickel nanoparticles decorated on silica spheres by microwave irradiation technique
Supported catalysts are of great interest because of their wide range of application possibilities. In this study, firstly silica spheres were synthesized and then platinum and nickel nanoparticles were incorporated on this silica by microwave irradiation, which is an efficient technique for catalyst preparation. Synthesized silica spheres and catalysts were characterized by BET, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and transmission electron microscopy techniques. Pt or Ni nanoparticles well dispersed over silica support were obtained using microwave irradiation.
4/5/2023 5:07:24 AM +00:00
Optimization of LiFePO4 synthesis by hydrothermal method
Optimization of the LiFePO4 cathode active material synthesis process in the hydrothermal method consists of many factors, including pH, carbon coating, particle size optimization, sintering and hydrothermal synthesis temperature. The main goal of this study is to determine the effect of particle size, pH and carbon coating on capacity and cycle performance. In this study, LiFePO4 cathode active materials were prepared at different pH (6.5 and 8.5) and temperature (160 and 180◦C) levels using the hydrothermal method.
4/5/2023 5:07:15 AM +00:00
Calixpenams: synthesis, characterization, and biological evaluation of penicillins V and X clustered by calixarene scaffold
Four 6-aminopenicillanic acid moieties were grafted at either rim of calix[4]arene, giving 2 novel generations of penicillin, which were named calixpenam. Antibiotic tests showed that they have amplified activity with respect to the corresponding penams against 3 gram-positive nonpenicillinase-producing strains of Streptococcus.
4/5/2023 5:07:09 AM +00:00
Synthesis and characterization of new (E)-N’-(substituted benzylidene)-2-(3-(2- methyl)-4-oxo-3,4-dihydroquinazolin-2-ylthio)acetohydrazides
A small library of new azomethine derivatives of 3-aryl-2-thioxo-2,3-dihydroquinazolin-4(1 H) -ones was synthesized. The key intermediates 2-thioxo-quinazolinones (3a–e), obtained in 2 steps from the corresponding anilines, were treated with methyl chloroacetate to afford S-substituted esters (4a,d), which were then converted into corresponding acetohydrazides (5a,d). Further, acetohydrazide (5d) was converted to the azomethines derivatives (6a–k) by reacting with a number of suitably substituted benzaldehydes.
4/5/2023 5:07:00 AM +00:00
Effect of boric acid on corrosion and electrochemical performance of Pb-0.08% Ca-1.1% Sn alloys containing Cu, As, and Sb impurities for manufacture of grids of lead-acid batteries
Impedance measurement was used to quantify the amounts of PbSO4 and PbO in the initial stage of the oxidation. H3BO3 decreased the positive grid corrosion of all alloys, while impurities increased it. Although impurities increased the self-discharge during constant current discharge, H3BO3 was found to decrease it, except for the alloy containing the 3 impurities and the Cu-containing alloy. Under open-circuit conditions, H3 BO3 increased significantly the self-discharge rate, but impurities were found to suppress it.
4/5/2023 5:06:53 AM +00:00
Study of the interaction between glucosamine hydrochloride and sodium dodecylsulphate micelles using conductometric, isothermal calorimetry, zeta-potential titrations, and NMR NOESY
In procedure 1, micellisation study by isothermal titration calorimetry (ITC) showed that the increase in Gl + concentration reduces the cmc and the micellisation enthalpy. Increasing of the micellisation entropy was also observed, suggesting desolvation of micellar structures as a consequence of electrostatic attraction with Gl+ ions. In procedure 2, titration of Gl+ with SDS solution at 7.7 mM showed the existence of 3 distinct ranges of glucosamine/SDS concentrations, which were attributed to I) Gl+ inducing micellisation, II) neutralisation of the micelles, and III) competition between the ions themselves in the micellar surface.
4/5/2023 5:06:46 AM +00:00
Selective synthesis of cyclododec-2-en-1-yl ethers via palladium-catalyzed allylic substitution reaction: a kinetic study
The palladium-catalyzed reaction between isomeric cyclododec-2-en-1-yl acetates and primary aliphatic alcohols was found to result in high yields of the reaction products obtained. The selectivity with respect to cyclododec-2- en-1-yl ethers formed as reaction products ranged from 73% to 93%. The kinetics of the reaction of acetoxycyclododec-2- enes with alcohols was studied within the temperature range of 328–358 K. A kinetic equation best fitting the experimental data was provided.
4/5/2023 5:06:40 AM +00:00
Synthesis and X-ray powder diffraction, electrochemical, and genotoxic properties of a new azo-Schiff base and its metal complexes
These mononuclear Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) complexes of the ligand were prepared and their structures were proposed by elemental analysis, and infrared and ultraviolet-visible spectroscopy; the proton NMR spectrum of the mbH ligand was also recorded. The azo-azomethine ligand, mbH, behaves as a bidentate ligand coordinating through the nitrogen atom of the azomethine (–CH=N–) and the oxygen atom of the phenolic group. Elemental analyses indicated that the metal:ligand ratio was 1:2 in the metal chelates. Powder X-ray diffraction parameters suggested a monoclinic system for the mbH ligand and its Ni(II), Cu(II), Co(II), and Zn(II) complexes, and an orthorhombic system for the Mn(II) complex.
4/5/2023 5:06:32 AM +00:00