Tài liệu miễn phí Hoá học
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Graphite oxide as an efficient solid reagent for esterification reactions
Esterification of organic acids with alcohols under mild conditions in high yields using graphite oxide, a readily available and inexpensive material, as an effective reagent is described. Esters are a class of compounds widely distributed in nature. Esters encompass a large family of organic compounds with broad applications in medicine, biology, chemistry, and industry as plasticizers, solvents, perfumes, and flavor chemicals and also as precursors for a gamut of pharmaceuticals, agrochemicals, and other fine chemicals.
4/5/2023 5:14:14 AM +00:00
Calixcephems: clustered cephalosporins analogous to calixpenams as novel potential anti-MRSA agents
Two novel clusters of cephalosporin based on calixarene were synthesized directly or by ring expansion of the penicillin arms of calixpenams to the corresponding cephem arms via sulfoxide intermediates. Antibiotic tests showed that calixcephems have a noteworthy increase in antibacterial activity against methicillin-resistant strains of Staphylococcus aureus (MRSA) with respect to parent calixpenams and their corresponding single cephems.
4/5/2023 5:14:06 AM +00:00
Performance degradation of LixFePO4 (x = 0, 1) induced by postannealing
Olivine LiFePO4 has been studied for more than a decade as a promising cathode material for rechargeable lithium batteries. However, the low electric conductivity and tap density still hinder its large-scale commercialization. Micro-sized LiFePO4 is prepared by an optimized hydrothermal method in this paper. The influence of postannealing on the physicochemical properties of LiFePO4 and FePO4 is investigated to understand the plausible mechanism for performance degradation.
4/5/2023 5:13:54 AM +00:00
Green synthesis of Fe3O4 nanoparticles by one-pot saccharide-assisted hydrothermal method
A saccharide-assisted hydrothermal route starting from a single iron precursor was employed to study the influence of reducing saccharides on the formation of iron oxide (Fe 3 O4) nanoparticles (NPs). Fe 3 O4 NPs, which were confirmed by X-ray diffraction analysis, were successfully synthesized by a hydrothermal method in which mannose, maltose, lactose, and galactose served as reducing agents. The formation of Fe 3 O4 NPs was also confirmed by Fourier transform infrared spectroscopy.
4/5/2023 5:13:43 AM +00:00
Synthesis, anticandidal activity, and cytotoxicity of some thiazole derivatives with dithiocarbamate side chains
Some thiazole derivatives bearing dithiocarbamic acid esters were synthesized in order to investigate their anticandidal activity and cytotoxicity. The structures of the obtained final compounds (6a–j) were confirmed by spectral data (IR, 1H NMR, 13C NMR, and MS) and elemental analysis. The anticandidal activity of the compounds was determined (6a–j) using the microbroth dilution method and their cytotoxicity was evaluated according to the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay against normal cells. Contrary to expectations, weak antifungal activity was observed with IC50 values ranging between 30 and 403 µg/mL.
4/5/2023 5:13:37 AM +00:00
The effects of ionic strength and temperature on the dissociation constants of adefovir and cidofovir used as antiviral drugs
The effects of ionic strength and temperature on the dissociation constants of adefovir (PMEA) and cidofovir (HPMPC) used as antiviral drugs were studied at 298 K, 308 K, and 318 K in aqueous media and at different ionic strength backgrounds of NaCl potentiometrically. The dissociation constants of the ligands were determined via the calculation of the titration data with the SUPERQUAD computer program. The thermodynamic parameters (∆G, ∆H , and ∆S) for all species were calculated. The dissociation order of nitrogen and oxygen atoms in the ligands according to proton affinities values were obtained using PM6 semiempirical methods.
4/5/2023 5:13:30 AM +00:00
Synthesis and characterization of magnesium borate minerals of admontite and mcallisterite obtained via ultrasonic mixing of magnesium oxide and various sources of boron: a novel method
Magnesium borates can be used as detergent compounds or hydrocarbon catalyzers and in the ceramics industry for superconductor material manufacture owing to their high elastic coefficient and resistance to corrosion at high temperatures. In the present study, the synthesis of magnesium borate was facilitated via a novel ultrasonic method of mixing and the identification and characterization of the material were carried out via X-Ray diffraction (XRD), Fourier transform infrared (FT-IR), and Raman spectroscopies, and the B2 O3 content was determined through titration.
4/5/2023 5:13:22 AM +00:00
Study on transportation of phenol through a nanotubule membrane
Gold nanochannels were prepared by plating electrolessly gold within the pores of polycarbonate filter membranes (PCTMs). These PCTMs with cylindrical Au nanotubules of uniform radius and high density can be used as a convenient model system to investigate the mechanism of particle transport through nanotubules. The transport properties of phenol through a modified Au nanotubule membrane were studied. The permeate flux of phenol transport through the nanotubule membrane can be spatially and temporally manipulated by controlling the magnitude and direction of the current applied across the separation cell, and the electroosmotic flow (EOF) was investigated by measuring the flux of phenol across the PCTM. The current values and modification of nanotubules affected the EOF generated inside the nanotubules.
4/5/2023 5:13:11 AM +00:00
Graphene oxide–magnetite nanocomposite as an efficient and magnetically separable adsorbent for methylene blue removal from aqueous solution
The spectroscopic studies reveal that the GO–Fe 3 O4 nanocomposite is a highly efficient adsorbent for MB removal from aqueous solution, providing an adsorption capacity of 172.6 mg/g, and the equilibrium for MB adsorption is attained in ∼70 min. Moreover, it is a magnetically separable and reusable material for MB removal from water, preserving 87% of its initial efficiency after 5 successive runs.
4/5/2023 5:13:04 AM +00:00
Ultrarapid catalytic reduction of some dyes by reusable novel erythromycin-derived silver nanoparticles
A novel green approach for the synthesis of silver nanoparticles using erythromycin as a reducing/capping agent is presented. Erythromycin-derived silver nanoparticles were characterized by ultraviolet-visible spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy, X-ray powder diffraction, and Fourier transform infrared spectroscopy. Monodispersed silver nanoparticles showed excellent and promising catalytic activity for reduction of 3 differently charged dyes (eosin B, methylene blue, and rose bengal) in the presence of NaBH4.
4/5/2023 5:12:57 AM +00:00
Simultaneous determination of dexpanthenol, lidocaine hydrochloride, and mepyramine maleate in combined pharmaceutical gel by capillary electrophoresis
A new capillary electrophoresis method was developed for the simultaneous determination of dexpanthenol (DEX), lidocaine (LID), and mepyramine (MEP) in pharmaceutical preparations. The best results were obtained using 20 mM (pH 3.0) phosphate buffer as the background electrolyte. Separation was obtained using a fused-silica capillary (75 µm internal diameter, 50 cm total length, 41 cm effective length) and a potential of +30 kV at 20 ◦ C. Standards and samples were injected using a pressure injection at 50 mbar for 5 s and the analytes were monitored at a detection wavelength of 200 nm.
4/5/2023 5:12:48 AM +00:00
Synthesis of novel triazoles bearing 1,2,4-oxadiazole and phenylsulfonyl groups by 1,3-dipolar cycloaddition of some organic azides and their biological activities
1,3-Dipolar cycloaddition of 5-azidomethyl-3-p-substituted phenyl-1,2,4-oxadiazoles to phenyl vinyl sulfone and bismaleimide gives rise straightforwardly to 1-((3-(p-substituted) phenyl-1,2,4-oxadiazol-5-yl)methyl)-4-(phenylsulfonyl)-4,5-dihydro-1H-1,2,3-triazoles and bisdihydropyrrolo[3,4-d][1,2,3]triazole-4,6(3aH,5H)-diones. The structures of the new cycloadducts were elucidated by means of IR, NMR (1H, 13C, 2D), mass spectra, and physical characteristics (mp and Rf values). In addition, anticancer activities of the cycloadducts against MCF-7 cells were also investigated.
4/5/2023 5:12:41 AM +00:00
Binding of flavanone with β -CD/ctDNA: a spectroscopic investigation
The inclusion complexation of flavanone with β -cyclodextrin was studied by ultraviolet absorption, steady state fluorescence, time-resolved fluorescence, and 2D ROESY nuclear magnetic resonance spectroscopic techniques. A 1:1 stoichiometric ratio was determined for the inclusion of flavanone with β -cyclodextrin. The Stern–Volmer constant for the accessible fraction of the binding of flavanone with β -cyclodextrin, and the binding constant for the flavanone–β - cyclodextrin complex are reported.
4/5/2023 5:12:33 AM +00:00
QSAR study of chalcone derivatives as anti-Leishmania agents
Quantitative structure activity relationship analyses were used to identify the ideal physicochemical characteristics of potential chalcone derivatives as anti-Leishmania agents. The HyperChem program was used to build chalcone structures and to perform conformational analyses through the semiempirical method followed by the PM3 force field. Dragon calculated a large number of molecular descriptors. Multilinear regression was used for quantitative structure activity relationship modeling. Based on our computational studies, 4 descriptors, SEigv, RDF125v, RDF055u, and O-058, can affect the activity of chalcone derivatives.
4/5/2023 5:12:27 AM +00:00
Effects of functional groups of triple bonds containing molecules on nickel electroplating
The effects of propargyl alcohol (PA), propynol ethoxylate (PME), propargyl sulfonate (PS), and diethylaminopropyne (DEP) compounds as additives in a Watts bath on coating brightness, thickness, and efficiency were investigated and compared using electrochemical methods such as linear and square wave voltammetry (SWV), chronoamperometry, chronopotentiometry, electrochemical impedance (EIS), and X-ray fluorescence (XRF) spectroscopy. The charge transfer resistance values obtained in the presence of PA and PME were similar and higher than the other values obtained; this result suggests that PA and PME have better adsorption.
4/5/2023 5:12:19 AM +00:00
Linear assembly and 3D networks of peptide modified gold nanoparticles
The charge and size of molecules chemically attached to nanoparticles (NPs) play an important role in their interaction behavior in suspensions. Gold nanoparticles (AuNPs) were modified systematically with peptides and the modification was verified with surface-enhanced Raman scattering (SERS). The behavior of the modified AuNPs in suspension and at the liquid–solid interface was monitored using small angle X-ray scattering (SAXS), UV/Vis spectroscopy and dynamic light scattering (DLS) in suspension, and atomic force microscopy (AFM) at the solid– liquid interface.
4/5/2023 5:12:08 AM +00:00
N-Heterocyclic carbene (NHC) palladium(II) complexes bearing chiral oxazoline ligands and their catalytic activities in allylic alkylation reactions
NHC–Pd(II) complexes bearing a chiral oxazoline ligand (IIIa–f) were synthesized by cleavage of dimeric palladium complexes with the oxazoline ligand. They were fully characterized by 1 H and 13 C NMR and elemental analyses. The catalytic activity of the complexes (IIIa–f) in allylic alkylation reactions was evaluated. The complex IIIa was found to be the most active catalyst. Very low ee values indicate that the oxazoline is dissociated from the active catalytic species.
4/5/2023 5:12:02 AM +00:00
Synthesis and characterization of a novel 3-amino-1,2,4-triazole lead(II) coordination polymer
The molecular structure shows that the complex is a coordination polymer in which there are 2 different lead(II) ions with coordination number of 5, Pb(2), and, with a coordination number of 4, Pb(1). Each atrz acts as a bridging ligand between 2 Pb(II) ions through the 2 adjacent nitrogen atoms of the triazole ring. The acetate anions show different types of coordination mode: one acts as a bridge by coordination of the same oxygen atom with Pb(II) ions and the other as a monodentate coordination by one of the oxygen atoms with Pb(2).
4/5/2023 5:11:55 AM +00:00
Thermal conversion of glycerol to value-added chemicals: pyridine derivatives by one-pot microwave-assisted synthesis
One-pot syntheses of the value-added heterocyclic compounds 3-methylpyridine and pyridine using a renewable chemical, glycerol, were achieved in acidic medium by thermal conversion reactions. Condensation/cyclization reactions of the thermal degradation products of glycerol were investigated in situ using different ammonia and acidic moiety producing inorganic ammonium salts under pyrolysis or microwave heating conditions.
4/5/2023 5:11:48 AM +00:00
Aqueous DABCO, an efficient medium for rapid organocatalyzed Knoevenagel condensation and the Gewald reaction
In the presence of water and 1,4-diazabicyclo[2.2.2]octane, several aldehydes and cyclic ketones underwent efficient Knoevenagel condensation with malononitrile and ethyl cyanoacetate to produce the respective α.β -unsaturated systems within fairly short time periods. As a result, high yields of conjugated products were easily obtained. Products could be engaged in a Gewald reaction, either stepwise or in situ, to produce efficiently their respective 2-aminothiophenes within 4–7 h.
4/5/2023 5:11:41 AM +00:00
Poly(vinyl chloride) functionalization by aliphatic and aromatic amines: application to the extraction of some metal cations
The aim of this study was to evaluate the efficiency of 3 new polymers obtained by functionalization of a commercial poly(vinyl chloride) by grafting amino-alkyl and amino-aryl groups to extract some metal cations from aqueous solutions. A kinetic study of the extraction shows that the optimal duration of extraction was obtained with the polymer that has more chlorine atoms substituted by diethylenetriamine groups. The influence of metal extraction on the infrared spectra, differential scanning calorimetry diagrams, and X-ray diffraction of metal-loaded polymers was also studied.
4/5/2023 5:11:35 AM +00:00
Convenient synthesis of new polysubstituted isoindole-1,3-dione analogues
Three new polysubstituted isoindole-1,3-diones were prepared from 2-ethyl-5-hydroxy-3a,4,5,7a-tetrahydroisoindole-1,3-dione. The reaction of 2-ethyl-5-hydroxy-3a,4,5,7a-tetrahydro-isoindole-1,3-dione with m-CPBA gave the corresponding epoxide. The triacetate derivative was obtained via cis-hydroxylation using OsO4 , followed by acetylation. An aromatic derivative, a secondary reaction product, was also formed during the acetylation. Finally, a tricyclic derivative from 2-ethyl-5-hydroxy-3a,4,5,7a-tetrahydro-isoindole-1,3-dione was synthesized via dichloroketene addition under microwave irradiation. The exact structures of epoxide and tricyclic derivatives were determined by X-ray diffraction analysis.
4/5/2023 5:11:28 AM +00:00
Organic biomolecules bind to phosphate through borate linkages in aqueous solutions
Solutions of salicyclic, ascorbic, and citric acids were reacted with boric acid, followed by NaH2PO4 . The products, triphosphateborate ester of salicylic acid (1), orthosphateborate ester of ascorbic acid (2), triphosphateborate ester of ascorbic acid (3), and orthosphateborate ester of citric acid (4), were flash precipitated with cold acetone and characterised by microanalysis, thermal analysis, FT-IR, Raman, 11 B NMR, 31P MAS NMR, and mass spectroscopic techniques. Analytical results indicated the presence of –C–O–B–O–P– linkages with the attached phosphate groups varying between orthophosphate and triphosphate, depending on the starting material.
4/5/2023 5:11:21 AM +00:00
Oxidation of hydrocarbons with tetra-n-butylammonium peroxy monosulfate catalyzed by β-tetrabromo-meso-tetrakis(4-methoxyphenyl)- and β-tetrabromo-meso-tetraphenylporphyrinatomanganese(III)
While significance differences were observed between the catalytic activities of the title complexes in the oxidation of alkanes, the 2 manganese porphyrins showed comparable activities in oxidation of most of the olefins used. However, the latter showed greater catalytic performance in the oxidation of the hydrocarbons. Moreover, the oxidative degradation of the former (60%) was greater than that of the latter (45%) in the oxidation of cyclooctene.
4/5/2023 5:11:14 AM +00:00
Catalytic conversion of carbon dioxide into cyclic carbonates by Cu(II) and Ni(II) acetylacetonates anchored onto Siral 80
Ni and Cu acetylacetonates were anchored onto Siral 80 and used in the catalytic conversion of carbon dioxide. The catalysts were characterized by several methods such as XRD, FTIR, SEM, and TGA/DTG. The catalytic domains of the prepared heterogeneous complexes and their homogeneous counterparts were examined for the conversion reaction of carbon dioxide into cyclic carbonates in the presence of different additives (1.5 MPa CO2 pressure, 100◦C, and 2 h).
4/5/2023 5:11:03 AM +00:00
Antioxidant, anticholinesterase, and antimicrobial activities and fatty acid constituents of Achillea cappadocica Hausskn. et Bornm.
This study was the first fatty acid analysis and biological activity report on an endemic Achillea species, Achillea cappadocica Hausskn. et Bornm. The major compounds in the fatty acid were identified as oleic (34.7%), palmitic (23.1%), and linoleic acids (20.6%). The methanol and water extracts indicated higher ABTS cation radical scavenging activity than that of α-tocopherol and BHT at 100 µg/mL. The acetone extract showed 70.62% inhibitory activity against butyrylcholinesterase at 200 µg/mL. The acetone and methanol extracts exhibited moderate antimicrobial activity.
4/5/2023 5:10:57 AM +00:00
Synthesis of novel imidazo[1,2-a]pyridines and evaluation of their antifungal activities
New 2-(imidazo[1,2-a]pyridin-2-ylcarbonyl)-N -substituted hydrazinecarbothioamides (4a–j), N ’-(3-substituted-4-oxo-1,3-thiazolidin-2-ylidene)imidazo[1,2- a]pyridine-2-carbohydrazides (5a–f), and N -(nonsubstituted/4-substituted phenyl)-5-(imidazo[1,2-a]pyridine-2-yl)-1,3,4-oxadiazole-2-amines (6a–d) were synthesized from imidazo[1,2-a]pyridine-2-carbohydrazide (3) and evaluated for antifungal activity against Microsporum gypseum NCPF 580, M. canis, Trichophyton tonsurans NCPF 245, T. rubrum, Candida albicans ATCC 10231, and C. parapsilosis ATCC 22019 using amphotericin B as the standard.
4/5/2023 5:10:51 AM +00:00
Selective CO methanation over CeO2–ZrO2 -composed NiO and Co3O4 catalysts
CeO2–ZrO2-composed NiO and Co3O4 catalysts were prepared by 3 different methods. Both CO methanation and selective CO methanation were carried out. All catalysts were prepared by (1) co-precipitation, (2) surfactantassisted co-precipitation, and (3) surfactant-assisted co-precipitation with ultrasound mixing methods. Catalysts were characterized by using N2 physisorption, XRD, SEM, TEM, and TPR-H2 techniques. The highest surface area value, uniform pore size distribution, and pores having small diameters were observed for the catalysts prepared by using the surfactant and ultrasound.
4/5/2023 5:10:39 AM +00:00
Development of 2-acetylpyridine-4-phenyl-3-thiosemicarbazone functionalized polymeric resin for the preconcentration of metal ions prior to their ultratrace determinations by MIS-FAAS
2-Acetylpyridine-4-phenyl-3-thiosemicarbazone (APPT) ligand was incorporated onto Amberlite XAD-2 resin through an azo spacer and characterized by FTIR spectroscopy, elemental analysis, TGA, and SEM analysis. The synthesized resin was used for the preconcentration of Pb(II), Zn(II), Co(II), Ni(II), Cu(II), and Cd(II) ions. The sorbed metal ions were eluted with 10 mL of 2.0 mol L−1 HCl and determined by microsample injection coupled flame atomic spectrometry (MIS-FAAS).
4/5/2023 5:10:29 AM +00:00
Application of 3-aroyl-4(5)-arylimidazols as efficient ligands in Pd-catalyzed Heck reactions
The Heck coupling of haloarenes with various alkenes was successfully performed in the presence of 0.25 mol% PdCl2 and 0.5 mol% biphenyl-4-yl-[4(5)-(biphenyl-4-yl)-1H -imidazol-2-yl]ketone 2f as a ligand with Na2CO3 as optimal base, in a 1:1 mixture of H2O/DMF as the reaction solvent at 80◦C for 8 h. Imidazole 2f was found to be an inexpensive, air-stable, easily available, and efficient ligand in the palladium-catalyzed Heck reactions of aryl iodides (76%–94%), bromides (52%–79%), and chlorides (40%–70%).
4/5/2023 5:10:22 AM +00:00