Tài liệu miễn phí Hoá học

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Synthesis of new pyrazole and antibacterial pyrazolopyrimidine derivatives

3-Substituted-1-phenyl-1H -pyrazolo[3,4-d]pyrimidin-4-amines 2a–c were synthesized by treating 5-aminopyrazole-4-carbonitriles 1a–c with formamide. The reactivity of compounds 1a–c towards some cyclic anhydrides was studied. The condensation of 5-aminopyrazole-4-carbonitrile 1b with triethylorthoformate gives imidate 7b, which reacts with a series of primary amines and leads to pyrazolo[3,4-d]pyrimidine-4-amines 9 and 10. The reaction of imidate 7b with ammonia and hydroxylamine afforded pyrazolopyrimidine 2b and pyrazolo[3,4-d]pyrimidin-5-(4H)-ol 11, respectively.

4/5/2023 5:06:26 AM +00:00

Fluorescence quenching study of moxifloxacin interaction with calf thymus DNA

Moxifloxacin (MOX) is a fourth-generation synthetic fluoroquinolone antibacterial agent with many important therapeutic properties. Fluorescence quenching was used to study the interaction of MOX with calf thymus DNA (ctDNA) in aqueous solution. As the most common genetic material of various biosomes in nature, deoxyribonucleic acid (DNA) plays a key role in different kinds of vital processes including gene expression, mutagenesis, cell death, etc. An increasing number of studies have suggested that there is an essential linkage between environmental factors (chemical drugs, nuclear radiations, etc.) and genetic damage.

4/5/2023 5:06:19 AM +00:00

Synthesis, biological evaluation, and molecular docking of N′ -(Aryl/alkylsulfonyl)-1-(phenylsulfonyl) piperidine-4-carbohydrazide derivatives

Molecular docking was accomplished for these compounds to examine their binding interactions with AChE and BChE human proteins. The strategy we applied for this purpose was a direct receptor-based approach. The binding modes of the inhibitors under study were determined using an automated docking program (AutoDock) and were compared with antienzymatic IC 50 values. Both studies confirmed the potential of compounds as excellent inhibitors for AChE and BChE.

4/5/2023 5:06:13 AM +00:00

Preparation of a lead sensor based on porous multiwalled carbon nanotubes/thiolated chitosan composite materials

Thiolated chitosan (CS–TGA) was prepared using chitosan (CS) and thioglycolic acid (TGA). Then MWCNTs were added to the mixture of CS–TGA and CS to prepare the CS/CS–TGA/MWCNs porous composite by freeze-drying method and this composite was used to modify an indium tin oxide glass electrode. The electrode was used as a sensor for Pb2+. The morphology and structure of the composite were characterized by infrared spectroscopy and scanning electron microscope, and their electrochemical behavior was also studied.

4/5/2023 5:05:57 AM +00:00

Speciation of chromium by the combination of dispersive liquid–liquid microextraction and microsample injection flame atomic absorption spectrometry

A microextraction procedure was established for the speciation of total Cr, Cr(III), and Cr(VI). Sudan blue II was used as a ligand for speciation works. Some factors affecting the recoveries of chromium species, including type of extraction and dispersive solvents, pH, ligand amount, extraction time, and matrix ions, were examined. Optimum values for the dispersive liquid–liquid microextraction method were pH 6, LOD 0.34 µg L−1 , and preconcentration factor 400.

4/5/2023 5:05:50 AM +00:00

Self-condensation reactions of acyl phosphonates: synthesis of tertiary O-protected α-hydroxyphosphonates

The self-condensation reaction of benzoyl dialkyl phosphonates was developed using cyanide ion as catalyst, affording versatile tertiary O-protected α-hydroxy phosphonates in moderate yield. Hydroxy phosphonic acids and their ester derivatives have gained considerable attention due to their inhibitory activity towards various important groups of enzymes.

4/5/2023 5:05:43 AM +00:00

Preparation of a novel solid acid catalyst with Lewis and Brønsted acid sites and its application in acetalization

A novel melamine–formaldehyde resin (MFR) supported solid acid with Lewis and Brønsted acid sites was synthesized through the immobilization of acidic ionic liquid and cuprous ion on MFR. The scanning electron microscopy (SEM) characterization showed that addition of PEG-2000 in the synthesis of MFR could promote the formation of regular particles with diameters around 3.7 µm. The XRD pattern demonstrated that some cuprous ions were aggregated.

4/5/2023 5:05:37 AM +00:00

Synthesis and antimicrobial activity of novel 2-[4-(1H-benzimidazol-1-yl)phenyl]-1H-benzimidazoles

A new class of 2-[4-(1H-benzimidazol-1-yl)phenyl]-1H-benzimidazoles (13–22) were synthesized via cyclocondensation reaction of the substituted 1,2-phenylenediamines (1,4–12) and 1-(4-formylpheny)-1H-benzimidazole (3). The synthesized compounds were evaluated for antibacterial and antifungal activities against S. aureus, methicillinresistant Staphylococcus aureus (MRSA), and Candida albicans by the tube dilution method. Compounds 13, 15, 18, 20, and 21 have moderate antifungal activity against C. albicans.

4/5/2023 5:05:30 AM +00:00

Experimental investigation of drag reduction effects of polymer additives on turbulent pipe flow using ultrasound Doppler velocimetry

Drag reduction in fully developed turbulent pipe flow with 4 concentrations (200 to 500 wppm or mg/kg) of low molecular weight sodium carboxymethylcellulose (CMC) in aqueous solutions was investigated experimentally. Drag reduction was determined by pressure drop measurements. Maximum drag reduction achieved was 22% using 500 wppm CMC solution. To observe the impact of the presence of CMC on the flow, ultrasound Doppler velocimetry (UDV) was employed to monitor the instantaneous velocity distributions.

4/5/2023 5:05:24 AM +00:00

Simulation of impedance spectra of oxalic acid electroreduction to glyoxylic acid: effect of chemical activator, pH, activation energy, and reduction potential

The aim of this study was to examine qualitatively the effect of important electrochemical parameters on the faradaic impedance spectra of oxalic acid electroreduction. The impedance spectrum of a 3-step oxalic acid electroreduction mechanism was simulated by the solution of a faradaic impedance equation based on 3 state variables. Before the solution of the faradaic impedance equation, the electroreduction mechanism was analyzed and it was seen that this mechanism can be represented by an electrical circuit composed of 2 resistors and a capacitance or inductance.

4/5/2023 5:05:17 AM +00:00

On the peculiar reactivity of a C,N-annelated isoindole core

In accordance with the HSAB principle, this soft methylating agent (MeI) leads mainly to the C,C-dimethylated product 11,11-dimethyl-11 H -isoindolo[2,1-a]quinazoline5-one, which was previously not observed, beside the N-methylated product, in a procedure using methyl tosylate as a hard methylating agent of the same substrate in the initial absence of a base. A mechanism is finally proposed for the formation of methyl 2-(3-methyl-4-oxo-3,4-dihydroquinazolin-2-yl)benzoate as an oxidation side product.

4/5/2023 5:05:11 AM +00:00

Comparison of chelating ability of NO-, NS-, ONS-, and ONO-type Schiff base derivatives and their stability constants of Bis-complexes with copper(II)

The present study includes important findings relating to the number of donor atoms, species of ligands, and stabilities of complexes. Stabilities of complexes between Cu(II) ion and NO-, NS-, ONS-, and ONO-type Schiff bases were compared. Acid-base properties of the Schiff bases were explained at 25±0.1◦C and ionic strength (I) of 0.1 M supported by NaCl. The Hyperquad computer program was used for calculation of dissociation and stability constants.

4/5/2023 5:05:04 AM +00:00

A combined first principles TDDFT and experimental study on the UV-Vis spectra properties of M(p-nitrophenyl azo resorcinol)3 complexes (M: Fe, Cr)

UV-Vis absorption data of p-nitrophenyl azo resorcinol (Magneson I) and its 2 Fe(III) and Cr(III) complexes were investigated both experimentally and theoretically. The geometries were optimized at BP86/TZVP level. The most stable spin states were computed as doublet and quartet for Fe(magneson) 3 and Cr(magneson) 3 complexes, respectively. Time-dependent density functional theory (TDDFT) was employed to explore the absorption spectra properties, whereas the solvent effects were taken into account using the polarizable continuum model (PCM).

4/5/2023 5:04:56 AM +00:00

A new and simple DP polarographic method for the determination of uric acid in serum after elimination of the interference of ascorbic acid and dopamine

The peak for UA appeared at about –0.15 V in this medium, which responded well to standard additions and high reproducibility was obtained. The validity of the proposed method was tested in serum samples by spiking known concentrations of UA to serum samples and high recovery was obtained. The interference effect of dopamine (DA) and ascorbic acid (AA) was eliminated simply by the addition of Fe(III), in a very fast and quantitative reaction.

4/5/2023 5:04:49 AM +00:00

Synthesis, structure, and luminescent properties of 2 novel 5-chlorhydroxybenzoate-imidazole metal-organic complexes

In 1 the Zn 2+ cation is tetracoordinated with 2 nitrogen atoms from 2 imidazoles and 2 oxygen atoms from the 2 carboxyl groups in 5-chlorhydroxybenzoate. In 2 the coordination polyhedrons of Cu 2+ center can be described as distorted square pyramidal geometry sharing common edges, with an oxygen atom on the top of the pyramid. The hydrogen bonds and π − π interactions between the 2 ligands contribute to the presence of the infinite one-dimensional chain in the structure. Furthermore, solid-state fluorescence spectra indicate that both complexes show violet-blue fluorescence and can be potentially used as violet-blue fluorescence materials.

4/5/2023 5:04:42 AM +00:00

Selective catalytic reduction of sulfur dioxide by carbon monoxide over iron oxide supported on activated carbon

The selective reduction of sulfur dioxide with carbon monoxide to elemental sulfur was studied over ACsupported transition-metal oxide catalysts. Catalyst samples were characterized by X-ray powder diffraction in order to relate the phase composition to the activation behavior and catalytic performance. The active phase of catalyst was detected as FeS2, and the formation of FeS2 was greatly dependent on the sulfidation temperature.

4/5/2023 5:04:34 AM +00:00

Economic synthesis of quinaldinium fluorochromate(VI), (QnFC), and solvent-free periodic acid oxidation of alcohols catalyzed by QnFC

A 1:1:1 stoichiometric reaction between CrO3, aqueous HF, and quinaldine affords orange crystalline quinaldinium fluorochromate(VI) (QnFC)(C10H9NH[CrO3F]) in 99.4% isolated yield. A highly efficient, simple, chemoselective, and environmentally benign procedure for QnFC (3 mol%) catalyzed oxidation of primary and secondary alcohols to aldehydes and ketones using 1.1 equiv of H5IO6 under solvent-free conditions is described.

4/5/2023 5:04:27 AM +00:00

NH-acidities and Hammett correlation of 3-para substituted phenyl-1,2,4-oxadiazol-5(4H)-ones and 1,2 λ43,5-oxathiadiazole 2-oxides in nonaqueous media

NH acidities of some 3-(p-substitutedphenyl)-1,2,4-oxadiazol-5(4H) -ones and 4-(p-substitutedphenyl)-1,2 λ43,5-oxathiadiazole 2-oxides were determined in methanol by means of potentiometric titration with sodium methoxide. pKa values of the title compounds calculated from the potentiometric data were interpreted on the basis of structural effects caused by para-substituted groups on the phenyl ring by plotting pKa values versus Hammett σ + p constants, which gave excellent linear correlations.

4/5/2023 5:04:21 AM +00:00

Hard chromium electrodeposition from a trivalent chromium bath containing water-soluble polymer

The effect of polyvinylpyrrolidones (PVPs) with different molecular weights as polymeric additives to a sulfate trivalent chromium bath was ascertained. Introduction of PVPs to the plating bath was stated to result in improvement in the surface appearance of chromium deposits and stabilization of current efficiency value in long-term electrolysis. The rate of metal deposition is practically independent of the deposition time.

4/5/2023 5:04:09 AM +00:00

Synthesis, spectral, and thermoanalytical studies on the new heterobimetallic [Mg(II)-Ti(IV)]-µ-oxoisopropoxide and its β-diketonates

The new heterobimetallic [Mg(II)-Ti(IV)]-µ-oxoisopropoxide was synthesized on treatment of magnesium acetate with titanium(IV) isopropoxide in refluxing decalin in 1:2 molar ratio and characterized by liberated isopropanol, elemental, spectral (IR, 1H and 13C NMR, and mass), thermal analysis, and molecular weight data. The reactions of [Mg(II)-Ti(IV)]-µ-oxoisopropoxide compound with β -diketones in different molar ratios (1:1–1:4) yielded mono to tetra derivatives [{MgO2Ti2(OPri)6−n Ln}] (where n is 1–4 and L = acetylacetonate/benzoylacetonate anion)] of the µ-oxo complex and were characterized by elemental, liberated isopropanol, and spectral analysis (IR and 1H and 13C NMR). These studies revealed interesting facets in support of plausible structures of the parent compound and its β-diketonates.

4/5/2023 5:03:44 AM +00:00

Immobilized metal ion affinity nanospheres for α-amylase immobilization

Immobilized metal chelate affinity chromatography (IMAC) support was practiced for α-amylase immobilization. Poly(hydroxyethylmethacrylate-methacryloylamidotryptophan)-Ni2+[p(HEMA-MAT)-Ni2+] nanospheres, average diameter 100 nm, were produced by surfactant free emulsion polymerization. Characterizations of p(HEMAMAT)-Ni2+ nanospheres were carried out by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscope (SEM). In addition, average particle size, size distribution, and surface charge were specified. The amount of N-methacryloylamidotryptophan (MAT) incorporated to polymer was determined as 1.95 mmol/g polymers by using nitrogen stoichiometry.

4/5/2023 5:03:36 AM +00:00

Azolylimidazoles: Synthetic strategies and medicinal applications

The current review summarizes the known routes to different azoles linked directly to imidazole. This review is divided into classes based on the type of azoles connected to an imidazole ring. Some medical applications are mentioned. As a continuation of our very recently published review article concerning the synthesis of biologically active heterocyclic systems, 20−23 we prepared this review to present for the reader a survey of the literature on different azoles linked directly with an imidazole nucleus. Some of the medicinal applications are also mentioned.

4/5/2023 5:03:26 AM +00:00

N -functionalized benzimidazol-2-ylidene silver complexes: synthesis, characterization, and antimicrobial studies

The 7 new silver-NHC complexes were fully characterized by means of 1 H NMR, 13 C NMR, and elemental analysis techniques. Using the agar dilution procedure recommended by the Laboratory and Clinical Standards Institute, the antimicrobial activities of all the silver-NHC complexes were studied against 2 gram-negative bacterial strains (Pseudomonas aeruginosa and Escherichia coli), 2 gram-positive bacterial strains (Enterococcus faecalis and Staphylococcus aureus), and 2 fungi (Candida tropicalis and Candida albicans).

4/5/2023 5:03:15 AM +00:00

Synthesis, characterization, and luminescence of zinc(II) and cadmium(II) coordination complexes: [Zn(phen)2(CH3COO)](ClO4), [Zn(bpy)2(ClO4)](ClO4), and [Cd(phen)2(NO3)2]

The synthesis of metal-organic frameworks has attracted considerable interest due to their potential applications as functional materials in catalysis; 1,2 gas sorption, storage, and separation; 3,4 molecular magnetism5 and recognition; 6 and nonlinear optics. 7 While the synthesis of fascinating self-assembly metal-organic coordination polymers occurs via bridging ligand and also through weak noncovalent interactions, such as π − π stacking or hydrogen bonding, 8−20 the construction of metal-organic compounds mainly depends on the nature of the organic ligands and metal ions.

4/5/2023 5:02:25 AM +00:00

Determination of Pb(II) in natural water with dibromo-p-methyl-sulfonazo by the light-absorption ratio variation approach

Pb ions can react sensitively with dibromo-p-methylsulfonazo (DMSA) to form a blue complex, whose absorption is maximal at 630 nm. By means of the light-absorption ratio variation approach (LARVA), the direct determination of Pb was developed in 0.3 M nitric acid and plots of ∆A−1r vs. c−1Pb are linear where ∆Ar is the lightabsorption ratio variation and cP b Pb(II) concentration is between 0 and 5.0 mg/L. The limit of detection (3σ) of Pb(II) is only 0.02 mg/L. This method was applied to direct analysis of natural water with satisfactory results.

4/5/2023 5:02:19 AM +00:00

Synthesis, characterization, and biological activity of coordination polymers derived from pyromellitic dianhydride

A new ligand, 2,5-bis(furan-2-ylmethylcarbamoyl)terephthalic acid (BFMTA), was synthesized using 1,2,4,5- benzenetetracarboxylic dianhydride (pyromellitic dianhydride-PMDA) with furan-2-ylmethanamine (2-furfurylamine). New coordination polymers of the ligand (BFMTA) were also prepared using transition metal ions Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II) metal salts. The coordination polymers and ligand were characterized by physicochemical characteristics, magnetic susceptibilities, spectroscopic investigations, and thermogravimetry.

4/5/2023 5:02:02 AM +00:00

Asymmetric Henry reaction catalyzed by Cu(I)-based chiral amino alcohol complex

The Cu(I)-based complex prepared from (S)-2-(furan-2-yl-methylamino)-2-phenylethanol (5c) and CuCl was used as catalyst in enantioselective Henry reactions of arylaldehydes and nitromethane, which gave 89% ee and 95% yield at ambient temperature. The proposed catalytic cycle of an asymmetric Henry reaction was suggested.

4/5/2023 5:01:56 AM +00:00

Electrochemical determination of Sudan IV in food samples by using graphene-modified glassy carbon electrodes

A simple and sensitive modified electrode was fabricated with graphene via the drop-casting method and applied for the electrochemical detection of Sudan IV. Cyclic voltammetry (CV) was used to investigate the electrochemical behaviors of Sudan IV in phosphate buffer solution (PBS). The experimental conditions such as determining medium, scan rate, and accumulation time were optimized for the determination of Sudan IV.

4/5/2023 5:01:40 AM +00:00

Novel flame retardant poly(thiourea-sulfone-imide)s for high temperature applications: synthesis and characterization

The synthesis and polymerization of a novel diamine monomer, 1,1-(sulfonylbis (4,1-phenylene)) bis (thiourea) (SPT), with various aromatic dianhydrides were carried out. In addition, the fabrication of poly(thiourea-sulfone-imide)s (PTSIs) with noble thermal properties and flame retardancy was conducted. The structures of SPT and polymers were characterized by FT-IR, 1 H NMR, and 13 C NMR spectroscopy along with elemental analysis. Crystallinity, organosolubility, inherent viscosity, and gel permeation chromatographic measurements were taken as well.

4/5/2023 5:01:33 AM +00:00

Syntheses, characterization, and antibacterial study of titanium complexes

The stoichiometry of the complexes was established by their elemental analysis (chlorine and titanium estimation). The unit cell parameters calculated by using the powder XRD tool confirm the monoclinic unit system and P lattice type for all complexes. Antibacterial screening of the ligands as well as the complexes was carried out to check their biological potential. It was found that the complex with 4,4’-dimethyl-2,2’-bipyridine ligand was a more potent bactericide than complexes with other ligands.

4/5/2023 5:01:27 AM +00:00