Tài liệu miễn phí Hoá học
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The catalytic effects of in situ prepared N-heterocyclic carbenes from benzimidazole salts in Suzuki–Miyaura cross-coupling reaction and uses in catalytic preparation of 1,3,5-triphenyl-1,3,5-triazinane-2,4,6-trione from phenyl isocyanate
Many benzimidazole salts bearing a 3-phenylpropyl substituent (1a–1h) were synthesized and their structures were identified by 1H NMR, 13C NMR, and IR spectroscopic methods and elemental analysis. These N-heterocyclic carbene (NHC) precursors were used as a part of a catalytic system including Pd(OAc) 2 and the base in the Suzuki– Miyaura cross-coupling reaction under microwave irradiation. They were also used as catalysts in the cyclotrimerization of phenyl isocyanate to yield 1,3,5-triphenyl-1,3,5-triazinane-2,4,6-trione. It has been observed that benzimidazole salts made a positive contribution to both catalytic reactions as a NHC precursor.
4/3/2023 10:28:51 PM +00:00
Quantification of flavonoids isolated from Mentha spicata in selected clones of Turkish mint landraces
Mint has been used extensively in traditional medicines, spices, and herbal teas throughout the world. Isolation of flavonoids from Mentha spicata and quantification of these compounds in selected clones of Turkish mints landraces were achieved. M. spicata was dried in shade and then boiled in water. After filtration, the aqueous extract was partitioned with ethyl acetate. The solvent was removed under reduced pressure to yield the extract, subjected to silica gel column chromatography to isolate 5-demethyl sinensetin (1), hesperidin (2), didymin (3), and linarin (4), the structures of which were elucidated by 1D NMR, 2D NMR, and LC-TOF/MS.
4/3/2023 10:28:45 PM +00:00
Novel optical sensor-based method for determining total tocopherol content in serum
Lipid-soluble endogenous antioxidants, such as tocopherols, protect biological structures from oxidative damage through their chain-breaking ability and thus the development of a simple method for tocopherol determination is important. In this study, a novel optical sensor-based method was proposed for determining total tocopherol content (TTC) of serum, with selectivity for α-tocopherol over β -carotene. The proposed method is based on the use of a copper(II)-neocuproine complex (Cu(II)-Nc) reagent immobilized onto a Nafion membrane, and the absorbance changes associated with the formation of Cu(I)-Nc chelate on the membrane strip as a result of reaction with serum tocopherols were measured at 450 nm.
4/3/2023 10:28:37 PM +00:00
Neutral atoms and ion energies, accurate ionization potential, and electron affinities by polynomial generator coordinate Hartree–Fock method
We have developed accurate Gaussian basis functions obtained with the polynomial generator coordinate Hartree–Fock (p-GCHF) method for H, Zn, and Ga-Kr atoms. These basis sets have been applied in the calculation of nonrelativistic energies for neutral atoms, monovalent cations, monovalent anions, ionization potential (IP), and electron affinity (EA), with the objective of proving the quality of the basis set generated by the p-GCHF method. The total energies calculated for neutral atoms and monovalent cations and respective IP were minimally affected by the addition of polarization functions and their precision was comparable to the values reported in the literature.
4/3/2023 10:28:30 PM +00:00
Synthesis and antimicrobial and antioxidant activities of hybrid molecules containing benzotriazole and 1,2,4-triazole
Eleven novel 1,2,4-triazolylbenzotriazoles have been prepared using 1-(hydrazinylcarbonylmethyl)-1H -benzotriazole (3) as a potent intermediate. Compound 3, however, was obtained from benzotriazole in two steps. All synthesized compounds were characterized by detailed spectral studies like IR, 1 H NMR, 13 C NMR, and mass spectrometry. All synthesized compounds were evaluated for their in vitro antimicrobial activity against seven strains of bacteria and four strains of fungi. Compounds 13, 17, 19, 20, and 21 were found to possess antibacterial activity comparable to that of ciprofloxacin against a Klebsiella pneumoniae strain.
4/3/2023 10:28:19 PM +00:00
Synergetic effect of Mn, Ce, Ba, and B modification and moderate desilication of nanostructured HZSM-5 catalyst on conversion of methanol to propylene
Modified mesoporous HZSM-5 catalysts were prepared by controlled desilication using a mixture of NaOH and TPAOH (tetrapropylammonium hydroxide) and impregnation of metals (Mn, Ce, and Ba) and metalloid B. The catalytic performances of all prepared catalysts for methanol to propylene (MTP) reaction were evaluated in a fixed bed reactor under atmospheric pressure at 480°C. The parent and modified catalysts were characterized by XRD, ICP-OES, FE-SEM, NH3 -TPD, FT-IR, BET, and TGA techniques.
4/3/2023 10:28:09 PM +00:00
Design and synthesis of new naphtho[2,1-b]pyrano [2,3-d]pyrimidinones under classical and microwave conditions
A fast and efficient method for the synthesis of naphthopyranopyrimidinones derivatives in excellent yields was developed through cyclocondensation reaction between previously prepared pyrimidinic hydrazides and some electrophilic species such as 2,4-pentanedione, 2,5-hexanedione, cyclic anhydrides, and phenylthioisocyanate under microwave irradiation. Compared to the conventional methods applied, it was found that better yields and shorter reaction times were achieved using microwave-assisted synthesis. Structures of all synthesized compounds were established on the basis of spectroscopic methods including 1 H NMR, 13 C NMR, and HRMS-ES.
4/3/2023 10:28:01 PM +00:00
Metal nanoparticles/carbon nanotube modified electrodes for voltammetric determination of boron
This study describes a sensitive and accurate voltammetric method for determination of boron using metal nanoparticles/carbon nanotube modified electrodes. The oxidation peak of Alizarin Red S (ARS) at –0.59 V in the boronARS complex formed in ammonium/ammonia buffer solution (pH 8.5) was evaluated as a response. The electrode modification conditions and experimental parameters affecting the peak height were optimized. The characteristics of modified electrodes were investigated using cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscope, energy dispersive X-ray spectroscopy, high resolution transmission electron microscopy, and X-ray photoelectron spectroscopy.
4/3/2023 10:27:52 PM +00:00
An efficient water-mediated synthetic route for the alkylation of heteroarenes
An efficient synthetic route has been described for the alkylation of 1H -indole, 1H -benzimidazole, and 1H -benzotriazole. This approach features the alkylation of heteroaromatics through in situ generated enones from ketonic Mannich bases under metal-free conditions. A series of alkylated heteroaromatics have been synthesized via the K10 catalyzed alkylation reactions of these heteroaromatics with a variety of ketonic Mannich bases. Environmentally benign K10 catalyst, water-mediated mild reaction conditions, and the efficient synthesis of alkylated products are the advantages of this alkylation method.
4/3/2023 10:27:45 PM +00:00
4D-QSAR analysis and pharmacophore modeling for alkynylphenoxyacetic acids as CRTh2 (DP2) receptor antagonists
In this study, we performed the pharmacophore modeling and 4D-QSAR research of alkynylphenoxyacetic acid analogues as CRTh2 receptor opponent agents by utilizing the electron conformational genetic algorithm method. Quantum chemical calculations and conformational analyses of the compounds were carried out at HF/6-31G* level. Then electron conformational matrices of congruity were prepared for each conformer of each compound, which are represented by electronic and structural properties. As a result of the comparison of the matrices that are called electron conformational submatrices of activity, the pharmacophoric group of the compounds responsible for the activity was found at the determined tolerance intervals.
4/3/2023 10:27:35 PM +00:00
Exploring inhibition of chemiluminescence mechanisms with fluorescence quenching studies and interaction energy calculations
Carbamates weaken the luminol-H2O2 chemiluminescence (CL) catalyzed by sodium copper chlorophyll (SCC). The capacity to inhibit the CL of three carbamates is in the order of carbaryl (CBL) >carbofuran (CBF) >metolcarb (MTC). Mechanisms of carbamates inhibiting SCC-luminol-H2O2 CL are investigated using fluorescence quenching and quantum chemistry simulations for the first time in this work. Carbamate-SCC interactions studied using fluorescence spectroscopy show that with the increasing concentration of the SCC, the fluorescence of carbamate is quenched regularly, and the quenching mechanism is a static quenching process.
4/3/2023 10:27:26 PM +00:00
Synthesis and investigation of langbeinite-related strontium- and iron-containing phosphates
The partial substitution of potassium atoms by strontium atoms in initial matrix K3Fe2(PO4)3 with formation of complex phosphates K3−2xSrx Fe2(PO4)3 (x = 0.75, 1.0, and 1.25) was determined using a solid-state reaction method. According to powder X-ray diffraction (XRD) data, the prepared phosphates with x = 1.0 and 1.25 crystallize in a cubic system (space group P213) and belong to langbeinite family compounds, while for the sample with x = 0.75 a mixture of langbeinite-type phase and a minor amount of K3Fe2(PO4)3 was obtained. The decreasing trend of lattice parameter a with increase of Sr amount in the phosphate confirmed the incorporation of strontium in the langbeinite-related structure.
4/3/2023 10:27:19 PM +00:00
Effect of pH on the complexation of irbesartan with β -, hydroxypropyl-β -, and γ -cyclodextrin: Solubility enhancement and physicochemical characterization
The affinity of irbesartan (IRB) to form inclusion complexes with β-cyclodextrin (β-CD), hydroxypropylβ-cyclodextrin (HP-β -CD), and γ-cyclodextrin (γ-CD) was investigated in aqueous buffered solutions at pH 1.7, 4.1, and 7.0. Analysis of the UV absorption-pH profiles revealed that IRB has two pKa values: pKa1 = 3.60 (imidazolinone ring moiety) and pKa2 = 4.70 (tetrazole moiety). In the presence of 5.0 mmol L−1β-CD, the tetrazole moiety became more acidic, indicating its inclusion within the β-CD cavity. Phase-solubility diagrams (PSDs) were obtained for IRB in aqueous buffered solutions of β-CD, HP-β -CD, and γ-CD at pH 4.1 (zwitterionic IRB), pH 1.7 (protonated IRB), and pH 7.0 (deprotonated IRB).
4/3/2023 10:27:11 PM +00:00
Determination of morin on an electrochemically activated carbon-paste electrode
In this paper, the possibility of using an electrochemically activated carbon-paste electrode (ECA-CPE) for the determination of morin has been studied. It is established that the oxidation current increases 1.85 times in comparison with untreated CPE. The adsorption nature of the anodic current and the number of electrons taking part in the oxidation of morin on ECA-CPE was established. The optimal conditions for the determination of morin (pH = 4, Eads = 200 mV, tads = 180 s) were established.
4/3/2023 10:27:00 PM +00:00
Synthesis of E-stilbene azomethines as potent antimicrobial and antioxidant agents
A series of new extensively conjugated E -stilbene azomethines (5a–5h) were synthesized and screened for their antioxidant and antimicrobial activity. The compounds were tested against bacterial (Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, and Bacillus subtilis) and fungal strains (Aspergillus niger, A. flavus, and Trichoderma harzianum) using the agar well diffusion method. Among the tested compounds, N ’-(4-nitrobenzylidene)- 2-((E)-styryl)benzohydrazide (5g) was found to possess potent antimicrobial activity higher than some drugs with significant activity reported in the literature, e.g., cefradine and terbinafine hydrochloride.
4/3/2023 10:26:52 PM +00:00
Synthesis, spectroscopic characterization, and computational studies of 2-cyano-6-hydroxybenzothiazole: A key synthetic intermediate of firefly luciferin
Firefly luciferin is widely applied as a biotechnological tool for visualizing various biological processes in vitro and in vivo. Chemically, 2-cyano-6-hydroxybenzothiazole, as a key synthetic intermediate of firefly luciferin, is obtained from 2-cyano-6-methoxybenzothiazole by changing the methoxy with a hydroxy group. However, this approach is costly and not suited for large-scale synthesis. Here we report cost-effective and efficient syntheses of 2-cyano-6- hydroxybenzothiazole through the catalytic Sandmeyer-type cyanation reaction. Our approach employs diazonium tetrafluoroborate salt of 2-amino-6-hydroxybenzothiazole as a cyanation substrate.
4/3/2023 10:26:26 PM +00:00
Fabrication and electrochemical performance of La0.595V0.005Sr0.4MnO3−δ (LV05SM) cathode material for solid oxide fuel cells
This study reports the effect of vanadium on the crystal structure and electrical and electrochemical properties of La0.6−x VxSr0.4MnO3−δ (x = 0.005–0.1) perovskite-based cathode materials in solid oxide fuel cells. Crystal structure, morphology, and porosity of prepared cathode materials are characterized by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy. Using XPS analysis it was established that the La3+ cation is exchanged by the V4+/5+ cation in the perovskite structure. This ion replacement improves the ionic conductivity and catalytic activity for oxygen reduction reaction in the perovskite structure, presumably due to the smaller size of the V4+/5+ cation than the La3+ ion.
4/3/2023 10:26:13 PM +00:00
Synthesis of acetamide derivatives of 1,2,4-triazole bearing azinane and their binding interactions with bovine serum albumin using spectroscopic techniques
A new series of acetamide derivatives containing 1,2,4-triazole and azinane moieties has been synthesized and characterized using 1H NMR, 13C NMR, IR, and EI-MS spectroscopic analysis. The intermediate triazole was synthesized through a sequential synthesis of carboxylate and carbohydrazide. The bovine serum albumin (BSA) binding of the newly synthesized 1,2,4-triazole derivatives was evaluated along with thermodynamics, site-selective binding, and synchronous study. The results obtained by BSA binding as well as thermodynamic studies justify that all the compounds show spontaneous interaction with BSA and could be effectively distributed and eliminated from the body. Therefore, the triazole-based analogs might be a useful strategy for designing new drug systems.
4/3/2023 10:26:04 PM +00:00
Recent synthetic methodologies for pyrimidine and its derivatives
Pyrimidine derivatives are well known due to their remarkable pharmacological potential in various fields of science, and they are also present in some natural substances like DNA and RNA. These scaffolds manifest diversified biological activities such as antimicrobial, antiinflammatory, anti-HIV, antitubercular, antitumor, antineoplastic, and antimalarial. A pyrimidine ring is constructed when chalcones, amidines, guanidine, nitriles, isocyanates, urea, thiourea, and aminopyrazoles undergo condensation, coupling, or cyclization reactions. In this context, the present review illustrates a variety of novel and efficient synthetic approaches towards the synthesis of pyrimidine and its derivatives that were reported recently.
4/3/2023 10:25:46 PM +00:00
A novel core-shell-based chromatographic method supported by ratio derivative spectrophotometry for the simultaneous determination of perindopril, indapamide, and amlodipine ternary mixtures
In this work, ratio spectra of the first derivative spectrophotometric and liquid chromatographic methods have been described for the first time for the simultaneous determination of perindopril (PER), indapamide (IND), and amlodipine (AML) in dosage forms. For chromatographic separations several mobile phase compositions were tested for efficient separation with the use of a new column technology related to superficially porous particles. Optimum chromatographic separation was achieved using a Kinetex C18 column (150 × 4.6 mm I.D. 5 µm) at a flow rate of 1.5 mL min−1 . The separation was carried out at 30◦C and the diode array detector was adjusted to 215 nm.
4/3/2023 10:25:30 PM +00:00
Investigation of the hydrogen bond donating ability of 1,8-naphthalenediol by NMR spectroscopy and its use as a hydrogen bonding catalyst
The hydrogen bond donating ability of 1,8-naphthalenediol was investigated via a series of 1H, 13C, and 31P NMR experiments. Complexation studies using triphenylphosphine oxide and cyclohexanone as hydrogen bond acceptors revealed that 1,8-naphthalenediol is a more effective hydrogen bond donor compared to 1-naphthol and 8-methoxy-1- naphthol. Afterwards, its effectiveness as a hydrogen bonding catalyst was demonstrated in the Friedel–Crafts-type addition reaction of indole to trans-β -nitrostyrene.
4/3/2023 10:25:16 PM +00:00
Synthetic strategies towards the carbenoid reactions of α, β -acetylenic carbonyls
Catalytic reactions of α, β -conjugated carbonyl compounds have been a practical tool towards the synthesis of different useful heterocyclic compounds. Despite the numerous reactions with carbon-carbon double bond conjugated carbonyls, reactions of acetylenic carbonyls are limited. In this study, efficient dioxole synthesis was carried out via acetylenic aldehydes and butadiene formation was preferred over cyclopropene formation via acetylenic esters as different functional groups on these substrates change the product distribution.
4/3/2023 10:25:09 PM +00:00
Synthesis, characterization, and application of monodisperse poly L-Dopa microspheres
In this study, 3,4-dihydroxy-L-phenylalanine (L-Dopa) was solvothermally polymerized to monodisperse microspheres 1 µm in diameter. Polymerization was carried out in dimethylformamide containing appropriate amounts of urea and L-Dopa at 120 ◦ C for 24 h. Synthesis of the polymer in basic aqueous solution under hydrothermal conditions or via conventional heating resulted in the formation of bulky powders including irregularly shaped particles of the polymer. The morphologies of the synthesized polymers were characterized by scanning electron microscopy (SEM). The microspheres synthesized by solvothermal method (with ∼1 µm average diameter) were clearly observable in SEM micrographs.
4/3/2023 10:24:54 PM +00:00
Synthesis of 2-substituted 8-propargyloxyquinoline derivatives and determination of their antioxidant, antibacterial, and DNA binding activities
2-Substituted 8-propargyloxyquinoline derivatives have been synthesized from 2-substituted-8-hydroxyquinolines by O-propargylation method (30%–98% yields). The newly synthesized compounds were tested for in vitro antioxidant activities such as DPPH radical scavenging, ferrous chelating, and reducing power activities. The maximum radical scavenging (46.5%) and reducing power activities were obtained from 1 and maximum ferrous chelating effect was obtained from 6 (72.1%) at the concentration of 500 µg/mL. To indicate DNA binding activity of the complexes calf thymus DNA was used.
4/3/2023 10:24:47 PM +00:00
Synthesis and biological evaluation of quinoline-triazole and quinolone-triazole conjugates
One-pot synthesis of novel quinoline- and quinolone-substituted 1,2,3-triazoles has been performed from the key intermediates, quinoline- and quinolone-substituted propargyl derivatives 1–3 (48%–88% yields). The antioxidant properties of the newly synthesized compounds, 1a–1c, 2a–2c, and 3a–3c, were evaluated by monitoring DPPH (2,2- diphenyl-1-picrylhydrazyl) radical scavenging abilities, metal chelating effects, and reducing power. The scavenging effects of compounds on the free radical decreased in the order of 3b > 3a > 1b and were found to be 36.3%, 34.9%, and 27.6% at the concentration of 500 µg/mL, respectively.
4/3/2023 10:24:41 PM +00:00
Synthesis and cytotoxicity evaluation of [(2,4-dichlorophenoxy)methyl]-5-aryl-1,3,4-oxadiazole/4H -1,2,4-triazole analogues
We report herein the synthesis, characterization, and cytotoxicity evaluations of some newer oxadiazole and triazole analogues (5a–j). The cytotoxicity of all the title compounds were evaluated as per the National Cancer Institute protocol in a one-dose assay (10 µM) on nine different panels of 59 cancer cell lines. 2-{5-[(2,4-Dichlorophenoxy)methyl]- 1,3,4-oxadiazol-2-yl}phenol (5e) showed the maximum cytotoxicity among the series of ten compounds. The cytotoxicity of 5e was comparable to that of the standard anticancer drug, 5-fluorouracil, and better than that of imatinib. The structure activity relationship was also discussed.
4/3/2023 10:24:31 PM +00:00
A new cocrystal explosive trinitrotoluene (TNT): 1-amino-4-bromonaphthalene with reduced sensitivity
A 1:1 cocrystal of TNT and 1-amino-4-bromonaphthalene was prepared via solvent evaporation. The structure of the cocrystal was determined via single-crystal and powder X-ray diffraction. Crystal structure determination studies indicated that the main mechanism of cocrystallization originates from the intermolecular hydrogen bonding (amino– nitro), halogen bonding, and π − π stacking. Investigation of intermolecular interactions by Hirshfeld surface and fingerprint plot analysis revealed that the structures were stabilized by H…H, O…H, C…C (π−π) and Br…O interactions. Hirshfeld surfaces showed that these weak interactions were significant for crystal packing.
4/3/2023 10:24:19 PM +00:00
The interaction between a zinc(II) phthalocyanine compound bearing octakis phenoxyacetamide substituents and calf thymus DNA
In this study, a zinc(II) phthalocyanine compound (PcZn) substituted with octakis phenoxyacetamide was synthesized and characterized. Calf thymus DNA (CT-DNA) was used to determine the DNA binding properties of the zinc(II) phthalocyanine compound. This interaction of CT-DNA with PcZn was investigated using electronic absorption spectra, emission spectroscopy, a thermal melting temperature study, cyclic voltammetry, and viscosity measurements in a Tris-HCl buffer solution at a pH of 7.2. The findings showed that zinc(II) phthalocyanine interacts with calf thymus DNA via partial intercalative binding mechanisms.
4/3/2023 10:24:09 PM +00:00
Antioxidant potential and secondary reactivity of bis{diphenyl(2-pyridyl)phosphino}copper(II) complex
Copper-based complexes with the general formulas [Cu(L)2]Cl2 (1) and [Cu2L2(µ2-L)µ2−Cl2] (2) and a mixed-ligand anionic complex [Cu(L)2 dedtc][LCl] (3b), where L = diphenyl(2-pyridyl)phosphine and dedtc = diethyldithiocarbamate, were synthesized and structurally characterized. X-ray analysis revealed that the coordination environment around the copper atom in complexes 1–3 is distorted tetrahedral. In monomeric complexes 1 and 3b both diphenyl(2-pyridyl) phosphine ligands are monodentate and are coordinated through the P-atom. In complex 3b two phosphine ligands are attached to copper through the P-atom. The third phosphine ligand acts as a bridged ligand, coordinated to the metal centers through the P-atom and N-atom.
4/3/2023 10:23:55 PM +00:00
Experimental and theoretical studies on cis-dioxomolybdenum(VI) complexes of ONN-donor thiosemicarbazone
The experimental data were compared with the theoretical results obtained by the quantum chemical calculations of the DFT/B3LYP method with LANL2DZ basis set. A detailed interpretation of the FT-IR spectra of the studied compounds was performed based on the total energy distribution. In order to investigate the electronic structures and the UV-Vis spectrum of complex 5, time-dependent density functional theory calculation was taken into account. The interaction energies between the oddand even-numbered alcohols and remaining parts of complexes 1–4 were evaluated with the help of natural bonding orbital analysis.
4/3/2023 10:23:44 PM +00:00