Tài liệu miễn phí Hoá học
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Calixarene-based receptors for molecular recognition
Calixarene-based molecular receptors have been a widely developing area in material science and technology for the last few decades. Due to their bowl-shaped geometry, calixarene macrocycles are used as hosts allowing organic and inorganic guests to coordinate/sorb onto their cavity. This work briefly reviews the recent development of calixarenes
4/5/2023 4:55:59 AM +00:00
DFT study of tautomerism in aklavinone
Aklavinone has an anthraquinone-based chromophore and its backbone highly resembles the kernel of some anthracycline antibiotics that possess anticancer activity, e.g., daunomycin. Since aklavinone’s structure possesses many –OH groups and 2 keto groups, it is quite probable that certain tautomeric equilibria may occur. Presently, aklavinone prototropic tautomers possessing embedded anthraquinone moiety have been investigated quantum chemically by using density functional theory at the levels of RB3LYP/6-31G(d) and RB3LYP/6-31G(d,p).
4/5/2023 4:55:50 AM +00:00
Photo- and electroluminescence behavior of biphenyl containing conjugated polymer
Light emitting properties of poly[4-(5-(biphenyl- 4-yl)-4-hexylthiophen-2-yl)-2-dodecyl-7-(4-hexyl-thiophen2-yl)-2H-benzo[d][1,2,3]-triazole] (PPhHTBT) and poly(9-vinylcarbazole) (PVK) blends were investigated with a configuration of ITO/PEDOT-PSS/BLEND/Ca/Al in ratios ranging from 5 to 100 wt% in PPhHTBT. Thin film and solution spectra of all blends revealed that energy transfer was completely achieved. Device performance increased for all blends and reached 1.1 cd/A for 30 wt% PPhHTBT.
4/5/2023 4:55:32 AM +00:00
An amphipathic thioxanthone-anthracene photoinitiator for free-radical polymerization
A novel thioxanthone-anthracene (TX-A) photoinitiator possessing an octyl group, TX-A-Oct, as amphipathic photoinitiator was synthesized by click chemistry. Its ability to initiate photopolymerization of various monomers, namely methyl methacrylate (MMA), acryl amide (Am), butyl acrylate (BA), styrene (St), and a multifunctional monomer trimethylolpropane triacrylate (TMPTA), was examined in both the presence and absence of air.
4/5/2023 4:55:12 AM +00:00
An expedient synthesis of 6-vinylfulvene
6-Vinylfulvenes constitute a class of fulvenes that are difficult to access due to the lack of a general method for their synthesis. In particular, the unsubstituted parent system has been very difficult to obtain by existing methods. In this communication we describe a convenient 3-step protocol for the synthesis of the title compound by way of sulfide oxidation and subsequent sulfoxide elimination.
4/5/2023 4:55:03 AM +00:00
Asymmetric synthesis of α-(heteroaryl)alkylamines and α-amino acids via nucleophilic 1,2-addition of lithiated heterocycles to aldehyde SAMP-hydrazones
The asymmetric synthesis of α-(heteroaryl)alkylamines was accomplished by employing a diastereoselective nucleophilic 1,2-addition of lithiated aromatic heterocycles to aldehyde SAMP-hydrazones, followed by BH3·THF or SmI 2 promoted removal of the chiral auxiliary. The CBz or benzoyl-protected amines were obtained in good yields (40%–78%) and excellent enantiomeric excesses (ee = 88%–99%). The methodology can be applied to the synthesis of highly enantioenriched α-amino acids (ee = 90%–99%).
4/5/2023 4:54:54 AM +00:00
Quasielastic light scattering studies of polypeptides: evidence for chain extension in solution
: Dynamic light scattering and viscosimetric methods were used to study polypeptides including polyleucine, poly (γ -benzyl-L-glutamate), poly (α-L-glutamic acid), and polyproline II. Chain extension showing rod-like and flexible conformations occurred in poly(γ -benzyl-L-glutamate) and polyproline II solutions as these solutions were diluted in glacial acetic acid or in a mixed solvent of acetic acid and dichloromethane.
4/5/2023 4:54:48 AM +00:00
Biotinylated N,N’-diarylureas as probes for the activation of adenosine monophosphate-activated kinase (AMPK)
Biotinylated analogs of drug candidates provide useful tools for studying the drug–target protein interactions. Polyhalogenated N,N’diarylureas are potent activators of adenosine monophosphate-activated kinase (AMPK) and potentially promising agents for the treatment of cancer. Various biotinylated versions of these N,N’-diarylureas were synthesized and evaluated in AMPK-activation studies.
4/5/2023 4:54:41 AM +00:00
Flavonoid constituents of Sideritis caesarea
The compounds were identified by the use of 1D- and 2D-NMR and UV spectroscopic techniques and by comparisons with the reported data. The acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activities of the acetone, methanol, and water extracts of the plant and of the flavones penduletin and apigenin were evaluated at 200 µg/mL. The water extract exhibited better activity against the enzyme AChE as compared to both the acetone and the methanol extracts. Penduletin (1) showed significant activity against BChE (66.58%) while apigenin (2) showed weak activity against both enzymes.
4/5/2023 4:54:35 AM +00:00
Exploring distinct binding site regions of β2-adrenergic receptor via coarse-grained molecular dynamics simulations
The system reached equilibrium at around 0.1 µs. The overall 3-dimensional structure was well preserved throughout the simulation. Local residue-based fluctuations were in good agreement with fully atomistic MD simulations. Four distinct snapshots were selected and reverse-mapped to all-atom representations with around 65,000 atoms. Each reverse-mapped system was later subjected to 100 ns of MD simulation for equilibration. Root mean square deviation clustering analysis yielded distinct receptor conformers for the binding site regions, which were suggested to be alternative representations of the binding pocket and thus were proposed as plausible targets in docking-based virtual screening experiments for the discovery of novel antagonists.
4/5/2023 4:53:48 AM +00:00
Potentiometric study of equilibrium constants of a novel triazine–thione derivative and its stability constants with Hg2+, Cu2+, Ni2+, Pb2+, and Zn2+ metal ions in ethanol and water mixed
The deprotonation constants of 5-hydroxy-5,6-di-pyridin-2-yl-4,5-dihydro-2H-[1,2,4] triazine-3-thione (HPT) and the stability constants of its Hg2+, Ni2+, Cu2+, Pb2+, and Zn2+ ion complexes were studied in 20% ethanol and water mixed at 25±0.1◦C and ionic strength (I) of 0.1 M supported by NaCl. Four pKa values of HPT were determined: 3.58, 6.30, 9.23, and 9.69. In various pH conditions, the different complex forms were formulated as ML, MHL, MH2 L, MH3 L, MH4L, and MH −2L between Hg2+, Ni2+, Cu2+, Pb2+, and Zn2+ ions and HPT.
4/5/2023 4:53:39 AM +00:00
Synthesis, spectroscopic characterization, and genotoxicity of a new group of azo-oxime metal chelates
The structures of the compounds were elucidated from the elemental analysis data and spectroscopic studies. The azo-oxime metal complexes were also characterized by XRD, magnetic moment, molar conductivity, and thermal analyses. Elemental analyses of the chelates suggested that the metal to ligand ratio was 1:2. It was found that the ligand acts as a bidentate bending through the phenolic oxygen and nitrogen atom of the C=N-OH group similar to most oximes.
4/5/2023 4:53:28 AM +00:00
New synthetic strategy for novel 6-arylazo-5-methyl-3-aryl-thiazolo[2,3-c]-[1,2,4]triazoles and study of their solvatochromic properties
Two series of 6-arylazothiazol[2,3-c][1,2,4]triazoles were prepared via oxidative cyclization of the respective aldehyde N-(5-arylazo-4-methylthiazol-2-yl)-hydrazones. The structures of the latter hydrazone precursors and the azo compounds were confirmed by spectral and elemental analyses. The solvatochromism of the title azo dyes is evaluated by means of the Kamlet–Taft equation and discussed.
4/5/2023 4:53:21 AM +00:00
Environmentally green synthesis of thioformamide derivatives
Reactions of isocyanides with thioacids in water proceeded smoothly at room temperature and in neutral conditions to afford thioformylamide and thioformamide derivatives in high yields. The reaction proceeded smoothly and cleanly under mild conditions and no side reactions were observed.
4/5/2023 4:53:14 AM +00:00
A phthalocyanine–fluorescein conjugate
A phthalocyanine–fluorescein conjugate was designed and prepared. Its photophysical properties (electronic absorption and fluorescence) were determined and compared with those of an analogous derivative functionalized by a simple triazole without chromophore. It is likely to be used as a theranostic agent in photodynamic therapy.
4/5/2023 4:53:05 AM +00:00
A two-component protocol for synthesis of 3-(2-(substituted phenylamino)thiazol-4-yl)-2H -chromen-2-ones
An efficient 2-component synthesis of a series of 3-(2-(substituted phenylamino)thiazol-4-yl)-2H -chromen-2- ones (3a–j) was achieved by the reaction of 3-(2-thiocyanatoacetyl)-2H -chromen-2-one (1) with a variety of suitably substituted anilines in 1:1 molar ratio in ethanol. The structures of the products were established by elemental analyses, and UV-vis, FTIR, 1H and 13C NMR, and mass spectroscopy. 3-(2-(4-Methylphenylamino)thiazol-4-yl)-2 H -chromen-2- one (3j) was further characterized by single crystal X-ray diffraction study.
4/5/2023 4:52:52 AM +00:00
C2 -Symmetric chiral diamine ligands for enantiomeric recognition of amino acid esters and mandelic acid by proton NMR titration method
Two novel C2 -symmetric chiral diamines containing α-phenylethyl and α-(1-naphthyl)ethyl chiral subunits were prepared with quantitative yields. Enantiomeric recognition properties of these simple structured diamine ligands towards D- and L-amino acid esters and D- and L-mandelic acid were examined by the 1 H NMR titration method. These ligands exhibited strong complexation (with Kf up to 2481 M−1 ) and good enantioselectivity (up to K L /K D = 4.08) towards the mandelic acid enantiomers.
4/5/2023 4:52:45 AM +00:00
Establishment of an electrochemical RNA aptamer-based biosensor to trace nanomolar concentrations of codeine
Codeine is an opium alkaloid with a great potential of abuse among opioid consumers. Detection of codeine is a routine procedure in the military and government of some countries for personnel recruitment. Therefore, a specific, selective, and easy to use method would be an important improvement in such detection procedures. According to previous reports, short single-stranded DNA or RNA sequences with high affinity and specificity to their targets, aptamers, could be used for designing an accurate and specific biosensor for codeine.
4/5/2023 4:52:38 AM +00:00
Adsorption equilibrium of water vapor on activated carbon and alumina and carbon and alumina impregnated with hygroscopic salt
The adsorption equilibrium of water vapor on different adsorbent materials has been studied. Small grains of commercial activated carbon and alumina, with a diameter of d g = 1.5 × 10−3 m, were impregnated with a hygroscopic salt (calcium chloride) to improve the performance of these materials. The main characteristics of the new composite materials were obtained by adsorption/desorption of nitrogen at 77 K and salt distribution on the adsorbent surface was shown using scanning electron microscopy.
4/5/2023 4:52:31 AM +00:00
Spectral, electrochemical, luminescence, and dye-sensitized solar cell studies of mono and d-f hetero binuclear cryptates
Mono and hetero binuclear cryptates, [Gd(III)ML] + [M = VO(IV), Co(II), Ni(II), Cu(II)], were synthesized by a 2-step method. The ligand L represents the deprotonated anionic cryptate obtained by the 2+3 condensation of tris- (2-aminoethyl)amine with 2,6-diformyl-4-nitrophenol. The complexes were characterized by elemental analysis, spectral, magnetic, and electrochemical studies. Fluorescence of Gd(III) ion in the cavity was quenched by the encapsulated Cu(II) and Ni(II) ions. [GdCoL(NO3)]+ cryptate had a high lifetime value compared to other cryptates.
4/5/2023 4:52:21 AM +00:00
Theoretical study on the addition reaction between propadienylidene and methyleneimine
The reaction mechanism between propadienylidene and methyleneimine was systematically investigated employing the second-order Møller–Plesset perturbation theory (MP2) method with the 6 – 31 + G* basis set. Geometry optimization, vibrational analysis, and energy property of the involved stationary points on the potential energy surface were calculated. The energies of the different species were corrected by single point energy calculations at the CCSD (T) // MP2 / 6 – 31 + G* level. From the surface energy profile, one important initial intermediate characterized by a 3-membered ring structure was located via a transition state firstly
4/5/2023 4:52:14 AM +00:00
Electrochemistry of 2,6-diaminopurine on multiwall carbon nanotube modified glassy carbon electrode
The electrochemical oxidation of 2,6-diaminopurine (2,6-DAP) was studied in pH 7.4 phosphate buffer solution on multiwall carbon nanotube modified glassy carbon electrode (MWCNT/GCE) over a temperature range of 20 to 50 ◦ C using cyclic voltammetry. 2,6-DAP oxidation on MWCNT/GCE showed a well-defined and irreversible oxidation peak at about 0.72 V vs. Ag/AgCl at pH 7.4. The oxidation potential of 2,6-DAP linearly varied with pH over the range of 3.0 to 10.0 with a slope of –0.0547 V/pH, implying that 2 protons were accompanied by 2 electrons transferred in the electrochemical reaction.
4/5/2023 4:52:06 AM +00:00
Application of experimental design on determination of aluminum content in saline samples by adsorptive cathodic stripping voltammetry
Adsorptive cathodic stripping voltammetric determination of aluminum at ng mL −1 levels in salt samples based on the metal complexation with Calcon (1-(2-hydroxynaphthylazo)-2 naphthol-4-sulfonic acid) and the subsequent adsorptive deposition onto a hanging mercury drop electrode was studied. Central composite design was used as a design method. Several chemical and instrumental parameters (pH, ligand concentration, deposition time, deposition potential, and complexing time) were involved in the experimental design. Analytical parameters such as repeatability, linearity, and accuracy were also investigated and the detection limit was found as 0.32 ng mL−1 .
4/5/2023 4:51:58 AM +00:00
Potentiometric determination of some food additives and their binding to a polycationic species using polyion sensors
Polycation-sensitive membrane electrodes based on dinonylnaphthalene sulfonate (DNNS) were examined for the determination of some polyanions, namely xanthan (Xanth), alginate (Alg), carboxymethyl cellulose (CMC), and carrageenan (Carr). The potentiometric titrations of polyanionic analytes yielded sharp end points and correlative stoichiometries. After the determinations were successfully performed in saline, these polyanions were also determined in some food products consumed in Bolu (Turkey). In addition, the titration data were used to estimate the interactions between titrant and polyanionic analytes.
4/5/2023 4:51:51 AM +00:00
Synthesis and characterization of new chromogenic substrates for exoglycosidases: α-glucosidase, α-mannosidase, and β -galactosidase
Glycosides of 4-nitrocatechol (1,2-dihydroxy 4-nitrobenzene) with α-D-glucopyranose and α-D-mannopyranose were synthesized by the glycosylation of phenol with peracetylated sugars in the presence of BF3·OBu2 . The glycoside of 4-nitrocatechol with β -D-galactopyranose was prepared by the glycosylation of this phenol as sodium phenoxide with tetra-O-benzoyl-α-D-galactopyranosyl bromide.
4/5/2023 4:51:45 AM +00:00
An efficient ligand-free method for the transfer hydrogenation of ketones and aldehydes catalyzed by different complexes
A very efficient ligand-free method was developed for the transfer hydrogenation of ketones and aldehydes catalyzed by different metal complexes. With this catalytic system, the catalytic performance and catalytic stability of different Ir, Ru, and Pd complexes were more favorable than those of the previously reported systems for transfer hydrogenation. This ligand-free catalytic system showed good stability and excellent activity even with lower catalyst concentrations for the ketones and aldehydes tested.
4/5/2023 4:51:38 AM +00:00
Synthesis and antimicrobial investigation of some 5H -pyridazino[4,5-b]indoles
Synthesis and in vitro antimicrobial activities are reported for a series of 1,3,5-substituted 4-oxo-3,4-dihydro5H -pyridazino[4,5- b]indole derivatives. Corresponding pyridazino[4,5- b]indoles were prepared from ethyl 3-formyl-1H - indole-2-carboxylate precursors and the functional group in question was installed with hydrazine and its derivatives. The purity and primary structures of pyridazino[4,5- b]indole were confirmed by IR, 1H NMR, and 13 C NMR spectroscopy and elemental analyses.
4/5/2023 4:51:32 AM +00:00
Synthesis and evaluation of acetylcholineesterase inhibitory potential and antioxidant activity of benzothiazine derivatives
The aim of the present study was to synthesize and characterize benzothiazine derivatives prepared by using 2-aminothiophenol and saccharine and in vitro screen their enzyme inhibition and antioxidant potential. Nine different derivatives were prepared and their structures were confirmed by spectral studies (EIMS, 1H and 13 C NMR). Enzyme inhibition potential of the synthesized compounds was evaluated by Ellman’s method, while antioxidant activity was determined by DPPH and FRAP assays.
4/5/2023 4:51:25 AM +00:00
A one-pot strategy for regioselective synthesis of 6-aryl-3-oxo-2,3-dihydropyridazine-4-carbohydrazides
A simple and efficient method for the synthesis of 6-aryl-3-oxo-2,3-dihydropyridazine-4-carbohydrazide derivatives was developed. The synthesis was achieved via one-pot multicomponent reaction of arylglyoxals, dialkylmalonates, and hydrazine hydrate in pyridine at room temperature. This procedure features high regioselectivity, generally good to excellent yields, the use of easily available starting materials, and operational simplicity. This chemistry provides an efficient and promising synthetic strategy for diversity-oriented construction of the 6-arylpyridazinone skeleton.
4/5/2023 4:51:19 AM +00:00
Ionic liquid mediated synthesis, reactions, and insecticidal activity of 1-[(1H-benzoimidazol-2-yl)amino]spiro[azetidine-4,4 -[4 H ]chroman]-2-ones
Ionic liquid mediated synthesis of novel heterocyclic compounds 1-[(1H -benzoimidazol-2-yl)amino]-2 - phenylspiro[azetidine-4,4 -[4 H ]chroman]-2-ones (3) and 1-[(1H -benzoimidazol-2-yl)amino]-3-chloro-2 -phenylspiro[aze tidine-4,4 -[4 H ] chroman]-2-ones (4) was accomplished by condensing substituted 2-hydrazino benzimidazole (1), flavanone (2), and acetyl chloride/chloroacetyl chloride in ionic liquid, [bmim]PF6 with or without using catalyst in excellent yield (90%–95%). Further, compounds 3 and 4 were acylated with trifluoroacetic anhydride to give N -acylated products (5 and 10); 3 when treated with HCHO and (C2 H5)2 NH gave Mannich bases (6) and with aldehydes afforded 3-arylidene-2-azetidinone (7).
4/5/2023 4:51:12 AM +00:00