Tài liệu miễn phí Hoá học
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Copper-free Sonogashira cross-coupling reactions catalyzed by an efficient dimeric C,N-palladacycle in DMF/H2O
Very small concentrations of a dimeric C,N-palladacycle were used as an efficient homogeneous catalyst for Sonogashira cross-coupling reactions between various aryl halides and phenylacetylene. The catalytic reactions were performed without the need for copper in DMF/H2O. This catalytic system shows excellent yields for aryl iodides and bromides and even in the case of aryl chlorides.
4/5/2023 5:30:09 AM +00:00
A simple approach to bis-spirocycles and spiroindole derivatives via green methods such as Fischer indolization, ring-closing metathesis, and Suzuki–Miyaura cross-coupling
We have developed a simple synthetic methodology for bis-spirocycles and spiroindole derivatives starting with a commercially available 6-bromo-2-tetralone. Here, we have used Fischer indolization, ring-closing metathesis, and Suzuki–Miyaura cross-coupling as key steps to assemble a variety of spirocyclic frameworks. The methodology developed here is simple and it may be useful to prepare various spirocycles containing indole moiety.
4/5/2023 5:30:02 AM +00:00
Sonogashira reactions for the synthesis of polarized pentacene derivatives
Five dissymmetrically functionalized anthracene analogues (3a–e) were synthesized from commercially available 9,10-dibromoanthracene through an efficient bromine–iodine exchange followed by two successive Sonogashira coupling reactions. The resulting TMS-anthracene analogues are interesting building blocks for the preparation of highly π-conjugated dissymmetric pentacene-based dyads, which could be used as active semiconducting layers for organic field-effect transistors (OFETs).
4/5/2023 5:29:56 AM +00:00
Palladium-catalysed Suzuki–Miyaura cross-coupling with imidazolylidene ligands substituted by crowded resorcinarenyl and calixarenyl units
Two N -heterocyclic carbene (NHC) palladium complexes of formula [PdBr2(NHC)(pyridine)] in which the carbenic ring is flanked by sterically crowded cavitand substituents were prepared from appropriate imidazolium salts bearing either two resorcinarene or a combination of resorcinarene and calixarene fragments. Both complexes displayed high stability and good activities in the cross-coupling of aryl bromides with phenyl boronic acid. One of the imidazolium salts was characterised by an X-ray diffraction study.
4/5/2023 5:29:46 AM +00:00
Contribution of heterobifunctional ligands to transition metal-catalysed C–C coupling reactions
In this account the authors’ latest results in C–C coupling catalysis are reviewed. First, an efficient catalytic system for the Kumada–Tamao–Corriu coupling reaction based on NHC-phosphine (NHC = N-heterocyclic carbene) nickel complexes is presented. Then the use of palladium complexes of chiral ferrocenyl NHC-phosphines in the asymmetric Suzuki–Miyaura coupling reaction is reported. High catalytic activities and moderate enantioselectivities (ee up to 46%) were obtained.
4/5/2023 5:29:39 AM +00:00
Cross coupling reactions catalyzed by (NHC)Pd(II) complexes
This review is focused on new developments reported during the last 3 years concerning the catalytic performances of in situ formed or preformed NHC–Pd(II) complexes (NHC: N-heterocyclic carbene) for cross-coupling reactions such as Heck–Mizoraki (often shortened to the Heck reaction), Kumada, Negishi, Suzuki–Miyaura (often shortened to the Suzuki reaction), Sonogashira and Hiyama couplings, and the Buchwald–Hartwig aminations, which are extremely powerful in the formation of C–C and C–heteroatom bonds.
4/5/2023 5:29:30 AM +00:00
Synthesis and in vitro cytotoxic activity of novel pyrazolo[1,5-a]pyrimidines and related Schiff bases
The newly synthesized compounds were characterized and confirmed by analytical and spectroscopic data (IR, MS, 1H NMR, and 13C NMR). Pyrazolo[1,5-a]pyrimidines 5a–c and 9a–c and Schiff bases 11b–f were investigated for their cytotoxicity against four human cancer cell lines (colon HCT116, lung A549, breast MCF-7, and liver HepG2) according to SRB assay and the structure–activity relationship was discussed.
4/5/2023 5:29:23 AM +00:00
Enzyme-assisted modification of cellulose/chitin fibers with NIPAAm
Both enzyme-activated and subsequently modified samples were characterized by ATR-FTIR, XPS, and SEM. All obtained results confirm the structural and morphological changes of the fiber surface after the application of the two-step procedure. The particular responsiveness to temperature and to pH of the coated fibers was evidenced by following the swelling behavior. It was established that the swelling kinetics followed a Fickian behavior.
4/5/2023 5:29:16 AM +00:00
Corrosion inhibition by naturally occurring Hibiscus sabdariffa plant extract on a mild steel alloy in HCl solution
The corrosion inhibition of mild steel alloys is of tremendous technological importance due to their increased industrial applications. Potentiodynamic polarization and electrochemical impedance spectroscopy techniques were used to establish the effect of different concentrations of HCl on the corrosion behavior of mild steel. A study was conducted on the inhibition of dissolution for a mild steel alloy in the most corrosive concentration of HCl (5 M) by adding different concentrations of aqueous extract of Hibiscus sabdariffa plant (named karkade or rosselle) as an ecofriendly inhibitor.
4/5/2023 5:29:09 AM +00:00
Green and efficient synthesis of novel bispyrazoles through a tandem Knoevenagel and Michael type reaction using nanowire zinc oxide as a powerful and recyclable catalyst
Zinc oxide nanowires (ZnO NWs) were prepared and characterized by scanning electron microscopy, powder X-ray diffraction, and transmission electron microscopy analyses. ZnO NWs were then employed as heterogeneous and recyclable catalyst for green synthesis of some new and known bispyrazole derivatives through a tandem Knoevenagel and Michael type addition reaction of aromatic aldehyde and pyrazolone. The synthetic method is operationally simple and affords product with high yields in short reaction times.
4/5/2023 5:29:00 AM +00:00
Spectrophotometric determination of iron species using ionic liquid ultrasound assisted dispersive liquid–liquid microextraction
A simple and efficient method for speciation and determination of iron in different water samples was developed. The method is based on ionic liquid ultrasound assisted dispersive liquid–liquid microextraction (IL-USADLLME) followed by spectrophotometric determination. Fe(II) is complexed with 2,4,6-tri(2’-pyridyl)-l,3,5-triazine (TPTZ), neutralized through ion pair formation with sodium dodecyl sulfate (SDS) and extracted into 1-hexyl-3- methylimidazolium hexafluorophosphate [C6MIM][PF6].
4/5/2023 5:28:54 AM +00:00
Properties and some in vitro studies of 6-phosphogluconate dehydrogenase purified from the liver of Chalcalburnus tarichi, the only fish living in Lake Van’s highly alkaline water (pH 9.8)
In this study, some enzymology parameters and some antibiotics affecting the enzyme activity of 6- phosphogluconate dehydrogenase (6PGD) extracted from t the livers of fish from Lake Van (Chalcalburnus tarichi) were investigated because it is an important enzyme-producing NADPH, a reductive power, protecting the cell against the oxidative agents by producing reduced glutathione. The crude enzyme solution was obtained by using the affinity chromatography method. The native molecular weight of the enzyme is ∼90,000 ± 3000 Da and it is composed of two subunits with identical molecular weights of ∼46,000 Da as exhibited on sodium dodecyl sulfate-polyacrylamide gel electrophoresis.
4/5/2023 5:28:47 AM +00:00
Separation and preconcentration of lead(II), cobalt(II), and nickel(II) on EDTA immobilized activated carbon cloth prior to flame atomic absorption spectrometric determination in environmental samples
The synthesis and characterization of ethylenediaminetetraacetic acid immobilized activated carbon cloth was performed in the present work. It was used for preconcentration-separation of lead(II), cobalt(II), and nickel(II) at trace levels as an adsorbent. Factors including pH, concentration and volume of eluent, sample and eluent flow rates, sample volume, and effect of coexisting ions on the solid phase extraction of analytes were examined. The preconcentration factor was 50.
4/5/2023 5:28:38 AM +00:00
Synthesis, characterization, and electrical and optical properties of magnesium-type boracite
Synthesis of the magnesium type of the mineral boracite (Mg 3 B7 O13 Cl) was studied. Several parameters affecting boracite synthesis were investigated. The raw materials selected were magnesium chloride hexahydrate (MgCl 2 .6H2 O), magnesium oxide (MgO), and boron oxide (B2 O3). Reaction temperatures were selected between 600 ◦ C and 900 ◦ C. Moreover, three different reaction times of 4, 1, and 0.5 h were studied with the determined optimum molar ratio, reaction temperature, and reaction medium. Synthesized boracite characterization analyses were done by the techniques of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscope (SEM).
4/5/2023 5:28:28 AM +00:00
Preparation and physicochemical characterizations of solid lipid nanoparticles containing DOTAP®R for DNA delivery
Crystallization processes of lipid matrices were characterized by X-ray diffractometry and differential scanning calorimetry. pDNA binding ability of SLNs and the stability of pDNA-SLN complexes with DNase I enzyme were also determined by gel electrophoresis. It was determined that all formulations became positively charged with DOTAP®R. They were able to bind DNA and were partially protective against enzyme degradation. Although additional studies are necessary, this study reveals the promising potential of this gene delivery system for gene therapy.
4/5/2023 5:28:13 AM +00:00
New tetrazolic azo dyes linked to (thio)barbiturate and electron-rich aromatics as potential antimicrobial agents
A series of new tetrazolic azo dyes based on (thio)barbiturate and electron-rich aromatics were synthesized in excellent yield. The electron-donor and tetrazole ring moieties were linked by a p-phenylazo bridge and the structural characterizations were achieved by FT IR, 1 H and 13 C NMR, and UV-visible spectrometry. The antibacterial activity of the synthesized compounds was tested against gram-positive and gram-negative bacterial strains, namely Acinetobacter calcoaceticus (ATCC23055), Escherichia coli (ATCC2592), Pseudomonas aeruginosa (ATCC27853), and Staphylococcus aureus (ATCC25923). As a result, potential antimicrobial effects were seen for some of the synthesized compounds.
4/5/2023 5:28:06 AM +00:00
Thermogravimetric analysis-based screening of metal (II) chlorides as dopants for the destabilization of solid-state hydrazine borane
Thermogravimetric analysis (TGA) is a powerful technique for screening boranes envisaged for chemical hydrogen storage. The demonstration is based on the use of six metal (II) chlorides (MCl2) (with M as 3d-metal or d8 - metal) as destabilizing agents of solid-state hydrazine borane (N2H4BH3). On the basis of TGA profiles combined with derivative thermogravimetric (DTG) curves, it is shown that: e.g. (1) CuCl 2 is an inefficient dopant whereas it is efficient towards ammonia borane (NH3BH3); (2) one of the best destabilization results is achieved with N2H4BH3 doped by 10 wt% CuCl2 -NiCl2.
4/5/2023 5:27:59 AM +00:00
Influence of acid and heavy metal cation exchange treatments on methane adsorption properties of mordenite
In this study, the adsorption of methane (CH4) capacities onto natural mordenite obtained from ˙Izmir, Turkey, and its cationic forms (CuM, AgM, FeM, and HM samples) were investigated at the temperatures of 0 and 25 ◦ C up to 100 kPa. Natural and modified samples were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared (FT-IR), thermogravimetry (TG-DTG), differential thermal analysis (DTA), scanning electron microscopy (SEM) coupled with energy dispersion spectroscopy (EDS), and N2 adsorption methods.
4/5/2023 5:27:51 AM +00:00
Synthesis of novel 1,2,4-triazoles and triazolo-thiadiazines as anticancer agents
In addition, the novel bis-(1,2,4-triazole-3-thione) was reacted with the appropriate hydrazonoyl chloride in dioxane under reflux in the presence of triethylamine to give the corresponding bis-(1,2,4-triazolethiohydrazonoate). The structures of the new compounds were established based on elemental and spectral data. The mechanism of the studied reaction was also discussed. Moreover, some of the new products were screened for their anticancer activity and the results obtained are promising and indicate that compounds 4a and 4i are the most active inhibitors against HEPG-2 and compounds 4a and 13b are active against HCT cell lines.
4/5/2023 5:27:40 AM +00:00
A new series of Cu(II) and Ni(II) complexes of NO bidentate 4-NO2 -benzoylhydrazones: synthesis, characterization, and biological studies
A series of new nickel(II) and copper(II) hydrazone complexes 1–14, containing a bidentate NO-donor hydrazone ligand, derived from 4-nitrobenzoylhydrazide and several aliphatic and aromatic aldehydes were synthesized, and their chemical structures were confirmed by means of FT-IR, UV-Vis, 1 H and 13 C NMR, mass spectral data, conductance measurements, and elemental analyses. The spectral data of the newly synthesized complexes show the formation of a 1:2 [metal:ligand] ratio.
4/5/2023 5:27:33 AM +00:00
Solid-phase total synthesis of cyclic peptide brachystemin A and its immunomodulating activity
Brachystemin A (1) is a biologically active peptide from a Chinese traditional plant Brachystemma calycinum D. Don. (Caryophyllaceae). The current study describes the complete solid-phase total synthesis of peptide 1 by using Kenner’s sulfonamide safety-catch linker strategy. It was identified by QTOF/MS data and NMR studies. Synthetic peptide 1 was tested for its immunomodulatory effect on different inflammatory parameters, including production of inflammatory cytokines, interleukin 2 (IL-2), tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β), and generation of nitric oxide (NO.).
4/5/2023 5:27:24 AM +00:00
Tetraphenylsilane group containing carbazoles as high triplet energy host materials for solution-processable PhOLEDs
A series of solution processable, wide band-gap host materials composed of carbazole and tetraphenylsilane groups were designed and synthesized. Their thermal, electrochemical, and photophysical properties were fully investigated. The introduction of bulky tetraphenylsilane and tert-butyl groups around the carbazole led to high glass transition temperatures (Tg) between 120 and 204◦C. The triplet energies (ET) of the synthesized materials were examined by low temperature (77 K) photoluminescence studies and determined as E T > 2.6 for all compounds.
4/5/2023 5:27:15 AM +00:00
Effective recognition of multiple anions by an azobenzene–Al3+ system
A ready-to-use multifunctional coordinative system, 2,2’-dihydroxyazobenzene –aluminum (III) (DHAB–Al3+), was created to recognize several anions effectively through three channels, namely colorimetric detection, UV-Vis spectroscopy, and fluorescence spectroscopy. Under naked eye visualization, the H2PO−4 can be readily distinguished from the other anions by the DHAB–Al3+ system through a change in color from reddish-orange to light yellow.
4/5/2023 5:26:49 AM +00:00
A comparative study on fabrication of Cu2ZnSnS4 (CZTS) nanofibers using acetate and chloride metal precursors
This study reports, for the first time, the fabrication of electrospun Cu 2 ZnSnS 4 (CZTS) nanofibers using metal acetate precursors. Viscous poly(vinyl pyrrolidone) (PVP) solution containing acetate or chloride salts of copper, zinc, and tin was electrospun onto a conductive substrate. The PVP nanofibers that have a mixture of metal salts were annealed at elevated temperatures. After calcination, these nanofibers were treated with the sulfur source and then annealed again in order to generate CZTS nanofibers.
4/5/2023 5:26:38 AM +00:00
Microwave-assisted synthesis of condensed 1,4-dihydropyridines as potential calcium channel modulators
This study reports the design, synthesis, and calcium channel modulatory activity evaluation of a series of 14 novel fused 1,4-dihydropyridine derivatives. The molecular design of the compounds was based on modifications of nifedipine, which is a calcium channel blocker. The compounds were achieved by one-pot microwave-assisted reaction of 4,4-dimethyl-1,3-cyclohexanedione, 5-chlorosalicylaldehyde/3,5-dichlorosalicylaldehyde, an appropriate alkyl acetoacetate, and ammonium acetate in ethanol according to a modified Hantzsch reaction.
4/5/2023 5:26:31 AM +00:00
Palladium nanoparticles supported on modified polystyrene resin as a polymeric catalyst for Sonogashira–Hagihara coupling reactions
This polymeric ligand was reacted with PdCl 2 to obtain a polymeric Pd(0) complex. The TEM image of the Pd catalyst showed good dispersion of catalytic sites. The Pd catalyst exhibits excellent activity and stability in copper-free Sonogashira–Hagihara cross-coupling reactions under aerobic conditions. This protocol can be applied efficiently to the coupling reactions of chloro- as well as iodo- and bromo-arenes. The catalyst can be reused several times without any considerable decrease in its activity.
4/5/2023 5:26:23 AM +00:00
Synthesis of 5-aryl-N -(trichloroacetyl)-1,3,4-oxadiazole-2-carboxamide via three-component reaction of trichloroacetyl isocyanate, (N -isocyanimino)triphenylphosphorane, and benzoic acid derivatives
The three-component reaction of benzoic acid derivatives, (N -isocyanimino)triphenylphosphorane, and trichloroacetyl isocyanate in a 1:1:1 ratio in CH3 CN occurred at room temperature, and the 5-aryl-N -(trichloroacetyl)- 1,3,4-oxadiazole-2-carboxamide derivatives produced were formed in high yields. The reaction proceeded smoothly and cleanly under mild reaction conditions and no side reactions were observed. The structures of the products were confirmed by IR, 1 H NMR, 13 C NMR, mass spectroscopy, and elemental analysis.
4/5/2023 5:26:17 AM +00:00
Microwave-assisted synthesis of novel 8-chloro-[1,2,4]triazolo[4,3-a]pyridine derivatives
A series of novel 1,2,4-triazolo[4,3-a]pyridine derivatives were synthesized from 2,3-dichloropyridine and hydrazine hydrate as starting materials by multistep reactions under microwave assistance, and their structures were characterized by 1 H NMR, MS, and elemental analysis. This method provides several advantages such as high yields, facile work-up, and environmental friendliness.
4/5/2023 5:26:08 AM +00:00
Synthesis and biological evaluation of a new series of 4-alkoxy-2-arylquinoline derivatives as potential antituberculosis agents
The new compounds 7a–k, 8a–k, and 9a–k were synthesized from flavonones 4–6, which can be considered new precursors for quinoline synthesis through a one-step reaction. All the target compounds (7a–k, 8a–k, and 9a–k) were evaluated for their in vitro antimicrobial activity against nine test microorganisms. They showed the most activity against Mycobacterium smegmatis with minimum inhibitory concentrations (MIC) of 62.5–500 µg/mL, indicating their potential uses as antituberculosis agents. Among them 8a–k (m-fluoride) were the most active compounds against M. smegmatis (MIC, 62.5–125 µg/mL).
4/5/2023 5:26:01 AM +00:00
Three-component synthesis of cyclic β-aminoesters using CeO2 nanoparticles as an efficient and reusable catalyst
CeO2 nanoparticles were used as an efficient catalyst for the preparation of cyclic β-aminoesters by threecomponent reaction between primary amines, ethyl acetoacetate, and chalcones in ethanol. Atom economy, low catalyst loading, reusable catalyst, and high yields of products are some of the important features of this protocol.
4/5/2023 5:25:54 AM +00:00