Tài liệu miễn phí Hoá học
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Analytical capabilities of two-phase hollow-fiber liquid phase microextraction for trace multielement determination in aqueous samples by means of portable total reflection X-ray instrumentation
Liquid phase microextraction (LPME) procedures have been widely used in combination with atomic and emission spectroscopic techniques for the isolation and preconcentration of trace elements. However, its application in combination with total reflection X-ray spectrometry (TXRF) is still scarce. In this paper, we evaluate the possibilities and drawbacks of a two-phase hollow fiber LPME procedure in combination with TXRF for the simultaneous determination of trace amounts of Cr, Ni, Cu, Zn, Pb, and Cd in aqueous samples.
4/5/2023 5:42:21 AM +00:00
A simple and efficient approach for preconcentration of some heavy metals in cosmetic products before their determinations by flame atomic absorption spectrometry
In the current study, a simple and efficient analytical method for preconcentration and determination of Cd(II), Pb(II), and Sn(II) in some cosmetic samples, using ultrasonic assisted-cloud point extraction and flame atomic absorption spectrometry, was developed. The method is based on the ternary complex formations of Sn(II), Pb(II), and Cd(II), which are available in the form of neutral and/or anionic hydroxo complexes (Sn(OH)−3, Pb(OH)−3, Cd(OH)2, and/or Cd(OH)−3), with Victoria Pure Blue BO (VPB +) in the presence of cetylpyridinium chloride at pH 8.5, and then extraction of the formed ternary complexes into the micellar phase of polyoxyethylene sorbitan monostearate (Tween 60).
4/5/2023 5:42:14 AM +00:00
An application of coacervate-based extraction for the separation and preconcentration of cadmium, lead, and nickel ions prior to their determination by flame atomic absorption spectrometry in various water samples
Cloud point extraction (CPE), which is the most popular coacervate-based extraction method, was utilized for the separation and preconcentration of trace amounts of cadmium, lead, and nickel. Quinalizarin was used as complexing agent and Triton X-114 was used as surfactant. After extraction, analyte ions were determined by flame atomic absorption spectrometry. The detection limits (3 s) of 1.8 µg L −1 for Cd(II), 3.2 µg L −1 for Pb(II), and 2.8 µg L −1 for Ni(II) were obtained using 50 mL of solutions.
4/5/2023 5:42:08 AM +00:00
Preparation of Fe3O4 @ montmorillonite composite as an effective sorbent for the removal of lead and cadmium from wastewater samples
A magnetic Fe3O4 @ montmorillonite composite was prepared and used for the separation of lead and cadmium from aqueous solutions. For this purpose, magnetite (Fe3O4) was generated by co-precipitation of FeSO4 and FeCl3 onto montmorillonite. The effects of various experimental parameters such as pH of the solution, amount of sorbent, initial concentration of analytes, and contact time on the sorption efficiencies of lead and cadmium ions were investigated and optimized by applying a batch technique. The concentrations of analytes were determined by high resolution continuum source flame atomic absorption spectrometry.
4/5/2023 5:42:01 AM +00:00
Spectrophotometric determination of mercury using vortex-assisted liquid–liquid microextraction
A novel method for the determination of mercury(II) is suggested. The procedure is based on the formation of an ion associate between the bromide complex of Hg(II) and Astrazon Red 6B dye and vortex-assisted liquid–liquid microextraction of the ion associate formed, with subsequent spectrophotometric detection. The variables that affect the procedure, such as pH, the concentration of ligand and dye, the type and volume of extraction solvent, and the rate and time of vortex mixing, were optimized.
4/5/2023 5:41:53 AM +00:00
Schiff base immobilized silica gel framework as an efficient sorbent for preconcentration of Pb and Zn ions in aqueous media
A novel preconcentration method for Pb and Zn ions using a column packed with Schiff base modified silica gel is described. The method was based on the sorption of analytes on N,N’-bis(4-methoxysalicylidene)-1,3-propanediamine modified silica gel and elution with HNO3 prior to flame atomic absorption analysis. The parameters pH, flow rate, sample volume, eluent volume, and concentration were optimized using a central composite design.
4/5/2023 5:41:47 AM +00:00
Determination of hexavalent chromium in aqueous and alkaline soil extracts
A fast, simple, and reliable method for determination of hexavalent chromium species in soil aqueous and alkaline extracts has been developed. The procedure is based on the ion-pair extraction of Cr(VI) with methyltrioctylammonium chloride (Aliquat 336) into xylene. The extract is analyzed by flame (FAAS) or electrothermal atomic absorption spectrometry (ETAAS).
4/5/2023 5:41:39 AM +00:00
A novel ion-imprinted polymeric sorbent for separation and determination of chromium(III) species in wastewater
A new chromium(III) ion-imprinted polymer (IIP) was prepared from a Cr(III)-nicotinate complex (template), acrylamide (functional monomer), and ethylene glycol dimethacrylate (cross-linking agent) using 2,2’-azobisisobutyronitrile as the radical initiator. IIP was characterised and used as a selective sorbent for the solid-phase extraction of Cr(III) ions. The conditions for dynamic separation of Cr(III) on IIP were optimised.
4/5/2023 5:41:32 AM +00:00
Chromate surface-imprinted silica gel sorbent for speciation of Cr in surface waters
This study is focused on the synthesis of chromate anion imprinted sorbent supported on silica gel for nonchromatographic Cr speciation in surface waters. The preparation procedure is based on grafting of 3-methyl-1- trimethoxysilylpropylimidazolium, preliminarily coordinated to CrO2− 4 as a template ion, onto the surface of silica gel. Sorption and desorption characteristics of surface-imprinted sorbent toward Cr(III) and Cr(VI) were examined by batch solid-phase extraction.
4/5/2023 5:41:24 AM +00:00
Remediation of Cr(VI) via combined self-reduction and adsorption by chemically modified carbon sorbents
Hexavalent chromium, Cr(VI), is a highly toxic species, while trivalent chromium, Cr(III), is an essential trace element for humans and other organisms. In the present work, a simple, rapid, and efficient procedure for water treatment of Cr(VI) is described. Active carbon (AC) was chemically treated with HCl and NaOH for the formation of surface modified Acidic-AC and Basic-AC sorbents, respectively. In addition, AC sorbent was treated with HNO3 as an oxidizing agent and sodium sulfite as a reducing agent for the formation of Ox-AC and Rd-AC sorbents, respectively.
4/5/2023 5:41:17 AM +00:00
Chromium redox speciation in food samples
Chromium is an element with important biological characteristics, depending on its different species. Cr(III) is considered as essential; however, the Cr(VI) form is classified as carcinogenic. For this reason, speciation analysis in food samples is a very important question. The proposed data procedures for chromium redox speciation in the literature can be divided into those with the use of online hyphenated techniques and those where appropriate sample pretreatment is necessary.
4/5/2023 5:41:11 AM +00:00
Latest trends, green aspects, and innovations in liquid-phase–based microextraction techniques: a review
Liquid-phase microextraction (LPME) methods including single-drop microextraction (SDME), hollow-fiber LPME (HF-LPME), and dispersive liquid-liquid microextraction (DLLME) have in the very short time since their invention grabbed the attention of scientists. Up to now, LPME methods have shown important innovations for the extraction and preconcentration of both inorganic and organic trace analytes from different matrices. These LPME methods offer unique advantages such as high preconcentration factor for target analytes in a single step, low cost, simplicity, excellent preconcentration capability, sample cleanup and integration of steps, and combined use with almost every analytical measurement technique.
4/5/2023 5:41:03 AM +00:00
Speciation of trace metals and metalloids by solid phase extraction with spectrometric detection: a critical review
Considerable interest is continuing to be shown in the speciation of metals, metalloids, and organometals due to the dependence of their toxicity and mobility on their chemical form. This review focuses on the speciation analysis of metals, metalloids, and organometals by solid phase extraction before spectrometric detection, and all aspects of analytical speciation such as determination of oxidation states and organometallic compounds. Some applications of speciation of metals and metalloids are also presented and discussed in this review.
4/5/2023 5:40:56 AM +00:00
An indirect model for sintering thermodynamics
A model was proposed and used to calculated the changes in enthalpy (∆Ho), entropy (∆So), and Gibbs energy (∆Go), as well as equilibrium constant (K) relating to the sintering of alumina compacts. Specific nanopore volume (V) of the compacts was assumed as a thermodynamic variable. A hypothetical equilibrium constant (Kh) and corresponding Gibbs energy (∆Goh) were calculated depending on the V value measured after each sintering.
4/5/2023 5:40:48 AM +00:00
Synthesis of new hexahydro-1H-isoindole-1,3(2H)-dione derivatives from 2-ethyl/phenyl-3a,4,7,7a-tetrahydro-1H-isoindole-1,3-(2H)-dione
A new and appropriate synthesis for hexahydro-1H-isoindole-1,3(2H)-dione derivatives has been developed starting from 3-sulfolene. The epoxidation of 2-ethyl/phenyl-3a,4,7,7a-tetrahydro-1H-isoindole-1,3-(2H)-dione and then the opening of the epoxide with nucleophiles gave hexahydro-1H-isoindole-1,3(2H)-dione derivatives. Amino and triazole derivatives of hexahydro-1H-isoindole-1,3(2H)-dione were synthesized from the formed product by the opening reaction of the epoxide with sodium azide. Hydroxyl analogues were obtained from cis-hydroxylation of 2-ethyl/phenyl-3a,4,7,7atetrahydro-1H-isoindole-1,3-(2H)-dione. The hydroxyl groups were converted to acetate.
4/5/2023 5:40:41 AM +00:00
Synthesis, (E)/(Z)-isomerization, and DNA binding, antibacterial, and antifungal activities of novel oximes and O-substituted oxime ethers
A series of novel positional oximes (2a–2d), O-methyl oxime ethers (3a–3d), and O-benzyl oxime ethers (4a–4d) were synthesized in high yields starting from their corresponding methyl 3-, 4-, 6-, and 13-keto tetradecanoates. The synthesized compounds were characterized by 1H NMR, 13C NMR, FT-IR, mass, and elemental analyses for their structures and (E) /(Z) isomerizations. Their DNA binding abilities were investigated in vitro by agarose gel electrophoresis. The antibacterial and antifungal activities were tested also in vitro against eleven bacterial strains and three fungal strains.
4/5/2023 5:40:35 AM +00:00
Production, purification, and characterization of a thermo-alkali stable and metal-tolerant carboxymethylcellulase from newly isolated Bacillus methylotrophicus Y37
A carboxymethylcellulose (CMC)-degrading bacterium was isolated from soil, identified as Bacillus methylotrophicus according to the physiological properties and analyses of 16S rRNA and a partial sequence of the gyrase A (gyrA) gene, and named as B. methylotrophicus Y37. The CMCase enzyme was purified to homogeneity by 20.4-fold with 21.73% recovery using single-step hydrophobic interaction chromatography and biochemically characterized. CMCase showed a molecular weight of approximately 50 kDa as determined by SDS-PAGE. The activity profile of the CMCase enzyme exhibited optimum activity at 45◦C and pH 5.0.
4/5/2023 5:40:28 AM +00:00
Degradation of bisphenol-a using a sonophoto Fenton-like hybrid process over a LaFeO3 perovskite catalyst and a comparison of its activity with that of a TiO2 photocatalyst
Oxidation of bisphenol-A (BPA) was investigated using a sonophoto Fenton-like hybrid process under visible light irradiation in the presence of iron-containing perovskite LaFeO3 catalysts. For this purpose, firstly the perovskite catalyst (LaFeO3) was prepared by the sol-gel method and calcined at different temperatures (500, 700, and 800◦C). The prepared catalysts were characterized using XRD, SEM, FTIR, nitrogen adsorption, UV-vis DRS, and ICP/OES measurements.
4/5/2023 5:40:18 AM +00:00
Speciation of inorganic selenium by solid phase extraction using nanozirconium oxide/boron oxide composite material
The speciation and preconcentration of selenium were carried out by solid phase extraction using nanozirconium oxide/boron oxide (ZrO2/B2O3). Electrothermal atomic absorption spectrometry (ETAAS) was used for detection. This preconcentration and/or speciation method depends on the retention of Se(IV) ions selectively as its ammonium pyrrolidine dithiocarbamate (APDC) complex on the sorbent. The effects of pH, flow rate, and volume of sample solution and eluent type were investigated for determining the optimum preconcentration and speciation conditions.
4/5/2023 5:40:12 AM +00:00
Mn-doped ZnS quantum dots as a room-temperature phosphorescent probe for analysis of glutamic acid in foodstuffs
L-cysteine–capped Mn-doped ZnS quantum dots (QDs) were used for the determination of glutamic acid in foodstuffs. This method is based on measurement of the quenching of the phosphorescence intensity of the QDs after interacting with glutamic acid. A linear response was observed from 50 to 500 ng mL−1 glutamic acid with a limit of detection of 6.79 ng mL−1 . Room temperature phosphorescence (RTP) intensity of the QDs was quenched rapidly upon the addition of the quencher and the reaction reached equilibrium within 2 min.
4/5/2023 5:40:05 AM +00:00
Zr(IV) complexes of some heterocyclic ligands: synthesis, characterization, and ethylene polymerization activity
Thirty-one complexes of bis-(benzimidazole, benzothiazole, and benzoxazole) compounds with Zr(IV) metal centers were synthesized, characterized, activated with methylaluminoxane (MAO), and then tested for catalytic ethylene polymerization. The activities of the various catalysts were found to be functions of the heteroatoms in the ligand frameworks and the structure around the active metal center. The highest activity was obtained with 38/MAO (424 kg E/mol cat. h).
4/5/2023 5:39:59 AM +00:00
Bismuth(III)–SiO2 catalyzed synthesis of polysubstituted imidazoles with the participation of azaaryl derivatives of aniline in four-component reactions
A series of novel polyaromatic derivatives of imidazole were synthesized by Bi(III) nitrate–SiO2 catalyzed four-component reactions of benzil, ammonium acetate, aromatic aldehydes, and N -heterocyclic derivatives of aniline under solvent-free conditions.
4/5/2023 5:39:48 AM +00:00
Adsorption of cellulase on poly(2-hydroxyethyl methacrylate) cryogels containing phenylalanine
The aim of this study was to prepare a supermacroporous cryogel that can be used for the adsorption of cellulase. The macroporous cryogel of poly(2-hydroxyethyl methacrylate-N-methacryloyl-l-phenylalanine) [p(HEMAMAPA)] was prepared by copolymerization of 2-hydroxyethyl methacrylate (HEMA) with a functional monomer of Nmethacryloyl-l-phenylalanine (MAPA). The cryogel was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and swelling tests.
4/5/2023 5:39:39 AM +00:00
Experimental and theoretical investigation of the reaction between CO2 and carbon dioxide binding organic liquids
The reaction kinetics of CO2 absorption into new carbon dioxide binding organic liquids (CO2 BOLs) was comprehensively studied to evaluate their potential for CO2 removal. A stopped-flow apparatus with conductivity detection was used to determine the CO2 absorption kinetics of novel CO2 BOLs composed of DBN (1,5-diazabicyclo[4.3.0]non-5- ene)/1-propanol and TBD (1,5,7-triazabicyclo[4.4.0]dec-5-ene)/1-butanol. A modified termolecular reaction mechanism for the reaction of CO2 with CO2 BOLs was used to calculate the observed pseudo-first–order rate constant k 0 (s−1) and second-order reaction rate constant k 2 (m3/kmol.s).
4/5/2023 5:39:31 AM +00:00
Comparison of influence of nanomaterials on a glassy carbon paste electrode-based bioanode in biofuel cells
This paper presents a comparative study of nanomaterial modified glassy carbon paste electrodes (GCPEs) used as bioanodes in enzymatic biofuel cells. The developed bioanode electrodes were obtained by modification of composite GCPEs with glucose oxidase (GOx) and different nanomaterials like manganese(IV) oxide nanoparticle (MnO2 np) and aluminum titanate (Al2O3–TiO2) bimetallic nanostructure. These nanostructures were utilized in a GCPEbased enzymatic bioanode construction for the first time.
4/5/2023 5:39:23 AM +00:00
Newly synthesized furanoside-based NHC ligands for the arylation of aldehydes
New furanoside-based NHC precursor salts (2) were synthesized using amino alcohols from the chloralose derivatives of glucose (a), galactose (b), and mannose (c). The novel compounds were fully characterized by 1H NMR, 13C NMR, and elemental analyses. The catalytic activities of these salts were tested in the arylation of aldehydes as catalysts that were generated in situ from [RhCl(COD)]2. In addition, 2a was converted to the rhodium complex 3a in order to compare the results obtained in situ. The newly synthesized compounds were very efficient in terms of yield; nevertheless they did not exhibit a chiral induction.
4/5/2023 5:39:17 AM +00:00
Ag(I) complexes of benzimidazol-2-ylidene ligands: a study of catalytic efficiency towards three-component coupling reactions
The compounds were characterized by spectroscopic and elemental analyses. The synthesized NHC–Ag(I) complexes (3a–c) were tested as catalysts for the catalytic threecomponent coupling reaction of aldehyde, alkyne, and amine to propargylamines in various solvents. All complexes were active catalysts for catalytic three-component coupling reactions with good yields under neat and mild conditions (after 4 h, yields of up to 94%).
4/5/2023 5:39:11 AM +00:00
Zr(IV), Ti(IV), and V(III) complexes of some benzimidazole, benzothiazole, and benzoxazole ligands: characterization and catalyst efficiency in ethylene polymerization
Fifteen complexes of 2, 2-bis- (benzimidazole, benzothiazole, and benzoxazole) compounds with Zr(IV), Ti(IV), and V(III) metal centers were synthesized, characterized, activated with methyalumoxane (MAO), and then tested for catalytic ethylene polymerization. The activities of the various catalysts were found to be functions of the hetero atoms in the ligand frameworks. The activity of the catalyst system 6/MAO was found to be 1372 kg PE/mol cat.
4/5/2023 5:38:59 AM +00:00
Isoquinoline-substituted triazole and pyran derivatives: synthesis and computational studies
The one-pot synthesis of novel 1,4-disubstituted 1,2,3-triazoles from isoquinoline-substituted homopropargyl alcohol backbone is described (42%–88% yields). A ring closing metathesis reaction and an intramolecular Pauson–Khand reaction of enyne system derived from a homopropargyl alcohol backbone to afford the corresponding isoquinolinesubstituted dihydropyran and cyclopentenone-pyran, respectively, are also described (54% and 78% yields). Information about the structural, electronic, and physico-chemical properties of the novel compounds, obtained by density functional theory application, is also reported.
4/5/2023 5:38:52 AM +00:00
Synthesis of novel thiazolylpyrazoline derivatives and evaluation of their antimicrobial activities and cytotoxicities
Several novel thiazolylpyrazoline derivatives were synthesized by reacting substituted 3,5-diaryl-1-thiocarbamoyl-2-pyrazolines with phenacylbromides. The structures of the synthesized compounds were confirmed by IR, 1 H NMR, 13 C NMR, and MS spectral data. Their antimicrobial activities against Staphylococcus aureus (ATCC-25923), Enterococcus faecalis (ATCC-29212), Enterococcus faecalis (ATCC-51922), Listeria monocytogenes (ATCC-1911), Klebsiella pneumoniae (ATCC-700603), Pseudomonas aeruginosa (ATCC-27853), Escherichia coli (ATCC-35218), Escherichia coli (ATCC-25922), Candida albicans (ATCC-90028), Candida glabrata (ATCC-90030), Candida krusei (ATCC-6258), and Candida parapsilosis (ATCC-22019) were investigated.
4/5/2023 5:38:45 AM +00:00