Kinetic spectrophotometric determination of amodiaquine and chloroquine

Abstract  

Two simple, sensitive, and selective spectrophotometric methods were developed for determining amodiaquine (AQ) and chloroquine (CQ) based on their oxidation with potassium iodate and potassium bromate, respectively. The initial rates of oxidation of AQ and CQ were monitored at 342 and 343 nm, the wavelengths of maximum absorptions of the two drugs. The various experimental parameters affecting oxidation reactions were thoroughly studied and optimized. Beer’s law was obeyed for 0.2–4.0 and 0.5–5.0 μg cm⁻³, with correlation coefficients of 0.9999 and 0.9998 (n = 6) and a detection limit (based on the 3S _b -criterion) of 0.04 and 0.06 μg cm⁻³ for AQ and CQ. The proposed methods were conveniently applied to determining AQ and CQ in pure and dosage forms.     

Analysis of captan, folpet, and captafol in apples by dispersive liquid–liquid microextraction combined with gas chromatography

A novel method was developed for the determination of captan, folpet, and captafol in apples by dispersive liquid–liquid microextraction (DLLME) coupled with gas chromatography–electron capture detection (GC–ECD). Some experimental parameters that influence the extraction efficiency, such as the type and volume of the disperser solvents and extraction solvents, extraction time, and addition of salt, were studied and optimized to obtain the best extraction results. Under the optimum conditions, high enrichment factors for the compounds were achieved ranging from 824 to 912. The recoveries of fungicides in apples at spiking levels of 20.0 μg kg⁻¹ and 70.0 μg kg⁻¹ were 93.0–109.5% and 95.4–107.7%, respectively. The relative standard deviations (RSDs) for the apple samples at 30.0 μg kg⁻¹ of each fungicide were in the range from 3.8 to 4.9%. The limits of detection were between 3.0 and 8.0 μg kg⁻¹. The linearity of the method ranged from 10 to 100 μg kg⁻¹ for the three fungicides, with correlation coefficients (r ²) varying from 0.9982 to 0.9997. The obtained results show that the DLLME combined with GC–ECD can satisfy the requirements for the determination of fungicides in apple samples. Figure Dispersive liquid–liquid microextraction (DLLME) coupled with gas chromatography–electron capture detection (GC–ECD) allows satisfactory determination of fungicides in apple samples     

Toward the synthesis and biological evaluation of hirsutide

Abstract  The present investigation deals with the synthesis of a N-methylated cyclotetrapeptide, hirsutide (2), by coupling of the dipeptide units Boc-l-phenylalanyl-l-N-methylphenylalanine-OH and l-valyl-l-N-methylphenylalanine-OMe followed by cyclization of the linear tetrapeptide fragment. The chemical structure was established on the basis of analytical as well as spectroscopic data. The newly synthesized cyclic peptide was subjected to pharmacological screening and found to be highly potent against the gram-negative bacteria Pseudomonas aeruginosa and Klebsiella pneumoniae at 6 μg cm⁻³. In addition, potent antihelmintic activity against the earthworms Megascoplex konkanensis and Pontoscotex corethruses at 1 and 2 mg cm⁻³, and potent cytotoxic activity against Dalton’s lymphoma ascites and Ehrlich’s ascites carcinoma cell lines with IC₅₀ values of 14 and 22 μM were also observed. Studies revealed that the pentafluorophenyl ester method employing a catalytic amount of N-methylmorpholine proved to be better for cyclization of the linear tetrapeptide unit. Graphical abstract        

On the protonation of dibenzo-18-crown-6

Abstract  The stability constant of the dibenzo-18-crown-6·H₃O⁺ cationic complex species dissolved in nitrobenzene saturated with water has been determined from extraction experiments in the two-phase water–nitrobenzene system and from γ-activity measurements. Various structures of protonated dibenzo-18-crown-6 are discussed. Graphical abstract        

(<Emphasis Type="Italic">S</Emphasis>)-(−)-α-Methylbenzylamine as chiral auxiliary in the synthesis of (+)-lortalamine

Abstract  (+)-Lortalamine was synthesised using (S)-(−)-α-methylbenzylamine as a chiral auxiliary. The stereochemistry of an intermediate compound was established on the basis of X-ray crystallography, allowing unambiguous assignment of the absolute configuration. Graphical abstract        

A combined extraction and DFT study on the complexation of K+ with valinomycin

Abstract  From extraction experiments in the two-phase water–nitrobenzene system and γ-activity measurements, the stability constant of protonated tetraethyl p-tert-butylcalix[4]arene tetraacetate in nitrobenzene saturated with water was determined. By using DFT calculations, the most probable structure of the tetraethyl p-tert-butylcalix[4]arene tetraacetate·H₃O⁺ complex species was derived. Graphical Abstract        

Design of a voltammetric immunosensor for determination of 1-nitropyrene

Abstract  In this study a design of an immunosensor for 1-nitropyrene is illustrated. First the response of 1-nitropyrene reduced at a glassy carbon electrode between 0 and −0.8 V was investigated with respect to pH and solvent. Then polyclonal anti-1-nitropyrene antibodies isolated from a rabbit antiserum were covalently bound to the surface of the glassy carbon electrode. This modified electrode was immersed in standard solutions or sample extracts for 5–15 min. 1-Nitropyrene was bound by the antibodies, accumulated and then analyzed at pH 6.5 in another supporting electrolyte by differential pulse voltammetry. Afterwards the immunosensor could be regenerated for the next measurement by rinsing with acetonitrile–water (40:60, v/v). A linear response was found between 20 and 100 ng/cm³. The limit of detection was 10 ng/cm³ and the intraday reproducibility of three immunosensors assembled during two months was between 4.5 and 10%. This sensor was applied to the analysis of 1-nitropyrene in air particulate matter and smoked tea. Graphical abstract        

Cholesterol complexes with some proton acceptors in benzene and toluene solutions

Abstract  Cholesterol complexes with tri-n-butyl phosphate, tri-n-octylamine, N,N-dimethylacetamide, and cyclohexanone in benzene and toluene solutions were studied using conventional IR spectroscopy. The spectra were recorded in the region of fundamental OH stretching (3,700–3,100 cm⁻¹) at 298 K. The experimental spectra were resolved into bands corresponding to the cholesterol monomer and particular oligomeric and complex species. The formation constants of complexes were determined from the-least squares plots of the linearized expressions of Bjerrum’s formation function. The stoichiometry of complexes was also identified in this way. The identification of the particular resolved bands was performed from their location, and from the dependence of their intensity on the cholesterol monomer and free base concentration. Graphical Abstract        

Inhibition of J-aggregation of <Emphasis Type="Italic">meso</Emphasis>-tetra(4-sulfonatophenyl)porphyrin by an ionic liquid with π-conjugated character

Abstract  UV–visible spectral observations indicate that the J-aggregation of protonated meso-tetra(4-sulfonatophenyl)porphyrin ([H₂TSPP]²⁺) under acidic conditions is completely inhibited by the π–π counteraction between 1-butyl-pyridinium tetrafluoroborate ([bpy]BF₄) and [H₂TSPP]²⁺. The studies also suggest that the intermolecular π–π force is of relative importance for the J-aggregates of [H₂TSPP]²⁺ and the intermolecular electrostatic force for the H-aggregates. Graphical Abstract        

Synthesis of 5-spirocyclohexyl-2,4-dithiohydantoin derivatives: a potential anti-leishmaniasis agent

Abstract  A series of spiro-dithiohydantoins were synthesized by heating a mixture of 5-spirocyclohexyl-2,4-dithiohydantoin potassium salt and 3-chloropropanoyl chloride. These compounds were synthesized and evaluated for their activity against five Leishmanial strains in the promastigote stage in vitro. Seventy-two hours inoculation of a variety of products gave an IC ₁₀₀ and average IC ₅₀ values of 1.25 and 0.376 mg/cm³ against all Leishmanial strains tested. Graphical Abstract   An erratum to this article can be found at     

Comparative study of screening methodologies for ochratoxin A detection in winery by-products

The worldwide contamination of winery by-products by mycotoxins may present a serious hazard to human and animal health. Mycotoxins are secondary metabolites of fungi with possible adverse effects on humans, animals, and crops that result in illnesses and economic losses. Mycotoxins are under continuous survey in Europe, but the regulatory aspects still need to be set up for winery by-products, which may be used in animal feed. The aim of this study was to implement a simple but reliable analytical methodology for ochratoxin A (OTA) quantification in grape pomaces in order to perform a survey of samples from the Douro Demarcated Region, Portugal. The method involved a unique preparation step, solvent extraction, followed by high-performance liquid chromatography (HPLC) with fluorescence (FL) detection. A comparative study was performed with two extraction solvents (ethyl acetate and methanol) as well as using extraction on an immunoaffinity column. The linearity range for OTA analysis was 0.05–23.5 μg L⁻¹ with a detection limit of 0.05 μg L⁻¹ and a precision (expressed by the coefficient of variation under repeatability conditions) of 0.4–14.7%. The percentage of recovery was on average 23.5 ± 3.6% (extraction with ethyl acetate) or 70.1 ± 2.5% (extraction with 70% methanol). Accounting for the recovery factor and the chromatographic detection limit, as well as the preconcentration factor, the limit of detection in grape pomaces is 0.04 μg kg⁻¹ (ethyl acetate extraction) and 0.33 μg kg⁻¹ (methanol extraction). Samples from 12 out of 13 sites in the Douro Demarcated Region showed OTA presence with concentrations not exceeding 0.4 μg kg⁻¹. Both developed methods for evaluation of OTA in grape pomace are simple but efficient. Figure Extraction of ochratoxin A (OTA) from grape pomaces allows simple but efficient quantification of OTA in winery by-products by HPLC-FL     

Chemistry of chromium bis-acetylide complexes

Abstract  Stable paramagnetic Cr(II) and Cr(III) bis(alkynyl) complexes of the type [trans(RC≡C)₂Cr(dmpe)₂] ⁿ⁺ (R = Ph, SiMe₃, SiEt₃, C≡C–SiMe₃ n = 0, 1) were prepared and characterised by NMR, cyclic voltammetry, EPR, magnetic measurements, and X-ray single-crystal diffraction studies. Graphical Abstract        

Ethylenebis(<Emphasis Type="Italic">N</Emphasis>-methylimidazolium) ditribromide (EBMIDTB): an efficient reagent for the monobromination of 1,3-diketones and β-ketoesters

Abstract  Ethylenebis(N-methylimidazolium) ditribromide, a stable crystalline solid, is easily prepared by reaction of the corresponding dibromide salt with bromine in n-hexane. 1,3-Diketones and β-ketoesters can be brominated chemoselectively to the corresponding α-monobrominated products by using this reagent at 0–5 °C. Under the same reaction conditions, diethyl malonate, ethyl cyanoacetate, and malonitrile were monobrominated at moderate yield. Graphical abstract        

Synthesis of benzohetero[3, 2-<Emphasis Type="Italic">a</Emphasis>]pyrimidines using cyclic β-keto lactone as a building block

Abstract  A novel method for the synthesis of 3-(2-substituted ethyl)-2-methylbenzohetero[3,2-a]pyrimidines in high yield (80–85%) was achieved, which involves a dihydrofuranone intermediate, readily obtained from β-ketolactone to 2-aminobenzoheterocycles. The major advantage of the methodology is the high yield and product purity. Graphical Abstract        

Cationic ring-opening polymerization of carbazolyl-containing epoxy monomers by triphenyl carbenium salts as thermal- and photolatent initiators

Abstract  Photoinitiated cationic polymerizations of various epoxy monomers bearing a carbazole moiety, 9-[3-(allyloxy)-2-(oxiran-2-ylmethoxy)propyl]-9H-carbazole, 9-[3-methoxy-2-(oxiran-2-ylmethoxy)propyl]-9H-carbazole, 9-[2-(oxiran-2-ylmethoxy)ethyl]-9H-carbazole, as well as a composition of 3,6-dibromo-9-(oxiran-2-ylmethyl)-9H-carbazole with 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate were investigated in bulk using triphenyl carbenium salts having anions such as BF₄ ⁻, SnCl₅ ⁻, and SbCl₆ ⁻. Dark polymerizations of the carbazolyl monomers in the presence of the initiators are studied. These photoinduced polymerization reactions give oligomers of degree of polymerization 4-22. The effect of the anion of the photoinitiator and polymerization time on the polymerization reaction is discussed. Graphical abstract        

Practical and general method for the direct synthesis of alkyl fluorides from alcohols under mild conditions: a reinvestigation

Abstract  In contrast to the results presented in a previous report, the direct conversion of alcohols to alkyl fluorides with triphenylphosphine and potassium fluoride in CCl₄/DMF under mild conditions failed. Graphical Abstract        

Biophysical,spectroscopic vis-à-vis biochemical investigation on DNA–metalloprotein interaction: a model study involving cobalt(II)-glutathione complex

Abstract  The interaction of cobalt(II)-glutathione (CoGSH) with deoxyribonucleic acid (DNA) has been studied by UV–vis, fluorescence, circular dichroism (CD), thin-film infrared (IR), and viscometric techniques. From the UV-spectroscopic method, binding constant (K _b) was determined and was found to be 2.3 × 10⁶ M⁻¹. In fluorimetric analysis, the quenching of fluorescence intensity of DNA bound to ethidium bromide (EB) was investigated. The Stern–Volmer quenching constant (K _sv) was also estimated from this study and was found to be 2.8 × 10⁶ M⁻¹at 37 °C. The solution CD spectra of DNA and DNA–CoGSH indicate that in each case, DNA exists in the ‘B’ conformation and suggested an intercalative binding mode. Thin-film IR data also reveal that DNA attains the ‘B’ family of conformations after interaction with CoGSH complex. The increase in DNA viscosity in the presence of CoGSH complexes is attributed to the lengthening of DNA helix due to intercalation. Graphical Abstract  The spectrophotometric, CD, thin film IR, viscometric and fluorimetric studies on the interaction of CoGSH with DNA indicated an intercalative binding mode with the retention of ‘B’ conformation of DNA.      

One-step regioselective green synthesis of 2,3-mannoepoxy-β-cyclodextrin under aqueous conditions

Abstract  A simple method for the straightforward regioselective synthesis of 2,3-mannoepoxy-β-cyclodextrin, which is a valuable precursor for further functionalization of β-cyclodextrin, is achieved under aqueous conditions without any organic solvents at a moderate yield. Graphical abstract        

A combined experimental and theoretical study on the complexation of Li<Superscript>+</Superscript> with valinomycin

Abstract  From extraction experiments in the two-phase water–nitrobenzene system and γ-activity measurements, the stability constant of the valinomycin–lithium complex in nitrobenzene saturated with water was determined. Further, the structure of the resulting complex was indicated by means of the density functional level of theory (DFT) calculations. Graphical abstract        

Excess molar volumes and viscosity deviations of the ternary system of 1-butanol + 2-butanol + 1,3-butanediol at 303.15 K

Abstract  The viscosity and density of ternary mixtures of 1-butanol + 2-butanol + 1,3-butanediol and the binary systems 1-butanol + 2-butanol, 1-butanol + 1,3-butanediol, and 2-butanol + 1,3-butanediol were measured at 303.15 K and atmospheric pressure over the entire range of compositions. Excess molar volumes V ^E and viscosity deviations Δη were obtained from the experimental results for the binary and ternary systems and fitted to Redlich–Kister’s and Cibulka’s equations in terms of mole fractions. The results obtained for the viscosity of liquid mixtures were used to test the semi-empirical relations of Grunberg–Nissan, Hind, and the two-parameter McAllister, Kendall, and Frenkel equations. The experimental data for the ternary system and the constituting binaries are analyzed to discuss the nature and strength of intermolecular interactions in these mixtures. Graphical abstract