Spectrophotometric determination of α-naphthol, β-naphthol,and oxine in aqueous solution

Diazotized orthanilic acid reagent has been devised as a novel chromogen for the trace determination of α-naphthol, β-naphthol, and oxine in aqueous solution. The developed method is characterized by simplicity and rapidness and does not resort to either temperature control or solvent extraction.     

Ultrasound-assisted dispersive liquid–liquid microextraction for the determination of six pyrethroids in river water

A simple ultrasound-assisted dispersive liquid–liquid microextraction method combined with liquid chromatography was developed for the preconcentration and determination of six pyrethroids in river water samples. The procedure was based on a ternary solvent system to formatting tiny droplets of extractant in sample solution by dissolving appropriate amounts of water-immiscible extractant (tetrachloromethane) in watermiscible dispersive solvent (acetone). Various parameters that affected the extraction efficiency (such as type and volume of extraction and dispersive solvent, extraction time, ultrasonic time, and centrifuging time) were evaluated. Under the optimum condition, good linearity was obtained in a range of 0.00059–1.52 mg L⁻¹ for all analytes with the correlation coefficient (r²) > 0.999. Intra-assay and inter-assay precision evaluated as the relative standard deviation (RSD) were less than 3.4 and 8.9%. The recoveries of six pyrethroids at three spiked levels were in the range of 86.2–109.3% with RSD of less than 8.7%. The enrichment factors for the six pyrethroids were ranged from 767 to 1033 folds.     

Asymmetric synthesis of α,β-substituted β-aminoalkanamides and stereochemical determination

Highly enantiomerically enriched β-aminoalkanamides 12 and β-phenylaminoalkanamides 13 have been prepared by the addition reaction of α-lithiated 2-alkyl-2-oxazolines 9-Li, derived from optically active oxazolines 9, to N-cumyl nitrones 2. The relative stereochemistry of alkanamides 5 and 6 has been established by 1D-NOESY experiments carried out on the related pyrimidinones 7, whereas the absolute configuration of alkanamides 12 and 13 has been confirmed by an X-ray analysis.     

The thermodynamics of ionization of α-alanine in methanol + water mixtures and the determination of single ion thermodynamics

In order to understand the effect of solvents on the thermodynamic parameters of amino acids, the thermodynamic dissociation constants, k₁ and K₂, for the reactions

and

(where RH^± = α-alanine) have been determined pH-metrically in methanol + water mixtures. The measurements were carried out in dilute solutions and in the absence of neutral electrolytes to minimize the “salt effect” as far as practicable so that the “medium effects” on the dissociation constants of the α-alanine can be properly understood.The enthalpy values for reactions (1) and (2) (up to 44.14 wt% of methanol) have been determined calorimetrically. It has been observed that the conversion of α-alanine into cations and anions is favourable both from enthalpic and entropic considerations, so that the reverse reactions of (1) and (2) are spontaneous. Attempts have been made to interpret the thermodynamics properties of α-alanine in terms of hydrophilic and hydrophobic interactions and other structural changes of the solvent molecules.In order to get a better insight into the nature of specific solute-solvent interactions, we have analysed the results in terms of single ion values using the thermodynamic values from the present work and other relevant data from previous work in our laboratory.     

Spectrofluorimetric study and determination of desipramine in the presence of β-cyclodextrin

The native fluorescence intensity of desipramine was enhanced in the presence of β-cyclodextrin in aqueous solution. The inclusion complex formation between these compounds was studied by spectrofluorimetry. A stable complex with a 2: 1 stoichiometry of β-cyclodextrin to desipramine was formed (logβ₂ = 9.29 ± 0.01). In the presence of an optimum concentration of β-cyclodextrin, the fluorescence intensity was linearly proportional to desipramine concentration in the range of 0.1–100 μg/mL (7.2 × 10^?7?1.0 × 10^?4 M) with a limit of detection of 7 × 10^?8 M. The method was successfully applied to the detection of desipramine in its tablets.     

Orthogonal array optimization of ultrasound-assisted emulsification–microextraction for the determination of chlorinated phenoxyacetic acids in river water

Orthogonal array design (OAD) was utilized for the first time to optimize the experimental conditions of ultrasound-assisted emulsification–microextraction (USAEME) for determining chlorinated phenoxyacetic acids (CPAs) in river water samples. The use of ultrasound facilitates the mass transfer of CPAs from an aqueous phase into a water-immiscible organic extraction solvent (dichloromethane, DCM) without adding dispersive solvent to form numerous microdroplets. The water-immiscible extractant was collected by centrifugation, dried under low pressure, reconstituted in methanol–water mixture (1:1), and injected into a HPLC system for the determination of CPAs. The linear range was 2–1000 ng mL⁻¹ (2, 5, 10, 50, 200, 500 and 1000 ng mL⁻¹) for each analyte and the relative standard deviations of CPAs among the seven different concentrations were in the range of 1.5–17.0% (n = 3). The detection limits (signal-to-noise ratio of 3) of CPAs ranged from 0.67 to 1.50 ng mL⁻¹. The ranges of intra-day precision (n = 3) for CPAs at the levels of 5 and 200 ng mL⁻¹ were 3.6–11.9% and 5.3–9.5%, respectively. The range of inter-day precision (n = 3) at 5 and 200 ng mL⁻¹ were 1.4–7.7% and 8.5–12.2%, respectively. The applicability of USAEME for environmental analysis was demonstrated by determining CPAs in river water. The recoveries of CPAs from five-spiked river water samples at 10 and 200 ng mL⁻¹ were 96.3–112.5% and 94.8–109.4%, respectively. The maximum contaminant level (MCL) of 2,4-D in drinking water and the tolerance of residues in food for p-CPA are 70 and 200 μg L⁻¹, respectively, according to the US EPA regulations. These contaminant levels fall in the linear range investigated in this study. In addition, this USAEME method provided detection limits lower than their contaminant levels, which made USAEME an effective sample preparation method for determining organic environmental contaminants, such as CPAs, in river water samples with little consumption of organic solvent.     

Synthesis of β-carbolines from aldehydes and ketones via the α-siloxy α,β-unsaturated esters

We report an efficient method for the synthesis of β-carbolines from α-siloxy α,β-unsaturated esters, which are accessible from a variety of aldehydes and ketones.     

HPLC–MS determination of the oxidation products of the reaction between α- and β-pinene and OH radicals

Biogenic non-methane hydrocarbons such as isoprene, alpha-pinene, and beta-pinene, are emitted by forests in very large quantities. To evaluate the role of alpha- and beta-pinene and their contribution to the global production of trace gases and especially aerosol precursors, a study of the oxidation mechanism of alpha- and beta-pinene with hydroxyl radicals must be conducted.The degradation products of both monoterpenes with hydroxyl radicals were identified and quantified in a fast-flow reactor. The products were collected on a liquid-nitrogen trap coated with a 2,4-DNPH solution to which two internal standards (benzaldehyde-2,4-DNPH and tolualdehyde-2,4-DNPH) had been added. The collection method was based on the in situ conversion of aldehyde and/or ketone compounds to their 2,4-dinitrophenylhydrazone derivatives. The derivatives were analyzed by HPLC-MS using APCI(-). TIC chromatograms and mass spectral data for the various oxidation products are presented.For alpha-pinene, pinonaldehyde is the most important degradation product, with smaller amounts of acetone, formaldehyde, campholenealdehyde, and acetaldehyde. For beta-pinene, nopinone and formaldehyde are the most abundant products, of almost equal importance, whereas acetone and acetaldehyde are minor compounds.     

UHPLC method for the simultaneous determination of β-blockers, isoflavones, and flavonoids in human urine

A simple method using solid-phase extraction (SPE) and ultra high-performance liquid chromatography (UHPLC) for the simultaneous determination of β-blockers, isoflavones, and flavonoids in human urine is developed. A statistical central composite design and response surface analysis is used to optimize the separation of the analytes. These multivariate procedures are efficient in determining the optimal separation condition using resolutions and retention time as responses. A gradient elution using a mobile phase consisting of 0.05% trifluoroacetic acid in water and acetonitrile is applied on a Hypersil GOLD column within a short analysis time of 4.5 min. UV detection was used to monitor the analytes. The suggested method was linear in a concentration range from 0.04-20.00 μg/mL, depending on the compound. The limits of detection ranged from 8.9 to 66.2 ng/mL. The precision was lower than 2.74%, and the accuracy was between 0.01-3.65%. The Oasis HLB column, with the highest recoveries, is selected for the pre-concentration step. This present paper reports, for the first time, a method for the simultaneous determination of β-blockers, isoflavones, and flavonoids in human urine samples. Furthermore, the developed method can also be applied to the routine determination of examined compounds concentrations in human urine.     

A peroxidase-based method for the determination of dopamine, adrenaline, and α-methyldopa in the presence of thyroid hormones in pharmaceutical forms

The analytical properties of two commercial plant peroxidases isolated from horseradish roots and soybean hulls in the catalysis of the transformation of some catecholamines were demonstrated in the absence and presence of thyroid hormones (l-thyroxine and 3,3′,5′-iodothyronine). For the first time the reactions of dopamine, adrenaline, and α-methyldopa oxidation with H₂O₂ catalysed by horseradish peroxidase with the addition of l-thyroxine as the amplification agent were studied and proposed as the indicator reactions for the simple and rapid enzymatic determination of the indicated catecholamines in their concentration ranges 0.5-300, 4-300, and 100-400 μM, respectively. The catalytic activity of the enzyme (characterized by the reaction rate) was controlled spectrophotometrically. The optimum conditions for the indicator reactions were thoroughly characterized. The mechanism of the stimulatory effect of l-thyroxine on the oxidation of the catecholamines was discussed. The developed enzymatic procedures were successfully applied for the determination of dopamine, adrenaline, and α-methyldopa in some pharmaceutical forms.     

Ultrasonic extraction followed by sulfuric acid silica gel cleanup for the determination of α-hexachlorocyclohexane enantiomers in biota samples

Interest in the analysis of -hexachlorocyclohexane (-HCH) enantiomers as an alternative or complementary approach to elucidating isomer ratios of /-HCH has grown in recent years because it can provide useful information to evaluate the influence of different degradation and transformation processes. In this paper, a simple and rapid method for the determination of -HCH enantiomers in biota samples is described. The method developed consists of ultrasonic extraction, sulfuric acid silica gel cleanup, solid-phase extraction (SPE) column fractionation, and final determination with chiral high-resolution gas chromatography. Ultrasonic extraction greatly shortens the extraction process time, and the sulfuric acid silica gel and SPE cleanup perfectly remove lipids and other interference compounds in the lipid-rich samples. The method is found to be simple, less time-consuming, and easy to operate, thus providing a useful alternative method to assess the enantioselective breakdown of -HCH in biota system.     

Solvent effects in the reactivity of phenylethyl hydroperoxide, II. Reactivity and β-scission of α-phenylethoxy radicals in the solutions of α-phenylethylhydroperoxide

Efficient cleavage of -phenylethoxy radicals (HRO^.) was observed in CH₃CN at 304 K. From measurements of the quantum yields of product formation, it was calculated that      

Sensitive determination of 17β-estradiol in river water using a graphene based electrochemical sensor

In this study, a novel material for the electrochemical determination of 17β-estradiol using an electrode based on reduced graphene oxide and a metal complex porphyrin has been applied to environmental monitoring. The electrochemical profile of the proposed electrode was analyzed by differential pulse voltammetry, which showed a shift of the oxidation peak potential of 17β-estradiol to 150 mV in a less positive direction compared to the bare reduced graphene oxide electrode. DPV experiments were performed in PBS at pH 7.0 to determine 17β-estradiol without any previous step of extraction, cleanup, or derivatization, in the range of 0.1–1.0 μmol L⁻¹ with a detection limit archived at 5.3 nmol L⁻¹ (1.4 μg L⁻¹). The proposed sensor was successfully applied in the determination of 17β-estradiol in a river water sample without any purification step and was successfully analyzed under the standard addition method. All the obtained results were in agreement with those from the HPLC procedure.     

Determination of γ-hexachlorocyclohexane and its metabolites in biological samples from rat

We have determined γ-hexachlorocyclohexane (lindane) and its metabolites in urine, serum and feces samples from rats using HPLC-UV-Vis and confirmation of mass with matrix assisted laser desorption/ ionization-time of flight (MALDI-TOF) analysis. Samples were collected from rats treated orally with lindane (17.6 mg/kg; 1/5 of LD₅₀) or vehicle for 2 weeks. Lindane and metabolites were extracted from samples with hexane and analyzed. The HPLC–MALDI-TOF is highly sensitive to the point of detecting very low level (5 ppm) of lindane and metabolites. The HPLC-UV-Vis analysis confirmed the presence of lindane in urine (386–1652 ppm), serum (207–371 ppm) and feces (5–74 ppm). Control samples had no peak corresponding to lindane. MALDI-TOF analysis of urine and serum samples showed a major peak at 293 m/z, whereas feces showed a minor peak at 292–293 m/z, which were consistent with the peak obtained for standard lindane (293 m/z). Our data indicates that HPLC-UV-Vis–MALDI-TOF combo method is sensitive for detecting and quantifying lindane and its metabolites in serum, urine and feces. Our results further showed that minor quantities of lindane and metabolites were excreted through feces confirming that the main pathway for excretion of lindane and metabolites is through urine.     

Lifetime of the long-lived isomer of 236Np from α-, β- and electron-capture decay measurements

The half-life of long-lived ²³⁶Np, due to α, β and electron-capture decay, was found to be 1.55 × 10⁵ yr. Of all decays, 88% populate excited states in ²³⁶U and 12% populate levels in ²³⁶Pu. Lifetimes measured by growth of the ground states of ²³⁶U and ²³⁶Pu agree with values from corresponding γ de-excitations in these daughter nuclei. Therefore, nearly all the electron-capture decays populate the 6⁺ level of the ground-state band in ²³⁶U. Similarily, essentially all the β⁻ decay populates an analogous 6⁺ level in ²³⁶Pu, which de-excites through a previously unreported transition of 158.3 keV. If a very weak γ-ray at 894 keV can be ascribed to a level in ²³²U populated by β decay of ²³²Pa, its existence establishes a 0.2% α-branching decay in ²³⁶Np.     

Convenient and rapid synthesis of α-aminonitriles starting directly from nitro compounds in water

A distinct approach for the synthesis of α-aminonitriles has been discovered by three-component reaction of nitroarenes, aldehydes, and TMSCN using indium in dilute aqueous HCl at room temperature. The products were formed in high yields (86-96%) within a short period of time (5-20 min). This one-pot conversion consists of the following steps: (i) reduction of nitro compounds to amines, (ii) formation of imines from amines and aldehydes and (iii) addition of cyanide anion to the imines.     

Synthesis of Chiral Cyclohexenones from α-Campholenic,Fencholenic, and β-Campholenic Derivatives

Summary. Optically active dimethylcyclohexenones, potential building blocks for enantioselective syntheses of various naturally active substances, were prepared. These compounds were obtained by oxidation with KMnO₄/Pb(OAc)₄ or ozonolysis of the corresponding cyclopentenic precursors, followed by aldol condensation. During the course of the preparation intermediate diols and chiral polyfunctional carbonyl derivatives were separated and identified analytically.     

Syntheses of carbocyclic analogues of α-D-glucosamine, α-D-mannose, α-D-mannuronic acid, β-L-idosamine, and β-L-gulose

A versatile synthesis of orthogonally protected derivatives of carba-α-D-glucosamine, carba-α-D-mannose, carba-α-D-mannuronic acid, carba-β-L-idosamine, and carba-β-L-gulose from methyl α-D-mannoside is described. Our synthetic strategy utilizes the palladium-promoted Ferrier carbocyclization and persistent butane-2,3-diacetal protection to produce a key chiral cyclohexanone intermediate, from which all five carbasugar derivatives can readily be obtained.     

Frequency characteristic of series piezoelectric sensor and application to the determination of water in organic solvents

Theoretical consideration was proposed for the frequency response of a series piezoelectric sensor to the properties of liquid and verified experimentally. This kind of sensor has sensitive and selective frequency response to the permittivity and specific conductivity of solution with excellent stability, and was applied to the determination of micro-content of water in organic solvents. The detection limit is 0.01 g/L in dioxane.     

Direct synthesis of carbonyl compounds from THP ethers with IBX in the presence of β-cyclodextrin in water

Water, an environmentally friendly reaction medium, has been utilized for the oxidative deprotection of tetrahydropyranyl ethers 1 with IBX at room temperature in the presence of β-cyclodextrin to give the corresponding carbonyl compounds 2.