Flow analysis-spectrophotometric determination of L-Dopa in pharmaceutical formulations by reaction with p-aminophenol

A new method has been developed for the spectrophotometric determination of L-Dopa in pharmaceutical formulations. The method is based on the reaction between the open-chain quinone of L-Dopa, obtained in NaOH, and the benzoquinoneimine form of p-aminophenol, in the presence of KIO(4). The reaction product is determined at 574 nm by using both alternately procedures, one based on the stopped-flow and another on a flow injection approach. Under the best experimental conditions L-Dopa can be determined with a limit of detection of 52 ng/ml and a relative standard deviation of 0.2% for three replicate measurements of a solution containing 4 microg/ml.     

Solid-phase extraction preconcentration of 2,4-dichlorophenoxyacetic acid on silica with immobilized polyethoxylated isooctylphenol groups

Silica with immobilized polyethoxylated isooctylphenol groups (SiO ₂ -TX) is studied as an adsorbent for the solid-phase extraction preconcentration of pesticides based on chlorophenoxyalkanecarboxylic acids from aqueous solutions. It is demonstrated that 2,4-dichlorophenoxyacetic acid (2,4-D) is efficiently (up to 96%) extracted as an ion associate with cetyltrimethylammonium bromide (CTMAB) with SiO₂-TX in the pH range 8–10. The optimum CTMAB-to-2,4-D molar ratio is 200: 1. The capacity of SiO₂-TX to 2,4-D in the Henry region is 0.42 mg/g of adsorbent, and the distribution coefficients reach 9 × 10² mL/g. It is shown that 2,4-D is quantitatively eluted with 1–2 mL of acetonitrile, which allowed us to use the adsorbent in a preconcentration cartridge before determining pesticides by HPLC. The procedure allowed pesticides to be recovered from aqueous solutions in concentrations beginning from 0.025 mg/L.     

Spectrophotometric flow injection determination of formetanate and m-aminophenol in water after reaction with p-aminophenol

An automated procedure has been developed for the determination of formetanate and its metabolite m-aminophenol (MAP) in water samples. MAP can be selectively determined in the presence of formetanate by direct on-line reaction with p-aminophenol and spectrophotometric measurement of the absorbance at 576 nm in the presence of KIO(4), as oxidizing agent. The method has a limit of detection of 5 x 10(-7)M, it provides a recovery percentage from 95 to 104% and permits one to carry out 120 measurements/hr. The spectrophotometric determination of formetanate must be carried out after a previous hydrolysis to MAP. To determine formetanate in the presence of MAP, two steps are necessary. Firstly, the MAP content is selectively determined as has been mentioned above. After that, the sample is treated with 0.05M NaOH at 90' degrees C, to hydrolyze the formetanate to MAP, and then the sum of both is determined spectrophotometrically. The difference between the results obtained in each step gives the formetanate concentration. The developed procedure for the determination of formetanate provides a sensitivity of 1070 absorbance units mol(-1) l and a limit of detection of 1.9 x 10(-7)M, which corresponds to 50 mug/l of formetanate hydrochloride. The method has been applied to the analysis of natural water samples fortified with formetanate and MAP, and formetanate has also been quantitatively recovered in irrigation waters at a concentration level of 1.9 x 10(-6)M which corresponds to 500 mug/l. On the other hand, working in the stopped-flow mode, for a reaction time of 100 sec, the sensitivity of the formetanate determination can be increased to 4642 absorbance units mol(-1) l but the limit of detection remains of the order of 44 mug/l.     

Power frequency magnetic field exposure and gap junctional communication in Clone 9 cells

Exposure to a power-frequency magnetic field has been reported to produce a statistically significant inhibition of gap junctional communication (GJC) in Clone 9 cells that have been pre-stressed by treatment with low concentrations of chloral hydrate (CH) [C.F. Blackman, J.P. Blanchard, S.G. Benane, D.E. House, J.A. Elder, Double blind test of magnetic field effects on neurite outgrowth, Bioelectromagnetics, 19 (1998) 204-209]. This observation might provide mechanistic insight into the possible role of electromagnetic fields (EMFs) in the carcinogenic process, since cancer cells frequently show decreased or absent GJC, and tumor promoting chemicals have been observed to inhibit GJC. Magnetic field exposure conditions were 45 Hz, 23.8 microT rms + parallel DC 36.6 microT, for 30 min of exposure. The responses of Clone 9 cells to the GJC-inhibiting effects of the tumor promoter 12-O-tetradecanoylphorbol 13-acetate and the chemical CH were evaluated and compared to reported results [S.G. Benane, C.F. Blackman, D.E. House, Effects of perchloroethylene and its metabolites on intercellular communication in Clone 9 rat liver cells, J. Toxicol. Environ. Health, 48 (1996) 427-437]. Before magnetic field exposure, cells were exposed for 24 h to either 3 (nine experiments) or 5 mM (11 experiments) CH to produce GJC of 67% or 50%, respectively, relative to unexposed controls. GJC was assessed microscopically using the scrape-loading technique and a blinded protocol. No statistically significant effect was observed due to magnetic field exposure with either CH concentration.     

Indirect determination of Hg(II) based on reaction with metallic silver

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Thin-layer chromatographic separation of fluorescent amino acid derivatives of 5-isothiocyanato-1,3-dioxo-2-p-tolyl-2,3-dihydro-1H-benz[de]isoquinoline

Teile der Dissertationen von H. Görgen und J. Dörpinghaus, Med. Hochschule Hannover, 1978     

MODERN FRIEDEL–CRAFTS CHEMISTRY. XIV. ON THE CYCLIZATION OF SELECTED ARYL HYDROXYALKYL SULFIDES

Abstract

The feasibility of cycloalkylation reactions in the presence of Friedel–Crafts catalysts was demonstrated in a number of aryl hydroxyalkyl sulfides (1–5), and benzyl hydroxyalkyl sulfides (6–7). Treatment of compounds (1–7) with Friedel-Crafts catalysts gave diaryl disulfides, diaryl sulfides, arene thiols, chlorohydrins, aryl chloroalkyl sulfides, aryl alkenyl sulfides and cyclization products. It is noteworthy to mention that cyclization products were isolated only in cases where the hydroxyl group is linked to a tertiary carbon atom as in compounds 3 and 7.

A suitable reaction pathway is suggested to rationalize the formation of the various reaction products.     

Modern Friedel–Crafts Chemistry. Part 37. Efficient Syntheses of Some New Julolidines via Cyclialkylations of Heteroaryl Carbinols

A simple and convenient procedure for the synthesis of some novel alkyl‐substituted and aryl‐substituted julolidines is reported. Julolidines were smoothly synthesized in excellent isolated yields via Friedel–Crafts intramolecular alkylations of heteroarylalkanols in the presence of both Brønsted (PPA) and Lewis (AlCl₃/CH₃NO₂) acid catalysts. The precursors alkanols, 1a , 1b , 1c , 1d , 1e , 1f , 1g , 1h , 1i , were readily prepared both by reaction of selectively synthesized carboxylic acid esters and ketones with different Grignard reagents and also by reduction of the synthesized ketones with LAH. A plausible carbocation mechanism is proposed to account for the results. The structures of the compounds are established using both spectral and analytical data.     

Evolution of ground state nuclear shapes in tungsten nuclei in terms of interacting boson model

The tungsten nuclei ^180–190W are investigated within the framework of the interacting boson model using an intrinsic coherent state formalism. The Hamiltonian operator contains only multipole operators of the subalgebra associated with the dynamical symmetries SU(3) and O(6). The study includes the behavior of potential energy surfaces (BES’s) and critical points in the space of the model parameters to declare the geometric character of the tungsten isotopic chain. Some selected energy levels and reduced E2 transition probabilities B(E2) for each nucleus are calculated to adjust the model parameters by using a computer code PH INT and simulated computer fitting programme to fit the experimental data with the IBM calculation by minimizing the root mean square deviations. The ^180–190W isotopes lies in shape transition SU(3)-O(6) region of the IBM such that the lighter isotopes comes very clare to the SU(3) limit, while the behavior ones tend to be near the γ-unstable O(6) limit.