Flow injection-spectrophotometric determination of cresol compounds in water by reaction withp-aminophenol

A spectrophotometric method has been developed for the simultaneous determination ofo-cresol andm-cresol in water by reaction withp-aminophenol (PAP). Three different methodologies have been assayed; (i) batch analysis, after reaction in an alkaline medium in the presence of dissolved molecular oxygen as oxidizing agent, (ii) a stopped-flow procedure, carried out in the presence of KIO₄ and (iii) a flow injection method based on the same approach. The batch procedure requires 22 min for the full development of colour witho-cresol and 12 min form-cresol. In the stopped-flow mode, using KIO₄ and a reaction time of 12 min, better sensitivity can be obtained for both compounds and limits of detection of 10 g 1^–1 foro-cresol and 30 g 1^–1 form-cresol were found. The flow injection method has a lower sensitivity but permits more than 80 injections per hour. Based on the different maximum absorbance wavelengths obtained for the reaction products of PAP witho-cresol (614 nm) andm-cresol (632 nm), both compounds can be simultaneously determined in water samples and recoveries of 90 to 115% were found in spiked water samples of different types.     

Polarographlc analysis for corticosteroids: Part 5. Reduction mechanism of halogen-containing corticosteroids and analysis of some preparations

In fluprednisolone and chloroprednisone acetate, the polarographic reduction of the carbon—halogen bond in position 6 occurs first. The carbanion—enolate formed is reduced at the dropping mercury electrode at more negative potentials than the conjugate acid. Controlled potential electrolysis at a mercury pool electrode where the carbanion—enolate can be protonated, yields the unsaturated ketone. Polarographic reduction of clobetasol-17-propionate and of clobetasone-17-butyrate results in cleavage of the C—Cl bond in the side-chain. This process is followed by reduction of the α,β-unsaturated ketone in the A-ring. Analytical methods for the determination of these compounds in ointments, creams and eye/ear drops gave results with standard deviations of 1–2%.     

Reagentless system for sulphite determination based on polyaniline

A new reagentless system for sulphite (or sulphur dioxide) determination is reported based on the use of an organic conducting polymer, polyaniline, and its absorbance variation at 550 nm, depending on the sulphite concentration. After chemical polymerisation of aniline a very thin film of polyaniline is obtained. Although the response is not fully reversible, each film can be used for at least 10 measurements for low analyte concentrations (up to 0.5 mg l⁻¹) and five measurements for higher sulphite concentrations. Moreover, the reproducibility, ease of preparation and low cost of the films, permit the use of a new disposable system for each measurement. When the change in absorbance at 550 nm was measured for 210 s (stabilisation time), the system showed a linear response, which ranged from 0.025 to 1.50 mg l⁻¹ of sulphite. A theory with regard to the reaction mechanism between the polyaniline films and sulphite is also proposed. The system was applied to sulphite determination in wine samples and the results were in agreement with those obtained by the Official Method of Analysis (iodometric titration).     

Chlorination of α-sulfonyl carbanions with hexachloroethane: A novel preparation of α-halosulfones

The cyclic sulfones1,2, and3 are lithiated in benzene with n-butyllithium. Lithiation is demonstrated to lead to α-mono, α,α′-di and/or α,α-di and α,α,α′ trimetallation. The lithiated sulfones are chlorinated with hexachloroethane (HCE). Some mechanistic aspects of the reaction of the lithiosulfones with vicinal dihalides are discussed.     

On the thin cell method in time domain spectroscopy

A simple physical picture is given of Fellner-Feldegg's thin cell method in time domain spectroscopy. From this picture an accurate analytical relation is derived for the total reflection coefficient.     

A low-cost non instrumental method for semiquantitative determination of mercury in fish

A non instrumental method for the semiquantitative determination of mercury in fish is described. The sample is acid digested and the mercury vapor released after chemical reduction with SnCl2. The mercury vapor is then collected on a detecting paper covered with an emulsion of Cu2I2, 3% carboxymethylcellulose and MgCl2 as moistener agent. The colored Cu2[HgI4] complex is formed and the color intensity is proportional to the mercury concentration in the original sample. Parameters such as sample mass/digestion solution volume ratio, emulsion composition, paper covering technique, carrier gas flow were investigated. Comparative studies using CVAAS and digital color analysis after scanning the papers confirmed the applicability of the method to real samples.     

Organometallic reactions of α-haloimines as a useful tool in organic synthesis

The reaction of organometallic reagents, e.g. alkyllithiums, cuprates and alkylcoppers, with α-haloimines gave selectively a variety of synthetically useful reactions, including coupling to 1,4-diimines, homologation, and production of heterocycles.     

SOLVENT-INDUCED PHOTOREVERSIBLE REACTIONS OF C-PHYCOCYANIN FROM SYNECHOCOCCUS SP.

Abstract— C-phycocyanin from Synechococcus sp. ( Anacystis nidulans ) shows photoreversible absorption changes when dissolved in buffer containing 75% ethylene glycol (vol/vol). Irradiation with red light (638 nm) causes a 7.5% decrease in absorbance around the absorption maximum (620 m), while the absorbance around 500 nm increases. Subsequent irradiation with green light (500 nm) partially reverses this change. Final photoreversibility at around 620 nm amounts to ca. 2.5% of the maximum absorbance. These reactions are ascribed to two interconvertible species PC_r and PC_g, the former with a higher absorbance in the red. the latter in the green. The rate of dark reversion from PC_g to PC_r is strongly enhanced by ferricyanide. It is proposed that with this reagent, dark reversion occurs via an oxidized form of PC_g. Furthermore, ferricyanide in the presence of ethylene glycol is capable of reversibly oxidizing part of the chromophores of C-phycocyanin, presumably to a radical. In the absence of ethylene glycol, however, ferricyanide causes total irreversible bleaching of the pigment in the dark. The induced photoreversibility of C-phycocyanin is ascribed to the perturbing action on the protein structure by ethylene glycol in high concentrations. This solvent proved the most suitable perturbant of several compounds tested.     

The Interaction of Walsh-Orbitols in Diademane and Related Hydrocarbons

To obtain further information concerning the interaction between Walsh-orbitols of ‘conjugated’ cyclopropane rings, the photoelectron spectra of the following compounds have been recorded: bicyclo[4.1.0]heptane 1 , cis- and trans-tricyclo[5.1.0^{3, 5}]octane 2, 3 , diademane 4 , trans-pentacyclo[3.3.2.0^{2, 9}.0^{4, 10}, 0^{6, 8}]decan 5 and bicyclo[4.1.0]heptene-2 6 . The first bands in the PE.-spectra of these compounds have been assigned on the basis of a ZDO HMO-approximation. For 2 and 4 the value for resonance integral between linked 2p atomic orbitals of two adjacent eclipsed cyclopropane rings is found to be ?1.73 eV.     

Integrated lot-sizing and one-dimensional cutting stock problem with usable leftovers

This paper addresses the integration of the lot-sizing problem and the one-dimensional cutting stock problem with usable leftovers (LSP-CSPUL). This integration aims to minimize the cost of cutting items from objects available in stock, allowing the bringing forward production of items that have known demands in a future planning horizon. The generation of leftovers, that will be used to cut future items, is also allowed and these leftovers are not considered waste in the current period. Inventory costs for items and leftovers are also considered. A mathematical model for the LSP-CSPUL is proposed to represent this problem and an approach, using the simplex method with column generation, is proposed to solve the linear relaxation of this model. A heuristic procedure, based on a relax-and-fix strategy, was also proposed to find integer solutions. Computational tests were performed and the results show the contributions of the proposed mathematical model, as well as, the quality of the solutions obtained using the proposed method.