Electrochemical investigations of amino acids at solid electrodes: Part I. Sulfur components: Cystine,cysteine, methionine

The electrochemical oxidation of sulfur amino acids has been investigated by ac measurements and cyclic voltammetry at solid electrodes (Au, vitreous carbon). Electrochemical oxidation proceeds first in the adsorbed state and second by diffusion at metal electrodes. Electrochemical oxidation is catalyzed by a labile metal oxide. At vitreous carbon electrode oxidation in the adsorbed state is only present in the case of methionine. XPS studies have shown the presence of

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as intermediate species. To explain the experimental results a reaction path is proposed.     

Photoinduced activation of molecular oxygen by various porphyrins,bis-porphyrins,phthalocyanines, pyridinoporphyrazins,and their metal derivatives

Aerobic irradiation of tetraphenylporphyrins, phthalocyanines, tetra-t-butylphthalocyanines, tetracarboxylphthalocyanines, tetrapyridinoporphyrazins and some of their metal derivatives with visible light (λ > 420 nm) give singlet oxygen by energy transfer and oxygen superoxide by electron transfer, but some of their Cu, Zn of Pt derivatives are efficient quenchers for superoxide formation.     

Distribution de la densite des electrons de valence dans Cu2As

The distribution of valency electron density in Cu₂As (C38) has been determined by Fourier synthesis using as coefficients the values ΔF = F_obs ? F_core (F_core corresponds to the structure factors of the inner orbitals). The bonding between the pyramidal-site copper atoms and the arsenic atoms is exposed, as well as the bonding between tetrahedral-site and pyramidal-site copper atoms.The structural evolution of the unit cell from the Cu₂Sb-type (C38) to the Fe₂P-type (C22) and Co₂P-type (C23) can be related to the metal-metalloid interaction. This interaction mainly involves the pyramidal-site metal atoms in the Cu₂Sb-type, and the tetrahedral-site metal atoms in the Fe₂P- and Co₂P-types.     

On-line sorbent extraction, preconcentration and determination of lead by atomic absorption spectrometry

A method for the quantitative preconcentration of lead based on an existing batch process was developed for implementation in a flow system including a flame AAS detector. Lead can be quantitatively preconcentrated as pyrrolidinedithiocarbamate or dithizonate on an activated carbon minicolumn. The chelates are eluted in methyl isobutyl ketone and introduced directly into the nebuliser-burner. An enrichment factor of 50 is typically obtained for a preconcentration time of 2 min (lead can be determined at concentrations between 15 and 400 ng/ml), which results in a throughput of ca. 25 samples per hr. The sensitivity achieved with the two reagents is similar, but the selectivity provided by APDC exceeds that of dithizone. Based on the results obtained in the determination of lead in reference materials (minerals and skim milk), the proposed APDC method is applicable to real samples.     

Correction of counting losses of the preloaded fil ter pulse processor

By adapting noise filtering to individual pulse intervals, the Preloaded Filter (PLF) pulse processor (1) combines high resolution with optimum throughput efficiency. As a consequence, its output pulse interval distribution contains strong non-random components which render conventional ADC dead-time correction an impossibility. Quantitative correction of dead-time and pileup losses of the PLF processor may be achieved, however, with the Virtual Pulse Generator (2), together with a new, distribution-independent method of measuring ADC losses which is based on a pulse counting technique.     

Synthesis of thiirane oximes from 3,4-dibromo-3-methyl-2-butanone oxime

2-(-Oximinoethyl)-2-methylthiirane was obtained by the reaction of 3,4-dibromo-3-methyl-2-butanone oxime with sodium sulfide. At the same time, the O-carbamoyl derivative of the ,-dibromo oxime was converted to the corresponding substituted ,-unsaturated oxime under the same conditions. Thiirane oxime, like its O-carbamoyl derivative, underwent the desulfuration that is characteristic for thirranes under the influence of tributylphosphine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 751–753, June, 1982.     

Dynamic light scattering,a probe of brownian particle dynamics

The principles and techniques of dynamic light scattering (DLS) are outlined and its application to the study of suspensions of interacting colloidal particles is discussed. We show how, under appropriate conditions, DLS can measure long-time collective and self-diffusion coefficients as well as study short-time motions (characterized by the cumulants). These theoretical considerations are illustrated by experimental data. Finally, we discuss the relevance of certain characteristic timescales to theories of the diffusion of interacting particles.     

Construction and analytical applications of an improved liquid-membrane electrode for salicylate

The construction and analytical applications of an improved liquid-membrane electrode for salicylate are described. Tests of various combinations of symmetrical tetraalkylammonium salicylates and solvents showed that the best liquid ion-exchanger was tetraoctylammonium salicylate in p-nitrocumene. Electrode response is Nernstian down to 2 × 10^?5 M. Major interferences are perchlorate and periodate; the working pH range is 6–9. The electrode is useful for direct potentiometric determinations of salicylate in pharmaceutical preparations.     

Theoretical treatment of the spectrophotometric titration of bivalent cations with complexon-iii and metal-specific indicators

It was derived theoretically that a sharp end-point of this spectrophotometrical titration is defined, in order of importance, by: 1. *K_C ? *K_I (numerically speaking, log$\text{*K}{}_{\mathrm{C}}\text{*K}{}_{\mathrm{I}}$ should be at least 4); 2. *K_I being large (numerically e.g. 10⁴-10⁵); this is already reached by choosing a high pH; 3. it being low; 4. m_t being as high as possible.     

Use of reference pools to compare the qualitative and quantitative determination of polychlorinated biphenyls by packed and capillary gas chromatography with electron capture detection. Part 1. Serum

Serum for reference pools of in vivo polychlorinated biphenyls (PCBs) was obtained from four goats that had received one dose (100 mg kg-1) of a selected technical Aroclor (AR) (1016, 1242, 1254 or 1260) and were allowed to recover for 30 d. These pools were used to assess the differences in an analytical method that determines and quantifies PCBs using packed-column gas chromatography (PCGC) (quantified on the basis of mean mass percent. data for grouped PCB peaks) and capillary-column gas chromatography (CCGC) (quantified on the basis of percent. composition data for specific congeners). With CCGC, results were statistically significantly different (p less than or equal to 0.0002) from results with PCGC for ARs 1016, 1242 and 1254 but not for AR 1260 (p = 0.23). When comparing these gas chromatographic methods using bovine serum spiked in vitro with the same ARs at 17-25 p.p.b., it was found that the methods were not statistically significantly different for any of the ARs (p = 0.30-0.92). Levels of serum PCB determined by the two methods for 12 persons, divided into two groups according to exposure, were compared using the paired t-test. Group 1 consisted of three persons with dietary and/or environmental exposure; one with dietary and/or environmental exposure in addition to occupational exposure dating back 20 years. Group 2 consisted of eight persons with recent occupational exposure.(ABSTRACT TRUNCATED AT 250 WORDS)