Flow-injection spectrofluorimetric determination of ethylenethiourea

A flow-injection configuration is proposed for the fluorimetric determination of ethylenethiourea. The procedure is based on the inhibitory effect of ethylenethiourea on the oxidation of thiamine to thiochrome by mercury(II). A linear calibration graph was obtained between 0.1 and 2.0 μg mL^–1, with a sampling rate of 40 samples per hour and a relative standard deviation of about 1.11%. The usefulness of the method was tested for the determination of ethylenethiourea residues in water, milk, potatoes, pear, grape and apple. Received: 26 January 1998 / Revised: 6 April 1998 / Accepted: 9 April 1998     

Serum estradiol measurement by solid-phase chemiluminescence immunoassay and direct radioimmunoassay

Estradiol017β is determined in serum extracts by solid-phase chemiluminescence immunoassay. The results are compared with those obtained from unextracted serum in routine conditions with a commercial radioimmunoassay (r.i.a.) kit. For the chemiluminescence procedure, a purified monoclonal antibody to estradiol-6-carboxymethyloxime/bovine serum albumin and the homologous chemiluminescent marker conjugate estradiol-6-carboxymethyloxime aminobutylethylisoluminol are used. Bound and free ligand are separated by washing and simple centrifugation. Results obtained by the chemiluminescence assay (y) and by r.i.a. (x) on 170 serum specimens from women during ovulation induction showed good correlation (y = 1.01x ? 16 with r = 0.95). The methods are similar in selectivity, detection limit (ca. 10 ng l^?1) and precision (interassay relative standard deviation, 8–13%).     

Possible Role of the Iron Coordination Sphere in Hemoprotein Electron Transfer Self-Exchange: (1)H NMR Study of the Cytochrome c-PMe(3) Complex

The rates of self-exchange electron transfer in the trimethylphosphine complex of cytochrome c have been measured by an NMR technique over a large range of ionic strengths. The rate constant is 1.56 x 10(4) M(-)(1) s(-)(1) at 23 degrees C (&mgr; = 0.34 M) at pH 6.9. Dependence on ionic strength of the rate constant is treated by van Leeuwen theory. Extrapolation of the rate constant to infinite ionic strength gives a rate constant of 3.9 x 10(5) M(-)(1) s(-)(1). This rate constant is compared with others reported for myoglobin and cytochrome b(5)(). The values for these systems range over 2 orders of magnitude with myoglobin-PMe(3) < cytochrome b(5)() < cytochrome c-PMe(3) < cytochrome c. Analysis of the data in terms of Marcus theory gives a reorganization energy, lambda, for self-exchange of 0.75 eV mol(-)(1) for cytochrome c-PMe(3). Substitution of Met-80 by PMe(3) appears to influence only weakly the rearrangement barrier to electron transfer.     

On triazoles. VII Synthesis of novel tri- and tetracyclic ring systems

The ring-closure of the 5-amino-1-(2-aminophenyl)-3-methylthio-1H-1,2,4-triazole derivatives 3 and 4 with different simple and cyclic C₁ components lead to the formation of 1,2,4-triazolo[1,5-α]-1,3,5-benzotriazepines 5–6 , their 4,5-dihydro- 7 , different 5-spiro-homocyclic- 8–13 , and 5-spiro-heterocyclic- 14-15 analogues. The structure of the compounds obtained was proved with the use of their ir, uv, ¹H-nmr and ¹³C-nmr spectra.     

Thermal analysis of the interaction of phosphorite with condensed phosphates of calcium

The thermal reactions between Maardu (Estonia) phosphorite and acidic phosphates were investigated. TG, DTG and DTA of mixtures with H₃PO₄, Ca(H₂PO₄)₂ · H₂O, Ca₂P₂O₇ and [Ca(PO₃)₂]_n in different molar ratios showed a maximum mass loss when the CaO P₂O₅ value was 2. The main temperature ranges of the mass losses were determined. The probable reactions relating to the mass losses are given on the basis of the thermal curves and IR spectra.

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Zusammenfassung Die thermische Reaktion zwischen Phosphorit aus Maardu (Estnien) und sauren Phosphaten wurde untersucht. TG, DTG und DTA von Gemischen mit H₃PO₄, Ca(H₂PO₄)₂ · H₂O, Ca₂P₂O₇ und [Ca(PO₃)₂]_n in verschiedenen molaren VerhÄltnissen zeigten den grö\ten Massenverlust bei dem VerhÄltnis von CaO P₂O₅=2. Die wichtigsten Temperaturbereiche der Massenverluste wurden bestimmt. Die den Massenverlusten zugeordneten wahrscheinlichen Reaktionen werden aus den erhaltenen thermischen Kurven und IR Spektren ermittelt.

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Résumé Etude de l'effet thermique lié à la réaction entre la phosphorite de Maardu (Estonie) et les hydrogénophosphates. Etude par TG, TGD et ATD de mélanges de H₃PO₄ avec Ca(H₂PO₄)₂ · 2 H₂O, Ca₂P₂O₇ et [Ca(PO₃)₂]_n réalisés avec différents rapports molaires; mise en évidence d'une perte de masse maximale pour le rapport CaO P₂O₅ égal à deux. Détermination des principaux domaines de température où s'effectuent les pertes de masse. On donne les réactions probables correspondant aux pertes de masse en s'appuyant sur les courbes d'analyse thermique et spectres infrarouges.

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() . TG, DTG DTA H₃PO₄, Cc(H₂PO₄)₂. H₂O, Ca₂P₂O₇ [Ca(PO₃)₂] _n , CaOP₂O₅ 2. . , .

     

Dissociation and rate constants of some human liver alcohol dehydrogenase isoenzymes.

ADH from human liver forms binary complexes with NADH, associated with a blue shift of the peak of the fluorescence emission of NADH. The wavelength shift is the same for all isoenzymes but the accompanying intensification of the fluorescence is different. The fluorescence is further increased by the formation of the very tight ternary enzyme-NADH-isobutyramide complexes. These properties are similar to those for the horse liver ADH, as well as the molecular weight of E=40 000 per active site of the dimer molecule (EE). "Stopped-flow" determined velocity constants (ER in equilibrium E+R) were found to be in good agreement with ethanol activity constants previously determined by activity measurement, confirming the validity of the ordered ternary complex mechanism also for the human ADH. No single isoenzyme activity as high as that reported by Mourad and Woronick or Drum has been found.     

Complex study of nickel skeleton catalysts: V. Study of novel non-pyrophoric nickel skeleton catalysts by derivatograph

The structure and properties of non-pyrophoric skeleton catalysts prepared from NiSi, NiAlSi, NiMg and NiZn alloys have been studied—apart from other thermal methods—by means of the derivatograph.Our experimental results have contributed to the explanation of the non-pyrophoric behaviour of these catalysts. We demonstrated that the desorption of the hydrogen content in our catalysts is not accompanied by the oxidation of active nickel. This oxidation takes place only at higher temperatures, above 200°C, at a rate proportional to the amount of active nickel.Other constituents of the catalysts (adsorbed water, hydroxide content) were also determined from the experimental data. The outstandingly high Mg(OH)₂ content of the NiMg catalyst indicates that its structure is dissimilar: Mg(OH)₂ also acts as support for the catalyst.     

Preparative Droplet Counter-Current Chromatography for the Separation of the New Nor-Seco-Triterpene and Pentacyclic Triterpenoids from Qualea Parviflora

The methanolic extract of the bark of the medicinal plant Qualea parviflora (Vochysiaceae) contains new nor-seco-triterpene and pentacyclic triterpenoids. They were separated in a preparative scale using droplet counter-current chromatography. The optimum solvent used was composed of a mixture of CHCl₃/MeOH/H₂O (43:37:20, v/v) in the descending mode and led to a successful separation of the new compound 28-nor-17, 22-seco-2α, 3β, 19, 22, 23-pentahydroxy-Δ¹²-oleanane, besides the known triterpenoids bellericagenin B, bellericaside B and arjunglucoside I . Identification was performed by ESI-MS, ¹H NMR and ¹³C NMR analyses.     

Electrospray ionization quadrupole time-of-flight and matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometric analyses to solve micro-heterogeneity in post-translationally modified peptides from Phoneutria nigriventer (Aranea, Ctenidae) venom

Previous studies of the fractionated venom of the Brazilian armed spider Phoneutria nigriventer, obtained by gel filtration, have demonstrated the presence of a fraction PhM, a pool of small peptides (up to 2000 Da) that provoke contractions in smooth muscle of guinea pig ileum. Initial attempts to sequence these peptides were largely unsuccessful because of the low purification yield and the fact that the majority seemed to be blocked at their N-termini. In the present work, analysis of this venom fraction by mass spectrometry has revealed the existence of a highly complex mixture of peptides with molecular weights corresponding to those observed for the muscle-active peptides previously described (800-1800 Da). These peptides appear to be a family of isoforms with some particular features. The amino acid sequences of 15 isoforms have been determined by tandem mass spectrometry (MS/MS) using both electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-Q/ToFMS) and matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry (MALDI-ToF/ToFMS). These molecules contain post-translational modifications such as proteolysis and C-terminal amidation, which combine to generate additional isoforms. All the isoforms sequenced in this study possess an N-terminal pyroglutamic acid residue. A search for sequence similarities with other peptides in databanks revealed that these peptides are structurally related to the tachykinins, a family of neuro-hormone peptides. The data obtained in this study will be essential for the subsequent steps of this research, the synthesis of these peptides and pharmacological characterization of their biological activity.