Influence of substrate and product concentrations on the production of cyclodextrins by CGTase of Bacillus firmus,strain no. 37

The influence of substrate or product level on the initial velocity of cyclodextrin (CD) production by cyclodextringlycosyltransferase from a Brazilian isolate of Bacillus firmus was studied. Our results indicate that the product γ-CD is a stronger inhibitor to the reaction than β-CD. Small saccharides could also inhibit CD production, although to a lesser extent than the products, and maltose was the strongest inhibitor among small saccharides. Increasing substrate concentration resulted in greater reduction on enzyme activity for the formation of β-CD than for γ-CD. We modeled the kinetics of CD production with a set of four reversible reactions including the cyclization/coupling reaction that forms/opens CDs, and three disproportionation reactions. Our model on the initial velocity data explained well the substrate inhibition phenomenon. Kinetic parameters were determined by fitting the initial velocity data into our model.     

HPLC determination of urinary 2,4- and 2,6-toluendiamines as potential degradation products of polyurethane breast implants

Summary A reversed-phase HPLC method has been developed for the urinary determination of mutagenic 2,4- and 2,6-toluendiamines. These amines are degradation products of polyurethane, a material used to cover textured silicone breast implants. FMOC-Cl was used as fluorescent derivatising agent in order to obtain a limit of detection of 15 ng/ml in urine. Pre-treatment of urine samples was by liquid/liquid extraction and urine specimens of patients after surgury were analysed.     

Structural analysis of the conformational flexibility of tris(pyrazolyl)borate ligands and their analogues

Database analysis and molecular mechanics were used to determine the conformational flexibility of tridentate scorpionate ligands. The tris(pyrazolyl)methane and tris(pyrazolyl)borate ligands act like molecular vises, opening their tripodal structure for larger metals and closing around smaller metal ions. Tris(3-tert-butylpyrazolyl)methane has significant preference for larger metal ions than its unsubstituted parent compound. Tris(pyrazolyl)methanes and tris(pyrazolyl)borates have similar conformational flexibilities. Placing sterically hindered groups on the central carbon or boron has only a minor effect on the geometry of the tris(pyrazolyl)methanes and tris(pyrazolyl)borates. However, it does influence the flexibility of the ligands, particularly when they have to open far from their ideal geometry, which commonly occurs.     

Production of exocellular polysaccharide by azotobacter chroococcwn

Environmental conditions affect the production of extracellular polysaccharide by Azotobacter chroococcum ATCC 4412. Production of exocellular polymer from a variety of carbon sources depended on the air flow rate. A high sucrose concentration in medium (8%) markedly favored expopolysaccharide production, which reached 14 g/L in about 72 h. In cell suspensions incubated in the presence of 8% sucrose in a nitrogen-free medium, biopolymer final concentration of 9 g/L corresponds to 68 g/g biomass. Maximum efficiency of sucrose conversion into exopolysaccharide peaked at 70% for initial disaccharide concentration of 6%. High performance liquid chromatography and gas liquid chromatography of acid hydrolysates of the exopolymer revealed the presence of mannuronosyl, guluronosyl, and acetyl residues, but not neutral sugars. The infrared spectrum corroborated the presence of carboxylate anions and O-acetyl groups in the exopolymer. Though the presence of more than one kind of polysaccharide cannot be ruled out, these data suggest that, under the experimental conditions used in this work, only a type of alginate-like exopolysaccharide is produced by A. chroococcum ATCC 4412.     

Quantitative gas-liquid chromatography of iproniazid and iproclozide.

Analytically packed columns prepared with Versamid-930, Versamid-900, XE-60, and OV-225 as stationary phases were examined for quantitative gas-liquid chromatography of the potent monamine oxydase inhibitor (MAOI) drugs iproniazid and iproclozide. With the aid of chemically related substances as internal standards, response ratios were determined and linearities calculated by regression analysis. Using the 2-butyl analogs of compounds all four column systems permit quantitation of iproniazid and iproclozide with a percent standard deviation sigmaK of about 1% or less.     

Complex copper(II) fluorides. XV. The Ternary System BaF2?CuF2?ScF3

The liquid-solid phase diagram of the binary system BaF₂? ScF₃ is established by D.T.A. and radiocrystallography. Three fluorides are disclosed: Ba₃Sc₂F₁₂, Ba₅Sc₃F₁₉ and a cubic high temperature phase Ba_1?xSc_xF_2+x (x = 0.17), the structure of which derives from that of BaF₂. A solid solution between BaF₂ and ScF₃ is also evidenced at high temperature. The ternary system BaF₂? CuF₂? ScF₃ is investigated by radiocrystallography and an isothermal section at 670°C is given. It shows the existence of four phases: a complex quaternary fluoride Ba₁₀Cu₁₂ScF₄₇, two “polytypic” phases the structure of which derives from that of BaCuF₄ and a tetragonal solid solution Ba₅Sc_3?xCu_xF_19?x with 0 ≤ x ≤ 1.     

Electronic structure and spectra of fused n/m ring systems with one or two bridgehead nitrogen atoms

The semiempirical ASMO-SCF-CI method has been applied to study the electronic structures and ultraviolet absorption spectra of the 4-azapentalenyl anion, 4,8-diazapentalene and related azaderivatives. The agreement between observed and calculated transition energies is, in general, satisfactory. Chemical reactivity and assignment of the observed bands are discussed.

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Zusammenfassung Mit Hilfe einer semi-empirischen ASMO-SCF-CI Methode wurden Elektronenstruktur und UV Absorptionsspektren des 4-Azapentalenylanions, des 4,8-Diazapentalens und der entsprechenden Azaderivate studiert. Im allgemeinen ist die Übereinstimmung zwischen experimentellen und theoretischen Übergangsenergien zufriedenstellend. Die Zuordnung der beobachteten Banden und Reaktivitäten werden diskutiert.

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Résumé La méthode semi-empirique ASMO-SCF-CI a été appliquée à l'étude de la structure électronique et des spectres d'absorption U.V. de l'anion 4-azapentalenil, du 4,8-diazapentalene et de composés aza-derivés apparentés. L'accord entre les énergies de transition observées et calculées est, dans l'ensemble, satisfaisant. La reactivité chimique et l'attribution des bandes observées ont été discutées.

     

Complex formation equilibria between Ag(I) and thioureas in n-propanol

Complex formation equilibria between Ag(I) and thiourea or N-alkyl-substituted thioureas have been investigated in n-propanol by potentiometry at 10 °C intervals from 5 to 50 °C. Stepwise formation of tris-coordinated AgL_n (n = 1-3) complexes has been found for the majority of the ligands. ΔH and ΔS values for the complex formation reactions have been evaluated from the dependence of ln β_n on temperature. The alkyl-substituents affect the ligand affinities in different ways in relation with the coordination level n.The reactions are exothermic with few exceptions. Enthalpy favoured complex formation with negative dependence of ΔG on temperature (ΔS > 0) have been found.The enthalpy and entropy changes for the stepwise complex formation equilibria are correlated by two linear compensative relationships with the same isoequilibrium temperature 50-51 °C.     

2′‐De­oxy‐5‐propynyl­cytidine: a nucleoside forming two solid‐state conformations

The title compound, 4‐amino‐1‐(2‐deoxy‐β‐d ‐erythropentofuranosyl)‐5‐(prop‐1‐ynyl)pyrimidin‐2(1H)‐one, C₁₂H₁₅N₃O₄, shows two conformations in the crystalline state which differ mainly in the glycosylic bond torsion angle and the sugar pucker. Both mol­ecules exhibit an anti glycosylic bond conformation, with torsion angles χ = −135.0 (2) and −156.4 (2)° for mol­ecules 1 and 2, respectively. The sugar moieties show a twisted C2′‐endo sugar pucker (S‐type), with P = 173.3 and 192.5° for mol­ecules 1 and 2, respectively. The crystal structure is characterized by a three‐dimensional network that is stabilized by several inter­molecular hydrogen bonds between the two conformers.     

Direct immobilization of native yeast iso-1 cytochrome C on bare gold: fast electron relay to redox enzymes and zeptomole protein-film voltammetry

Cyclic voltammetry shows that yeast iso-1-cytochrome c (YCC), chemisorbed on a bare gold electrode via Cys102, exhibits fast, reversible interfacial electron transfer (k(0) = 1.8 x 10(3) s(-1)) and retains its native functionality. Vectorially immobilized YCC relays electrons to yeast cytochrome c peroxidase, and to both cytochrome cd(1) nitrite reductase (NIR) and nitric oxide reductase from Paracoccus denitrificans, thereby revealing the mechanistic properties of these enzymes. On a microelectrode, we measured nitrite turnover by approximately 80 zmol (49 000 molecules) of NIR, coadsorbed on 0.65 amol (390 000 molecules) of YCC.