Stochastic description of a reaction scheme with autocatalysis and saturation law

We apply the master equation and non-linear Fokker-Planck techniques to a model with autocatalysis and (Michaelis-Menten, Langmuir-Hinshelwood) saturation law and the minimal set of reactive steps for a well posed problem is given.     

Detection of conformational and net charge differences in DNA-protein complexes by quantitative electrophoresis on polyacrylamide-agarose copolymer gels

The Galactosidase repressor (GalR) of Escherichia coli modulates the expression of the gal operon by binding to two DNA operators, OE and O1. The OE and O1 elements are 16 bp pallindromic DNA sequences, differing in four of the base pairs. OE and O1 DNA fragments, both free and complexed with repressor, were analyzed by "quantitative gel electrophoresis". By the criteria of that method, applied to the linear Ferguson plots of both DNA fragments and the linear ranges of those of the DNA-GalR complexes, it was shown that the apparent size of DNA increases upon repressor binding. Moreover, this size increase is greater for the complex with the O1 operator than for the complex with the OE operator in the case that GalR is located in the center of a 155 bp DNA fragment. This is not the case when GalR is located in a peripheral position. By contrast with their size differences, the centrally located GalR-O1 and GalR-OE complexes appear to possess indistinguishable net surface charge densities as judged from the intercepts with the mobility axis. The larger size of the complex with centrally located O1 fragment, as compared with that bearing the OE fragment, is interpreted as being due to bending of the DNA-protein complex, since an authentically bent fragment of a plasmid with bent upstream activator sequence also exhibits a larger slope of the Ferguson plot, and thus the larger size, than predicted on the basis of its DNA chain length (bp).(ABSTRACT TRUNCATED AT 250 WORDS)     

Temperature induced structural changes of Cu(II) and Ni(II) complexes and their thermal decomposition

The paper discusses the structural changes of some Cu(II) and Ni(II) complexes during the heating and their influence upon the decomposition stoichiometry. The influence of the interactions inside of coordination polyhedra, bonding and stereochemical properties of the counter ions or molecules are discussed in this connection as well. The expressive influence of the plasticity or rigidity of the Cu(II) and Ni(II) coordination polyhedra, respectively, is emphasized.

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Zusammenfassung Es werden wÄrmebedingte StrukturverÄnderungen einiger Cu(II) bzw. Ni(II)-Komplexe sowie deren Einflu\ auf die Stöchiometrie der Zersetzung beschrieben. In diesem Zusammenhang wird auch ebenso der Einflu\ von Wechselwirkungen innerhalb des Koordinationspolyeders sowie von Bindungs- und stereochemischen Eigenschaften der Gegenionen oder -moleküle beleuchtet. Es wird der ausdrucksvolle Einflu\ der PlastizitÄt und HÄrte von Cu(II)- und Ni(II)-Koordinationspolyedern hervorgehoben.

     

Automated multiresidue analysis of pesticides in olive oil by on-line reversed-phase liquid chromatography-gas chromatography using the through oven transfer adsorption-desorption interface

A multiresidue, automated and rapid method for the determination of pesticide residues in olive oil is presented. The method employs the through oven transfer adsorption-desorption interface for the on-line coupling of reversed-phase liquid chromatography and gas chromatography. In this fully automated system, olive oil is directly injected with no sample pre-treatment step other than filtration. Methanol-water is used as eluent in the liquid chromatography pre-separation step. The selected liquid chromatography fraction containing the pesticides is automatically transferred to the gas chromatography. The liquid chromatography column flow during elution is different from the flow during the transfer. Using a flame ionisation detector, pesticide detection limits varied from 0.1 to 0.3 mg/l.     

Relativistic molecular wavefunctions: XeF2

A new method is presented to calculate binding energies and eigenfunctions for molecules, using the relativistic Dirac hamiltonian. A numerical basis set of four component wavefunctions is obtained from atom-like Dirac-Slater wavefunctions. A discrete variational method has been developed and applied to the linear XeF₂ molecule.     

Investigation on the chemistry of berbans—VII: Synthesis of 10,11-dimethoxy(depyrrolo)raunescine stereoisomers

Acyloxy-ketone rearrangement, proceeding by the action of base, has been observed in the case of ketone 2. By the reduction of ketones 2 and 3 with sodium boron hydride, new 10, 11-dimethoxy(depyrrolo)raunescine stereoisomers (5a–7a) have been prepared. Previously known alcohols with alloberban skeleton (12,13) have been similarly converted into tetracyclic raunescine stereoisomers (8a,9) by the oxido-reductive method. The stereochemistry of these compounds has been investigated by physical (¹H NMR, IR) and by chemical methods.     

Potentiometric studies of dithiooxamide with a sulphide-selective membrane electrode

The sulphide-selective electrode is applicable to the determination of dithiooxamide by titration with silver nitrate. The effect of the alkali content of the solutions on the reaction has been studied. The reaction products are silver sulphide, oxalic acid, and nitric acid. If the alkali concentration of the solution is lower than that equivalent to the acid formed during the titration, the amount of sulphide produced by hydrolysis decreases and the equilibrium potential is established more slowly.The determination is rapid and accurate in the presence of 1 M sodium hydroxide.     

Molecular orbital study of molecular nitrogen fixation

The model systems of molecular nitrogen fixation [N₂ + H]?, [N₂ + H]⁺, [N₂ + H]^?, [N₂ + H₂], [N₂ + H₂]⁺, and [N₂ + H₂]^? were studied by the semiempirical INDO method. The study was based on the formal analogy between the catalytic reactions and the photochemical, radical, and ionic reactions on the other side. Symmetrical and donor-acceptor properties of necessary catalytic systems were proposed using the dependence of energy characteristics and electron structure on reaction coordinate. On the basis of this MO study we have proposed the appropriate symmetry types of catalysts for each of acceptable models of nitrogen fixation. For one of the proposed systems there was realised a model MO computation with explicit inclusion of atoms of transition metals (Fe, V).     

Behavior and characteristics of biogenic amines, ornithine and lysine derivatized with the o-phthalaldehyde-ethanethiol-fluorenylmethyl chloroformate reagent

The stability and characteristics of the ornithine (Orn), lysine (Lys), putrescine (Put), cadaverine (Cad), 1,7-diaminoheptane (Diah), spermidine (Spd) and spermine (Spm) derivatives obtained with the o-phthalaldehyde (OPA)-ethanethiol (ET)-fluorenylmethyl chloroformate (FMOC) reagent has been investigated. The stoichiometry of the introduced, two-step derivatization process has been followed by photodiode array (DAD) and fluorescence (FL) detections, simultaneously, while the composition of derivatives was confirmed by on-line HPLC-electrospray ionization (ESI) MS measurements. Depending on the composition of the OPA reagents, in addition to the secondary amino group-containing Spd and Spm, under common aqueous conditions also Orn and Lys do react with FMOC resulting in derivatives of various compositions. Applying the OPA-ET reagent of increasing methanol (Met) content (38-80%, v/v) the formation of the FMOC group containing Orn and Lys derivatives could be considerably decreased. Optimum elution condition (18 min, including equilibration) was developed for the simultaneous quantitation of Orn, Lys, Put, Cad, Diah, Spd and Spm, in the presence of the rest of protein amino acids. The practical utility of the method was demonstrated by the analysis of mouse tissues. Average reproducibility of quantitations, characterized with the relative standard deviation percentages of fluorescence intensities and UV responses, in order of listing, proved to be 2.1% and 2.1%, respectively.     

Thermal and FTIR spectroscopic analysis of the interactions of aniline adsorbed on to MCM-41 mesoporous material

The adsorption of aniline on Na-AlMCM-41 synthesized by us has been characterized by infrared spectroscopy, temperature programmed desorption (TPD), and differential thermal analysis methods. Aniline would be mostly bound to the mesostructure through weak pi interactions. On the mesostructure containing adsorbed water, the co-adsorption of aniline could occur by weak hydrogen bonding through surface water molecules. For water, two possible modes of adsorption have been identified. Different associations between aniline and hydrated and nonhydrated mesostructures have been evaluated in order to favor the posterior in situ polymerization of adsorbed aniline.