Development of an HPLC method with electrochemical detection of femtomoles of 8-oxo-7,8-dihydroguanine and 8-oxo-7,8-dihydro-2'-deoxyguanosine in the presence of uric acid

A selective method based on high performance liquid chromatography with electrochemical detection (HPLC-ECD) was developed to enable simultaneous detection of 8-oxo-7,8-dihydroguanine (8-oxoGua) and 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodGuo), products of DNA oxidative damage, in the presence of uric acid (UA), a strong interferent in their electrochemical detection. The method developed consists of HPLC isocratic elution with amperometric detection on a glassy carbon electrode, enabling a detection limit for 8-oxoGua and 8-oxodGuo lower than 1 nM in standard mixtures. Detection of low concentrations up to 25 nM of 8-oxoGua and 8-oxodGuo in the presence of UA in a 10⁴-fold higher concentration was achieved after one-step solid phase extraction (SPE). The method was tested with urine samples and it was possible to detect and quantify the presence of 8-oxoGua, and to confirm that UA was eliminated after uricase degradation and SPE. The LOD found in urine samples was about 80 nM, a value higher than in standard mixtures, due to the increase of background current in the urine matrix. The results presented here contribute to the development of a methodological approach to simultaneous determination of 8-oxoGua and 8-oxodGuo in urine samples.     

Corrosion Protection by Self-Assembly

The inhibition effect and properties of adsorption layers formed by molecule series ,-diphosphono-alkane on iron surface are investigated. A significant difference is obtained in inhibition effect between compounds having alkyl chains with odd and even numbers of carbon atoms; better protection can be achieved by use of diphosphonates containing odd numbers of methylene groups. The best corrosion inhibition could be attained with 1,7-diphosphono-heptane (1,7-DPH). It is found that a certain threshold concentration of the diphosphonate (c > 4 × 10^–4 M) is necessary to ensure sufficient inhibition. The influence of solution concentration on inhibition effect can be interpreted with the layer formation properties and the surfactant nature of molecules. A significant effect of the diphosphonate is appeared on the kinetic of anodic iron dissolution process. Diphosphonates act as anodic inhibitors, the inhibitor layer formation results in a passivation of the metal surface. Well-ordered self-assembled layer with high corrosion protection effect is obtained in aqueous solution of ,-diphosphonic acids. The self-assembly process takes a longer time, few days are necessary to reach the optimal organization of adsorbed organic layer. It is found that aqueous conditions are preferred for the protective layer formation. It is supposed that with simple chemical surface modification, i.e. with immersion of iron into the solution of alkane-diphosphonates, a new surface pre-treatment could be developed.     

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.

     

Fractal calibration in size-exclusion chromatography I. An introduction

The elution behaviour of different polymer-solvent systems in three types of organic columns for SEC has been compared and interpreted. The experimental data show that the classical universal calibration is not accomplished. Deviations from a unique curve are observed due to the binary and ternary interactions between the components of the system (solvent, polymer and gel) which results on secondary mechanisms accompanying the main pure or "ideal" SEC separation mechanism. Both, enthalpic and entropic effects are interpreted in terms of the swelling and crosslinking degrees of the gel packings, and are also related with the fractal characteristics of their surfaces, such as the fractal dimension and the available pore size. Moreover, a relationship between the fractal dimension of the pore surface and the chromatographic distribution coefficient is proposed.     

Accurate double many-body expansion potential energy surface for triplet H3+. II. The upper adiabatic sheet (2(3)A')

We report on a global potential energy hypersurface for the upper sheet of the lowest triplet state of H3+. The analytic representation is based on the double many-body expansion theory. The ab initio data points, calculated with a large cc-pV5Z basis, are represented with a root mean square deviation of only 5.54 cm(-1) in the energy region below the H(+)+2H(2S) dissociation threshold. The quasi-bound vibronic states supported by this surface have also been calculated.     

Photochemistry of condensed isoxazolines

Summary The condensed bridged isoxazolines4 are rearranged on irradiation with a low-pressure mercury lamp exclusively into condensed derivatives of tetrahydropyridine5. The selectivity of the rearrangement is due to a stabilization of the biradical8 by the overlap of the radical-electrons with -electrons of the C=C double bond and the heterocyclic ring. Quantum yields of the photorearrangement, established from the consumption of the starting materials4, were determined.

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Photochemie kondensierter Isoxazoline

Zusammenfassung Die kondensierten überbrückten Isoxazoline4 werden durch Bestrahlen mit einer Niederdruckquecksilberlampe ausschließlich zu kondensierten Tetrahydropyridinderivaten (5) umgelagert. Die Selektivität der Umlagerung beruht auf der Stabilisierung des Diradikals8 durch Überlappung der ungepaarten Elektronen mit -Elektronen der C=C-Doppelbindung und des Heterocyclus. Aus dem Verbrauch an Ausgangsmaterial (4) wurden Quantenausbeuten der Photoumlagerung bestimmt.

     

Photoinduced metalation of nonactivated C-Cl bonds with samarium diiodide: synthesis of alkenes with high (Z)-selectivity through beta-elimination reactions

[reaction: see text] The photoinduced metalation of nonactivated C-Cl bonds of O-acetyl chlorohydrins is promoted by samarium diiodide. As a result of this, beta-elimination of O-acetyl chlorohydrins is achieved, affording the corresponding (Z)-alkenes with total or high stereoselectivity.     

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.