New approach to calibrating conductivity meters in the low conductivity range

There is currently a major issue with the calibration of conductivity meters used for high purity water: the lack of availability of a reference material or reference methods for low conductivity ranges (conductivity below 1 S cm^–1 at 25.0 °C, resistivity >1 M cm at 25.0 °C). This paper describes the current status of conductivity measurements in high purity water. A new and improved approach, currently being investigated, should allow us to make the calibration of conductivity meters used for low conductivity ranges traceable to the SI.Milipore, Milli-Q and Elix are registered trademarks of Millipore Corporation.     

5-isobutyl-3-methyl-2-furancarbaldehyde,a new monoterpenoid from the essential oil of tagetes glandulifera schrank

The new monoterpenoid 5-isobutyl-3-methyl-2-furancarbaldehyde was isolated from Tagetes glandulifera Schrank and its structure confirmed by synthesis.     

Ester synthesis catalyzed by Mucor miehei lipase immobilized on magnetic polysiloxane-polyvinyl alcohol particles

Mucor miehei lipase was immobilized on magnetic polysiloxane-polyvinyl alcohol particles by covalent binding with high activity recovered. The performance of the resulting immobilized biocatalyst was evaluated in the synthesis of flavor esters using heptane as solvent. The impact on reaction rate was determined for enzyme concentration, molar ratio of the reactants, carbon chain length of the reactants, and alcohol structure. Ester synthesis was maximized for substrates containing excess acyl donor and lipase loading of 25 mg/mL. The biocatalyst selectivity for the carbon chain length was found to be different concerning the organic acids and alcohols. High reaction rates were achieved for organic acids with 8 or 10 carbons, whereas increasing the alcohol carbon chain length from 4 to 8 carbons gave much lower esterification yields. Optimal reaction rate was determined for the synthesis of butyl caprylate (12 carbons). Esterification performance was also dependent on the alcohol structure, with maximum activity occurring for primary alcohol. Secondary and tertiary alcohols decreased the reaction rates by more than 40%.     

Metal phosphonates applied to biotechnologies: a novel approach to oligonucleotide microarrays

A new process for preparing oligonucleotide arrays is described that uses surface grafting chemistry which is fundamentally different from the electrostatic adsorption and organic covalent binding methods normally employed. Solid supports are modified with a mixed organic/inorganic zirconium phosphonate monolayer film providing a stable, well-defined interface. Oligonucleotide probes terminated with phosphate are spotted directly on to the zirconated surface forming a covalent linkage. Specific binding of terminal phosphate groups with minimal binding of the internal phosphate diesters has been demonstrated. The mixed organic/inorganic thin films have also been extended for use arraying DNA duplex probes, and therefore represent a viable general approach to DNA-based bioarrays. Ideas for interfacing mixed organic/inorganic interfaces to other bioapplications are also discussed.     

Theoretical and experimental investigation of the effect of proton transfer on the (27)al MAS NMR line shapes of zeolite-adsorbate complexes: an independent measure of solid Acid strength

Assessing the degree of proton transfer from a Br?nsted acid site to one or more adsorbed bases is central to arguments regarding the strength of zeolites and other solid acids. In this regard certain solid-state NMR measurements have been fruitful; for example, some (13)C, (15)N, or (31)P resonances of adsorbed bases are sensitive to protonation, and the (1)H chemical shift of the Br?nsted site itself reflects hydrogen bonding. We modeled theoretically the structures of adsorption complexes of several bases on zeolite HZSM-5, calculated the quadrupole coupling constants (Q(cc)) and asymmetry parameters (eta) for aluminum in these complexes and then in turn simulated the central transitions of their (27)Al MAS NMR spectra. The theoretical line width decreased monotonically with the degree of proton transfer, reflecting structural relaxation around aluminum as the proton was transferred to a base. We verified this experimentally for a series of adsorbed bases by way of single-pulse MAS and triple quantum MQMAS (27)Al NMR. The combined theoretical and experimental approach described here provides a strategy by which (27)Al data can be applied to resolve disputed interpretations of proton transfer based on other evidence.     

Mechanistic study of thermal behavior and combustion performance of epoxy resins: I homopolymerized TGDDM

Tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM) undergoes homopolymerization on heating. Intramolecular reactions which compete with crosslinking favor the formation of cyclic structures with increasing thermal and fire resistance of the resin, whereas physical mechanical properties tend to decrease. The mechanism of thermal decomposition of TGDDM is studied by thermogravimetry, differential scanning calorimetry and thermal volatilization analysis with characterization of volatiles evolved and residue left. Thermal degradation of poly-(TGDDM) starts at 260°C with elimination of water from secondary alcoholic groups which is a typical pathway for epoxy resin degradation. Resulting unsaturations weaken bonds in the β-position and provoke the first chain breaking at allyl–amine and allyl–either bonds. With increasing temperature, saturated alkyl–ether bonds and alkyl carbon–carbon bonds are broken first, followed by the most stable alkyl–aryl bonds at T>365°C. The combustion performance of TGDDM is discussed on the basis of the thermal degradation behavior.     

Influence of structural changes on the ion selectivities of magnesium ionophores based on malonic acid diamides

In an investigation of octamethylene bis(malonic acid diamides) and their selectivities for magnesium, it was found that presence of secondary amides within the particular ionophore played a considerable role in the enhancement of magnesium selectivity. Similar effects in other ionophores, i.e. tris(malonic acid diamides), were thus systematically looked at with the help of selectivity measurements with the hope of optimizing the number of secondary and tertiary amides so as to improve the magnesium selectivity. The syntheses of several investigated tris(malonic acid diamide) isologues are equally reported.Deceased in November 1992     

Trinuclear heterobimetallic complexes with binucleating dithioxamides: stereoselective synthesis and solution behavior involving Pd-N bond rupture

Bischelate platinum(II) complexes of the type [Pt(H-R(2)-N(2)C(2)S(2))(2)] (H-R(2)-N(2)C(2)S(2)(-) = dialkyl-dithioxamidate) are ditopic receptors which, after coordination of the first Pd(eta(3)-allyl)(+) moiety, induce the orientation of the second palladium-allyl fragment. Thus, a series of trimetallic complexes of formula bis-[(eta(3)-allyl)-palladium(II)](mu-bis-dialkyl-dithioxamidate-platinum(II) kappa-S,S-kappa-S',S'-Pt-kappa-N,N-Pd-kappa-N',N'-Pd') has been prepared in which the allyl fragments are oriented toward the same side of the molecular plane. We have also prepared the trimetallic complex using a dithioxamide obtained from the racemic phenylethylamine. Only two isomers were produced in equimolar ratio: the racemate that has four homochiral alkyl substituents and the mesoform containing the meso-dithioxamide that has homochiral substituents on the same side of molecular plane. Under the effect of the temperature, the trimetallic Pd-Pt-Pd complexes undergo rapid allyl isomerization; the mechanism of the isomerization, which is similar to that found by us in an analogue Pt-Pd bimetallic complex, is discussed. The crystal and molecular structure of bis-[(eta(3)-allyl)-palladium(II)](mu-bis-[S]-phenylethyl-dithioxamidate-platinum(II) kappa-S,S-kappa-S',S'-Pt-kappa-N,N-Pd-kappa-N',N'-Pd') has been reported.     

THE CONTROL OF METABOLISM BY BLUE LIGHT IN Acetabularia mediterranea—II. SELECTIVE TRANSLATIONAL CONTROL AND DIFFERENTIAL DEGRADATION OF ENZYMES

Abstract— During prolonged continuous irradiation with red light the specific activity of uridine 5'-diphosphoglucose (UDPG) pyrophosphorylase (uridine 5'-triphosphate: glucose 1-phosphate uridylyl-transferase EC 2.7.7.9) decreased in Acetabularia mediterranea Lamouroux (=A. acetabulum (L.) Silva). Subsequent blue light restored the original activity within a comparatively short period of 3 to 4 days. Computer-aided quantitative evaluation of density labelling experiments showed that the synthesis of the enzyme was accelerated about four-fold during the period of activation by blue light. A similar increase in the rate of synthesis was found for hydroxypyruvate reductase (EC 1.1.1.81), a control enzyme that showed no blue light-dependent changes in the specific activity under these conditions. The increase in the rate of enzyme synthesis was caused by an overall stimulation of the cytosolic translation. Degradation of UDPG pyrophosphorylase was unaffected by blue light, while the half life of hydroxypyruvate reductase was shortened about two-fold compared to continuous red light. Thus, degradation of proteins appears to be selectively light dependent in Acetabularia.
Model calculations for enzyme amount and enzyme synthesis were carried out using the measurements of enzyme activity, rates of cytosolic protein synthesis, and degradation constants of the enzymes. Assuming that activities represented amounts of the given enzymes, these calculations indicated a selective activation of UDPG pyrophosphorylase synthesis by blue light since it did not coincide with the overall stimulation of protein synthesis in the cytosol, in contrast to hydroxypyruvate reductase.     

Structure du radical cyano-vinyle CH2=Ċ-CN Etude expérimentale et théorique

Résumé Tout d'abord, on montre par RPE que le radical CH₂=-CN possède à basse température une structure instable pliée et à température plus élevée une structure stable linéaire. Un calcul théorique sur ce radical ainsi que sur le radical butatriényle est en bon accord avec les résultats expérimentaux.

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The structure of the Cyano-Vinyl Radical CH₂=-CN experimental and theoretical study

First, it is shown by ESR that the radical CH₂=-CN at low temperature presents an unstable bent structure and at higher temperature a stable linear structure. A theoretical calculation on this radical and on the butatrienyl one is in good agreement with the experimental results.

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Zusammenfassung Aus ESR Messungen wird gefolgert, daß das Radikal CH₂=-CN bei tiefer Temperatur in einer instabilen gebogenen Struktur und bei höherer Temperatur in einer stabilen linearen Struktur vorliegt. Theoretische Berechnungen stehen sowohl für dieses als auch für das Butatrienyl-Radikal in guter Übereinstimmung mit experimentellen Daten.