Efficient primer strand extension beyond oxadiazole carboxamide nucleobases

Two oxadiazole carboxamide deoxyribonucleoside analogues are described that can be incorporated and efficiently extended by Taq DNA polymerase. The primer strand extension beyond oxadiazole nucleoside analogues occurs at rates similar to the values observed for the canonical Watson-Crick base pairs irrespective of the template nucleobase. These distinctive chemical effects in DNA polymerase extensions are attributed to the smaller size and unique electronic properties of the oxadiazole nucleobase.     

Raman spectral study of the constitution and equilibria of nitric acid and d-nitric acid

From relative integrated intensity measurements of the symmetric stretching vibration of nitrate ion in nitric acid solutions (both HNO ₃ /H ₂ O and DNO ₃ /D ₂ O), the mass law concentration quotients, Q were obtained as functions of concentration. By extrapolation the limiting dissociation constants were estimated to be 24.4 and 15 respectively at 25°C. It is shown that this constant refers to a process in which the ion pair H ₃ O⁺ NO ₃ ^– is in equilibrium with the dispersed, solvated H ₃ O⁺ and NO ₃ ^– ions.     

Synthesis,spectroscopic studies,and x-ray crystallographic analysis of the organotin carbohydrate: 1,2∶3,4-di-O-isopropylidene-6-O-triphenylstannylmethyl-α-D-galactopyranose

The title organotin carbohydrate, C₃₁H₃₆O₆Sn, has been synthesized and its molecular structure has been determined in solution and in the solid state. NMR, infrared, mass and X-ray crystallographic techniques were used. The chiral molecules crystallize in the monoclinic space group P2₁ withZ=2. The triphenyltin and carbohydrate moieties are linked by a trans methylene-oxygen-methylene arrangement. The pyranosyl ring adopts a twist-boat conformation and the isopropylidene rings adopt different (half-chair and envelope) forms. Solution and solid-state conformations are similar as only three ¹³C shift values are greater than 2ppm; the ¹¹⁹Sn value is 12 ppm.     

Metal-containing ditopic receptors for molecular recognition of diammonium cations

Two new ditopic receptors for α,ω-alkanediyldiammonium cations based on a tetraazamacrocyclic (cyclidene) nickel(II) complex bearing two crown-ether residues were synthesized. The studies of the host-guest interaction between the receptors and a series of α,ω-diammonium salts by NMR titration in acetonitrile-d₃ showed that 1:1 complexes are formed with K_assoc∼10³-10⁵ M⁻¹. Receptor 1 with benzo-15-crown-5 arms showed substantial selectivity in binding of trimethylene- and tetramethylenediammonium dications, and 1-2 orders of magnitude weaker binding of shorter (C₂) or longer (C₅ and C₆) diammonium cations. Receptor 2 with benzo-18-crown-6 arms showed higher affinity to all studied diammonium cations, but the recognition of the length of α,ω-diammonium cations was less pronounced.     

Graph and hypergraph models of molecular structure: A comparative analysis of indices

Eight series of molecular structures represented by molecular hypergraphs and molecular graphs are considered. A comparative analysis is performed for 23 integral topological and information theoretical indices for the graph and hypergraph models. For each series, the sensitivity is studied on both models, correlations are established for indices inside the models, and indices not correlating with each other are found. The results of this analysis showed that the sensitivity of most indices is higher in the hypergraph model. The total number of noncorrelated indices also increases in the latter model. Translated fromZhurnal Struktumoi Khimii, Vol. 39, No. 6, pp. 1163–1171, November–December, 1998.     

Mass spectra of substituted pyrrolidine-N-oxyl radicals

Electron impact mass spectra of 65 pyrrolidine-N-oxyl derivatives have been assigned on a ‘peak-to-subgraph’ basis. On average, 50% of the total ion current is represented by structurally significant fragments associated with the nitroxide group. Secondary fragmentation is, as a rule, of a minor importance (30%), and fragments due to functional groups other than NO^· seldom contribute more than 10% of the total ion current An enhanced specificity of fragmentation is observed when one or more of the 2,2, 5,5-methyl groups is replaced by a longer aliphatic chain or an aromatic group.     

Bestimmung von Tellur in Mikrogrammengen mit Hilfe der Simultankomparationsmethode

Zusammenfassung Ein Verfahren zur Bestimmung von Tellurspuren mit Hilfe der Simultankomparationsmethode wurde ausgearbeitet, das auf der Bichromat-Ferriin-Reaktion beruht. Ferriin wird von Tellur(IV) reduziert; dieser Prozeß wird von Bichromat induziert. Bei diesem Verfahren werden die Tellurspuren durch Natriumhypophosphitreduktion mit Arsen oder Selen als Träger abgeschieden, der Metallniederschlag wird mit Salpetersäure zu Tellur(IV) oxydiert, die zu untersuchenden Proben und die Standardreihe gleichzeitig gestartet und verglichen. Mit dieser Methode kann Tellur auch in Mikrogrammengen mit einem Fehler von weniger als ±10% bestimmt werden. Störend wirken nur die Pt-Metalle und Au(III).

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Determination of tellurium in microgram amounts with the aid of the simultaneous comparation method

Summary A procedure has been worked out for the determination of traces of tellurium with the aid of the simultaneous comparation method, and based on the bichromate-ferriin reaction. Ferriin is reduced by tellurium(IV); this process is induced by bichromate. In this procedure the traces of tellurium are precipitated by means of sodium hypophosphite-reduction with arsenic or selenium as carriers. The metal precipitate is oxidized to tellurium(IV) with nitric acid; the samples under investigation and the standard series are started at the same time and compared. By means of this method it is possible to determine tellurium, even in microgram amounts, with an error of less than ± 10%. Only the platinum metals and gold(III) interfere.

     

Novel radial oligothienyl silanes

A series of thiophene-based homologues with a silicon core surrounded by mono-, bi-, terthiophene, and their derivatives with alkylsilyl linkages has been prepared using hydrosilylation and Stille coupling methods.     

Proton-induced supramolecular dimerization of aminomethylbenzo-15-crown-5 accompanied by a covalent dimerization of cyanoborohydride anion

Reductive amination of 4′-formyl[benzo-15-crown-5] with sodium cyanoborohydride in the NH₄Ac/MeOH medium followed by acid addition and extraction with CHCl₃ unexpectedly lead to the isolation of the salt (B15C5-CH₂-NH₃)⁺-(H₃BCNBH₂CN)⁻ with an unusual dicyanodiborohydride anion. The self-complementary 4′-ammoniomethyl[benzo-15-crown-5] cation was found to exist as a supramolecular dimer in the solid state, acetonitrile solution, and gas phase as revealed by X-ray crystallography, NMR and mass spectrometry, respectively.     

A simple procedure for the quantitative microdetermination of rhamnose

Summary A simple spectrophotometric procedure for microdetermination of rhamnose is described. It is based on breakdown of the sugar with sulphuric acid followed by treatment withp-hydroxydiphenyl. The coloured product is measured spectrophotometrically at 560 nm. A linear relationship exists between the amount of rhamnose (10-0g–) and the absorbance. The method is recommended for determination of rhamnose in samples containing rhamnose, different neutral sugars, amino-sugars, sugar alcohols, uronic acids, and muramic acid.

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Zusammenfassung Ein einfaches spektralphotometrisches Verfahren zur Mikrobestimmung von Rhamnose wurde beschrieben. Es beruht auf der Spaltung des Zuckers mit Schwefelsäure und nachfolgender Behandlung mit p-Hydroxydiphenyl. Das gefärbte Reaktionsprodukt wird spektralphotometrisch bei 560 nm gemessen. Die Extinktion steht mit der Rhamnosemenge in linearer Beziehung. Das Verfahren wird für die Rhamnosebestimmung in Proben empfohlen, die verschiedene Neutralzucker, Aminozucker, Zuckeralkohole, Uronsäuren und Muramsäure enthalten.