Efforts to expand the genetic alphabet: identification of a replicable unnatural DNA self-pair

Six unnatural nucleotides featuring fluorine-substituted phenyl nucleobase analogues have been synthesized, incorporated into DNA, and characterized in terms of the structure and replication properties of the self-pairs they form. Each unnatural self-pair is accommodated in B-form DNA without detectable structural perturbation, and all are thermally stable and selective to roughly the same degree. Furthermore, the efficiency of polymerase-mediated mispair synthesis is similar for each unnatural nucleotide in the template. In contrast, the efficiency of polymerase-mediated self-pair extension is highly dependent on the specific fluorine substitution pattern. The most promising unnatural base pair candidate of this series is the 3-fluorobenzene self-pair, which is replicated with reasonable efficiency and selectivity.     

Highly regioselective construction of spirocycles via phosphine-catalyzed [3 + 2]-cycloaddition

A direct entry to spirocycles with low to moderate regioselectivity was achieved by triphenylphosphine-catalyzed [3 + 2]-cycloaddition of active exo-methylenecycles (1) and ethyl 2,3-butadienoate (2). The regioselectivity of the reaction was greatly improved by using the bulky tert-butyl ester of the 2,3-butadienoate (5). The regioselectivity of the reaction was further enhanced by using the tert-butyl 2-butynoate as the substrate. This protocol provided an efficient entry to the skeleton of spirocarbocycles, especially spiro[4.n]alkanes.     

Preparation and steric structure of 2-Alkoxy-2,5-dioxo-4,4-bis(trifluoromethyl)-7(8)-chloro-1,3,2λ5-benzodioxaphosphepins

The reaction of hexafluoroacetone with 2-alkoxy-6(7)-chloro-1,3,2-benzodioxaphosphorin-4-ones yielded 7-and 8-chloro-substituted 2-alkoxy-2,5-dioxo-4,4-bis(trifluoromethyl)-1,3,2λ⁵-benzodioxaphosphepines. Their steric structure was studied by single-crystal X-ray diffraction. The effect of fluorinated substituents on the crystal packing of the benzophosphepines was demonstrated. Hydrolysis of these compounds gave the corresponding 4-and 5-chloro-substituted 2-(2-hydroxyphenyl)-2-oxo-1,1-bis(trifluoromethyl)-ethanols; the structure of 2-(2-hydroxy-5-chlorophenyl)-2-oxo-1,1-bis(trifluoromethyl)ethanol was also proved by single-crystal X-ray diffraction.     

On the origin of the splitting of the second maximum in the radial distribution function of amorphous solids

The splitting of the second maximum of the radial distribution function of an irregular atomic packing is regarded as an indication of the amorphous state of a substance. This paper describes the splitting-forming atomic configurations using Delaunay simplices, representing chains of elementary configurations. It is shown that the splitting is formed of chains in which all simplices are nearly regular tetrahedra and quartoctahedra. Translated fromZhumal Struktumoi Khimii, Vol. 38, No. 1, pp. 78–88, January–February, 1997.     

Structure of aconifine

The structure of the new alkaloid aconifine, which has been isolated from the tubers and epigeal part ofAconitum karakolicum Rapcs. has been established on the basis of the results of chemical transformations and spectral characteristics. Some features of the selective acetylation of aconitine and aconine have been elucidated. Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 665–672, September–October, 1980.     

A CNDO/2 calculation of a rearrangement in cyclopentadienylsilane

The ground state geometry of cyclopentadienylsilane and the transition state geometry for SiH₃ group migration have been calculated by the CNDO technique, a semi-empirical version of the LCAO MO SCF approach.     

Liquid-liquid extraction in the absence of usual organic solvents: Application of two-phase aqueous systems based on a water-soluble polymer

Summary Capabilities of liquid-liquid extraction systems without organic solvents have been examined. Ternary poly(ethylene glycol)-inorganic salt-water systems have been proposed for extraction of complexes of metals with water-soluble organic reagents and inorganic ligands.Phase diagrams for such two-phase systems have been studied. The distribution of some inorganic ions and organic reagents in PEG 2000-ammonium sulphate systems has been examined at different pH values of the salt-phase. It is shown that the distribution coefficients are lower than unit for all the cations studied while reagents, containing aromatic rings, are extracted into the PEG-phase with distribution coefficients higher than one hundred. Conditions are reported which provide effective extraction of iron(III) in presence of several water-soluble photometric reagents. Extraction in the PEG 2000-ammonium sulphate-water system in presence of ammonium thiocyanate and sulphuric acid has been studied. Copper, zinc, cobalt, iron(III), indium, molybdenum(V) are extracted into the PEG-phase with high distribution coefficients.

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Flüssig-flüssig-Extraktion ohne übliche organische Lösungsmittel: Anwendung wäriger Zweiphasen-Systeme mit einem wasserlöslichen Polymerisat

Zusammenfassung Die Eignung von Flüssig-flüssig-Extraktions-Systemen ohne organisches Lösungsmittel wurde geprüft. Ternäre Systeme aus Polyethylenglykol-anorganischem Salz-Wasser wurden für die Extraktion von Metallkomplexen mit wasserlöslichen organischen Reagenzien und anorganischen Liganden vorgeschlagen.Die Phasendiagramme solcher Zwei-Phasen-Systeme wurden untersucht. Die Verteilung einiger anorganischer Ionen und organischer Reagenzien in Polyethylenglykol (PEG) 2000-Ammoniumsulfat-Systemen wurde bei verschiedenem pH der Salzphase geprüft. Dabei ergab sich, daß die Verteilungskoeffizienten für alle untersuchten Kationen geringer sind als eins, während Reagenzien, die einen aromatischen Ring enthalten, in die PEG-Phase mit Verteilungskoeffizienten über 100 extrahiert werden. Versuchsbedingungen für die wirkungsvolle Extraktion von Fe(III) in Gegenwart verschiedener wasserlöslicher photometrischer Reagenzien wurden angegeben. Die Extraktion mit PEG 2000-Ammoniumsulfat-Wasser in Gegenwart von Ammoniumrhodanid und Schwefelsäure wurde untersucht. Kupfer, Zink, Kobalt, Eisen (III), Indium und Molybdän werden mit hohem Verteilungskoeffizienten in die PEG-Phase extrahiert.

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The paper has been presented at the Fifth European Conference on Analytical Chemistry (Euroanalysis V), Cracow, August 26–31, 1984.     

Anomalies of the partition coefficient and properties of crystals in the region of low concentrations of an isomorphous admixture. 1. Unusual decomposition of solid solutions of the NaCl—CdCl2 system

Solid solutions NaCl—CdCl₂ were studied in an interval of CdCl₂ concentrations of 0.05—3 mol.% by Raman spectroscopy. The molecular form Na₂CdCl₄ decomposes: Na₂CdCl₄ 2Na⁺ + Cd²⁺ + 2Cl₂ ^– + 2e^–; 2Na + 2e^– 2Na⁰. Free sodium atoms form color centers of crystal (F centers) in the region of jumpwise changing the partition coefficient of CdCl₂ in NaCl (K jump).     

Crystal and molecular structures of 1,8-diacetyl-3-methyl-DL-allantoin

DL-Allantoin (I) has been isolated from an alcoholic extract of a marine spongeAxinellidae gen. sp., and derivatives of it have been obtained: 1, 8-diacetyl-DL-allantoin (II) and 1,8-diacetyl-3-methyl-DL-allantoin (III). The crystal and molecular structures of (III) have been established by X-ray structural analysis.Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Branch, USSR Academy of Sciences, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 422–426, May–June, 1988.     

Electron Transfer through Monolayers of Mixed Long-chain Aliphatic Acids and Alcohols

Properties of monolayers of cetyl, stearyl, and eicosyl alcohols and stearic and behenic acids and their mixtures are studied, along with the kinetics of a redox reaction of hemin adsorbed on these monolayers. Three-dimensional computer models of corresponding monolayers are constructed and compared with their electrochemical behavior. Properties of monolayers of cetyl alcohol in acid and alkaline solutions and stearyl alcohol in acid solutions correspond to package of molecules in a stretched conformation oriented normally to the electrode surface; for the other one-component systems, the monolayer structure is less regular. The hemin redox reaction rate has no correlation whatsoever with the monolayer thickness and is defined by the length of the electron transfer path (over a chain of covalent bonds and through van der Waals contacts between molecules). The stronger the deviation of the conformation of molecules from the stretched one, the shorter the effective path of the electron transfer. In mixed films of stearic acid and cetyl alcohol (1 : 6), it is sometimes possible to keep molecules of stearic acid in a stretched conformation, thus inhibiting the electron transfer along the hydrocarbon chain of this molecule to a maximum extent. The other mixed systems, while making the conformation more stretched, fail to provide for a completely regular structure.