New pyrazino[1,2-a]benzimidazole derivatives

1-Ethoxycarbonyl-3-phenyl- and 3-phenylpyrazino[1,2-a]benzimidazoles were synthesized by reaction of 2-ethoxalyl- and 2-diethoxymethyl-N-phenacylbenzimidazoles, obtained from the corresponding sodium derivatives of benzimidazole and phenacyl bromide, with ammonium acetate.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1266–1267, September, 1976.     

Cumulated double bond systems as ligands : V. Dialkylsulfurdiimine compounds M(CO)4(RNSNR) (M = Cr,Mo, W) and M(CO)5(RNSNR) (M = Cr,W); structural,spectroscopic and fluxional properties.

The preparation and properties are reported of M(CO)₄(RNSNR) (M = Cr, Mo, W; R = i-Pr, t-Bu), in which the ligand is bidentate and in the trans,trans configuration, and of M(CO)₅(RNSNR) (M = CR, W; R = Et, i-Pr) in which the sulfurdiimine is monodentate and in the cis,trans configuration. In both cases the ligand is linked to the metal atom via the N-atom(s). With M(CO)₅(MeNSNMe) a second isomer is found in which the sulfurdiimine is probably bonded via the S-atom to the metal. All the pentacarbonyl compounds are fluxional; this is attributed to a gliding movement of the metal atom along the NSN system.Both W(CO)₄(t-BuNSN-tBu) and W(CO)₅(MeNSNMe) show vibronic coupling of metal to ligand charge transfer transitions with sulfurdiimine vibrations, as shown with Resonance Raman, but only for W(CO)₅(MeNSNMe) also with the symmetric mode of the equatorial carbonyl groups. The metalsulfurdiimine bond appears to be weak for M(CO)₅(RNSNR), but strong for M(CO)₄(RNSNR).     

The Effect of Solute Concentration on Equilibrium Partitioning in Polymeric Gels

The effect of solute concentration on the equilibrium partitioning of sphere-like, colloidal solutes in stiff polymer hydrogels is examined theoretically and experimentally. The theoretical development is a statistical mechanics approach, and allows quantitative calculations to be performed to determine the concentration-dependent partition coefficient correct to first order in solute concentration at specific surface charge densities. The theory predicts that repulsive steric and/or electrostatic solute-fiber interactions exclude solute from the gel phase, but that repulsive solute-solute interactions cause partitioning into the gel to increase with increasing solute concentration. These trends are enhanced for larger solutes, increased fiber volume fractions, or stronger electrostatic repulsion. Partition coefficients have also been measured for two proteins, bovine serum albumin (BSA) and alpha-lactalbumin (ALA), in a system consisting of a salt solution and cubes of agarose hydrogel. To investigate the effect of electrostatic interactions, the experiments were performed at 0.15 M KCl and 0.01 M KCl. The theory underpredicts the strong electrostatic repulsion between BSA macromolecules at the lower ionic strength. The experimental results for ALA show the influence of an attractive interaction between the protein macromolecules, in addition to hard-sphere repulsive and electrostatic interactions. Copyright 2001 Academic Press.     

A symmetry-based formal synthesis of zaragozic acid A

A symmetry-based strategy for the synthesis of the zaragozic acids is reported. Two enantioselective dihydroxylations were used to establish the absolute configuration of a C(2) symmetric intermediate. Noteworthy transformations include a group-selective lactonization, which accomplished an end-differentiation of a pseudo-C(2) symmetric intermediate. Late stage protecting group adjustments and oxidations accomplished a formal synthesis of zaragozic acid A.     

Spectrophotometric determination of molybdenum(VI) with 2-mercaptobenzo-γ-thiopyrone and ammonium thiocyanate

Molybdenum(VI) in 1.4–3.6 M hydrochloric acid medium forms an acetophenone-extractable orange-red complex with the potassium salt of 2-mercapto-benzo-γ-thiopyrone and ammonium thiocyanate in the presence of tin(II) chloride. The limit of identification of the spot test based on this reaction is 0.1 μg of molybdenum (dilution limit, 1:1·10⁶). The spectrophotometric method is fairly selective, the sensitivity being 0.005μg Mo cm^-2 at 470 nm. The colour system obeys Beer's law; the optimal concentration range is 0.75–8.5 μg Mo ml^-1, the relative photometric error being 1.675%. The complex is stable for over 24 h. Common ions can be tolerated in amounts greater than 1000-fold. Interferences of Co²⁺, Ni²⁺, Cu²⁺ and Ag⁺ are avoided by complexing these ions with 2-mercaptobenzo-γ-thiopyrone at pH 6–10 and extracting with ethyl acetate or chloroform. The proposed method is applied to the determination of molybdenum in steel and in artificial mixtures.     

Novel acyclic and macrocyclic highly unsaturated silahydrocarbons

Two novel silicon-containing acetylenic synthons, 1-[dimethyl(ethynyl)silyl]-2-[ethynyl(methyl)-(vinyl)silyl]ethyne and bis[(ethynyldimethylsilyl)ethynyl](methyl)vinylsilane, were obtained by the reaction of diethynyl(methyl)vinylsilane with ethylmagnesium bromide and ethynylfluorodimethylsilane. The reaction of magnesium derivatives of the products and diethynyl(methyl)vinylsilane with organylhalosilanes gave macrocyclic polyunsaturated silahydrocarbons containing numerous endo- and exocyclic miltiple bonds.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 10, 2004, pp. 1612–1616.Original Russian Text Copyright © 2004 by O. Yarosh, Zhilitskaya, N. Yarosh, Istomina, Albanov, Chuvashev, Voronkov.This revised version was published online in April 2005 with a corrected cover date.     

Optimization of time resolution and detection limit for online measurements of 222Rn in water

The online measurements of radon in flowing water with high temporal resolution and a lower limit of detection of some Bq/l is of growing interest in environmental research and earth sciences. Promising new fields of application in hydrogeology are the study of exchange and mixing processes and the monitoring of pumping procedures before and during groundwater sampling. A suitable, simple method has been proposed by Surbeck based on the separation of air and water by a diffusion membrane. Process parameters influencing the temporal resolution as well as the radon detection efficiency have been studied. Considering these results a new instrument has been developed enabling online radon-in-water measurement with time resolution of about one minute.     

A New Chemo‐Enzymatic Route to Side‐Chain Liquid‐Crystalline Polymers: The Synthesis and Polymerization of 6‐(4‐Methoxybiphenyl‐4′‐oxy)hexyl Vinyl Hexanedioate

A novel synthetic method combining chemo and enzymatic synthesis strategies was employed to prepare a vinyl acetate type monomer, 6‐(4‐methoxybiphenyl‐4′‐oxy)hexyl vinyl hexanedioate (VA‐LC). Homo‐ and copolymers of VA‐LC with maleic anhydride (MAn) were prepared by conventional free radical polymerization using 2,2′‐azobisisobutyronitrile (AIBN) and 1,1′‐azobis (cyclohexane carbonitrile) (AHCN) as an initiator at 95 and 60 °C, respectively. The thermal properties of the generated polymeric material were investigated by differential scanning calorimetry (DSC), and the optical texture was inspected by polarizing optical microscopy (POM). While the monomer VA‐LC does not exhibit liquid‐crystalline properties, poly(VA‐LC), and the alternating copolymer of VA‐LC with maleic anhydride both displayed such properties.

     

Studies on Fe complexes produced by yeast. IV. Mechanism of Fe transport from an Fe(II)-oligosaccharide complex across the mucosal membrane of the rat intestine

The mechanism of Fe transport across the rat duodenal membrane from an Fe(II)-oligosaccharide complex (designated B1-c) produced in wine by yeast and showing high hematopoietic activity in rats was examined. The Fe uptake from B1-c by brush border membrane (BBM) vesicles isolated from the rat intestine was based mainly on the Fe binding to membrane components which were suggested to be inside the vesicles. Evidence that Fe was transported into the vesicles by a special transport system other than simple diffusion was obtained by observing saturation kinetics under conditions of isotope exchange, and temperature and pH dependence. This Fe uptake was not inhibited by any metal ions tested, including inorganic Fe(II), and the BBM vesicles from the duodenum had a higher Fe uptake than those from the other parts of the small intestine. Furthermore, the BBM vesicles isolated from rats with Fe deficiency showed a significantly increased Fe uptake. The Km value for B1-c uptake was 0.16 mM, lower than the values for FeSO4 and ferrous ascorbate. These results suggest that a special transport system selective for B1-c may be present on the mucosal membrane. B1-c was taken up by the BBM vesicles in the form of Fe-oligosaccharide complex. From the preloaded vesicles, B1-c was released temperature- and pH-dependently.(ABSTRACT TRUNCATED AT 250 WORDS)     

Beiträge zur Chemie der Alkylverbindungen von Übergangsmetallen. XLIV. Tetrakis(alkoxycarbonylmethyl)titan-Verbindungen

Contributions to the Chemistry of Transition Metal Alkyl Compounds. XLIII. Tetrakis(alkoxycarbonylmethyl)titanium Compounds Organotitanium(IV) compounds of the type (ROCOCH₂)₄Ti (R ? C₂H₅, i-C₃H₇, t-C₄H₉, C₆H₅, C₆H₅CH₂) were obtained by reactions of ROCOCH₂Li derivatives with TiCl₄ at low temperature. The compounds which decompose only above 90°C were characterized by the hydrolysis products, anaerobic reactions with iodine, and the i.r. spectra. The bond conditions are discussed.