Quantitative1H and13C NMR spectroscopies of cottonplant dioxane lignin

A comparative analysis has been made of the dioxane lignins of the stems, seedling shoots, and seed coats of the cotton plant. The ratio of p-hydroxyaromatic, guaiacyl, and syringyl units in the macromolecules of the lignins has been determined, and so have the amounts of functional groups and bonds. It has been established that the main difference between the dioxane lignins from seedling shoots and seed coats of the cotton plant, on the one hand, and the lignin from the woody stems, on the other hand is a lower content of syringyl and guaiacyl units in the former.     

Bioconversion of D-glucose in heavy water: Effect of water isotopomeric composition on deuterium fragment distribution in ethanol

The relative distribution of deuterium between methyl and methylene groups in ethanol at the bioconversion of D-glucose in heavy water was studied.     

Formation,nature of activity,and hydrogenation catalysis by nickel bis(acetylacetonate)-lithium tetrahydroaluminate systems

A new approach to synthesis of nickel catalysts under the action of lithium tetrahydroaluminate was proposed which allows preparation of high-performance nanosized catalytic systems with well-reproducible properties. The major stages of formation and the nature of catalytically active species and inhibitors formed in the Ni(acac)₂-LiAlH₄ system were determined. The catalytic properties of the nickel nanoclusters were studied in relation to the nature and concentration of the proton-containing compounds. Factors responsible for the promoting action exhibited by these compounds were analyzed.     

Polysaccharides of Fabaceae. VI. Galactomannans from seeds of <Emphasis Type="Italic">Astragalus alpinus</Emphasis> and <Emphasis Type="Italic">A. tibetanus</Emphasis>

Galactomannans with galactose:mannose ratios 1:1.48 and 1:1.33, [α]_D +67.9 and +76.4°, [η] 870.3 and 1337.1 mL/g, and molecular weights 999 and 1549 kDa, respectively, were isolated in 0.59 and 4.65% yields (of seed mass) from seeds of Astragalus alpinus and A. tibetanus (Fabaceae). Physicochemical methods (CrO₃ oxidation; methylation–GC/MS; IR, NMR, and ¹³C spectroscopy) found that the main polysaccharide chain consisted of 1,4-β-D-mannopyranose units substituted 67.5% (A. alpinus) and 75.2% (A. tibetanus) at the C-6 position by single α -D-galactopyranose units. The contents of mannobiose blocks Man–Man, (Gal)Man–Man/Man–Man(Gal), and (Gal)Man–Man(Gal) variously substituted with galactose were according to ¹³C NMR spectroscopy 15.9, 55.5, and 28.6% in A. alpinus galactomannan and 9.9, 42.3, and 47.8% in A. tibetanus galactomannan.     

Schematic structure of a fragment of the cottonplant lignin macromolecule

A schematic structure has been proposed for an average fragment of the macromolecule of cottonplant dioxane lignin on the basis of the results of a chemical study and quantitative¹H and¹³C NMR spectroscopy.Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 234–236, March–April, 1996. Original article submitted June 27, 1994.     

Fabaceae Polysaccharides. III. Galactomannan from <Emphasis Type="Italic">Astragalus cicer</Emphasis> seeds

Seeds of Astragalus cicer L. (Fabaceae) afforded a galactomannan (5.90% yield of seed mass) of molecular weight 1064 kDa, solutions of which had high viscosity [η] 925.5 mL/g and optical activity [α]_D +71.9°. The galactomannan consisted of galactose and mannose units in a 1:1.39 ratio. Physicochemical methods established that the main chain of the polysaccharide consisted of 1,4-β-D-mannopyranose units substituted at 72% of the C-6 positions by single α-D-galactopyranose units. The content of variously substituted galactose mannobiose units Man–Man, (Gal)Man–Man/Man–Man(Gal) and (Gal)Man–Man(Gal) in the galactomannan were 18.7, 19.8, and 61.5%, respectively.     

Reaction of palladium bisacetylacetonate with elemental phosphorus. Effect of water on the composition of palladium phosphides

Reaction of palladium bisacetylacetonate with elemental phosphorus in an inert atmosphere is shown to proceed as a redox process forming palladium phosphides of different compositions: PdP₂, Pd₅P₂, Pd_4,8P, and Pd₁₂P_3,2. The conversion of Pd(acac)₂ and the composition of palladium phosphides formed in benzene is established to be affected by water. A tentative scheme of the formation of palladium phosphides is suggested.     

Reactions of Pd β-Diketonate Complexes with Triethylaluminium

Reactions of Pd(Acac)₂ and Pd(Acac)₂PPh₃ complexes with triethylaluminium in an inert atmosphere are studied by the NMR and IR, electronic microscopy, and X-ray powder diffraction methods. The final products of conversion of the initial Pd(II) complexes are the Pd(0) nanoparticles with the predominant diameter 2–4 nm. The main factors determining the size of Pd(0) particles and the nature of the ligand shell are considered.