The synthesis of imidazole-2-thione nucleosides

Ribosylation of the trimethylsilyl derivative ( 1b ) of imidazole-2-thione ( 1a ) using either stannic chloride or silver perchlorate as catalyst resulted in the formation of the acylated derivatives of 1-(β-D-ribofuranosyl)imidazole-2-thione ( 3c ) and 1,3-di-(β-D-ribofuranosyl)imidazole-2-thione ( 4c ) with the latter predominating ( 4c:3c , ca. 2:1 ). The diribosylated nucleoside 4c was shown to be the N,N-disubstituted product rather than the N,S-disubstituted product by ¹H nmr and ¹³C nmr spectroscopy. Employment of the iodine-catalyzed fusion procedure reversed the aforementioned product ratios and provided the monoriboside 3c in excellent yield. When the trimethylsilyl derivative ( 5b ) of 2-methylthioimidazole ( 5a ) was reacted with 2,3,5-tri-O-benzoyl-D-ribofuranosyl bromide ( 2d ) in acetonitrile, the major product was 1,3-di-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)-imidazole-2-thione ( 4b ). The formation of 4b in this reaction is thought to arise via the Hilbert-Johnson mechanism.     

Control of Redox Potential by Deprotonation of Coordinated 1H‐Imidazole in Complexes of 2‐(1H‐Imidazol‐2‐yl)pyridine

Complexes [ML₃]²⁺ of the bidentate ligand 2‐(1H‐imidazol‐2‐yl)pyridine were prepared with iron(II), cobalt(II), and ruthenium(II). The electronic spectra suggest the ligand to be a weaker σ‐donor and π‐acceptor than the closely related 2,2′‐bipyridine. The complexes are readily deprotonated by addition of base, and the effect of the deprotonation is to lower the M^III/M^II redox potential by roughly 900 mV. This is roughly 75% of the drop observed for related complexes of 2,6‐di‐1H‐imidazol‐2‐ylpyridine, and suggests the effect to be largely coulombic in origin.     

Kinetics of poly(ethylene terephthalate) glycolysis by diethylene glycol. I. Evolution of liquid and solid phases

The kinetics of uncatalysed glycolysis, at 220 °C, of poly(ethylene terephthalate) (PET) by diethylene glycol (DEG) in high excess has been studied. An experimental device allowing good separation, at reaction temperature, of the solid and liquid phases was set up.The results suggest that PET is initially depolymerized in the slightly swollen solid phase, by glycolysis of the amorphous interlamellar chains. This mechanism continues until a solid phase of highly crystallized polyester is obtained.The internal tensions engendered by this chemical modification cause cracks, delamination and mechanical disintegration of the polymer. The transfer towards the liquid phase is then strongly accelerated and the solvolysis of the depolymerization products continues in the liquid phase, up to equilibrium.     

New transesterification reaction between acetylated wood and tetramethoxysilane: A feasibility study

Novel transesterification of acetylated maritime pine sapwood (Pinus pinaster Soland) reaction was performed with tetramethoxysilane (TMOS) in presence of dibutyltin oxide as a catalyst. Transesterification was confirmed by weight percent gain calculations (WPG), infrared spectroscopy (FTIR) as well as ¹³C and ²⁹Si NMR CP-MAS analysis. The results showed that transesterification indeed occurs via exchange of acetate groups from acetylated wood and methoxysilane groups from TMOS. The effect of temperatures and reaction time upon transesterification efficiency was also investigated.     

An efficient way to 1,7-enynes and ethyl 8-yn-2-enoates from aldohexoses and to polyhydroxylated 1-vinylcyclohexenes

In this paper, we report the synthesis of carbohydrate-derived 1,7-enynes and subsequent metathesis to yield polyhydroxylated 1-vinylcyclohexenes. For example, we converted D-glucose 2 to the (6,7)-dideoxy-D-gluco-hept-6-ene-pyranose 7, which led to the desired 1,7-enyne 16. The ring-closing metathesis of this 1,7-enyne 16 with the second generation Grubbs catalyst, under Mori's conditions, gave the corresponding polyhydroxylated 1-vinylcyclohexene 25 in 76% yield. The conversion of several aldohexoses into polyhydroxylated 1-vinylcyclohexenes was carried out with satisfying yields. We report also the synthesis of two carbohydrate-derived ethyl 8-yn-2-enoates from D-glucose derivatives.     

Effects of alkali metal halide salts on the hydrogen bond network of liquid water

Measurements of the oxygen K-edge X-ray absorption spectrum (XAS) of aqueous sodium halide solutions demonstrate that ions significantly perturb the electronic structure of adjacent water molecules. The addition of halide salts to water engenders an increase in the preedge intensity and a decrease in the postedge intensity of the XAS, analogous to those observed when increasing the temperature of pure water. The main-edge feature exhibits unique behavior and becomes more intense when salt is added. Density functional theory calculations of the XAS indicate that the observed red shift of the water transitions as a function of salt concentration arises from a strong, direct perturbation of the unoccupied molecular orbitals on water by anions, and does not require significant distortion of the hydrogen bond network beyond the first solvation shell. This contrasts the temperature-dependent spectral variations, which result primarily from intensity changes of specific transitions due to geometric rearrangement of the hydrogen bond network.     

Monomeric (dialkylamino)boranes: a new and efficient boron source in palladium catalyzed C-B bond formation with aryl halides

Thermal decomposition of hindered amine-borane adducts leads in high yields to monomeric (dialkylamino)boranes R1R2N-BH2 (R1 and R2 = alkyl) that are new and efficient boron-sources in the Pd0 catalyzed borylation reaction affording monomeric aryl(dialkylamino)boranes R1R2N-BHR3 (R3 = aryl).     

Co(II)5(OH)6(SO4)2(H2O)4: the first ferromagnet based on a layered cobalt-hydroxide pillared by inorganic...OSO3-Co(H2O)4-O3SO..

The synthetic mineral Co(II)5(OH)6(SO4)2(H2O)4 (1), obtained by hydrothermal reaction of CoSO4.7H2O and NaOH at 165 degrees C and consisting of brucite-like Co4(OH)6O2 layers pillared by OSO3-Co(H2O)4-O3SO, is a ferromagnet (T(Curie)= 12 K, Hc= 580 Oe).     

Comparative reactivity of glycols in PET glycolysis

The kinetics of poly(ethylene terephthalate) (PET) glycolysis by diethylene glycol (DEG), dipropylene glycol (DPG), glycerol (Gly) and mixtures of these glycols have been studied with two experimental procedures: uncatalysed at 220 °C and catalysed at 190 °C. An experimental device was set up allowing the isothermal kinetics to be monitored. A precise initial reaction time was obtained by separately warming the glycol and the polyester at the temperature of reaction before mixing them.The reactivity order of different glycols varies according to the conditions of temperature and catalysis. Schematically, the global reactivity does depend not only on the chemical reactivity of the glycol but also on its physico-chemical properties: ability to solvate the solid polyesters and polarity of the reaction mixture. Attempts to find synergic effects failed for almost all mixtures, except the mixture DPG + Gly in which the PET is digested more quickly than in pure DPG or Gly.     

Chiral discrimination within disordered adlayers on metal surfaces

Using a novel non-linear optical technique enantiomeric excess within a translationally disordered overlayer on a metal surface has been monitored for the first time.