Ruthenium complex-catalyzed allylic alkylation of carbonucleophiles with allylic carbonates

Allylic carbonates except for allyl methyl carbonate reacted with carbonucleophiles such as ethyl acetoacetate in the presence of a catalytic amount of Ru(cod)(cot) [cod = cycloocta-1,5-diene, COT = cycloocta-1,3,5-triene] in N-methylpiperidine at 80°C to give the corresponding monoallylated carbonucleophiles in high yields with high regioselectivity. The regioselectivity was quite different from that in the palladium-catalyzed reactions. The allylation of carbonucleophiles using allyl methyl carbonate selectively gave the diallylated carbonucleophiles in high yields.     

A new automatic recording titrator and its applications

A new type of automatic recording titrator has been developed. The titrant is added intermittently and the titration curve is recorded stepwise, potential changes being registered in the intervals between deliveries of titrant. The increments of titrant and the intervals can be pre-set, but give the best results if controlled automatically during the titration. The end-point and the volume of titrant consumed are read from the recorded titration curve.     

Ruthenium-catalyzed formal [4 + 2] cycloaddition of alkynes with alkenes: formation of cyclohexenedicarboxylates via isomerization of alkynes and successive Diels-Alder reaction

Formal [4 + 2] cycloaddition of alkynes with electron-deficient alkenes, which affords 3,6-dialkyl-4-cyclohexene-1,2-dicarboxylates, was achieved using Ru(η⁶-1,3,5-cyclooctatriene)(η²-dimethyl fumarate)₂ as a catalyst. The reaction mechanism consists of two steps, isomerization of an alkyne to conjugated dienes and successive Diels-Alder reaction of the generated dienes with an electron-deficient alkene.     

Dioxygenation of human serum albumin having a prosthetic heme group in a tailor-made heme pocket

Human serum albumin (HSA) is the most abundant plasma protein in our bloodstream and serves as a transporter for small hydrophobic molecules such as fatty acids, bilirubin, and steroids. Hemin dissociated from methemoglobin is also bound within a narrow D-shaped cavity in subdomain IB of HSA. In terms of the general hydrophobicity of the alpha-helical pocket, HSA potentially has features similar to the heme-binding site of myoglobin (Mb) or hemoglobin (Hb). However, the reduced ferrous HSA-heme complex is immediately oxidized by O2, because HSA lacks the proximal histidine that enables the heme group to bind O2. In this paper, we report the introduction of a proximal histidine into the subdomain IB of HSA by site-directed mutagenesis to construct a tailor-made heme pocket (I142H/Y161L), which allows a reversible O2 binding to the prosthetic heme group. Laser flash photolysis experiments revealed that this artificial hemoprotein appears to have two different geometries of the axial-imidazole coordination, and these two species (I and II) showed rather low O2 binding affinities (P1/2O2 = 18 and 134 Torr) relative to those of Mb and Hb.     

Investigation of accidental explosion of raw garbage composting system

Cellulose, chitosan and piroxicam were investigated by TG and DSC at heating up to 215°C, and by X-ray powder diffraction before and after the heating. Dehydration of cellulose and chitosan comes to the end near 160°C. Thermal decomposition of chitosan starts at the final stage of its dehydration, and the mass losses after these two reactions overlap with one another. Enthalpy of dehydration is 47.1±2.4 kJ mol^–1 of water for cellulose and 46.2±2.0 kJ mol^–1 for chitosan. Thermal decomposition of chitosan is an exothermic process. Crystal structure of cellulose after heating remains unchanged, but that of chitosan contracts. Piroxicam melts at 200.7°C with the enthalpy of melting 35 kJ mol^–1. Heat capacity of the liquid phase is greater than that of the solid phase by approximately 100 J mol^–1K^–1. Cooled back to ambient temperature, piroxicam remains glassy for a long time, crystallizing slowly back into the starting polymorph.     

Total synthesis of the disaccharide of bleomycin, 2-0-(α-D-mannopyranosyl)-L-gulopyranose

2-0-(α-$\text{D}$-Mannopyranosyl)-$\text{L}$-gulopyranose, the sugar portion of bleomycin has been synthesized.     

Convenient synthesis of 2-alkylamino-6-carboxy-5,7-diarylcyclopenteno[1,2-b]pyridines via direct acylamination with imidoyl chlorides

A robust synthetic method for 2-alkylamino-6-carboxy-5,7-diarylcyclopenteno[1,2-b]pyridines via acylamination at the alpha position of the functionalized pyridine system has been developed. The key step in this method was achieved by treatment of the corresponding pyridine N-oxides with 2.5 equiv of imidoyl chlorides in the presence of triethylamine, thus producing the desired 2-acylaminopyridines in good yields (74-96%).     

Influence of Si doping on the optical and structural properties of InGaN films

Influence of Si doping on the optical and structural properties of InGaN epilayers with different Si concentrations was investigated in detail by means of high-resolution X-ray diffraction (HRXRD), scanning electron microscope (SEM), Cathodoluminescence (CL) and photoluminescence (PL). It was found that a small amount of Si doping in InGaN could enhance luminescence intensity, improve the crystal quality of InGaN and suppress the formation of V-defects in InGaN. Further investigation by CL showed that V-defects act as nonradiative center, which lower the luminescence efficiency of InGaN. Based on above-mentioned results, one possible mechanism of influence of Si doping on the formation of V-defects in InGaN was also proposed in this paper.     

Novel synthesis of high molecular weight polymers with extremely low polydispersity by the unique initiation properties of organo-lanthanide complexes

Organolanthanide(III) complexes such as |(C₅Me5₅)₂SmH|₂ and (C₅Me₅)₂SmMe(THF) were found to initiate the living polymerizations of methyl methacrylate (MMA) to give high molecular weight polymers (M _n > 500 × 10³) with extremely low polydispersity (M _w/M_n = 1.04). The syndiotacticity increased up to 95.2% by lowering the temperature to −95°C. The molecular structure of the 1:2 adduct of (C₅Me₅)₂SmH with MMA determined by X-ray method indicates that this intermediate assumes the 8 membered ring conformation where the Sm atom is bound to MMA in an enolate form and the ester of penultimate MMA is coordinated to the metal. Based upon these results, an anionic coordination mechanism has been proposed for the present reaction. Organolanthanide(II) complexes also exhibit high activity and proceed the living polymerizations. Organolanthanide(III) complexes also initiate the living polymerizations of lactones such as ϵ-caprolactone and δ-valerolactone. The stoichiometric reactions indicate that real active species assumes the alkoxylanthanide(III) form.