Vinyl addition polymerization of norbornene using cyclopentadienylzirconium trichloride activated by isobutyl‐modified methylaluminoxane

Norbornene polymerization using the commercially available and inexpensive catalyst system, cyclopentadienylzirconium trichloride (CpZrCl₃) and isobutyl‐modified methylaluminoxane (MMAO), were carried out over a wide range of polymerization temperatures and monomer concentrations. For the CpZrCl₃ catalyst system activated by aluminoxane with a 40 mol % methyl group and a 60 mol % isobutyl group (MMAO_40/60), the polymerization temperature and monomer concentration significantly affected the molecular weight (M_n) of the obtained polymer and the catalytic activity. With an increase in the polymerization temperature from 0 to 27 °C, the catalytic activity and M_n increased, but these values dramatically decreased with the increasing polymerization temperature from 27 to 70 °C, meaning that the most suitable temperature was 27 °C. The CpZrCl₃/MMAO_40/60 ([Al]/[Zr] = 1000) catalyst system with the [NB] of 2.76 mol L^?1 at 27 °C showed the highest activity of 145 kg mol_Zr^?1 h^?1 and molecular weight of 211,000 g mol^?1. The polymerization using the CpZrCl₃/MMAO_40/60 catalyst system proceeds through the vinyl addition mechanism to produce atactic polynorbornene, which was soluble in chloroform, toluene, and 1,2‐dichlorobenzene, but insoluble in methanol. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1185–1191, 2008     

A stereocontrolled construction of 2-azido-2-deoxy-1,2-trans-β-glycosidic linkages utilizing 2-azido-2-deoxyglycopyranosyl diphenyl phosphates

A high-yielding and stereocontrolled construction of 2-azido-2-deoxy-1,2-trans-β-glycosidic linkages has been achieved by exploiting TMSOTf-promoted 1,2-trans-glycosidation of 2-azido-2-deoxyglycopyranosyl diphenyl phosphates with various glycoside alcohols in propionitrile at −78°C. The present method exhibits the highest levels of 1,2-trans-β-selectivity reported to date for this type of glycosidation.     

Photochemistry of a putative new class of sensory rhodopsin (SRIII) coded by xop2 of Haloarcular marismortui

Baliga et al. (2004) [1] reported the existence of a functionally unpredictable opsin gene, named xop2, in Haloarcula marismortui, a holophilic archaeon. Ihara et al. [38] performed molecular phylogenetic analysis and determined that the product of xop2 belonged to a new class of opsins in the sensory rhodopsins. This microbial rhodopsin was therefore named H. marismortui sensory rhodopsin III (HmSRIII). Here, we functionally expressed HmSRIII in Escherichia coli cell membranes to examine the photochemistry. The wavelength of maximum absorption (λ(max)) for HmSRIII was 506nm. We observed a very slow photocycle that completed in ～50s. Intermediates were defined as M (λ(max)～380nm), N (λ(max)～460nm) and O (λ(max)～530nm) 0.01s after the flash excitation. The nomenclature for these intermediates was based on their locations along the absorption maxima of bacteriorhodopsin. Analysis of laser-flash-photolysis data in the presence and absence of azide gave the following results: (1) an equilibrium between N and O was attained, (2) the direct product of the M-decay was O but not N, and (3) the last photo-intermediate (HmSRIII') had a λ(max) similar to that of the original, and its decay rate was very slow. Resonance Raman spectroscopy revealed that this N-intermediate had 13-cis retinal conformation. Proton uptake occurred during the course of M-decay, whereas proton release occurred during the course of O-decay (or exactly N-O equilibrium). Very weak proton-pumping activity was observed whose direction is the same as that of bacteriorhodopsin, a typical light-driven proton pump.     

A stereocontrolled construction of 2-azido-2-deoxy-1,2-cis-α-galactosidic linkages utilizing 2-azido-4,6-O-benzylidene-2-deoxygalactopyranosyl diphenyl phosphates: stereoselective synthesis of mucin core 5 and core 7 structures

TMSOTf-promoted glycosidation of 2-azido-4,6-O-benzylidene-2-deoxygalactosyl diphenyl phosphates with fluorenylmethoxycarbonyl (Fmoc)-protected serine and threonine derivatives in THF/Et₂O (1:1) gave glycosyl amino acids in high yields and with excellent levels of α-selectivity (α/β=94:6–95:5). The synthetic utility of the present glycosidation method was demonstrated by a stereoselective synthesis of mucin-type glycopeptide core 5 and core 7 building blocks, which are suitable for Fmoc-based solid-phase synthesis of O-glycopeptides.     

Imidazo[1,5-a]pyridine-1-ylalkylalcohols: synthesis via intramolecular cyclization of N-thioacyl 1,2-aminoalcohols and their silyl ethers and molecular structures

Iodine-mediated cyclization of N-thioacyl 1,2-aminoalcohols derived from aromatic aldehydes and ketones mainly produced bis(1-imidazo[1,5-a]pyridyl)arylmethanes, whereas the reaction of N-thioacyl 1,2-aminoalcohols derived from aliphatic aldehydes and N-thioacyl 1,2-aminoalcohols protected with a silyl group with iodine gave imidazo[1,5-a]pyridine-1-ylalkylalcohols as a major product.     

Insulator-metal transitions induced by electric field and photoirradiation in organic Mott insulator deuterated κ-(BEDT-TTF)2Cu[N(CN)2]Br

The Mott insulator-metal transition induced by an external stimulus such as electric field, pressure, chemical doping, or photoirradiation has received considerable attention because of the potential use in new optoelectronic functional devices. Here we report an abrupt Mott insulator-metal transition observed as a current jump in a molecular-based Mott insulator, namely, deuterated κ-(BEDT-TTF)(2)Cu[N(CN)(2)]Br, where BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene, upon application of a pulsed voltage of certain magnitude (threshold voltage). Furthermore, the threshold voltage needed for the transition is shown to be reduced by photoirradiation. Thus, the Mott insulator-metal transition can be controlled by a combination of an external electric field and photoirradiation.     

Analysis of oligomeric transition of silkworm small heat shock protein sHSP20.8 using high hydrostatic pressure native PAGE

The small heat shock proteins (sHSPs) solubilize thermo-denatured proteins without adenosine triphosphate energy consumption to facilitate protein refolding. sHSP20.8 is one of the silkworm (Bombyx mori) sHSPs having only one cystein in the N-terminal domain: Cys43. We report a simple measurement of oligomeric transition of sHSP20.8 using high hydrostatic pressure native polyacrylamide gel electrophoresis (high hydrostatic pressure (HP) native polyacrylamide gel electrophoresis (PAGE)). At ambient pressure under oxydative condition, the native PAGE of thermal transition of sHSP20.8 oligomer displayed a cooperative association. In contrast, HP native PAGE clearly demonstrated that sHSP20.8 dissociated at 80 MPa and 25°C, and the resultant molecular species gradually reassociated with time under that condition. In addition, the reassociation process was suppressed in the presence of the reductant. These results are consistent with the idea that sHSP20.8 oligomer temporally dissociates at the first thermo-sensing step and reassociates with the oxidation of Cys43.     

The role of trimethylsilyl group in highly stereoselective eposidation of allylic alcohols

The epoxidation of allylic alcohols carrying Me₃Si group on the double bonds with VO(acac)2-tBuOOH or MCPBA provides erythro or threo epoxy alcohols, respectively with high stereoselectivity.     

Silicon-wire-based ultrasmall lattice filters with wide free spectral ranges

Using silicon-on-insulator-based silicon-wire waveguides with submicrometer cross sections, we constructed ultrasmall channel-dropping lattice filters for 1.5-microm infrared systems. The waveguide's low-loss bends with 2.5-microm radius reduce the total length of the filter to less than 100 microm and enlarge the free spectral range to more than 80 nm. The measured spectra show fine channel-dropping characteristics, and the results agree well with numerical predictions. Moreover, we have succeeded in tuning the dropping wavelength by adjusting the lengths of the delay lines.