Reactivity of methacrylates in anionic copolymerization with methyl methacrylate by n-BuLi

Monomer reactivity ratios, r₁ and r₂ were determined in the anionic copolymerizations of methyl methacrylate (MMA, M₁) with ethyl (EtMA), isopropyl (i-PrMA), tert-butyl (t-BuMA), benzyl (BzMA), α-methylbenzyl (MBMA), diphenylmethyl (DPMMA), α,α-dimethylbenzyl (DMBMA), and trityl (TrMA) methacrylates (M₂) by use of n-BuLi as an initiator in toluene and THF at -78°C. The order of the reactivity of the monomers towards MMA anion was DPMMA > BzMA > MMA > EtMA > MBMA > i-PrMA > t-BuMA > TrMA > DMBMA in toluene and TrMA > BzMA > MMA > DPMMA > EtMA > MBMA > i-PrMA > DMBMA > t-BuMA in THF. Except for the extremely low reactivity of TrMA and DPMMA in toluene due to steric hindrance, the order was explained in terms of the polar effect of the ester groups. A linear relationship was found between log (1/r₁) and Taft's σ* values of the ester groups, where the ρ* value was 1.1. The plots of log (1/r₁) vs. the ¹H_a (cis to the carbonyl) and ¹³C_ß chemical shifts of the monomers were also on straight lines. The polymer obtained in the copolymerization of MMA with TrMA in toluene by n-BuLi at -78°C was a mixture of poly-MMA and a copolymer, suggesting that there exist two kinds of growing centers.     

Effects of strain on the dissociation dynamics of O2 on Si(001)

There are two distinctive channels in the dissociation reaction of O2 on Si(001)-(2 x 1): a trapping-mediated channel and a direct-activated channel. Externally applied tensile strain along the <110> direction on the (001) surface is found to suppress the dissociation via a direct-activated channel and to enhance that via a trapping-mediated channel in the temperature range between 200 and 300 K. It has been demonstrated that the dissociation dynamics involving elementary processes such as inelastic scattering and trapping, desorption and/or dissociation from a trapping precursor, and direct dissociation are sensitively influenced by the strain to change the branching ratio of the dissociation reaction.     

Interaction of Natronobacterium pharaonis phoborhodopsin (sensory rhodopsin II) with its cognate transducer probed by increase in the thermal stability

Pharaonis phoborhodopsin (ppR, also called Natronobacterium pharaonis sensory rhodopsin II) and its transducer protein, pharaonis halobacterial transducer of ppR (pHtrII), form a signaling complex, and light signals are transmitted from the sensor to the transducer by the protein-protein interaction. A truncated pHtrII(1-159) consisting of intramembrane helices (expressing amino acid residues from the first to the 159th position) and ppR form the complex in a solution containing 0.1% n-dodecyl-beta-D-maltoside. At 75-85 degrees C, the time-dependent color loss of ppR was caused by denaturation. We found that pHtrII(1-159) retarded the denaturation rate of ppR. This increase in the thermal stability was used as a probe for the binding ability in the dark. Tyr199 of ppR and Asn74 of pHtrII(1-114) were proposed as amino acid residues interacting with each other through hydrogen bonding. Then,ppR and pHtrII(1-159) mutants at these positions were prepared to examine the effect on the binding in the dark. The wild-type and Y199F mutant can bind pHtrII(1-159), suggesting that the hydrogen bonding between these specific amino acid residues may not be the only cause of the binding, but the hydrophobic interaction via phenyl ring of ppR may contribute dominantly.     

Phase structures of the N-acetyl-L-glutamic acid oligomeric benzyl esters (exact residue numbers 4, 6, 8, and 12)–dioxane systems and their optical properties

A series of N-acetyl-L-glutamic acid oligomeric benzyl esters with exact residue numbers (4, 6, 8, 10, and 12) has been synthesized by a stepwise procedure. It has been found that the phase maps of these oligomer-dioxane systems consist of three regions (I : an isotropic solution, II : a liquid crystalline phase, and III : a two-phase (I and II) solution). In particular, for the samples with residue numbers 6, 8, and 12, selective light scattering of coloured regions in the transparent II and III (bottom-layer) regions have been investigated by the use of UV-visible absorption spectra, leading to the conclusion that there exists a helical axis in the structure of the supramolecular aggregates formed by these oligomeric molecules.     

Exafs study of bromine-doped polyacetylene

Extended-X-ray-absorption-fine-structure (EXAFS) measurements have been made on the Br K absorption of Br-doped polyacetylene at 300 K. The analysis of the EXAFS data shows that Br-C and Br-Br bonds exist in Br-doped polyacetylene with the ratio nearly independent of Br concentration over its range from 5% to 60%. This result indicates that substitution and/or addition reactions of bromine take place even at the low doping level.     

Solubilisation of [60]fullerenes using block copolymers and evaluation of their photodynamic activities

Unmodified [60]fullerenes (C60) were solubilised with high stability using various type of poly(ethylene glycol) (PEG) based block copolymer micelles. Block copolymer micelle-incorporated C60 fullerenes were studied in cultures for biological activities using human cervical cancer HeLa cells. As a result, the cationic block copolymer micelles delivered C60 into the cells depending on their surface densities and showed cytotoxicity under photoirradiation.     

Tris(trimethylsilyl)silane promoted radical reaction and electron-transfer reaction in benzotrifluoride

Tris(trimethylsilyl)silane (TTMSS) promoted free radical reaction in benzotrifluoride (BTF) was investigated. Compared to same reaction using environmentally less desirable tri-n-butyltin hydride (TBTH) in benzene, less quantity of BTF than that of benzene can be used because of slower hydrogen atom transfer from TTMSS than that from TBTH toward primary alkyl radicals. Also, electron-transfer reactions promoted by tris(p-bromophenyl)aminium hexachloroantimonate (TBPA) and FeCl₃ were conducted in BTF. Then, TBPA was found to be effective in BTF comparably to that in methylene chloride. In addition, an interesting observation that FeCl₃ promoted reaction was accelerated by the addition of imidazolium salt was made. All the results suggest that BTF is a tolerable solvent for free radical reaction with TTMSS and electron-transfer reactions using TBPA as well as FeCl₃.