Star-shaped poly(lactic acid) with carboxylic acid terminal groups via poly-condensation

A series of star-shaped poly(lactic acid)s with carboxylic acid terminal groups have been synthesized by direct poly-condensation of lactic acid in the presence of a poly-carboxylic acid core molecule with triphenylphosphonium trifluoromethanesulfonate (TPP-T) catalyst.These star-polymers had thermal properties not very much different from those of star-shaped poly(lactic acid) with hydroxyl terminal groups and linear poly(lactic acid), irrespective of the structure of the core molecule and number of polymer arms. Solubility and degradability of these star-polymers were, however, greatly enhanced compared to those of star-polymers with hydroxyl terminal groups and increased depending on the number of polymer arms. From the star-shaped polymers, a variety of ammonium salts and the corresponding carboxyamides were successfully prepared.     

Ultrafast Phase-Coherence in Normal State of Underdoped Bi2Sr2CaCu2O8 + δ Thin Film

A phase-sensitive time-domain terahertz-transmission spectroscopy was carried out on a c-axis oriented underdoped Bi₂Sr₂CaCu₂O_{8 +} thin film. We directly extracted the complex refractive index and conductivity at frequencies from 0.3 to 1.5 THz by numerically solving the observed complex transmittance without Kramers–Kronig analysis. The frequency-resolved real and imaginary part of the conductivity (1.0 THz < f) showed a measurable increase below the characteristic temperature of T* 210 K because of the appearance of partial phase-coherence with an ultrashort lifetime less than about 1 ps.     

Deletion and insertion of a 192-residue peptide in the active-site domain of glycosyl hydrolase family-2 beta-galactosidases

The monomeric multimetal-binding beta-galactosidase of Saccharopolyspora rectivirgula (srbg), a glycosyl hydrolase family-2 enzyme, has a unique sequence consisting of 192 amino acid residues with no similarity to known proteins. This 192-residue sequence (termed the "iota [iota] sequence") appears to be inserted into a sequence homologous to the active-site domain of the Escherichia coli lacZ enzyme (lacZbg). To assess the effects of the t sequence at specific sites of beta-galactosidase on the catalytic functioning and molecular properties of beta-galactosidase, deletion or insertion mutants of beta-galactosidases were constructed, expressed in LacZ- E. coli strains, and characterized: srbgdelta in which the iota sequence was deleted from srbg, and lacZbgI, in which the 192-residue iota sequence was inserted into the corresponding position (between Asp591 and Phe592) in the active-site domain of lacZbg. srbgdelta was a catalytically inactive, dimeric protein which retained multimetal-binding characteristics, suggesting that the iota sequence is very important for maintaining the structure necessary for the catalytic functioning and the monomeric structure of srbg but is not responsible for the unique metal ion requirements of srbg. On the other hand, lacZbgI existed as a mixture of a monomer, a tetramer, and higher multimers. The monomeric species was inactive, whereas the tetramer and other multimers were catalytically active (V(max )K(m) value, 25% of that of lacZbg) and highly specific for beta-D-galactoside. The tetrameric lacZbgI was activated by Mg2+ and Mn2+ with lowered metal affinities, and the stoichiometry of metal binding was unchanged from that of lacZbg. These results, along with the published stereo structure of lacZbg, suggest that, in lacZbgI, the inserted 192-residue iota peptide could fold independently of the lacZbg domains into a "sub-domain," lying distant from the active site and subunit interfaces.     

Effects of pore diameter, bath surface pressure, and nozzle diameter on the bubble formation from a porous nozzle

The effects of the pore diameter, bath surface pressure, and nozzle diameter on the bubble formation from a porous bottom nozzle placed in a water bath and on the behavior of rising bubbles were investigated with still and high-speed video cameras and a two-needle electroresistivity probe. Three types of bubble dispersion patterns were observed with respect to gas flow rate, and they were named the low, medium, and high gas flow rate regimes. The transition boundaries between these gas flow rate regimes were expressed in terms of the superficial velocity at the nozzle exit, i.e., the volumetric gas flow rate per unit nozzle surface area. These transition boundaries were dependent on the pore diameter but hardly dependent on the bath surface pressure and the porous nozzle diameter. The characteristics of rising bubbles in each gas flow rate regime were investigated as functions of the three parameters.     

Composite materials reinforced with polyoxymethylene whiskers

Various composite samples reinforced with polyoxymethylene (POM) whisker crystals were prepared and their Young's moduli were measured and analysed, on a theoretical equation, to estimate the modulus of the filler itself. Good reinforcement was obtained with matrix resins such as an epoxide and an unsaturated polyester, the results giving the modulus of the whisker to be approximately 1×10¹¹ N m^–2, i.e., almost equivalent to the ideal crystal modulus of POM. Some acoustic properties were investigated for sheet composite materials prepared with a polyolefin polymer for matrix. The sonic velocity attained was more than twice that of the matrix polymer, at larger filler contents, while the internal dynamic loss was maintained at a reasonably high level. Loudspeakers carrying diaphragms of the composite sheets showed improved frequency characteristics in the high-frequency region. Some morphological observations were made for the crystals embedded in resins.     

Cautionary observations on preparing and interpreting brain images using molecular biology-based staining techniques

Though molecular biology-based visualization techniques such as antibody staining, in situ hybridization, and induction of reporter gene expression have become routine procedures for analyzing the structures of the brain, precautions to prevent misinterpretation have not always been taken when preparing and interpreting images. For example, sigmoidal development of the chemical processes in staining might exaggerate the specificity of a label. Or, adjustment of exposure for bright fluorescent signals might result in overlooking weak signals. Furthermore, documentation of a staining pattern is affected easily by recognized organized features in the image while other parts interpreted as "disorganized" may be ignored or discounted. Also, a higher intensity of a label per cell can often be confused with a higher percentage of labeled cells among a population. The quality, and hence interpretability, of the three-dimensional reconstruction with confocal microscopy can be affected by the attenuation of fluorescence during the scan, the refraction between the immersion and mounting media, and the choice of the reconstruction algorithm. Additionally, visualization of neurons with the induced expression of reporter genes can suffer because of the low specificity and low ubiquity of the expression drivers. The morphology and even the number of labeled cells can differ considerably depending on the reporters and antibodies used for detection. These aspects might affect the reliability of the experiments that involves induced expression of effector genes to perturb cellular functions. Examples of these potential pitfalls are discussed here using staining of Drosophila brain.     

Ultraviolet bonding of perfluoropolyethers to carbon surfaces investigated using quantum chemical methods

For improving the tribological performance of hard disk drives, nanometer-thick perfluoropolyether (PFPE) lubricant films are generally treated with ultraviolet (UV) irradiation to bond them to the carbon overcoats of the disks. By modeling UV irradiation as an electron emission and attachment process, we investigate the UV bonding of nonfunctional PFPE Z and functional PFPE Zdol to hydrogenated and nitrogenated carbon surfaces with quantum chemical methods. Our calculation results show that, upon electron attachment, Z dissociates at its main chain to two fragments terminated by CF₂CF₂ and CF₂O groups, whereas Zdol dissociates to a hydrogen fluoride and a fragment. The perfluoromethoxy oxygen in one of the Z fragments and the carbon radical and the hydrogen-truncated end group in the Zdol fragment interact strongly with sp² and oxidized sites on carbon surfaces. Imine moieties on the CNx surface also contribute considerably to the UV bonding of Zdol.     

Disinfection of Legionella pneumophila by ultrasonic treatment with TiO2

An ultrasonic treatment system, using a TiO₂ photocatalyst, was used to disinfect Legionella pneumophila. A kinetic study of the process indicates that TiO₂ significantly improves the disinfection process. The concentrations of viable cells were reduced to 6% of the initial concentrations in the presence of 0.2 g/ml TiO₂ after a 30 min of treatment period, while only an 18% reduction was observed in the absence of TiO₂. The potency of the disinfection could be enhanced, to some extent, by increasing the amount of TiO₂ used. Cell concentrations were decreased by an order of 3 within 30 min of treatment in the presence of 1.0 g/ml TiO₂. The disinfection power in the presence of TiO₂ versus Al₂O₃ was also compared and the findings showed that TiO₂ induced a higher cell killing. No significant effect of initial cell concentration on the disinfection was found in the range of 10²-10⁷ CFU/ml after a 30 min of treatment period. The mechanism of cell killing was investigated by examining the effects of OH radical scavengers such as ascorbic acid, histidine and glutathione. The disinfection power was reduced in samples that contained these radical scavengers, thus indicating the importance of OH radicals.