Effect of various precipitants on the nucleation rate of tetragonal hen egg-white lysozyme crystals in an AC external electric field

It was observed that the effect of an external electric field on the nucleation rate of tetragonal hen egg-white lysozyme crystals varied depending on the precipitant used (NaCl, NiCl₂ or YbCl₃) and that the electric double layer (EDL) played an important role in generating an external electric field of the necessary strength to control the nucleation rate. This phenomenon depended on the ionic strength of the precipitant used; that is, a precipitant of greater ionic strength resulted in a thinner EDL and increased the effect of the external electric field as the driving force for nucleation. The dependence of the nucleation rate on the precipitant was attributed to the magnitudes of the external electric fields generated in EDLs of varying thickness which were formed in the presence of different precipitants.     

Direct coating of quantum dots with silica shell

This paper describes a method for direct coating of fluorescent semiconductor nanoparticles with silica shell. The fluorescent semiconductor nanoparticles used were CdSe _x Te_1–x nanoparticles coated with ZnS and succeedingly surface-modified with carboxyl groups, or quantum dots (Q-dots). The Q-dots were silica-coated by performing sol–gel reaction of tetraethyl orthosilicate (TEOS) using NaOH as a catalyst in the presence of the Q-dots. Quasi-perfect Q-dots/silica core-shell particles were formed at 5.0 M H₂O and 4.0 × 10⁻⁴ M NaOH. Under these concentrations of H₂O and NaOH, the particle size of Q-dots/silica particles could be varied from 20.1 to 38.1 nm as the TEOS concentration increased from 2.5 × 10⁻⁴ to 50 × 10⁻⁴ M. The Q-dots/silica particles showed fluorescence as well as the uncoated Q-dots.     

Pancreatic β-cell signaling: toward better understanding of diabetes and its treatment

Pancreatic β-cells play a central role in the maintenance glucose homeostasis by secreting insulin, a key hormone that regulates blood glucose levels. Dysfunction of the β-cells and/or a decrease in the β-cell mass are associated closely with the pathogenesis and pathophysiology of diabetes mellitus, a major metabolic disease that is rapidly increasing worldwide. Clarification of the mechanisms of insulin secretion and β-cell fate provides a basis for the understanding of diabetes and its better treatment. In this review, we discuss cell signaling critical for the insulin secretory function based on our recent studies.     

One-Pot Preparation of 1-Substituted Imidazole-2-thione from Isothiocyanate and Amino Acetal

Isothiocyanates were treated with amino acetal and conc. HCl (0.5 eq.) successively in one-pot to afford 1-substituted imidazole-2-thiones in good yields.     

Organic-inorganic hybrid liquid crystals: hybridization of calamitic liquid-crystalline amines with monodispersed anisotropic TiO2 nanoparticles

A novel organic-inorganic hybrid thermotropic liquid crystal (LC) is developed by the hybridization of an organic amine with a mesogenic core and an acicular anisotropic TiO2 particle through the adsorption of the amino group to the surfaces of the TiO2. The hybrid LC shows nematic phases in wide ranges of temperatures. Variable-temperature small-angle X-ray measurements reveal that the formation of the one-dimensional nematic order of the acicular particles on a submicrometer scale induces thermotropic liquid crystallinity. This technique would lead to induction of dynamic functions in inorganic particles.     

Synthesis of uniform anatase TiO2 nanoparticles by gel-sol method. 1. Solution chemistry of Ti(OH)(4-n)+(n) complexes

The mole fractions of hydroxo complexes of titanium(IV) ion in an aqueous solution with 0.10 mol dm(-3) NaClO4 at 25 degrees C have been determined as a function of pH by a newly developed analytical procedure based on UV spectrophotometry, using a metastable homogeneous solution of 1.25 x 10(-4) mol dm(-30 in total concentration of Ti(IV). Also, the total concentration of the hydroxo complexes in equilibrium with Ti(OH)4 solid, or the solubility of Ti(OH)4 solid in an inhomogeneous system, has been obtained by ICP measurement for the solution phase. A combination of these data yielded the absolute concentration of each complex species in equilibrium with Ti(OH)4 solid. Finally, Ti(OH)+3 complex has been assigned to the precursor for the formation of anatase TiO2 nanoparticles transformed from Ti(OH)4 gel from a comparison between the above equilibrium data and a kinetic study on the formation rate of the anatase TiO2 particles in the gel-sol system.     

Vacancy spectroscopy of radiation cross-linked and degraded polytetrafluoroethylenes

Polytetrafluoroethylene samples having different morphology were prepared by radiation induced cross-linking and degradation, and positron annihilation lifetimes were measured to extract information about the vacancy structure from the orth-positronium (o-Ps) component. The o-Ps intensity I₃ was inversely correlated with the crystallinity confirming that this component is associated with the amorphous part. The o-Ps lifetime τ₃ was distinctly different depending on the phase of the polymer. Below the γ relaxation temperature, the vacancies produced by degradation could be seen from an increase in the τ₃ value, but at temperatures between the γ and β relaxations such vacancies became invisible due to the activated segment motion. And above the β relaxation temperature vacancies in the interface between crystalline and amorphous parts appear to affect τ₃. The o-Ps intensity did not show stable reproducible results. Accumulation of positive charge can be responsible for it. The results, not only unveiling the not yet well understood behavior of the o-Ps component, demonstrate the uniqueness of the vacancy spectroscopy using o-Ps as a probe.     

Radiation-induced oxidation of polymers. Effect of antioxidant and antirad agent on oxygen consumption and gas evolution

The effects of antioxidants and of an antirad agent mixed in polyethylene and ethylene-propylene copolymer were investigated by means of oxygen consumption and gas evolution. The antioxidants were NBC, Irganox 1010, and DPPD, and the antirad agent was propyl fluoranthene (PFR). A small amount of the antioxidant (0.5 phr) in polymer decreased oxygen consumption by one-half or one-third compared with pure polymer, but the activity was lost with increasing irradiation. The antirad agent also decreased oxygen consumption and it was assumed to act as the energy transfer agent in the polymer matrix.     

An effective synthesis of α-glycosides of -acetylneuraminic acid derivatives by use of 2-deoxy-2β-halo-3β-hydroxy-4,7,8,9-tetra- -acetyl- -acetylneuraminic acid methyl ester

Condensation of a new glycosyl donor, methyl 5-acetamido-4, 7,8,9-tetra- -acetyl-2,3-dibromo-2,3,5-trideoxy-β- -2-nonulopyranosonate with various acceptors such as methyl 2,3,4-tri- -benzyl-α- -glucopyranoside, cholesterol, methyl 2,4,6-tri- -bonzyl-α- -galactopyranoside, and nethyl 5-acetamido-4,7,9-tri- -acetyl-2,6-anhydro-3,5-dideoxy- -non-2-enopyranosonate gave only the corresponding β-glycosides. The 3α-bromo group of the glycoaides obtained above was reduced with tributylstannane to the corresponding glycosids, which were deprotected to give the free glycoaides in high yields.     

Stereochemistry of iejimalide B

The absolute configurations at five chiral centers, except for C-32(S) reported previously, in iejimalide B (1), a potent cytotoxic 24-membered macrolide isolated from a tunicate Eudistoma cf. rigida, were assigned as 4R, 9S, 17S, 22S, and 23S on the basis of detailed analysis of NMR data and chemical means. Furthermore, the structure of iejimalide B was revised from 2 (original: 13E) to its 13Z-isomer (1).