Kinetic Studies of Chromic Acid Oxidation of Glyoxal

The kinetics of chromic acid oxidation of glyoxal is reported. The reaction is first-order in glyoxal and indicates a gradual change from a first-order to a zero-order dependence on acidity. The kinetic nature of this reaction has been studied and the rate law is consistent with a proposed mechanism as follows; rate = kK_b, K[Cr⁺⁶][Gx][H⁺]/(l+0.238[H⁺]) at 25°C. The product analysis indicates that formic acid is the oxidation product under similar kinetic condition.     

Preparation and characterization of polyimide-nanogold nanocomposites from 3-mercaptopropyltrimethoxysilane encapsulated gold nanoparticles

In this study, we report a new design to prepare polyimide-nanogold nanocomposites of high Au content and good thermal stability. The nanocomposites were prepared from the coupling agent (3-aminopropyltriethoxysilane, APS) capped poly(amic acid) (PAA-APS) and 3-mercaptopropyltrimethoxysilane (MPS) stabilized gold nanoparticles (MPS-Au). The Si-OR groups of MPS on the surface of MPS-Au provided further reaction with APS, hence the covalent bonds between PAA and MPS-Au were formed. PAA-Au was converted into PI-Au nanocomposite by a multiple-step baking. The results of particle-sized analysis show that the sizes of the synthesized MPS-Au from different MPS/Au mole ratios (2 and 0.5) are about 2 nm and 5 nm, respectively. FE-SEM images show that MPS-Au particles are dispersed well in the prepared nanocomposites and no large-scale aggregation occurs. TGA results indicate that the decomposition temperature of each nanocomposite prepared from its washed precursor is lower than that of APS-capped polyimide, but the temperature of maximum decomposed rate of each nanocomposite is higher than that of APS-capped polyimide. The results show the high thermal stability and application potentials of the prepared polyimide-nanogold nanocomposites.     

Acyl and silyl group effects in reactivity-based one-pot glycosylation: synthesis of embryonic stem cell surface carbohydrates Lc4 and IV(2)Fuc-Lc4

Relative reactivity evaluations showed the graded arming of toluenyl thioglucosides by variously positioned silyl groups but not by their acyl counterparts. These findings were applied in reactivity-based one-pot assembly of linker-attached Lc(4) and IV(2)Fuc-Lc(4), which are components of human embryonic stem cell surface. The sugar-galectin-1 binding was also examined.     

Phase transitions of pure and Ba-doped BiFeO3 under high pressure

In order to evaluate the effect of impurity substitution on phase transition of BFO, we report high-pressure X-ray diffraction experiments on pure and Ba-doped BiFeO₃ powders in diamond-anvil cells up to 18.7 GPa. A low-temperature hydrothermal synthesis route was utilized to fabricate these two samples. The experimental results reveal that two structural phase transitions take place in these two different samples in the investigated pressure range. As two ADXRD data sets are compared, it is shown that the intermediate phase II is not detected in Ba-doped sample. In addition, modifications in phase transition behavior and compressibility due to a minor Ba incorporation highlight the high sensitivity of BFO to variations of chemical composition.     

Polarization-Sensitive Optical Coherence Tomography using only Linearly Polarized Light

This work presents polarization-sensitive optical coherence tomography (PS-OCT) using only linearly polarized light. The main characteristics of linear PS-OCT include the following. (1) In a turbid medium with linear birefringence, the degree of polarization (DOP) of backscattered linearly incident polarized light does not change significantly with the increase of birefringence value; (2) the phase retardation of the sample can be obtained from only the phase difference between the orthogonal polarization heterodyne signals, so a common phase noise rejection mode is introduced. These advantages may not only support the immunity of background phase noise and laser frequency noise, but also increase the sensitivity of phase retardation measurements; (3) the dynamic range of phase retardation in this system is between 0° and 180°