Aqueous phase-synthesized small CdSe quantum dots: adsorption layer structure and strong band-edge and surface trap emission

We synthesized, in aqueous solution at room temperature, small water-soluble CdSe quantum dots (QDs) with strong photoluminescence (PL) and then correlated the PL with their adsorption layer structure. For synthesizing the QDs, their initial synthesis condition was controlled to form small Cd-containing species capable of passivating dangling bonds on the CdSe core surface. Each CdSe QD (d ~ 2.5 nm) consisted of a CdSe core (d ~ 2.1 nm), a cysteine (cys)-ligand shell, and an adsorption layer composed of Cd–cys complexes (mainly CdL(-H)⁻, cys ≡ H₂L), cys (as L²⁻), Cd(OH)₂, and CdO _x (x ≥ 1). Our CdSe QDs showed strong blue band-edge PL as well as strong green surface trap PL. Their PL quantum yield (QY) of ~18% was unexpectedly high, considering their extremely small core size and their absence of any wide-bandgap inorganic shell. We attributed the QY to their adsorption layer species. The small weakly charged Cd–cys complex and the small neutral cadmium oxides in the adsorption layer could relatively readily diffuse into the unprotected surface sites on the core. These wide-bandgap species coalesced selectively on the unprotected surface sites with minimal spatial disturbance to the preexisting surface Cd-ligand coordination, and passivated them effectively. These decreased nonradiative recombination of the excitons significantly and thus led to the unexpectedly high QYs.     

An asymmetric approach to the synthesis of trans-dihydrindandione

A three-step asymmetric approach to the synthesis of (3aS,7aS)-3a,4-dihydro-7a-methyl-1,5(7aH)-indandione in 60% enantiomeric excess is described.     

Fluid-dynamic interaction between two spheres

Experiment of fluid-dynamic interaction between two spheres was conducted to obtain basic information concerning the two-phase flow, especially in dense phase. Two or three spheres were set up in a water tunnel in the longitudinal or transverse direction with Reynolds numbers less than 10³. The flow behind the sphere was visualized by the use of condense milk and change in vortex structure due to the interaction was observed in detail. Additionally, drag force on the sphere was measured by a pendulum method which was developed to detect small drag, and the range of distance in which the drag is affected by the interaction was shown.     

Accurate quantitation of salivary and pancreatic amylase activities in human plasma by microchip electrophoretic separation of the substrates and hydrolysates coupled with immunoinhibition

A high-performance determination system for alpha-amylase isoenzyme activities in human plasma involving microchip electrophoresis with a plastic chip was developed. The combination of microchip electrophoresis for substrate and hydrolysate separation and an immunoinhibition method for the differentiation of isoenzyme activities using antihuman salivary amylase (S-AMY) mAb allowed the highly selective determination of amylase isoenzyme (S-AMY and pancreatic amylase (P-AMY)) activities even in a complex matrix such as a crude plasma sample. We used 8-aminopyrene-1,3,6-trisulfonic acid (APTS)-labeled maltohexaose (G6) as a substrate. Amylase in a human plasma sample hydrolyzed APTS-G6 into APTS-maltotriose (G3) and G3, which was measured as the fluorescence intensity of APTS-G3 on microchip electrophoresis. A double logarithm plot revealed a linear relationship between amylase activity and fluorescence intensity in the range of 5-500 U/L of amylase activity (r2=0.9995, p<0.01), and the LOD was 4.38 U/L. Amylase activities in 13 subjects determined by the present method were compared with the results obtained by conventional methods with nitrophenylated oligosaccharides as substrates, respectively. Good correlations were observed for each method on simple linear regression analysis (both p<0.01). The reproducibilities of within-days for total amylase and P-AMY were 2.98-6.27 and 3.83-6.39%, respectively, and these between-days were 2.88-5.66 and 3.64-5.63%, respectively. This system enables us to determine amylase isoenzyme activities in human plasma with high sensitivity and accuracy, and thus will be applicable to clinical diagnosis.     

Microchip analysis of plant glucosinolates

We describe a new and selective analytical method for the separation and quantitation of plant glucosinolates. The new method, which utilizes microchip CE (micro-CE) with fluorescence detection, circumvents the multistep procedures characteristic of conventional methods. Glucosinolates form charge transfer complexes with the xanthene dyes phloxine-B and eosin-B. The glucosinolates-phloxine-B complex cannot be excited at 470 nm. Thus, the decrease in peak intensity of phloxine-B after complex formation is used to quantitatively measure total glucosinolates in Arabidopsis thaliana seeds. For qualitative analysis, complex formation with eosin-B is used. The sensitivity of eosin-B detection at excitation/emission 470 nm/540 nm was low. However, sensitivity increased following complex formation with sinigrin (> or =3 microg/mL). A batch-learning, self-organizing map was applied to visualize and organize analytical data into 2-D matrix with similar and related data clustered together or near each other. This organized matrix was used to optimize electrophoretic conditions for the analysis. This study suggests potential applications of micro-CE in plant metabolomics analyses without use of labeling fluorophores.     

Synthesis and reactions of a stable 1,2-diaryl-1,2-dibromodisilene: a precursor for substituted disilenes and a 1,2-diaryldisilyne

Synthesis and isolation of the stable diaryldibromodisilene, Bbt(Br)SiSi(Br)Bbt, has been accomplished for the first time. The dibromodisilene underwent substitution reactions with organometallic reagents on the low-coordinated silicon atom to afford the corresponding substituted disilenes. Furthermore, the reaction of 1 with t-BuLi afforded the corresponding 1,2-diaryldisilyne, BbtSi[triple bond]SiBbt, the characters of which were revealed by spectroscopic and crystallographic analyses.     

Properties of TiO2-polyacrylic acid dispersions with potential for molecular recognition

Titanium dioxide (TiO₂)/polyacrylic acid (PAA) (TiO₂/PAA) particles were formed by mixing PAA and an acidic solution of TiO₂ nanoparticles in dimethylformamide (DMF) followed by heat treatment. TEM and particle analysis showed that the resulting particles had a narrow size distribution. The colloid was very stable and aggregation was not observed over a wide pH range (3–9) or at high salt concentration. The residual carboxylic acid of PAA could be modified via EDC/NHS activation to form an amide bond with a protein. An antibody was attached to the hybrid nanoparticle and specific binding to antigen was monitored by surface plasmon resonance. The results suggest that TiO₂/PAA nanoparticles are candidates as the base component of a photocatalytic system with potential for substrate selectivity.     

An anthracene-based photochromic macrocycle as a key ring component to switch a frequency of threading motion

A concept and demonstration of a switching in frequencies of molecular motions are described using a pseudorotaxane system. The setup consists of dibenzylammonium hexafluorophosphate and a photochromic dianthrylethane-based [24]crown-8-type macrocycle, which we designed as a key ring component for the pseudorotaxane system having photocontrollable threading functionality by changing the size of ring component due to the action of light.     

Structural analysis of polymer-brush-type cellulose β-ketoesters by molecular dynamics simulation

The reason for anomalous NMR patterns of cellulose β-ketoesters, which were prepared by reaction between cellulose and ketene dimers having long alkyl chains (AKDs) under homogeneous conditions using a cellulose solvent system, was studied by molecular dynamics simulation. Cellulose/AKD β-ketoester models with degree of substitution (DS) 2.0 and degree of polymerization (DP) 5, 10, 20 or 40, and cellulose/fatty acid ester models with DS 3.0 and DP 5, 10, 20 or 40 were assembled in the simulation. The calculated results were compared with those obtained by NMR and conformation analyses of the actually prepared cellulose derivatives. The molecular dynamics simulation data showed that the average velocities of anhydroglucose units in cellulose/AKD β-ketoesters were approximately one tenth of those in cellulose/fatty acid esters. Thus, cellulose chains in the cellulose/AKD β-ketoesters are extremely restricted in motion by the β-ketoester substituents. The solid-like behavior of cellulose chains in cellulose/AKD β-ketoesters in solution state is, therefore, explainable by strong restriction in motion of cellulose chains by long, branched and bulky substituents introduced into cellulose hydroxyls in high densities via β-ketoester bonds.