Stereoselective Aldol Reaction of α-Phenylseleno Esters

Abstract

The TiCl₄-catalyzed reaction of a-phenylseleno esters with aldehydes in the presence of Ph₃P or Ph₃P=O gives aldol products with high syn selectivity.     

Spectral diffusion in nitride quantum dots: Emission energy dependent linewidths broadening via giant built‐in dipole moments

We present a study about the origin of the huge emission linewidths broadening commonly observed for wurtzite GaN/AlN quantum dots. Our analysis is based on a statistically significant number of quantum dot spectra measured by an automatized µ‐photoluminescence mapping system applying image recognition techniques. A clear decrease of the single quantum dot emission linewidths is observed with rising overall exciton emission energy. 8‐band k · p based model calculations predict a corresponding decrease of the built‐in exciton dipole moments with increasing emission energy in agreement with the measured behavior for the emission linewidths. Based on this proportionality we explain the particular susceptibility of nitride quantum dots to spectral diffusion causing the linewidth broadening via the linear quantum‐confined Stark effect. This is the first statistical analysis of emission linewidths that identifies the giant excitonic dipole moments as their origin and estimates the native defect‐induced electric field strength to ～2 MV/m. Our observation is in contrast to less‐polar quantum dot systems as e.g. arsenides that exhibit a naturally lower vulnerability to emission linewidth broadening due to almost negligible exciton dipole moments. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A simple hemostasis model for the quantitative evaluation of hydrogel-based local hemostatic biomaterials on tissue surface

Several hemostat hydrogels are clinically used, and some other agents are studied for safer, more facile, and more efficient hemostasis. In the present paper, we proposed a novel method to evaluate local hemostat hydrogel on tissue surface. The procedure consisted of the following steps: (step 1) a mouse was fixed on a cork board, and its abdomen was incised; (step 2) serous fluid was carefully removed because it affected the estimation of the weight gained by the filter paper, and parafilm and preweighted filter paper were placed beneath the liver (parafilm prevented the filter paper's absorption of gradually oozing serous fluid); (step 3) the cork board was tilted and maintained at an angle of about 45 degrees so that the bleeding would more easily flow from the liver toward the filter paper; and (step 4) the bleeding lasted for 3 min. In this step, a hemostat was applied to the liver wound immediately after the liver was pricked with a needle. We found that (1) a careful removal of serous fluid prior to a bleeding and (2) a quantitative determination of the amount of excess aqueous solution that oozed out from a hemostat were important to a rigorous evaluation of hemostat efficacy. We successfully evaluated the efficacy of a fibrin-based hemostat hydrogel by using our method. The method proposed in the present study enabled the quantitative, accurate, and easy evaluation of the efficacy of local hemostatic hydrogel which acts as tissue-adhesive agent on biointerfaces.     

Palladium-catalyzed sp(3) CH activation of simple alkyl groups: direct preparation of indoline derivatives from N-alkyl-2-bromoanilines

The sp3 C-H activation of a simple alkyl group catalyzed by palladium(0) provides a novel and convenient strategy for the synthesis of various indolines from simple precursors, such as N-alkyl-2-bromoanilines. This study demonstrates that assisting moieties in the substrate such as a pyridine or quaternary carbon are not always necessary for sp3 C-H activation.     

Convergent synthesis and biological activity of the WXYZA'B'C' ring system of maitotoxin

The WXYZA'B'C' ring system ( 1) of maitotoxin (MTX) was synthesized in a convergent manner via successive coupling of the W, Z, and C' ring fragments through construction of the XY and A'B' ring systems. The synthetic segment 1 blocked the hemolytic activity elicited by MTX.     

Combinatorial synthesis of the 1,5-polyol system based on cross metathesis: structure revision of amphidinol 3

Combinatorial synthesis of a 1,5-polyol system corresponding to the C1-C14 unit of amphidinol 3 (AM3) and its diastereomers was achieved via chemoselective cross metathesis as the key step. Comparison of (13)C NMR data of the synthetic specimens with that of AM3 led to a controversy regarding the originally proposed structure. From GC-MS analysis of the degradation product, the absolute configuration at C2 of AM3 has been revised to be R.     

High-throughput turbidimetric screening for heparin-neutralizing agents and low-molecular-weight heparin mimetics

Safer heparin-neutralizing agents are currently required to replace protamine, the use of which causes adverse effects such as anaphylaxia. Low-molecular-weight (LMW) heparin mimetics that potentiate antithrombin III (AT) action are also valuable as anti-thrombotics. This paper describes a high-throughput assay for both heparin-neutralizing agents and LMW heparin mimetics without the use of blood preparations. The assay is based on turbidimetric measurement of a solution of collagen, heparin, and a test compound. Native collagen molecules spontaneously form insoluble fibrils when transferred to a physiological buffer, and this process is inhibited by heparin. In the presence of a heparin-neutralizing agent or an LMW heparin mimetic, the inhibitory effect of heparin is canceled and turbidity increase is retrieved. We demonstrated that this assay is effective in detecting potential agents with high reliability (Z' factor=0.9). The screening of a chemical library (34400 compounds) was further performed in a 384-well format, and led to the identification of a novel heparin-neutralizing agent. Since this assay protocol is feasible for an automated high-throughput screening (HTS) system, it could enhance the lead seeking process for drugs related to heparin/heparan sulfate (HS) functions.     

Fast algorithms for floating-point interval matrix multiplication

We discuss several methods for real interval matrix multiplication. First, earlier studies of fast algorithms for interval matrix multiplication are introduced: naive interval arithmetic, interval arithmetic by midpoint-radius form by Oishi-Rump and its fast variant by Ogita-Oishi. Next, three new and fast algorithms are developed. The proposed algorithms require one, two or three matrix products, respectively. The point is that our algorithms quickly predict which terms become dominant radii in interval computations. We propose a hybrid method to predict which algorithm is suitable for optimizing performance and width of the result. Numerical examples are presented to show the efficiency of the proposed algorithms.     

Exciton localization of single-walled carbon nanotubes revealed by femtosecond excitation correlation spectroscopy

Photoluminescence (PL) dynamics in single-walled carbon nanotubes (SWNTs) has been studied by the femtosecond excitation correlation method with a 150 fs time resolution. The SWNT samples were synthesized by different methods and suspended in gelatin films or D2O solutions. The PL dynamics of SWNTs depends on the local environment surrounding the SWNTs rather than the synthesis methods. The very weak temperature dependence of tauPL and the environment-dependent tauPL reveal that the PL relaxation process is dominated by the interplay between free excitons and weakly localized excitons.