Enantioselective synthesis of silanol

An enantioselective nucleophilic substitution reaction of achiral dialkoxysilane has been developed. The reaction proceeds with efficient stereocontrol on the silicon chirality center to give the enantioenriched silyl ether, which can be converted to the silanol without loss of enantiopurity. We have analyzed the steric course of the reaction by using DFT calculations and propose a transition state model to explain the observed enantioselectivity.     

Determination of cadmium in grains by isotope dilution ICP–MS and coprecipitation using sample constituents as carrier precipitants

A coprecipitation method using sample constituents as carrier precipitants was developed that can remove molybdenum, which interferes with the determination of cadmium in grain samples via isotope dilution inductively coupled plasma mass spectrometry (ID-ICPMS). Samples were digested with HNO₃, HF, and HClO₄, and then purified 6 M sodium hydroxide solution was added to generate colloidal hydrolysis compounds, mainly magnesium hydroxide. Cadmium can be effectively separated from molybdenum because the cadmium forms hydroxides and adsorbs onto and/or is occluded in the colloid, while the molybdenum does not form hydroxides or adsorb onto the hydrolysis colloid. The colloid was separated by centrifugation and then dissolved with 0.2 M HNO₃ solution to recover the cadmium. The recovery of Cd achieved using the coprecipitation was >97%, and the removal efficiency of Mo was approximately 99.9%. An extremely low procedural blank (below the detection limit of ICPMS) was achieved by purifying the 6 M sodium hydroxide solution via Mg coprecipitation using Mg(NO₃)₂ solution. The proposed method was applied to two certified reference materials (NIST SRM 1567a wheat flour and SRM 1568a rice flour) and CCQM-P64 soybean powder. Good analytical results with small uncertainties were obtained for all samples. This method is simple and reliable for the determination of Cd in grain samples by ID-ICPMS. Figure Overview of a coprecipitation method using sample constituents     

Dynamic crack-tip singular stress in a cylindrically orthotropic elastic solid

Anti-plane wave motion is induced in a cylindrically orthotropicelastic solid containing a semi-infinite stress-free crack,by a point impulsive body force. First, the static version ofthe problem is solved for the fracture stress _z. Here, a globalsolution is obtained and then examined at the crack tip in orderto determine the nature of the spatial singularity. Next, thedynamic problem is treated and it is found that the dominantspatial singularity for _z at the crack tip is the same as inthe static case. However, the dynamic part of the stress intensityfactor, T, may introduce a further singularity. Several equivalentexpressions are presented for T, one of which is examined insome detail.     

Sequential injection chemiluminescence immunoassay for nonionic surfactants by using magnetic microbeads

A rapid and sensitive immunoassay based on a sequential injection analysis (SIA) using magnetic microbeads for the determination of alkylphenol polyethoxylates (APnEOs) is described. An SIA system was constructed from a syringe pump, a switching valve, a flow-through type immunoreaction cell equipped with a photon counting unit and a neodymium magnet. Magnetic beads, to which an anti-APnEOs monoclonal antibody was immobilized, were used as a solid support in an immunoassay. The introduction, trapping and release of the magnetic beads in and from the immunoreaction cell were controlled by means of a neodymium magnet and adjusting the flow of a carrier solution. The immunoassay was based on an indirect competitive immunoreaction of an anti-APnEOs monoclonal antibody immobilized on the magnetic beads with a sample APnEOs and a horseradish peroxidase (HRP)-labeled APnEOs in the same sample solution, and was based on the subsequent chemiluminscence reaction of HRP on the magnetic microbeads with a luminol solution containing hydrogen peroxide and p-iodophenol. The anti-APnEOs antibody was immobilized on the magnetic microbeads by coupling the antibody with the magnetic beads after activation of a carboxylate moiety on the surface of the magnetic beads that had been coated with a polylactic acid film. The antibody immobilized magnetic beads were introduced in the immunoreaction cell and trapped in it by the neodymium magnet, which was equipped beneath the immunoreaction cell. An APnEOs sample solution containing the HRP-labeled APnEOs at a constant concentration, and a luminol solution containing hydrogen peroxide and p-iodophenol were sequentially introduced into the immunoreaction cell, according to an SIA programmed sequence. Chemiluminescence emission was monitored by means of a photon counting unit located at the upper side of the immunoreaction cell by collecting the emitted light with a lens. A typical sigmoidal calibration curve was obtained, when the logarithm of the concentration of APnEOs was plotted against the chemiluminescence intensity as the number of photons in 100 ms using standard APnEOs sample solutions at various concentrations (0–1000 ppb) under optimum conditions. The lower detection limit defined as IC₈₀ is ca 10 ppb. The time required for analysis is less than 15 min per a sample. The present method was successfully applied to the determination of APnEOs in river water.     

N-long-chain monoacylated derivatives of 2,6-diaminopyridine with antiviral activity

N-Monoacyl-2,6-diaminopyridines (2a-c) and N,N'-diacyl-2,6-diaminopyridines (3a-c) were synthesized from 2,6-diaminopyridine by acylation with the corresponding acyl halide or by dehydration with the corresponding carboxylic acid using 1,3-dicyclohexylcarbodiimide (DCC). The antiviral activities of N-monoacyl- and N,N'-diacyl-2,6-diaminopyridines (2a-c and 3a-c) were estimated using plaque reduction assay with HSV-1. All N-monoacyl derivatives (2a-c) showed significant anti-herpes simplex virus (HSV)-1 activity (EC(50) = 15.3-18.5 microg/ml). The CC(50) values of 2a-c measured using Vero cells ranged at 37.5-50.0 microg/ml. These compounds showed no significant antibacterial activities with Escherichia coli or Staphylococcus aureus even at a concentration of 1 mg/ml. The N,N'-diacyl derivatives (3a-c) showed no significant anti-HSV-1 activity.     

Investigation of molecular chain orientation change of polymer crystals in phase transitions by friction anisotropy measurement

Direct observation of the molecular orientation change in polymer crystals provides us visible information for understanding their structural phase-transition mechanisms. In this letter, we successfully identified the main-chain orientation of poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) crystals over all directions using friction anisotropy measured by lateral-modulation friction force microscopy (LM-FFM). This technique made possible our investigation of molecular orientation changes caused by a ferroelectric phase transition and also a fabrication process for artificial nanometer-scale structures. These results give us visual information that is directly connected to the transition mechanisms.     

Gelation in Multiple Link System

The critical point theory is generalized to include gelation in multilink system with f functional units and J junction points. The equations derived include, as special cases, the cyclotrimerization model of J = 3, and the R–A_f model of J = 2. The theory is applied to the recent observation of the cyclotrimerization of bisphenol‐A dicyanate. The theoretical prediction agrees exactly with the Stutz‐Simak observation, D_c = 0.504, and accords with the Georjon‐Galy‐Pascault observation, giving a confirmation of the physical soundness of the theory. Under the smoothness assumption, we derive post‐gelation relationships with loop formation, the result suggesting the formation of permanent sol molecules that resist being absorbed into gel phase throughout an entire reaction process.

Representation of binary branching.     

An accurate numerical multicenter integration for molecular orbital theory

A powerful and accurate numerical three‐dimensional integration scheme was developed especially for molecular orbital calculations. A multicenter integral is decomposed into the sum of single‐center integrals using nuclear weight functions and calculated using Gaussian quadrature rules. The decomposed single‐center integrands show strong anisotropy. With a careful selection of the Gaussian quadrature rule according to the anisotropy, it is possible to obtain an accuracy of 13 digits with a small number of integration points for the overlap integrals, normalization integrals, and molecular integrals for the hydrogen molecule. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 72: 509–523, 1999     

Controlling chaos in dynamic-mode atomic force microscope

We successfully demonstrated the first experimental stabilization of irregular and non-periodic cantilever oscillation in the amplitude modulation atomic force microscopy using the time-delayed feedback control. A perturbation to cantilever excitation force stabilized an unstable periodic orbit associated with nonlinear cantilever dynamics. Instead of the typical piezoelectric excitation, the magnetic excitation was used for directly applying control force to the cantilever. The control force also suppressed the cantilever's occasional bouncing motions that caused artifacts on a surface image.