Search for CP violation in tau--> K(pi)nu(tau) decays

We search and find no evidence for CP violation in tau decays into the K(pi)nu(tau) final state. We provide limits on the imaginary part of the coupling constant Lambda describing a relative contribution of the CP violating processes with respect to the standard model to be -0.172相似文献   

Alkali Metal- and Ammonium Picrate Extraction and Complex Forming Capabilities of d-Glucose and d-Mannose-based Lariat Ethers

The alkali metal- and ammonium picrate extracting ability of d-glucose- and d-mannose-based 15-crown-5 ethers and related lariat ethers was investigated in dichloromethane – water system. A heteroatom was waried in the crown ether containing a 4,6-O-benzylidene-α-d-glucopyranoside unit 6, (X=O), 2 (X=S) and 8a (X=NH). Extracting ability of the latter species (8a) was excellent (97–99%) in regard of all cations (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺ and NH₄⁺) examined, it was not, howewer, selective. Introduction of a side arm on the nitrogen atom of 8a decreased the extracting ability, but increased the selectivity. In this series of compounds (8b–f, 4), 4 with a pyridylethyl substituent allowed the extraction of sodium picrate in 72%. The glucose-based macrocycles 8a, 8e and 8f formed a stronger complex with the cations examined than the mannose-based analogues 9a, 9e and 9f, that can be explained by the all-gauche conformation of the former ones. It was pointed out that in the case of crowns with tertiary amine moieties, the basicity increases the quantity of the picrates extracted. According to complex forming measurements by FAB-MS, the best sodium ion selectivity was achieved by the γ-hydroxypropyl substituted lariat ether (8e). Possible structures of the complexes formed by the two types of monosacharides with sodium cation were evaluated by molecule modelling calculations.     

Ionized bicyclo[2.2.2]oct-2-ene: a twisted olefinic radical cation showing vibronic coupling

The bicyclo[2.2.2]oct-2-ene radical cation (1(.+)) exhibits matrix ESR spectra that have two very different types of gamma-exo hydrogens (those hydrogens formally in a W-plan with the alkene pi bond), a(2H) about 16.9 G and a(2H) about 1.9 G, instead of the four equivalent hydrogens as would be the case in an untwisted C(2v) structure. Moreover, deuterium substitution showed that the vinyl ESR splitting is not resolved (and under about 3.5 G); this is also a result of the twist. Enantiomerization of the C(2) structures is rapid on the ESR timescale above 110 K (barrier estimated at 2.0 kcalmol(-1)). Density functional theory calculations estimate the twist angle at the double bond to be 11-12 degrees and the barrier as 1.2-2.0 kcalmol(-1). Single-configuration restricted Hartree-Fock (RHF) calculations at all levels that were tried give untwisted C(2v) structures for 1(.+), while RHF calculations that include configuration interactions (CI) demonstrate that this system undergoes twisting because of a pseudo Jahn-Teller effect (PJTE). Significantly, twisting does not occur until the sigma-orbital of the predicted symmetry is included in the CI active space. UHF calculations at all levels that include electron correlation (even semiempirical) predict twisting at the alkene pi bond because they allow the filled alpha and the beta hole of the SOMO to have different geometries. The 2,3-dimethylbicyclo[2.2.2]oct-2-ene radical cation (2(.+)) is twisted significantly less than 1(.+), but has a similar temperature for maximum line broadening. Neither the 2,3-dioxabicyclo[2.2.2]octane radical cation (3(.+)) nor its 2,3-dimethyl-2,3-diaza analogue (5(.+)) shows any evidence of twisting. Calculations show that the orbital energy gap between the SOMO and PJTE-active orbitals for 3(.+) is too large for significant PJTE stabilization to occur.     

Probing affinity via capillary electrophoresis: advances in 2003–2004

This review addresses recent advances in capillary electrophoresis of biological-based molecular interaction from a broader perspective, based on applications reported during the period 2003–2004. These capillary electrophoresis-based studies of molecular interactions include affinity capillary electrophoresis, electrokinetic chromatography, and free zone electrophoresis. The review is written as a general synopsis of applications and does not cover the theory or protocol involved in the implementation of the analyses.The caption to Fig. 3 was incorrect. This revised version replaces the article published online on 10 February 2005.     

An atomic-emission study of the removal and recovery of chromium from solution by an algal biomass (Chlorella vulgaris)

Inductively coupled plasma atomic-emission spectrometry has been used to study the removal of chromium, principally in the sexivalent oxidation state, from solution by an algal biomass, Chlorella vulgaris, and its subsequent recovery. Binding of the chromium at the 5-100 mug/ml level was maximal (75%) at pH 3 within 3 min, with 5 mg of algae. Quantitative recovery of chromium was achieved by lowering the pH. The algae could be used four times in removal/recovery cycles before losing their 75% removal efficiency.     

Isolation and spectroscopic study of pectic substances from kenaf (Hibiscus cannabinus L.)

Pectins were isolated from bark, wood and pith of kenaf (Hibiscus cannabinus L.) variety Cuba108. Imidazole was used as extractant. The isolated pectins were studied by 13C nuclear magnetic resonance (13C-NMR) spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). From the spectroscopic investigation, the isolated pectic substances were found similar to commercial pectins.     

The simultaneous determination of As,Cd, Co,Hg, Mo,and Zn in fresh water by neutron activation analysis

A radiochemical neutron activation method for the simultaneous determination of arsenic, cadmium, cobalt, mercury, molybdenum, and zinc in fresh water is described. The method is based on anion-exchange separation in hydrochloric acid media followed by simple precipitations. The determination limits, based on analysis of a 5-ml sample without preconcentration, and with a well-type NaI(Tl) detector, are as follows: As, 10^-3 μg l^-1 ; Cd, 6 × 10^-2 μg l^-1 ; Co, 4 × 10^-3 μg l^-1 ; Hg, 7 × 10^-3 μg l^-1 ; Mo, 10^-1 μg l^-1 ; Zn, 2 × 10^-1 μg l^-1. The method is adequate for the analysis of natural fresh waters.     

Unambiguous 13C-NMR assignments for isocyanate carbons of isophorone diisocyanate and reactivity of isocyanate groups in Z - and E-stereoisomers

Unambiguous ¹³C-NMR assignments for the primary (prim-) and secondary (sec-) isocyanate carbons of isophorone diisocyanate (IPDI) have been made by using two-dimensional NMR measurements. On the basis of the assignments, relative reactivity of the prim- and sec-isocyanate groups with n-butanol was studied by quantitative ¹³C-NMR analysis. The individual stereoisomers of IPDI (Z-IPDI and E-IPDI) and their equimolar mixture were reacted with n-butanol (IPDI/n-butanol = 2/1 molar ratio) at 50°C for 3 days. It was found that the sec-NCO is about 1.6 times more reactive than the prim-NCO in both Z- and E-isomers. Reactivity of the E-isomer was found to be slightly higher than that of the Z-isomer. When di-n-butyltin dilaurate (DBTDL) was used as a catalyst, the reactivity of the sec-NCO became about 12 times higher than that of the prim-NCO with both isomers. In the case of 1,4-diazabicyclo [2.2.2] octane (DABCO) catalyst, the prim-NCO was 1.2 times more reactive than the sec-NCO with both isomers.     

Biocatalytic Self-Assembly Cascades

The properties of supramolecular materials are dictated by both kinetic and thermodynamic aspects, providing opportunities to dynamically regulate morphology and function. Herein, we demonstrate time-dependent regulation of supramolecular self-assembly by connected, kinetically competing enzymatic reactions. Starting from Fmoc-tyrosine phosphate and phenylalanine amide in the presence of an amidase and phosphatase, four distinct self-assembling molecules may be formed which each give rise to distinct morphologies (spheres, fibers, tubes/tapes and sheets). By varying the sequence or ratio in which the enzymes are added to mixtures of precursors, these structures can be (transiently) accessed and interconverted. The approach provides insights into dynamic self-assembly using competing pathways that may aid the design of soft nanostructures with tunable dynamic properties and life times.