Beta-structure of polypeptides in non-aqueous solutions. I. Spectral characteristics of the polypeptide backbone

The optical rotatory features of the beta-structure of the polypeptides in non-aqueous solutions and films cast from these solutions have been investigated. The beta-structure of poly-S-benzyl-L-cysteine, poly-S-carbobenzoxy-L-cysteine and poly-S-benzyl-L-cysteine, poly-S-carbobenzoxy-L-cysteine and poly-O-carbo-bands of their films. The optical rotatory dispersion (ORD) and circular dichroism (CD) spectra of these polypeptides are found to be very similar in both film and solution. In solvents promoting the beta-structure, the polypeptides are characterized by CD troughs in the n-pi* transition region of the peptide chromophore. The ORD spectra are found to be positive in sign throughout the visible and accessible ultraviolet regions and are interpreted in terms of the possible existence of a relatively much larger positive pi-pi* CD bands as compared with the negative n-pi* band. The rotatory data obtained in the non-aqueous solution are compared with those obtained for other poly peptides in aqueous solutions, with respect to the type and extent of beta-structure present.

Beta-structure of polypeptides in non-aqueous solutions. II. Side-chain orientation

The specific side-chain orientations of the phenyl group in the polypeptides poly-S-benzyl-L-cysteine, poly-S-carbobenzoxy-L-cysteine and poly-O-carbobenzoxy-L-serine in the beta-structure have been studied by spectral measurements in solutions. All the three polypeptides exhibit aromatic CD bands, indicating the asymmetric placement of the side-chain phenyl rings when the polypeptide backbone takes up the antiparallel beta-structure. Supporting evidence for this is derived from n.m.r. spectra of the polypeptides, which show upfield shift of the phenyl protons due to the stacking of the aromatic rings. Molecular model building studies reveal the stacking of alternate phenyl groups along the polypeptide chain.

On the athermal nature of the beta to omega transformation

One characteristic feature of the athermal beta -> omega transformation is the short time scale of the transformation. So far, no clear understanding of this issue exists. Here we construct a model that includes contributions from a Landau sixth-order free energy density, kinetic energy due to displacement, and the Rayleigh dissipation function to account for the dissipation arising from the rapid movement of the parent product interface during rapid nucleation. We also include the contribution from omega-like fluctuations to local stress. The model shows that the transformation is complete on a time scale comparable to the velocity of sound. The estimated nucleation rate is several orders higher than that for diffusion-controlled transformations. The model predicts that the athermal omega phase is limited to a certain range of alloying composition. The estimated nucleation rate and the size of ``isothermal'' particles beyond 17% Nb are also consistent with experimental results. The model provides an explanation for the reprecipitation process of the omega particles in the ``cleared'' channels formed during deformation of omega-forming alloys. The model also predicts that acoustic emission should be detectable during the formation of the athermal phase. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Designed three-stranded beta-sheet in an alpha/beta hybrid peptide

The incorporation of beta-amino acid residues into the antiparallel beta-strand segments of a multi-stranded beta-sheet peptide is demonstrated for a 19-residue peptide, Boc-LV(beta)FV(D)PGL(beta)FVVL(D)PGLVL(beta)FVV-OMe (BBH19). Two centrally positioned (D)Pro-Gly segments facilitate formation of a stable three-stranded beta-sheet, in which beta-phenylalanine ((beta)Phe) residues occur at facing positions 3, 8 and 17. Structure determination in methanol solution is accomplished by using NMR-derived restraints obtained from NOEs, temperature dependence of amide NH chemical shifts, rates of H/D exchange of amide protons and vicinal coupling constants. The data are consistent with a conformationally well-defined three-stranded beta-sheet structure in solution. Cross-strand interactions between (beta)Phe3/(beta)Phe17 and (beta)Phe3/Val15 residues define orientations of these side-chains. The observation of close contact distances between the side-chains on the N- and C-terminal strands of the three-stranded beta-sheet provides strong support for the designed structure. Evidence is presented for multiple side-chain conformations from an analysis of NOE data. An unusual observation of the disappearance of the Gly NH resonances upon prolonged storage in methanol is rationalised on the basis of a slow aggregation step, resulting in stacking of three-stranded beta-sheet structures, which in turn influences the conformational interconversion between type I' and type II' beta-turns at the two (D)Pro-Gly segments. Experimental evidence for these processes is presented. The decapeptide fragment Boc-LV(beta)FV(D)PGL(beta)FVV-OMe (BBH10), which has been previously characterized as a type I' beta-turn nucleated hairpin, is shown to favour a type II' beta-turn conformation in solution, supporting the occurrence of conformational interconversion at the turn segments in these hairpin and sheet structures.

Copper-Catalyzed Decarboxylative Sulfonylation of alpha,beta-Unsaturated Carboxylic Acids

Copper-catalyzed, ligand-promoted decarboxylative coupling of readily available a,fi-unsaturated acids with sodium aryl sulfinates is presented. This method provides a new avenue for the synthesis of vinyl sulfones via a decarboxylative radical coupling strategy by employing a catalytic amount of Cu(ClO4)(2)center dot 6H(2)O, TBHP in decane as an oxidant, and 1,10-phenanthroline as a ligand. The salient feature of this method is that it furnishes exclusively the (E)-isomer.

C-11/C-9 Helices in Crystals of alpha beta Hybrid Peptides and Switching Structures between Helix Types by Variation in the alpha-Residue

Close-packed helices with mixed hydrogen bond directionality are unprecedented in the structural chemistry of alpha-polypeptides. While NMR studies in solution state provide strong evidence for the occurrence of mixed helices in (beta beta)(n) and (alpha beta)(n) sequences, limited information is currently available in crystals. The peptide structures presented show the occurrence of C-11/C-9 helices in (alpha beta)(n) peptides. Transitions between C-11 and C-11/C-9 helices are observed upon varying the alpha-amino acid residue.

Sulfenyiation of beta-Diketones Using C-H Functionalization Strategy

Sulfenylation of beta-diketones is challenging as beta-diketones undergo deacylation after sulfenylation in the reaction medium. The sulfenylation of beta-diketones without deacylation under metal-free conditions at ambient temperature via a cross dehydrogenative coupling (CDC) strategy is reported. The resultant products can be further manipulated to form alpha,alpha-disubstituted beta-diketones and pyrazoles.

Catalytic Aldol-Cyclization Cascade of 3-Isothiocyanato Oxindoles with alpha-Ketophosphonates for the Enantioselective Synthesis of beta-Amino-alpha-hydroxyphosphonates

A cascade aldol cyclization reaction between 3-isothiocyanato oxindoles and alpha-ketophosphonates has been developed for the synthesis of beta-amino-alpha-hydroxyphosphonate derivatives. Catalyzed by a quinine-based tertiary amino-thiourea derivative, this reaction delivers 2-thioxooxazolidinyl phosphonates based on a spirooxindole scaffold bearing two contiguous quaternary stereogenic centers in high yields with excellent diastereo- (up to >20:1 dr) and enantioselectivities (up to >99:1 er).

Residuos de antibióticos (tetraciclinas y betalactámicos) en leche entera de acopios de Matiguás - Matagalpa, mediante la prueba de Beta Star Combo en el período de noviembre 2010 a abril 2011

Al evaluar la presencia de residuos de antibióticos en leche cruda en acopios de Matiguás, Matagalpa, durante el periodo de noviembre 2010 – abril 2011, se determinó la presencia de residuos de antibióticos betalactámicos y tetraciclinas, estableciendo la familia de antibiótico con mayor presencia ,el mes con mayor positividad, estimando además la cantidad de leche con residuos de antibióticos. Se tomaron muestras de leche fresca de los acopios: San Martin, La patriota, San José de Paiwas y Lácteos Matiguas. Las muestras se sometieron a una prueba rápida para detección de residuos de antibióticos con el dispositivo Beta Star Combo. Para el análisis de los datos se usó el programa estadístico SPSS, aplicando la prueba de Chi2, resultando un 24 % de presencia de residuos de antibióticos del total de muestras, derivándose en 73.9% correspondiente a Tetraciclinas y 26.1 % correspondiente a Betalactámicos; correspondiendo al acopio San Martin y La patriota un 29% con 5 muestras positivas cada uno, Lácteos Matiguás con 6 % con una muestra positiva y San José de Paiwas con 35% con 6 muestras positivas a tetraciclinas. Para Betalactámicos: La patriota presentó 3 muestras positivas para un 50%, Lácteos Matiguás 17% (1 muestra positiva), San Jose de Paiwas 33% (2 muestras positivas), en la época lluviosa se presentaron 13 muestras positivas y en la época seca 10 muestras, concluyendo con la presencia de residuos de antibióticos en los acopios de Matiguás, siendo la familia de las Tetraciclinas la de mayor presencia. Los acopios con mayor cantidad de muestras positivas con residuos de antibióticos fueron San José de Paiwas y La Patriota, el mes con mayor presencia de antibióticos fue noviembre (6 muestras positivas), se estimó que la cantidad de leche contaminada por residuos de antibióticos fue de 138 000 L.

Experiments in Neutrino Mass and Mixing: Part I - New Limits on Heavy Neutrino Emission in Nuclear Beta Decay. Part II - Fast Neutron Backgrounds for the San Onofre Neutrino Detector

In Part I of this thesis, a new magnetic spectrometer experiment which measured the β spectrum of ^(35)S is described. New limits on heavy neutrino emission in nuclear β decay were set, for a heavy neutrino mass range between 12 and 22 keV. In particular, this measurement rejects the hypothesis that a 17 keV neutrino is emitted, with sin^2 θ = 0.0085, at the 6δ statistical level. In addition, an auxiliary experiment was performed, in which an artificial kink was induced in the β spectrum by means of an absorber foil which masked a fraction of the source area. In this measurement, the sensitivity of the magnetic spectrometer to the spectral features of heavy neutrino emission was demonstrated.

In Part II, a measurement of the neutron spallation yield and multiplicity by the Cosmic-ray Underground Background Experiment is described. The production of fast neutrons by muons was investigated at an underground depth of 20 meters water equivalent, with a 200 liter detector filled with 0.09% Gd-loaded liquid scintillator. We measured a neutron production yield of (3.4 ± 0.7) x 10^(-5) neutrons per muon-g/cm^2, in agreement with other experiments. A single-to-double neutron multiplicity ratio of 4:1 was observed. In addition, stopped π^+ decays to µ^+ and then e^+ were observed as was the associated production of pions and neutrons, by the muon spallation interaction. It was seen that practically all of the π^+ produced by muons were also accompanied by at least one neutron. These measurements serve as the basis for neutron background estimates for the San Onofre neutrino detector.

Synthesis and biological evaluation of N-acetyl-beta-aryl-1,2-didehydroethylamines as new HIV-1 RT inhibitors in vitro

A variety of N-acetyl-o-aryl-1,2-didehydroethylamines were synthesized by direct reduction-acetylation of beta-aryl-nitroolefins and assayed as HIV-1 non-nucleoside reverse transcriptase inhibitors (NNRTIs) for the first time. Compound 7a exhibited a TI v

Efficiency calibration of neutron detector array for beta decay of exotic nuclei

The research of the in-beam efficiency calibration of Neutron Detector Array of Peking University using N-17 and C-16 beams was introduced in this paper. The efficiency of neutron wall and ball are comparable to the foreign similar devices and neutrons can be detected from low to high energies in high efficiency.