Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.     

Rational design of combination enzyme therapy for celiac sprue

Celiac sprue (also known as celiac disease) is an inheritable, gluten-induced enteropathy of the upper small intestine with an estimated prevalence of 0.5%-1% in most parts of the world. The ubiquitous nature of food gluten, coupled with inadequate labeling regulations in most countries, constantly poses a threat of disease exacerbation and relapse for patients. Here, we demonstrate that a two-enzyme cocktail comprised of a glutamine-specific cysteine protease (EP-B2) that functions under gastric conditions and a PEP, which acts in concert with pancreatic proteases under duodenal conditions, is a particularly potent candidate for celiac sprue therapy. At a gluten:EP-B2:PEP weight ratio of 75:3:1, grocery store gluten is fully detoxified within 10 min of simulated duodenal conditions, as judged by chromatographic analysis, biopsy-derived T cell proliferation assays, and a commercial antigluten antibody test.     

Heterologous expression, purification, refolding, and structural-functional characterization of EP-B2, a self-activating barley cysteine endoprotease

We describe the heterologous expression in Escherichia coli of the proenzyme precursor to EP-B2, a cysteine endoprotease from germinating barley seeds. High yields (50 mg/l) of recombinant proEP-B2 were obtained from E. coli inclusion bodies in shake flask cultures following purification and refolding. The zymogen was rapidly autoactivated to its mature form under acidic conditions at a rate independent of proEP-B2 concentration, suggesting a cis mechanism of autoactivation. Mature EP-B2 was stable and active over a wide pH range and efficiently hydrolyzed a recombinant wheat gluten protein, alpha2-gliadin, at sequences with known immunotoxicity in celiac sprue patients. The X-ray crystal structure of mature EP-B2 bound to leupeptin was solved to 2.2 A resolution and provided atomic insights into the observed subsite specificity of the endoprotease. Our findings suggest that orally administered proEP-B2 may be especially well suited for treatment of celiac sprue.     

β—（酚酯基）乙基锗倍半氧化物的合成及对体外培养细胞的作用

β-羧基乙基锗倍半氧化物(即Ge-132)是一种无毒和具较强抗癌活性的有机锗化合物。为了进一步提高其抗癌活性。已对Ge-132进行了化学结构修饰。本文介绍8种未见报导的Ge-132衍生物,β-酚酯基乙基锗倍半氧化物的合成和体外培养细胞实验结果。     

A laser infrared source of nanosecond pulses tunable from 1.4 to 22 μm

A reliable source of coherent ns pulses of infrared radiation continuously tunable between 1.4 and 22 m has been designed and built with the aim of developing a time-resolved infrared vibrational spectroscopy for species adsorbed on surfaces. The system is based on a Nd: YAG-laser and dye-laser combination which drive difference mixing processes in a sequence of nonlinear optical crystals (two LiNbO₃, and a CdSe or AgGaS₂). The system operates at MW peak power levels above 2500 cm^–1, at kW power levels from 1000–2500 cm^–1 and at 10–100 W levels down to 450 cm^–1. These power levels are certainly sufficient for spectroscopic purposes, and at shorter wavelengths molecular pumping and applications requiring high-power should be possible. Vibrational spectra of a monolayer of CO adsorbed on Pt in an electrochemical cell have been obtained in an initial application of this source.     

Metal atoms and clusters in fullerene cages

Fullerenes containing metal atoms and clusters can be formed by the arc-vaporization method. The electronic structure of these metallofullerenes can be probed using magnetic resonance techniques. Electron paramagnetic resonance (EPR) spectra of LaC₈₂, YC₈₂, ScC₈₂ and Sc₃C₈₂ have been obtained. Metallofullerenes containing a single metal atom (MC₈₂ with M = La, Y, or Sc), have small hyperfine couplings and g-values close to 2, implying that they can be described as + 3 metal cations within — 3 fullerene radical anion cages. In the La and Y cases, additional EPR active MC₈₂ species have been found. The EPR spectrum of Sc₃C₈₂ shows that the metal atoms are equivalent, suggesting that they may form a triangular molecule. No EPR spectrum is found for Y₂C₈₂ or for Sc₂C_2n species (with 2n = 82,84,86), suggesting that they are diamagnetic. Sc NMR spectra of a solution containing Sc₂C_2n species have been obtained which confirm the diamagnetism of the discandium metallofullerenes.     

Fermentations of pectin-rich biomass with recombinant bacteria to produce fuel ethanol

Pectin-rich residues from sugar beet processing contain significant carbohydrates and insignificant amounts of lignin. Beet pulp was evaluated for conversion toethanol using recombinant bacteria as biocatalysts. Hydrolysis of pectin-rich residues followed by ethanolic fermentations by yeasts has not been productive because galacturonic acid and arabinose are not ferm entable toethanol by these organisms. The three recombinant bacteria evaluated in this study, Escherichia coli strain KO11, Klebsiella oxytoca strain P2, and Erwinia chrysanthemi EC 16 pLOI 555, ferment carbohydrates in beet pulp with varying efficiencies. E. coli KO11 is able to convert pure galactu ronic acid to ethanol with minimal acetate production. Using an enzyme loading of 10.5 filter paper un its of cellulase, 120.4 polygalactu ronase units of pectinase, and 6.4 g of cellobiase (per gram of dry wt sugar beet pulp), with substrate addition after 24 h of fermentation, 40 g of ethanol/L was produced. Other recombinants exhibited lower ethanol yields with increases in acetate and succinate production.     

On the efficacy of electrocatalysis in nonaqueous Li-O2 batteries

Heterogeneous electrocatalysis has become a focal point in rechargeable Li-air battery research to reduce overpotentials in both the oxygen reduction (discharge) and especially oxygen evolution (charge) reactions. In this study, we show that past reports of traditional cathode electrocatalysis in nonaqueous Li-O(2) batteries were indeed true, but that gas evolution related to electrolyte solvent decomposition was the dominant process being catalyzed. In dimethoxyethane, where Li(2)O(2) formation is the dominant product of the electrochemistry, no catalytic activity (compared to pure carbon) is observed using the same (Au, Pt, MnO(2)) nanoparticles. Nevertheless, the onset potential of oxygen evolution is only slightly higher than the open circuit potential of the cell, indicating conventional oxygen evolution electrocatalysis may be unnecessary.