Characterization of the acid/base and redox chemistry of phytochelatin analogue peptides

The phytochelatins are a family of polydisperse, thiol-rich peptides that are synthesized by plants in response to exposure to heavy metals. The amino acid sequence of the phytochelatin peptides is (gamma-glutamyl-cysteinyl)n-glycine, where n typically ranges from 2 to 5. In the first phase of a program to characterize the coordination chemistry of the phytochelatins with heavy metals, the phytochelatin analogue peptides acetyl(gamma-glutamyl-cysteinyl)n-glycine amide (Ac-(gamma-Glu-Cys)n-NH2, n = 2-6) have been synthesized by solid-phase peptide synthesis methods and characterized by 1H NMR spectroscopy. The 1H NMR spectra of the analogue peptides were completely assigned by using band-selective homonuclear-decoupled (BASHD) two-dimensional NMR experiments to achieve spectral resolution. The acid dissociation constant of each cysteine residue in each peptide was determined from chemical shift-pH titration data for the CalphaH protons of the cysteine residues. The resonances for the CalphaH protons were resolved in BASHD-total correlation spectroscopy spectra that were measured as a function of pH. The pKA values for a given thiol group depend on the position of the cysteine residue in the sequence, with the thiol group of the cysteine residue attached to the C-terminal glycine being the most acidic. The pKA values also depend on the size of the peptide, increasing as the size, and thus the negative charge, of the peptide increases. The redox potential for oxidation of the two thiol groups of Ac(gamma-Glu-Cys)2-NH2 to form an intramolecular disulfide bond was also determined by measuring the equilibrium constant for its thiol/disulfide exchange reaction with glutathione.     

Sensitivity to change of the Brief Psychiatric Rating Scale-Extended (BPRS-E): An item and subscale analysis.

The Brief Psychiatric Rating Scale (BPRS) is the most commonly used outcome measure for the severely and persistently mentally ill (SPMI) population, possessing good interrater reliability, concurrent validity, and a strong factor structure. However, psychometric study of the extended version of the BPRS (the BPRS-E) is limited when compared with earlier versions (BPRS and BPRS-A). This study examined the item, factor, and diagnosis-specific sensitivity to change of the BPRS-E, the most recent version of this popular scale. Assessments were conducted at 90-day intervals with 201 adult psychiatric inpatients at the Utah State Hospital, yielding 786 symptom ratings. Of note was that ratings were conducted by independent assessors who were unaware of patients' treatment status. All but 2 of the 24 BPRS-E items, all 4 factors, and the total score were found to be sensitive to change when comparing patients' admission and discharge scores. Patient diagnosis was not associated with item, factor, or total score sensitivity to change. These findings extend the psychometric support for the BPRS-E and have implications for assessing outcome with the SPMI population. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of phosphatidylserine and phosphatidylethanolamine on farnesol tolerance in Candida albicans

Candida albicans is among the most common human fungal pathogens. The ability to undergo the morphological transition from yeast to hyphal growth is critical for its pathogenesis. Farnesol, a precursor in the isoprenoid/sterol pathway, is a quorum‐sensing molecule produced by C. albicans that inhibits hyphal growth in this polymorphic fungus. Interestingly, C. albicans can tolerate farnesol concentrations that are toxic to other fungi. We hypothesized that changes in phospholipid composition are one of the factors contributing to farnesol tolerance in C. albicans. In this study, we found that loss of enzymes that synthesize the phospholipids phosphatidylserine (PS) and/or phosphatidylethanolamine (PE) compromise the tolerance of C. albicans to farnesol. Compared with wild type, the phospholipid mutant cho1?/? (loss of PS and decreased PE synthesis) shows greater inhibition of growth, loss of ATP production, increased consumption of oxygen, and increased formation of reactive oxygen species in the presence of farnesol. The cho1?/? mutant also exhibits decreased sensitivity to mitochondrial ATPase inhibition, suggesting that cells lacking PS and/or downstream PE rely less on mitochondrial function for ATP synthesis. These data reveal that PS and PE play roles in farnesol tolerance and maintaining mitochondrial respiratory function.     

Designing Optimal Perovskite Structure for High Ionic Conduction

Solid-oxide fuel/electrolyzer cells are limited by a dearth of electrolyte materials with low ohmic loss and an incomplete understanding of the structure–property relationships that would enable the rational design of better materials. Here, using epitaxial thin-film growth, synchrotron radiation, impedance spectroscopy, and density-functional theory, the impact of structural parameters (i.e., unit-cell volume and octahedral rotations) on ionic conductivity is delineated in La_0.9Sr_0.1Ga_0.95Mg_0.05O_3–δ. As compared to the zero-strain state, compressive strain reduces the unit-cell volume while maintaining large octahedral rotations, resulting in a strong reduction of ionic conductivity, while tensile strain increases the unit-cell volume while quenching octahedral rotations, resulting in a negligible effect on the ionic conductivity. Calculations reveal that larger unit-cell volumes and octahedral rotations decrease migration barriers and create low-energy migration pathways, respectively. The desired combination of large unit-cell volume and octahedral rotations is normally contraindicated, but through the creation of superlattice structures both expanded unit-cell volume and large octahedral rotations are experimentally realized, which result in an enhancement of the ionic conductivity. All told, the potential to tune ionic conductivity with structure alone by a factor of ≈2.5 at around 600 °C is observed, which sheds new light on the rational design of ion-conducting perovskite electrolytes.     

Impact of Triticum mosaic virus infection on hard winter wheat milling and bread baking quality

BACKGROUND: Triticum mosaic virus (TriMV) is a newly discovered wheat virus. Information regarding the effect of wheat viruses on milling and baking quality is limited. The objective of this study was to determine the impact of TriMV infection on the kernel characteristics, milling yield and bread baking quality of wheat. Commercial hard winter varieties evaluated included RonL, Danby and Jagalene. The TriMV resistance of RonL is low, while that of Danby and Jagalene is unknown. KS96HW10‐3, a germplasm with high TriMV resistance, was included as a control. Plots of each variety were inoculated with TriMV at the two‐ to three‐leaf stage. Trials were conducted at two locations in two crop years. RESULTS: TriMV infection had no effect on the kernel characteristics, flour yield or baking properties of KS96HW10‐3. The effect of TriMV on the kernel characteristics of RonL, Danby and Jagalene was not consistent between crop years and presumably an environmental effect. The flour milling and bread baking properties of these three varieties were not significantly affected by TriMV infection. CONCLUSION: TriMV infection of wheat plants did not affect harvested wheat kernel characteristics, flour milling properties or white pan bread baking quality. Copyright © 2011 Society of Chemical Industry     

Polyampholyte polymer as a stabiliser for subgrade soil

This study evaluates the potential of selected ionic polymers to act as pavement subgrade binders. Investigations were based on their relative performance with a Qatari soil which was selected as typical of a pavement subgrade to be found in the Middle East and North African region. The polymeric binders chosen were three synthetic ionic variations of polyacrylamide: cationic poly(acrylamidopropyl trimethyl ammonium chloride) (designated PAMTAC), anionic hydrolysed poly(acrylamide) (HPAM) and the ampholitic terpolymer poly(acrylamide-co-sodiumacrylate-co-(3-acrylamidopropyl) trimethylammonium chloride) (TPAM). The polymers were characterised by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic spectroscopy (¹H-NMR and ¹³C-NMR). The comparative performance of the polymer-treated soil was judged on the basis of results obtained from selected standard mechanical test data: specifically, the unconfined compressed strength, the stiffness modulus and the toughness. It is concluded that a 50% w/w aqueous solution of the ampholitic terpolymer applied at a dosage of 2.0% by dry weight of the soil gives the best subgrade stabilisation. Of some significance, it is further noted that this ampholitic polymer was superior as a binding agent to the traditional standard, Portland cement, judged under equivalent but nonstandard conditions. Modifying the polymer to act as a binder for subgrade soils in general is also discussed.     

Quantification of low and high levels of Salmonella enterica serovar Typhimurium on leaves

Precise and rapid quantification of low levels of pathogens associated with fresh produce may be particularly challenging and yet evermore necessary to guarantee microbial safety of the produce and to carry out research on the subject of persistence of the pathogens. Here, microbiological and molecular based methods were examined for their ability to precisely quantify different amounts of Salmonella enterica serovar Typhimurium artificially inoculated on parsley leaves. Recovery of S. Typhimurium from parsley by mechanical detachment using stomacher, mortar and pestle, vortex, sonicator or homogenizer followed by plating resulted in underestimation with less than 1% recovery when leaves were inoculated with 3.5–6.5 log CFU/g. Lower levels were undetectable by most assayed methods, and only recovery with mortar and pestle or adding of enrichment step resulted in partial detection of 300 CFU/g. Implementation of PCR based methods with/without pre extraction of the DNA from the contaminated leaves resulted in more accurate values of the pathogen (about 20% of the initial inocula) and as low as 300 CFU/g were detected even without an enrichment step. These methods can be applied to study transfer of Salmonlla from contaminated water or soil to plants using low and more reasonable levels of contamination.     

Reactive adsorption for the selective dehydration of sugars to furans: Modeling and experiments

5‐hydroxymethylfurfural (HMF) can be produced from the acid‐catalyzed dehydration of fructose, but its yield is limited due to subsequent HMF degradation to side products. A reactive adsorption process is proposed to improve the yield to HMF. Separate experimental single‐component isotherms of fructose, HMF, formic acid, and levulinic acid on carbon BP2000 and reaction kinetics of the fructose dehydration to HMF in aqueous solution of HCl are presented to develop empirical isotherms and kinetic rate constants, respectively. These submodels are subsequently integrated in an adsorptive reactor at a range of temperatures (100–150^°C) with different loadings of adsorbent. It is shown that the adsorbent improves HMF yield compared to the single‐solution phase (adsorbent‐free case). Low temperatures and high‐adsorbent loadings improve HMF yield. Under certain conditions both reactive adsorption and the commonly used reactive extraction can result in a similar improvement in HMF yield. HMF recovery from the solid adsorbent has been identified as a major challenge that can be ameliorated through adsorbent and solvent selection. The framework outlined here can be applied to any aqueous phase chemistry where the desired product is an intermediate in a reaction cascade. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3378–3390, 2013