HPLC-ICP-MS method development to monitor arsenic speciation changes by human gut microbiota

Inorganic arsenic (iAs) has been classified as a type 1 carcinogen and has also been linked to several noncancerous health effects. Prior to 1995, the As^V methylation pathway was generally considered to be a detoxification pathway, but cellular and animal studies involving MMA^III (mono metyl arsonous acid) and DMA^III (dimethyl arsinous acid) have indicated that their toxicities meet or exceed that of iAs, suggesting an activation process. In addition, thiolated arsenic metabolites were observed in urine after oral exposure of inorganic arsenic in some studies, for which the toxicological profile was not yet fully characterized in human cells. Studies have revealed that microorganisms from the gut environment are important contributors to arsenic speciation changes. This presystemic metabolism necessitates the development of protocols that enable the detection of not only inorganic arsenic species, but also pentavalent and trivalent methylated, thiolated arsenicals in a gastrointestinal environment. We aim to study the biotransformation of arsenic (As) using a Simulator of the Human Intestinal Microbial Ecosystem (SHIME). To be able to analyze the arsenicals resulting from biotransformation reactions occurring in this system, a method using liquid chromatography hyphenated to an inductively coupled plasma mass spectrometer (HPLC‐ICP‐MS) was developed. A Hamilton PRP‐X100 anion exchange column was used. The method allowed separation, identification and quantification of As^III(arsenite), As^V(arsenate), DMA^V(dimethylarsinicacid), MMA^V(monomethylarsonicacid) and MMMTA (monomethylmonothioarsenate). Attempts to optimize the same method for also separating MMA^III and DMA^III did not succeed. These compounds could be successfully separated using a method based on the use of a Zorbax C₁₈ column. The properties of the column, buffer strength, pH and polar nature of mobile phase were monitored and changed to optimize the developed methods. Linearity, sensitivity, precision, accuracy and resolution of both methods were checked. The combination of the two methods allowed successful quantification of arsenic species in suspensions sampled in vitro from the SHIME reactor or in vivo from the human colon and feces. Copyright © 2011 John Wiley & Sons, Ltd.     

Failure of viral shells

We report a combined theoretical and experimental study of the structural failure of viral shells under mechanical stress. We find that discontinuities in the force-indentation curve associated with failure should appear when the so-called F?ppl-von Kármán (FvK) number exceeds a critical value. A nanoindentation study of a viral shell subject to a soft-mode instability, where the stiffness of the shell decreases with increasing pH, confirms the predicted onset of failure as a function of the FvK number.     

Phase diagram of Bose-Fermi mixtures in one-dimensional optical lattices

The ground state phase diagram of the one-dimensional Bose-Fermi Hubbard model is studied in the canonical ensemble using a quantum Monte Carlo method. We focus on the case where both species have half filling in order to maximize the pairing correlations between the bosons and the fermions. In case of equal hopping we distinguish among phase separation, a Luttinger liquid phase, and a phase characterized by strong singlet pairing between the species. True long-range density waves exist with unequal hopping amplitudes.     

Iodonium-Ion Assisted Stereospecific Glycosylation: Synthesis of Oligosaccharides Containing α(1-4)-Linked L-Fucopyranosyl Units

ABSTRACT

The terminal glycosyl acceptor methyl 2,3-di-O-benzyl-α-L-fucopyranoside (6) was extended three times with the non-terminal glycosyl donor ethyl 4-O-acetyl-2,3-di-O-benzyl-1-thio-ß-L-fucopyranoside (13) via iodonium-ion assisted glycosylations and intermittent removal of the C-4 acetyl group in intermediate dimer 16 and trimer 18. The 4-O-acetyl group in trimer 18 and tetramer 20 was highly resistant towards basic hydrolysis. The latter could be nullified by using dichloroacetyl instead of acetyl to protect the C-4-OH in the donor. The exclusive formation of 1,2-cis-linked oligomers could be explained by through-bond interactions exerted by the electron-withdrawing C-4 acyl group in the glycosyl donor.     

Synthesis and Photophysics of a Red‐Light Absorbing Supramolecular Chromophore System

In search of supramolecular antenna systems for light‐harvesting applications, we report on a short and effective synthesis of a fused NDI–zinc–salphen‐based chromophore (salphen = bis‐salicylimide phenylene) and its photophysical properties. A supramolecular recognition motif is embedded into the chromophoric π‐system of this compound. The fused π‐chromophore behaves as one pigment, absorbs light between 600 and 750 nm and displays a modest Stokes shift. Upon binding pyridines, the compound ( DATZnS ) does not change its redox potentials, does not undergo any internal excited state quenching and does not appreciably alter its excited state lifetime. These notable properties define DATZnS as an alternative to porphyrin‐based components used in supramolecular light‐harvesting architectures.     

Peptide block copolymers by N‐carboxyanhydride ring‐opening polymerization and atom transfer radical polymerization: The effect of amide macroinitiators

The synthesis of polypeptide‐containing block copolymers combining N‐carboxyanhydride (NCA) ring‐opening polymerization and atom transfer radical polymerization (ATRP) was investigated. An amide initiator comprising an amine function for the NCA polymerization and an activated bromide for ATRP was used. Well‐defined polypeptide macroinitiators were obtained from γ‐benzyl‐L ‐glutamate NCA, O‐benzyl‐serine NCA, and N‐benzyloxy‐L ‐lysine. Subsequent ATRP macroinitiation from the polypeptides resulted in higher than expected molecular weights. Analysis of the reaction products and model reactions confirmed that this is due to the high frequency of termination reactions by disproportionation in the initial phase of the ATRP, which is inherent in the amide initiator structure. In some cases selective precipitation could be applied to remove unreacted macroinitiator to yield well‐defined block copolymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

The importance of cooling of urine samples for doping analysis

Storing and transporting of urine samples for doping analysis, as performed by the anti-doping organizations associated with the World Anti-Doping Agency, does not include a specific protocol for cooled transport from the place of urine sampling to the doping laboratory, although low cost cooling facilities can easily be made available. As a result, microbial and thermal degradation of the chemical substances in the urine may occur, which may lead to false negative or false positive results in the subsequent doping analysis. This scientifically and morally unacceptable practice is still maintained in spite of publications demonstrating that immediate cooling is an absolute requirement. Given the enormous societal consequences of positive tests, the lack of a controllable chain of custody during transport should be outlawed. This paper proposes a simple method, based on immediate cooling and cooled transport, which can easily be implemented in developed countries at low cost.     

Stochastic games on a product state space: the periodic case

We examine so-called product-games. These are n-player stochastic games played on a product state space S ¹ × ... × S ⁿ , in which player i controls the transitions on S ⁱ . For the general n-player case, we establish the existence of 0-equilibria. In addition, for the case of two-player zero-sum games of this type, we show that both players have stationary 0-optimal strategies. In the analysis of product-games, interestingly, a central role is played by the periodic features of the transition structure. Flesch et al. (Math Oper Res 33, 403–420, 2008) showed the existence of 0-equilibria under the assumption that, for every player i, the transition structure on S ⁱ is aperiodic. In this article, we examine product-games with periodic transition structures. Even though a large part of the approach in Flesch et al. (Math Oper Res 33, 403–420, 2008) remains applicable, we encounter a number of tricky problems that we have to address. We provide illustrative examples to clarify the essence of the difference between the aperiodic and periodic cases.     

Wheat gluten amino acid composition analysis by high-performance anion-exchange chromatography with integrated pulsed amperometric detection

A simple accurate method for determining amino acid composition of wheat gluten proteins and their gliadin and glutenin fractions using high-performance anion-exchange chromatography with integrated pulsed amperometric detection is described. In contrast to most conventional methods, the analysis requires neither pre- or post-column derivatization, nor oxidation of the sample. It consists of hydrolysis (6.0 M hydrochloric acid solution at 110 °C for 24 h), evaporation of hydrolyzates (110 °C), and chromatographic separation of the liberated amino acids. Correction factors (f) accounted for incomplete cleavage of peptide bonds involving Val (f = 1.07) and Ile (f = 1.13) after hydrolysis for 24 h and for Ser (f = 1.32) losses during evaporation. Gradient conditions including an extra eluent (0.1 M acetic acid solution) allowed multiple sequential sample analyses without risk of Glu contamination on the anion-exchange column. While gluten amino acid compositions by the present method were mostly comparable to those obtained by a conventional method involving oxidation, acid hydrolysis and post-column ninhydrin derivatization, the latter method underestimated Tyr, Val and Ile levels. Results for the other amino acids obtained by the different methods were linearly correlated (r > 0.99, slope = 1.03).