An Iron-Catalyzed Protein Desulfurization Method Reminiscent of Aquatic Chemistry

One pillar of protein chemical synthesis based on the application of ligation chemistries to cysteine is the group of reactions enabling the selective desulfurization of cysteine residues into alanines. Modern desulfurization reactions use a phosphine as a sink for sulfur under activation conditions involving the generation of sulfur-centered radicals. Here we show that cysteine desulfurization by a phosphine can be effected efficiently by micromolar concentrations of iron under aerobic conditions in hydrogen carbonate buffer, that is using conditions that are reminiscent of iron-catalyzed oxidation phenomena occurring in natural waters. Therefore, our work shows that chemical processes taking place in aquatic systems can be adapted to a chemical reactor for triggering a complex chemoselective transformation at the protein level, while minimizing the resort to harmful chemicals.     

Mapping Properties of Some Singular Operators in Besov Type Subspaces of C( − 1, 1)

We study mapping properties, boundedness and invertibility of some Cauchy singular integral operators in a scale of pairs of Besov type subspaces of C( − 1, 1). Our results include all those already available in the literature.     

Measuring productivity growth under factor non-substitution: An application to US steam-electric power generation utilities

A theoretical framework is developed for decomposing partial factor productivity and measuring technical inefficiency when the underlying technology is characterized by factor non-substitution. With Farrell’s (1957) radial index of technical inefficiency being inappropriate in this case, Russell non-radial indices are adapted to measure technical inefficiency in a Leontief-type model. A system of factor demand equations with a regime specific technical inefficiency term is proposed and estimated allowing for dependence across inputs using a copula approach. Then the paper presents a complete decomposition of partial factor productivity changes using a dataset of US steam-power electric generation utilities.     

Production ofK0 and Λ in hadronic Z decays

Measurements of the inclusive cross-sections forK ⁰ and production in hadronic decays of the Z are presented together with measurements of two-particle correlations within pairs of andK ⁰. The results are compared with predictions from the hadronization models Jetset, based on string fragmentation, and Herwig, based on cluster decays. TheK ⁰ spectrum is found to be harder than predicted by both models, while the spectrum is softer than predicted. The correlation measurements are all reproduced well by Jetset, while Herwig misses some of the qualitative features and overestimates the size of the correlation. Finally, the possibility of Bose-Einstein correlation in theK _S ⁰ K _S ⁰ system is discussed.Supported by CICYT, Spain     

The Approximability Behaviour of Some Combinatorial Problems with Respect to the Approximability of a Class of Maximum Independent Set Problems

We prove that the existence of a polynomial time-approximation algorithm (where < 1 is a fixed constant)for a class of independent set problems, leads to a polynomial timeapproximation algorithm with approximation ratio strictly smallerthan 2 for vertex covering, while the non-existence of such analgorithm induces a lower bound on the ratio of every polynomialtime approximation algorithm for vertex covering. We also prove asimilar result for a (maximization) convex programming problemincluding quadratic programming as subproblem.     

Synthesis of 11beta-perfluorohexylestradiol

[reaction: see text] We report the synthesis of 11beta-perfluorohexylestradiol 1e using a perfluoroorganometallic reagent for the introduction of the fluorous part. This compound is useful for biological studies and for imaging the ERalpha estradiol receptor distribution in the whole cell by secondary ion mass spectrometry (SIMS). The key step of this synthesis involves the radical reduction of an 11beta-oxalate derivative. The stereochemical outcome of this reaction was studied for a range of C11 substituents, and we attempted to rationalize the apparent abnormal behavior of the phenyl group.     

Fs/ns-dual-pulse orthogonal geometry plasma plume reheating for copper-based-alloys analysis

Plasma plume emission spectroscopy signal enhancements between 12- and 280-fold were obtained in air at atmospheric pressure by reheating the fs-laser ablation plume (energy 0.75 and 3.0 mJ) with a 45 mJ ns-pulse in orthogonal geometry. The emission enhancements induced by the double pulse configuration (DP) at various inter-pulse delay times and distances of the second laser beam from the target surface were investigated for copper-based-alloy standards. Temporal surveys of the plasma plume temperatures induced by both fs-single pulse (fs-SP) and DP placed at a fixed distance of 0.5 mm from the target surface were carried out. Several copper-based-alloy standards were employed for drawing Zn calibration curves by using either fs-SP or DP configurations and considering Cu as internal standard. The experimental data show that, for high Zn contents, the fs-SP set-up is affected by a self-absorption phenomenon so that a deviation from the assumed calibration single linear response is observed and two linear regressions are considered. Conversely, it has been observed that the DP configuration is not affected by any self-absorption effect and provides an improvement of the Zn limit of detection (LOD) but worse calibration linear regressions than the fs-SP. Thus, the DP scheme can increase the analytical sensitivity of fs-SP and, furthermore, its process can be supposed to be independent from the matrix composition even for largely different Zn contents of the Cu-based-alloy standards used.     

Comparison of silver nanoparticles confined in nanoporous silica prepared by chemical synthesis and by ultra-short pulsed laser ablation in liquid

Hexagonally ordered mesoporous silica materials, MCM-41 and SBA-15, have been synthesized and loaded with Ag nanoparticles, utilizing both chemical synthesis and ultra-short pulsed laser ablation in liquid. In laser ablation, a silver target, immersed in aqueous suspension of ordered mesoporous silica SBA-15, was irradiated by ultra-short laser pulses to generate silver nanoparticles. For comparison, samples of similar silver contents were prepared either by incorporating silver into the SBA-15 during a hydrothermal synthesis or by introducing silver in MCM-41 by template ion-exchange. Samples were characterized by XRD, N₂ physisorption, TEM and UV–vis spectroscopy. All preparations contained significant amount of 5–50 nm size silver agglomerates on the outer surface of the silica particles. The laser ablation process did not cause significant destruction of the SBA-15 structure and metallic silver (Ag⁰) nanoparticles were mainly generated. It is demonstrated that by laser ablation in aqueous silica suspension smaller and more uniform metallic silver particles can be produced and loaded on the surface of the silica support than by synthesis procedures. Catalytic properties of the samples have been tested in the total oxidation of toluene. Because of its favorable Ag dispersity, the Ag/SBA-15 catalyst, generated by the laser ablation method, had better catalytic stability and, relative to its Ag load, higher activity than the conventional Ag/SBA-15 preparations.     

Approximation of max independent set, min vertex cover and related problems by moderately exponential algorithms

Using ideas and results from polynomial time approximation and exact computation we design approximation algorithms for several NP-hard combinatorial problems achieving ratios that cannot be achieved in polynomial time (unless a very unlikely complexity conjecture is confirmed) with worst-case complexity much lower (though super-polynomial) than that of an exact computation. We study in particular two paradigmatic problems, max independent set and min vertex cover.