Complexation of Uranium(VI) by Gluconate in Alkaline Solutions

Gluconate (C₆H₁₁O₇) is a polyhydroxycarboxylic acid that can be assumed as a representative model compound for a wide variety of additives in cement formulations. It can play an important role in the cementitious environments characteristic of radioactive waste disposal sites, as actinides (such as U(VI)) may form stable complexes with gluconate. As a consequence, the presence of the organic ligand can lead to an enhancement of actinide mobility. The results presented in this work show that gluconate increases significantly the uranium solubility at pH_c = 12; the study of U(VI) speciation in alkaline solutions is complex, mainly due to formation of sparingly soluble uranates of varying compositions (e.g. sodium and potassium uranates). UV–Vis measurements in the alkaline pH range have been used to determine the stability constant for the formation of a 1:1 U(VI):gluconate complex. The results obtained with spectroscopic techniques allow explaining the results from solubility experiments, from both over- and under-saturation conditions.     

On the Brownian-directed polymer in a Gaussian random environment

In this paper, we introduce a model of Brownian polymer in a continuous random environment. The asymptotic behavior of the partition function associated to this polymer measure is studied, and we are able to separate a weak and strong disorder regime under some reasonable assumptions on the spatial covariance of the environment. Some further developments, concerning some concentration inequalities for the partition function, are given for the weak disorder regime.     

Electronic state of the molecular oxygen released by catalase

In catalases, the high redox intermediate known as compound I (Cpd I) is reduced back to the resting state by means of hydrogen peroxide in a 2-electron reaction [Cpd I (Por(*+)-Fe(IV)O) + H(2)O(2) --> Enz (Por-Fe(III)) + H(2)O + O(2)]. It has been proposed that this reaction takes place via proton transfer toward the distal His and hydride transfer toward the oxoferryl oxygen (H(+)/H(-) scheme) and some authors have related it to singlet oxygen generation. Here, we consider the possible reaction schemes and qualitatively analyze the electronic state of the species involved to show that the commonly used association of the H(+)/H(-) scheme with singlet oxygen production is not justified. The analysis is complemented with density functional theory (DFT) calculations for a gas-phase active site model of the reactants and products.     

On-line monitoring of gas-phase bioreactors for biogas treatment: hydrogen sulfide and sulfide analysis by automated flow systems

Biogas is produced by biological processes under anaerobic conditions and may contain up to 20,000 ppm_v hydrogen sulfide (H₂S), a corrosive substance that attacks power engines and can affect the health of the industrial staff. H₂S must be removed from the biogas, especially in co-generation facilities where the biogas is burnt for energy production. Nowadays, biofiltration is being studied and considered as an interesting alternative for removing H₂S from the biogas besides classical chemical processes. The novelty of this work is the design and construction of an automated H₂S on-line analyser to assess the composition of the liquid and gas phases of gas-phase bioreactors. The analyser is made of two parallel flow configurations which share the same detection device. The first configuration is a single-channel flow injection analyser (FIA) to detect S²⁻ in the liquid phase. The second configuration is a continuous flow analyser (CFA) with a gaseous diffusion step (GD–CFA) for detecting H₂S in the gas phase. The diffusion step enables separation of the H₂S_(g) from the sample and its conversion into a detectable chemical species (S²⁻). S²⁻ detection was performed with an Ag₂S ion-selective electrode (ISE) selective to . The main response parameters of the FIA system are a linear range between 3 × 10⁻⁵ and 1 × 10⁻¹ mol L⁻¹ S²⁻ (0.61–3,200 mg L⁻¹), with a sensitivity of 27.9 mV decade⁻¹ and a detection limit of 1.93 × 10⁻⁵ mol L⁻¹ S²⁻. The GD–CFA configuration presents a linear range between 400 and 10,000 ppm_v H₂S_(g) with a sensitivity of 26.1 mV decade⁻¹ and a detection limit of 245 ppm_v H₂S. The proposed analyser was used by analysing real gas and liquid samples with optimal results at a full-scale biotrickling filter for biogas treatment at a municipal wastewater treatment plant. Figure The novelty of this work is the design and construction of an automated H₂S on-line analyzer to assess the composition of the liquid and gas phases of gas-phase bioreactors. The analyser is made of two parallel flow configurations which share the same detection device. The first configuration is a single-channel flow injection analyser (FIA) to detect S^2- in the liquid phase. The second configuration is a continuous flow analyser (CFA) with a gaseous diffusion step (GD-CFA) for detecting H₂S in the gas phase.     

Comparative Study of Hard‐ and Soft‐Modeling Algorithms for Kinetic Data Processing

This article critically compares the efficacy of three algorithms, namely Alternating Least‐squares Multi Curve Resolution (ALS‐MCR), Hard Modeling Alternating Least‐squares (HM‐ALS), and classical Hard Modeling Multi Curve Resolution (HM‐MCR) in finding the true values of rate constants associated with a kinetic model. Simulated experiments on the simple system () indicate that soft‐modeling ALS‐MRC methodology, which is subject only to linear constraints, does not ensure that experimental responses are correctly deconvolved, thus preventing further calculations to determine the true rate constants. Inclusion of the kinetic model in the ALS scheme, which gives rise to the HM‐ALS methodology, was found to yield a correct assessment of the rate coefficients but had a large computational cost. Numerical experiments employing a more complex model () were also carried out, mainly to evaluate strategies for performing efficient searches on multidimensional multimodal least‐squares surfaces using HM‐ALS and HM‐MCR. This study again revealed the efficiency and reliability of classical HM‐MCR methods. Results from simulations were corroborated by analysis of data from an experimental study of chromate reduction by hydrogen peroxide; the mechanism of which is similar in complexity to those considered in simulations. The present work suggests that HM‐MCR algorithms implementing a multiminimum search strategy are the method of choice for analyzing two‐dimensional kinetic data.