Catalytic asymmetric hydrometallation of cyclobutenes with salicylaldehydes

Chiral, substituted cyclobutanes are common motifs in bioactive compounds and intermediates in organic synthesis but few asymmetric routes for their synthesis are known. Herein we report the Rh-catalyzed asymmetric hydrometallation of a range of meso-cyclobutenes with salicylaldehydes. The ortho-phenolic group promotes hydroacylation and can be used as a handle for subsequent transformations. The reaction proceeds via asymmetric hydrometallation of the weakly activated cyclobutene, followed by a C–C bond forming reductive elimination. A prochiral, spirocyclic cyclobutene undergoes a highly regioselective hydroacylation. This report will likely inspire the development of other asymmetric addition reactions to cyclobutenes via hydrometallation pathways.

Chiral, substituted cyclobutanes are common motifs in bioactive compounds and intermediates in organic synthesis but few asymmetric routes for their synthesis are known.     

Engineering Protein Venoms as Self-Assembling CXCR4-Targeted Cytotoxic Nanoparticles

Protein venoms are effective cytotoxic molecules that when conveniently targeted to tumoral markers can be exploited as promising anticancer drugs. Here, it is explored whether the structurally unrelated melittin, gomesin, and CLIP71 could be functionally active when engineered, in form of GFP fusions, as self-assembling multimeric nanoparticles. Incorporated in modular constructs including a C-terminal polyhistidine tag and an N-terminal peptidic ligand of the cytokine receptor CXCR4 (overexpressed in more than 20 human neoplasias), these venoms are well produced in recombinant bacteria as proteolytically stable regular nanoparticles ranging between 12 and 35 nm. Being highly fluorescent, these materials selectively penetrate, label, and kill CXCR4⁺ tumor cells in a CXCR4-dependent fashion. The obtained data support the concept of recombinant venoms as promising drugs, through the precise formulation as tumor-targeted nanomaterials for selective theragnostic applications in CXCR4⁺ cancers.     

Arsenic determination by ICP-QMS with octopole collision/reaction cell. Overcome of matrix effects under vented and pressurized cell conditions

The determination of arsenic by inductively coupled plasma mass spectrometry (ICP-MS) in natural waters with high sodium and chloride content has been investigated. The instrument used is equipped with an octopole collision/reaction cell to overcome spectroscopic interferences. Thus, the optimization of collision/reaction gas flow rates is required when using a pressurized cell. A mixture of 2.9 mL min⁻¹ of H₂ and 0.5 mL min⁻¹ of He has been found to be suitable for the removal of ⁴⁰Ar³⁵Cl⁺ interference.The effect of the introduction of small amounts of alcohol has also been studied in this work under both vented and pressurized cell conditions. It has been observed that the presence of 4% (v/v) of ethanol or methanol results in an increase in arsenic sensitivity. Moreover, under vented cell conditions the addition of alcohol also decreases the formation of polyatomic interference. However, this decrease is not observed under pressurized cell conditions.Different elements have been studied as possible internal standards for arsenic determination in presence of high amounts of sodium. Good results have been obtained for rhodium and yttrium under both vented and pressurized cell conditions. Although the presence of alcohol in the sample matrix also affects their behaviour, rhodium and yttrium are still the most suitable elements to correct for these matrix effects.Different experimental conditions have been compared for arsenic determination in spiked, certified and natural waters with high sodium and chloride content. The best results have been obtained under pressurized cell conditions, in the presence of ethanol and using rhodium as internal standard.     

Synthesis of an aryl 2-deoxy-β-glycosyl tetrasaccharide to probe retaining endo-glycosidase mechanism

The synthesis of the 1,3–1,4-β-glucanase substrate analogue 4-nitrophenyl O-β-d-glucopyranosyl-(1→4)-O-β-d-glucopyranosyl-(1→4)-O-β-d-glucopyranosyl-(1→3)-2-desoxi-β-d-glucopyranoside 2 is reported. Starting from the main tetrasaccharide obtained by enzymatic depolymerization of barley β-glucan, the synthetic scheme involves preparation of the corresponding 3-O-substituted glycal which was converted into a 2-deoxy-α-glycosyl iodide as a glycosyl donor. The key glycosylation step was successfully achieved by nucleophilic substitution of the iodide donor with 4-nitrophenolate with high β-selectivity.     

Hydrolysis of Hydrophobic Esters in a Bicontinuous Microemulsion Catalysed by Lipase B from Candida antarctica

Selective enzyme‐catalysed biotransformations offer great potential in organic chemistry. However, special requirements are needed to achieve optimum enzyme activity and stability. A bicontinuous microemulsion is proposed as reaction medium because of its large connected interface between oil and water domains at which a lipase can adsorb and convert substrates in the oil phase of the microemulsion. Herein, a microemulsion consisting of buffer–n‐octane–nonionic surfactant C_iE_j was used to investigate the key factors that determine hydrolyses of p‐nitrophenyl esters catalysed by the lipase B from Candida antarctica (CalB). The highest CalB activity was found around 44 °C in the absence of NaCl and substrates with larger alkyl chains were better hydrolysed than their short‐chained homologues. The CalB activity was determined using two different co‐surfactants, namely the phospholipid 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine (DOPC) and the sugar surfactant decyl β‐D ‐glucopyranoside (β‐C₁₀G₁). The results show the CalB activity as linear function of both enzyme and substrate concentration with an enhanced activity when the sugar surfactant is used as co‐surfactant.     

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-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.