Synthesis and spin-trapping properties of a new spirolactonyl nitrone

Spin trapping using electron paramagnetic resonance (EPR) spectroscopy is commonly employed for the identification of transient radicals in chemical and biological systems. A spirolactonyl-nitrone with rigid H-bond acceptor, 7-oxa-1-azaspiro[4.4]non-1-en-6-one 1-oxide, CPCOMPO, has been synthesized and characterized, and its spin-trapping properties were investigated. The rate of formation of CPCOMPO-O2H was determined using competition kinetics between the superoxide/hydroperoxyl radical (O2*-/HO2*) trapping by CPCOMPO and the spontaneous dismutation of this radical in aqueous media. The rate constant of 60 M-1.s-1 is the highest rate constant thus far observed at neutral pH for any nitrones using the kinetic method employed. Decay kinetics were also experimentally investigated for CPCOMPO-O2H. The effect of rigid H-bond acceptor on the stability of the CPCOMPO-O2H were computationally rationalized and compared to that of EMPO-O2H, which has flexible H-bond acceptor, and results show the need of a "loose" H-bond acceptor for improved adduct stability.     

Inner Regularizations and Viscosity Solutions for Pessimistic Bilevel Optimization Problems

Pessimistic bilevel optimization problems are not guaranteed to have a solution even when restricted classes of data are involved. Thus, we propose a concept of viscosity solution, which satisfactorily obviates the lack of optimal solutions since it allows to achieve in appropriate conditions the security value. Differently from the viscosity solution concept for optimization problems, introduced by Attouch (SIAM J Optim 6:769–806, 1996) and defined through a viscosity function that aims at regularizing the objective function, viscosity solutions for pessimistic bilevel optimization problems are defined through regularization families of the solutions map to the lower-level optimization. These families are termed “inner regularizations” since they approach the optimal solutions map from the inside. First, we investigate, in Banach spaces, several classical regularizations of parametric constrained minimum problems giving sufficient conditions for getting inner regularizations; then, we establish existence results for the corresponding viscosity solutions under possibly discontinuous data.     

Trace elements in surface sediments from Kongsfjorden,Svalbard: occurrence,sources and bioavailability

Concentration levels, potential sources and bioavailability of trace elements in marine sediments from Kongsfjorden (Svalbard Islands, Norwegian Arctic) were assessed and discussed. Surface sediments were collected by a Ponar grab and characterised in terms of mineralogical composition, grain-size distribution, total organic carbon and nitrogen percentage contents, and major and trace elements concentrations. Anthropogenic and natural sources of trace elements were inferred from lead isotope ratios, while the potential metal bioavailability was evaluated by size-fractionation and solid-phase speciation studies and by the analysis of acid-volatile sulphides (AVS) and simultaneously extracted metals (SEM). Concentrations of metals, their enrichment factors and solid speciation patterns collectively indicated that the anthropogenic impact of trace elements in the fjord is generally low, with a minor enrichment with respect to crustal values (by a factor of 2–11) for As, Cr, Ni and V. The lead isotope ratios (²⁰⁸Pb/²⁰⁷Pb: 2.474–2.498 and ²⁰⁶Pb/²⁰⁷Pb: 1.206–1.212) were close to the natural signature except in the outer fjord, due to the influence of the Atlantic marine circulation. Many elements of toxicological concern (e.g. Pb, V, Zn) were enriched in the finest sediment fraction, which was by far the preponderant one, especially in the inner fjord. However, less than 15% of most trace elements (exceptions Cd and Mn) in the finest fraction was actually associated with easily leachable sediment phases. Finally, the high SEM/AVS ratios determined on samples from sites close to the glacier fronts (11–15), due to low AVS content, highlighted that the sediment in that zone cannot remove additional inputs of heavy metals by sulphide precipitation.     

Designing Interactive Instructional Software: Students as Educators

This paper reviews a project conducted as part of a general chemistry course. The primary goal of the assignment was to involve our students in the process of teaching chemistry. Our work is part of STEMTEC, the Science, Technology, Engineering, and Mathematics Teacher Education Collaborative, which has been developed to improve the preparation of preservice teachers, stimulate the interest of undergraduate science and mathematics majors in the teaching profession, and increase the educational effectiveness of science and mathematics courses. The assigned project required students to create an interactive computer module that could be used to educate other students about concepts taught in general chemistry. The paper includes examples of these modules and evaluates this method of instruction. The software programs designed by the students are available for download from the Internet ().     

HS-SPME-GC-MS approach for the analysis of volatile salivary metabolites and application in a case study for the indirect assessment of gut microbiota

In this work, a straightforward analytical approach based on headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry was developed for the analysis of salivary volatile organic compounds without any prior derivatization step. With a sample volume of 500 μL, optimal conditions were achieved by allowing the sample to equilibrate for 10 min at 50 °C and then extracting the samples for 10 min at the same temperature, using a carboxen/polydimethylsiloxane fibre. The method allowed the simultaneous identification and quantification of 20 compounds in sample headspace, including short-chain fatty acids and their derivatives which are commonly analysed after analyte derivatization. The proof of applicability of the methodology was performed with a case study regarding the analysis of the dynamics of volatile metabolites in saliva of a single subject undergoing 5-day treatment with rifaximin antibiotic. Non-stimulated saliva samples were collected over 3 weeks from a nominally healthy volunteer before, during, and after antibiotic treatment. The variations of some metabolites, known to be produced by the microbiota and by bacteria that are susceptible to antibiotics, suggest that the study of the dynamics of salivary metabolites can be an excellent indirect method for analysing the gut microbiota. This approach is novel from an analytical standpoint, and it encourages further studies combining saliva metabolite profiles and gut microbiota dynamics.

Graphical abstract

     

Versatile Visible-Light-Driven Synthesis of Asymmetrical Phosphines and Phosphonium Salts

Asymmetrically substituted tertiary phosphines and quaternary phosphonium salts are used extensively in applications throughout industry and academia. Despite their significance, classical methods to synthesize such compounds often demand either harsh reaction conditions, prefunctionalization of starting materials, highly sensitive organometallic reagents, or expensive transition-metal catalysts. Mild, practical methods thus remain elusive, despite being of great current interest. Herein, we describe a visible-light-driven method to form these products from secondary and primary phosphines. Using an inexpensive organic photocatalyst and blue-light irradiation, arylphosphines can be both alkylated and arylated using commercially available organohalides. In addition, the same organocatalyst can be used to transform white phosphorus (P₄) directly into symmetrical aryl phosphines and phosphonium salts in a single reaction step, which has previously only been possible using precious metal catalysis.