On the Erdős-Straus non-averaging set problem

Acta Mathematica Hungarica -     

Detection and switching of the oxidation state of Fe in a self-assembled monolayer

A self-assembled monolayer of ferrocene-capped alkanethiols is produced in two stable oxidation states of Fe (Fe²⁺ and Fe³⁺). These oxidation states are detected with sub-monolayer sensitivity by the fine structure of the Fe2p absorption edge. The native Fe²⁺ ferrocene layer is converted chemically to Fe³⁺, and the Fe³⁺ layer can be transformed back to Fe²⁺ or possibly Fe⁰ by irradiation with soft X-rays. The results have implications on switching mechanisms in molecular electronics.     

Metabolic profiling of valproic acid in patients using negative-ion chemical ionization gas chromatography-mass spectrometry

A negative-ion chemical ionization gas chromatographic-mass spectrometric method for the determination of valproic acid (VPA) and fourteen of its metabolites in a single chromatographic run is reported. The assay features the use of four internal standards and is applicable to the analysis of small serum and urine volumes. A combination of pentafluorobenzyl and trimethylsilyl derivatization resulted in the [M - 181]- ion as the base peak for all the metabolites measured. When these ions were monitored sensitivities in the low picogram levels were achieved. The VPA metabolite profile was determined in pediatric patients on VPA monotherapy and on combined VPA therapy with either carbamazepine or clobazam. The recently characterized diene metabolite, (E,E)-2,3'-diene-VPA, was found to be a major serum metabolite of VPA. In the patient groups taking VPA in combination with carbamazepine, the induction of omega and omega-1 pathways of VPA metabolism was apparent, while the levels of the beta-oxidation products were significantly decreased.     

Redox‐Triggered Orientational Responses of Liquid Crystals to Chlorine Gas

Surface‐supported liquid crystals (LCs) that exhibit orientational and thus optical responses upon exposure to ppb concentrations of Cl₂ gas are reported. Computations identified Mn cations as candidate surface binding sites that undergo redox‐triggered changes in the strength of binding to nitrogen‐based LCs upon exposure to Cl₂ gas. Guided by these predictions, μm‐thick films of nitrile‐ or pyridine‐containing LCs were prepared on surfaces decorated with Mn²⁺ binding sites as perchlorate salts. Following exposure to Cl₂, formation of Mn⁴⁺ (in the form of MnO₂ microparticles) was confirmed and an accompanying change in the orientation and optical appearance of the supported LC films was measured. In unoptimized systems, the LC orientational transitions provided the sensitivity and response times needed for monitoring human exposure to Cl₂ gas. The response was also selective to Cl₂ over other oxidizing agents such as air or NO₂ and other chemical targets such as organophosphonates.