Siloxane‐Crown Ether Polyamide Based Electrode for Electrochemical Determination of Lead(II) in Aqueous Solution

A siloxane‐crown ether polyamide copolymer (PDMS‐PA‐DB18C6) was electrochemically investigated for fabrication of lead‐sensitive electrodes for trace analysis in aqueous solutions. The PDMS‐PA‐DB18C6 electrodes were successfully evaluated for anodic stripping voltammetric determination of lead(II) as a promising alternative for the detection of lead at ppb levels. By a judicious choice of the deposition time, electrolyte concentration and pulse amplitude, good analytical performance of the developed sensor could be achieved, with a linear response in the range of 20–700 ppb, when LOD of 3.5 ppb could be attained. This method showed a good degree of selectivity and sensitivity for lead, suitable for the determination of Pb²⁺ in wastewater sample.     

Electrochemical impedance spectroscopy at single-walled carbon nanotube network ultramicroelectrodes

Electrochemical impedance spectroscopy (EIS), coupled with chemical vapour deposition (CVD) grown single-walled carbon nanotube (SWNT) network disk-shaped ultramicroelectrodes (UMEs), gives stable, very well-defined and highly reproducible EIS responses for electrolysis of a simple outer sphere redox couple (FcTMA^+/2+). The resulting EIS data can be fitted accurately using a simple electrical circuit model, enabling information on double-layer capacitance, diffusion coefficient of the electroactive species and the rate constant of ET (k⁰) to be extracted in a single EIS experiment. These values are replicated for a range of mediator concentrations and UME sizes (in the range 25–100 μm diameter) demonstrating the robustness of the method. These initial studies bode well for impedance based electroanalysis using SWNT network UMEs.     

Nickel-catalyzed cross-coupling of potassium aryl- and heteroaryltrifluoroborates with unactivated alkyl halides

A method for the cross-coupling of alkyl electrophiles with various potassium aryl- and heteroaryltrifluoroborates has been developed. Nearly stoichiometric amounts of organoboron species could be employed to cross-couple a large variety of challenging heteroaryl nucleophiles. Several functional groups were tolerated on both the electrophilic and the nucleophilic partners. Chemoselective reactivity of C(sp(3))-Br bonds in the presence of C(sp(2))-Br bonds was achieved.     

Uniqueness of the Group Measure Space Decomposition for Popa’s {\mathcal{HT}} Factors

We prove that if ${\Gamma\curvearrowright (X, \mu)}$ is a free ergodic rigid (in the sense of Popa in Ann Math 163:809–889, 2006) probability measure preserving action of a group Γ with positive first ${\ell^2}$ -Betti number, then the II₁ factor ${L^{\infty}(X)\rtimes\Gamma}$ has a unique group measure space Cartan subalgebra, up to unitary conjugacy. We deduce that many ${\mathcal{HT}}$ factors, including the II₁ factors associated with the usual actions ${\Gamma\curvearrowright \mathbb{T^2}}$ and ${\Gamma\curvearrowright}$ ${{\rm SL}_2(\mathbb R)/{\rm SL}_2(\mathbb Z)}$ , where Γ is a non-amenable subgroup of ${{\rm SL}_2(\mathbb Z)}$ , have a unique group measure space decomposition.     

Thermo-responsiveness of polysiloxanes grafted with poly(dimethyl acrylamide) segments

Thermo-sensitive polymers are of outstanding importance due to their ability to undergo controlled major changes in their properties as a response to minor modifications in temperature. The syntheses of novel polymers by grafting polysiloxane containing chlorobenzyl groups in the side chain by the homopolymerization of N,N′-dimethyl acrylamide (DMA) or the copolymerization of DMA and methyl methacrylate (MMA) using SET-LRP technique are presented. The polymers were characterized by 1H-NMR, UV, and fluorescence spectroscopy, and DSC. The thermo-sensitivity and the lower critical solution temperature (LCST), as well as the aggregation phenomena during the phase transition are evidenced by dynamic light scattering (DLS) and rheology.      

A contribution to the identification of the E5 defect level as tri-vacancy (V3)

Silicon particle detectors in tracking devices for the high luminosity Large Hadron Collider will suffer from an extremely intense radiation field of mainly hadronic particles. The main radiation induced deep defect centres in silicon, responsible for the increase of the dark current and corresponding noise, are the cluster related defect levels E5 and E205a. This work confirms the identification of the E5 level as tri-vacancy (V₃). This defect transforms into the tri-vacancy-oxygen complex (V₃O) at temperatures above 200 °C. The defect concentrations were obtained by means of Deep Level Transient Spectroscopy (DLTS) and Thermally Stimulated Current technique (TSC) performed on float zone (FZ), epitaxially grown (Epi) and Magnetic Czochralski (MCz) silicon diodes, irradiated with 1 MeV neutrons and 23 GeV protons.     

Conformational Isomers of Calcineurin Follow Distinct Dissociation Pathways

In the gas-phase, ions of protein complexes typically follow an asymmetric dissociation pathway upon collisional activation, whereby an expelled small monomer takes a disproportionately large amount of the charges from the precursor ion. This phenomenon has been rationalized by assuming that upon activation, a single monomer becomes unfolded, thereby attracting charges to its newly exposed basic residues. Here, we report on the atypical gas-phase dissociation of the therapeutically important, heterodimeric calcium/calmodulin-dependent serine/threonine phosphatase calcineurin, using a combination of tandem mass spectrometry, ion mobility mass spectrometry, and computational modeling. Therefore, a hetero-dimeric calcineurin construct (62?kDa), composed of CNa (44?kDa, a truncation mutant missing the calmodulin binding and auto-inhibitory domains), and CNb (18?kDa), was used. Upon collisional activation, this hetero-dimer follows the commonly observed dissociation behavior, whereby the smaller CNb becomes highly charged and is expelled. Surprisingly, in addition, a second atypical dissociation pathway, whereby the charge partitioning over the two entities is more symmetric is observed. The presence of two gas-phase conformational isomers of calcineurin as revealed by ion mobility mass spectrometry (IM-MS) may explain the co-occurrence of these two dissociation pathways. We reveal the direct relationship between the conformation of the calcineurin precursor ion and its concomitant dissociation pathway and provide insights into the mechanisms underlying this co-occurrence of the typical and atypical fragmentation mechanisms.     

The Liar Game Over an Arbitrary Channel

We introduce and analyze a liar game in which t-ary questions are asked and the responder may lie at most k times. As an additional constraint, there is an arbitrary but prescribed list (the channel) of permissible types of lies. For any fixed t, k, and channel, we determine the exact asymptotics of the solution when the number of queries goes to infinity.     

Stationary state of a heated granular gas: Fate of the usual H-functional

We consider the characterization of the nonequilibrium stationary state of a randomly driven granular gas in terms of an entropy-production-based variational formulation. Enforcing spatial homogeneity, we first consider the temporal stability of the stationary state reached after a transient. In connection, two heuristic albeit physically motivated candidates for the nonequilibrium entropy production are put forward. It turns out that none of them displays an extremum for the stationary velocity distribution selected by the dynamics. Finally, the relevance of the relative Kullbach entropy is discussed.     

Thermal stability, antioxidant activity, and photo-oxidation of natural polyphenols

The thermal stability (60°C, 80°C, 100°C), antioxidant activity, and ultraviolet C light (UV-C) stability of standard polyphenols solutions (catechin, gallic acid, and vanillic acid) and of vegetal extracts from spruce bark and grape seeds were investigated. Exposure of the standard solutions and vegetal extracts to high temperatures revealed that phenolic compounds were also relatively stable (degradations ranged from 15 % to 30 % after 4 h of exposure). The highest antioxidant activity was obtained for ascorbic acid and gallic acid followed by catechin and caffeic acid and the grape seeds. The results show that, after 3 h of UV-C exposure, approximately 40 % of vanillic acid, 50 % of gallic acid, and 83 % of catechin were removed. Similar degradation rates were observed for vegetal extracts, with the exception of the degradation of catechin (40 %) from grape seeds. In addition, the photo-oxidation of polyphenols in the presence of food constituents such as citric acid, ascorbic acid, sodium chloride, and sodium nitrate was assessed.