Double-layer structure and mechanism of electrode reactions: Part II. Nitrobenzene reduction on mercury from aqueous solutions

Kinetic measurements of nitrobenzene (RNO₂) electroreduction to phenylhydroxylamine in aqueous solutions of pH ranging from 2 to 12 were carried out with the polarographic technique under different experimental conditions. In particular, different concentrations of non-specifically and specifically adsorbed supporting electrolytes were employed to change the potential φ_d at the outer Helmholtz plane and/or the charge density q_i at the inner Helm-holtz plane. The effects of these changes are amenable to a straightforward interpretation provided the overall electrode process is assumed to be controlled by the electron-transfer step $RN{O}_{2}H\stackrel{+e}{\to }RN{O}_2{H}^{?}$ (step a) for 2<pH<5, by the heterogeneous protonation step $RN{O}_2^{?}\stackrel{+H^{+}}{\to }RN{O}_{2}H$ (step b) for 6<pH<9, by the electron-transfer step $RN{O}_2^{?}\stackrel{+e}{\to }RN{O}_2^{2?}$ (step c) for pH>11, and by both the parallel steps (b) and (c) for 9<pH<11.     

1H and 13C NMR spectral assignment of alkyl and polyamine-linked bis(2-thioxo-[1,3,5]-thiadiazinan-3-yl) carboxylic acids

The 1H and 13C NMR spectroscopic data for alkyl and polyamine-linked bis(2-thioxo-[1,3,5]thiadiazinan-3-yl) carboxylic acids, prepared from alkyl diamines and N4-(benzyl) spermidine have been fully assigned by combination of one- and two-dimensional experiments (DEPT, HMBC, HMQC, COSY).     

Influence of gel-phase microdomains and lipid rafts in lipid monolayers on the electron transfer of a lipophilic redox probe: dioctadecylviologen

Gel-phase microdomains and lipid rafts form spontaneously in monolayers of lipid mixtures of dioleoylphosphatidylcholine (DOPC), palmitoylsphingomyelin (PSM) and cholesterol (Chol), self-assembled on mercury. The influence of microdomains on the electron transfer properties of 2 mol% dioctadecylviologen (DODV), incorporated in these lipid monolayers, was investigated by cyclic voltammetry. In pure DOPC, the DODV molecules tend to aggregate, giving rise to strong attractive lateral interactions. With an increase in the PSM mole fraction in DOPC/PSM binary mixtures, the edges of the resulting gel-phase microdomains act as docking sites for the DODV molecules, decreasing lateral interactions and modifying the DODV redox properties. A similar behavior is shown by lipid rafts formed by adding Chol to the above binary mixtures. By varying the DOPC/PSM molar ratio, the midpoint between the peak potentials of the DODV reduction and oxidation peaks shifts in parallel with the surface dipole potential of the lipid mixture. This behavior indicates that the formal (half-reduction) potential of a redox pair, as measured versus a given reference electrode, may include a surface dipole potential if one or both members of the redox pair are embedded in a medium different from the bulk phase containing the reference electrode.     

Tethered bilayer lipid micromembranes for single-channel recording: the role of adsorbed and partially fused lipid vesicles

A mercury-supported bilayer lipid micromembrane was prepared by anchoring a thiolipid monolayer to a mercury cap electrodeposited on a platinum microdisc about 20 μm in diameter; a lipid monolayer was then self-assembled on top of the thiolipid monolayer either by vesicle fusion or by spilling a few drops of a lipid solution in chloroform on the cap and allowing the solvent to evaporate. Single-channel recording following incorporation of the alamethicin channel-forming peptide exhibits quite different features, depending on the procedure followed to form the distal lipid monolayer. The "spilling" procedure, which avoids the formation of adsorbed or partially fused vesicles, yields very sharp single-channel currents lasting only one or two milliseconds. These are ascribed to ionic flux into the hydrophilic spacer moiety of the thiolipid. Conversely, the vesicle-fusion procedure yields much longer single-channel openings analogous to those obtained with conventional bilayer lipid membranes, albeit smaller. This difference in behavior is explained by ascribing the latter single-channel currents to ionic flux into vesicles adsorbed and/or partially fused onto the tethered lipid bilayer, via capacitive coupling.     

Solvent dependence of the photophysical properties of 2-chlorothioxanthone, the principal photoproduct of chlorprothixene

2‐chlorothioxanthone (CTX) is used as photoinitiator for the reticulation of synthetic resins and for the preparation of pharmaceuticals. It was previously determined that CTX is the primary photoproduct of z‐chlorprothixene (CPTX) when irradiated at 313 nm and is formed in an autocatalyzed reaction through an energy‐transfer mechanism (Piñero et al. [2009] Photochem. Photobiol., 85 , 895–900). In this work, the photophysical properties of CTX were measured in acetonitrile/water solutions to determine if their magnitude can affect the side effects of CPTX. The results show that CTX has higher absorption coefficients in the visible region (400–420 nm) and higher triplet quantum yields than its parent compound. Similar to TX, both properties strongly depend on the solvent polarity/hydroxylicity. The quantum yield of the triplet intermediate is very close to the value of the phenothiazine triplets. The phenothiazines are the most phototoxic antidepressants. Therefore, given the appropriate microenvironment, the photosensitization side effects of CPTX can be intensified on the production of CTX.     

Two-dimensional Fourier transform ion cyclotron resonance mass spectrometry: reduction of scintillation noise using Cadzow data processing

In two-dimensional Fourier transform ion cyclotron resonance mass spectrometry (2D FTICR-MS), scintillation noise, caused mostly by fluctuations in the number of ions in the ICR cell, is the leading cause for errors in spectrum interpretation. In this study, we adapted an algorithm based on singular value decomposition and first introduced by Cadzow et al. (IEE Proceedings Pt. F 1987, 134, 69) to 2D FTICR-MS and we measured its performance in terms of noise reduction without losing signal information in the 2D mass spectrum.     

Stability in an overdetermined problem for the Green’s function

In the plane, we consider the problem of reconstructing a domain from the normal derivative of its Green’s function (with fixed pole) relative to the Dirichlet problem for the Laplace operator. By means of the theory of conformal mappings, we derive stability estimates of Hölder type.     

Surgery on a Stratified Space

Let Y be a closed manifold with a locally flat submanifold \({Z\subset Y}\) and X be a manifold with a boundary \({\partial X}\) . In this paper we construct the algebraic surgery theory of a stratified space that is homeomorphic to \({Y\cup X}\) with transversal intersection \({Y\cap X= Z=\partial X}\) . We develop the algebraic surgery theory of Ranicki to this case and we obtain relations between the introduced spectra that realize the obstruction groups and the structure sets.     

Synthesis of Tri-O-acetyl-d-allal from Levoglucosenone

Tri-O-acetyl-d-allal has been enantiospecifically synthesized in six steps from levoglucosenone in 55% overall yield. A key step in the synthesis is the anhydro bridge ring-opening with concomitant formation of a 1,3-oxathiolane-2-thione ring.     

Optimal reparametrization and large sample likelihood inference for the location-scale skew-normal model

Motivated by results in Rotnitzky et al. (2000), a family of parametrizations of the location-scale skew-normal model is introduced, and it is shown that, under each member of this class, the hypothesis H ₀: ?? = 0 is invariant, where ?? is the asymmetry parameter. Using the trace of the inverse variance matrix associated to a generalized gradient as a selection index, a subclass of optimal parametrizations is identified, and it is proved that a slight variant of Azzalini??s centred parametrization is optimal. Next, via an arbitrary optimal parametrization, a simple derivation of the limit behavior of maximum likelihood estimators is given under H ₀, and the asymptotic distribution of the corresponding likelihood ratio statistic for this composite hypothesis is determined.