Electrostatic effect of specifically adsorbed electroinactive ions upon electrode processes: Part VIII. Cu2+ reduction and Cu°(Hg) oxidation in perchloric acid

The effect of the specific adsorption of the ClO₄^? ion upon the kinetics of Cu²⁺ reduction and Cu⁰(Hg) oxidation in aqueous solutions of HClO₄ was investigated using chronocoulometry, d.c., normal pulse, and a.c. polarography. For this purpose three different sets of data for ClO₄^? adsorption were used. In the first set the absolute surface excess of water as reckoned at the outer Helmholtz plane (o.H.p.) was disregarded, in the second set it was accounted for by postulating a complete adsorbed monolayer of water molecules [32], whereas in the third set partial displacement of water molecules from this monolayer by adsorbed ClO₄^? ions was accounted for. Kinetic data were found to the compatible with the latter set, indicating that ClO₄^? adsorption affects the rate-determining step Cu²⁺+e→Cu⁺ only by altering the average electric potential σ_d-effect). The absence of any additional electrostatic effect points out that, in the transition state for Cu²⁺ reduction to Cu⁺, the centre of charge of the reacting particle falls in the proximity of the o.H.p.     

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.     

A rationalization of the enthalpy of protonation of polyamines

The enthalpies of protonation of polyamines in aqueous solution are interpreted in terms of a simple model that does not involve any tautomeric equilibrium. The enthalpies are calculated as the sum of two contributions; bond formation enthalpy (E _B ) and solvation enthalpy (E _S . The results agree well with experimental data.     

Synthesis of sulfur-containing aryl and heteroaryl vinyls via Suzuki-Miyaura cross-coupling for the preparation of SERS-active polymers

The preparation of sulfur-containing aryl and heteroaryl vinyl co-monomers via Suzuki-Miyaura cross-coupling between the corresponding mercaptomethyl arylboronates and in situ-generated vinyl bromides is described. Surface-enhanced Raman scattering (SERS) studies of the target compounds on gold nanoparticles confirmed their potential as spectroscopic tags in the fabrication of SERS-encoded polymers for combinatorial screening and biomedical diagnostics.     

Asymmetric construction of substituted pyrrolidines via 1,3-dipolar cycloaddition of azomethine ylides and chiral acrylates derived from biomass

The first application of chiral auxiliaries synthesized from levoglucosenone (a biomass-derived anhydrosugar) in asymmetric 1,3-dipolar cycloaddition reactions of azomethine ylides is herein reported. The corresponding pyrrolidinic cores were obtained in excellent levels of regio and stereocontrol, good to excellent π-facial selectivities, and could be isolated enantiomerically pure by column chromatography. Unexpected NMR observations coupled with DFT calculations allowed the stereochemical assignment of the synthesized adducts. The stereochemical assignment performed in silico was further unambiguously validated by structural X-ray diffraction analysis.     

Traceless solid-phase synthesis of bicyclic dihydropyrimidones using multidirectional cyclization cleavage

Solid-phase and solution-phase protocols for the synthesis of furo[3,4-d]pyrimidines, pyrrolo[3,4-d]pyrimidines, and pyrimido[4,5-d]pyridazines are reported. The multistep solid-phase sequence involves the initial high-speed, microwave-promoted acetoacetylation of hydroxymethylpolystyrene resin with methyl 4-chloroacetoacetate. The immobilized 4-chloroacetoacetate precursor was subsequently subjected to three-component Biginelli-type condensations employing urea and a variety of aromatic aldehydes. The resulting 6-chloromethyl-functionalized resin-bound dihydropyrimidones served as common chemical platforms for the generation of the desired heterobicyclic scaffolds using three different traceless cyclative cleavage strategies. The corresponding furo[3,4-d]pyrimidines were obtained by microwave flash heating in a rapid, thermally triggered, cyclative release. Treatment of the chloromethyl dihydropyrimidone intermediates with a variety of primary amines followed by high-temperature microwave heating furnished the anticipated pyrrolo[3,4-d]pyrimidine scaffolds via nucleophilic cyclative cleavage. In a similar way, reaction with monosubstituted hydrazines resulted in the formation of pyrimido[4,5-d]pyridazines. All compounds were obtained in moderate to good overall yields and purities.     

A subsystem-independent generalization of entanglement

We present a generalization of entanglement based on the idea that entanglement is relative to a distinguished subspace of observables rather than a distinguished subsystem decomposition. A pure quantum state is entangled relative to such a subspace if its expectations are a proper mixture of those of other states. Many information-theoretic aspects of entanglement can be extended to this observable-based setting, suggesting new ways of measuring and classifying multipartite entanglement. By going beyond the distinguishable-subsystem framework, generalized entanglement also provides novel tools for probing quantum correlations in interacting many-body systems.     

Organic syntheses with sulfones noxxxvi: conversion of sulfones into aldehydes and ketones.

Alkyl and allyl sulfones can be converted into boronic esters, oxidation of which leads to aldehydes or ketones.