Surface and electrocatalytic properties of well-defined and vicinal RuO2 single crystal faces

The kinetics of Cl₂ evolution from concentrated NaCl solutions on the (110) and (230) faces of RuO₂ single crystals has been investigated by determining the Tafel slope, the stoichiometric number and the reaction orders with respect to Cl^– and H⁺. The experimental parameters suggest that the mechanism is presumably similar to that put forward earlier by Krishtalik [51] for RuO₂ layers, but a step common to oxygen evolution, like the case of polycrystalline samples, is present only with the (230) face. Reasons for this difference and for the apparent lower activity of the (110) face with respect to the (230) are discussed. A detailed analysis of the surface behavior of the two faces in Cl^– free acid and alkaline solutions has also been carried out by cyclic voltammetry.Dedicated to Professor G. Horanyi on the occasion of his 70th birthday     

Pseudopeptide foldamers: the homo-oligomers of pyroglutamic acid

As a part of a program evaluating substituted gamma-lactams as conformationally constrained building blocks of pseudopeptide foldamers, we synthesized the homo-oligomers of L-pyroglutamic acid up to the tetramer level by solution methods. The preferred conformation of this pseudopeptide series in structure-supporting solvents was assessed by FT-IR absorption, 1H NMR and CD techniques. In addition, the crystal structure of the N alpha-protected dimer was established by X-ray diffraction. A high-level DFT computational modeling was performed based on the crystallographic parameters. In this analysis, we demonstrated that an alpha C-H...O=C intramolecular hydrogen bond is responsible for the stabilization of the s-trans L-pGlu-L-pGlu conformation by 1.4 kcal mol-1. This effect can be easily detected by 1H NMR spectroscopy, owing to the anomalous chemical shifts of the alpha CH protons present in all of the oligomers. In summary, we have developed a new polyimide-based, foldameric structure that, if appropriately functionalized, has promise as a rigid scaffold for novel functions and applications.     

Evaluation of 1-methyl-3,4-hydroxypyridinecarboxylic acids as possible bidentate chelating agents for iron(III): Metal–ligand solution chemistry

The chemical interactions of 1-methyl-3-hydroxy-4-pyridinecarboxylic acid (1M3H4P) and 1-methyl-4-hydroxy-3-pyridinecarboxylic acid (1M4H3P) with Fe(III) were investigated in aqueous 0.6 m (Na)Cl at 25 °C by means of potentiometric titrations and UV–Vis spectrophotometry. A large number of complexes were formed in solution with stoichiometry FeL_xH_y, x = 1, 2, 3 and y = 0, −1, −2. In view of a possible application to Fe(III) chelation therapy, the efficiencies of the ligands to chelate the metal ion were evaluated in vitro at physiological pH. 1M3H4P and 1M4H3P show a lower complexation efficiency with Fe(III) than that of other available chelators, but higher than that of their non-methylated analogs 3H4P and 4H3P.     

Cavitand-based nanoscale coordination cages

This communication reports design, self-assembly, solution, and solid-state characterization of nanoscale coordination cages formed by tetradentate cavitand ligands and appropriate metal precursors. The preorganization of the cavitand ligand in terms of structural rigidity and relative orientation of the pyridyl units leads to the exclusive formation of coordination cages in a wide temperature and concentration range. Desired features of the cage self-assembly process, such as reversibility in the presence of a competitive ligand and self-recognition of the cavitand components, have been assessed.     

Outline of a transition-state hydrogen-bond theory

Though the H-bond is well characterized as a D–H:A three-center-four-electron interaction, the formulation of a general H-bond theory has turned out to be a rather formidable problem because of the extreme variability of the bonds formed (for instance, O–HO energies range from 0.1 to 31 kcal mol⁻¹). This paper surveys our previous contributions to the problem, including: (a) the H-bond chemical leitmotifs (CLs), showing that there are only four classes of strong H-bonds and one of moderately strong ones; (b) the PA/pK_a equalization principle, showing that the four CLs forming strong H-bonds are actually molecular devices apt to equalize the acid–base properties (PA or pK_a) of the H-bond donor and acceptor groups; (c) the driving variable of the H-bond strength, which remains so identified as the difference ΔpK_a=pK_AH(D–H)−pK_BH(A–H⁺) or, alternatively, ΔPA=PA(D⁻)−PA(A); and, in particular, (d) the transition-state H-bond theory (TSHBT), which interprets the H-bond as a stationary point along the complete proton transfer pathway going from D–HA to DH–A via the DHA transition state. TSHBT is verified in connection with a series of seven 1-(X-phenylazo)-2-naphthols, a class of compounds forming a strong intramolecular resonance-assisted H-bond (RAHB), which is switched from N–HO to NH–O by the decreasing electron-withdrawing properties of the substituent X. The system is studied in terms of: (i) variable-temperature X-ray crystallography; (ii) DFT emulation of stationary points and full PT pathways; (iii) Marcus rate-equilibrium analysis correlated with substituent LFER Hammett parameters.     

1‐(1,2,3‐triazol‐4‐yl)‐benzimidazolones,a new series of heterocyclic derivatives

New 1‐(1,2,3‐triazol‐4‐yl)‐benzimidazolone derivatives were obtained on pursuing research about new tricyclic derivatives of medicinal interest, bearing a 1,2,3‐triazole ring fused with another heterocyclic ring. 1‐[(5‐Carboxamido)‐1,2,3‐triazol‐4‐yl]‐benzimidazolone was prepared by four different chemical routes and it was unequivocally confirmed by spectroscopic methods. Its chemical behaviour, was evaluated by some common chemical reactions such as hydrolysis, esterification, decarboxylation, nitration and N‐methylation.     

Nanosphere lithography with variable deposition angle for the production of one‐directional transparent conductors

The production of high quality and cheap transparent electrodes is a fundamental step for a variety of optoelectronic devices. We present a method for the production of transparent conducting films optimised for electrical conduction in one direction. The deposition of a metal film through a perfectly aligned nanosphere‐lithography mask at variable incidence angle gave origin to parallel nanowires with thin interconnections. This structure showed excellent conductivity in one direction and high optical transparency.

Glass substrates under the crystalline areas of the polystyrene‐nanospheres mask.     

Excitonic effects in solids described by time-dependent density-functional theory

Starting from the many-body Bethe-Salpeter equation we derive an exchange-correlation kernel f(xc) that reproduces excitonic effects in bulk materials within time-dependent density functional theory. The resulting f(xc) accounts for both self-energy corrections and the electron-hole interaction. It is static, nonlocal, and has a long-range Coulomb tail. Taking the example of bulk silicon, we show that the -alpha/q(2) divergency is crucial and can, in the case of continuum excitons, even be sufficient for reproducing the excitonic effects and yielding excellent agreement between the calculated and the experimental absorption spectrum.