The Molecularly Controlled Synthesis of Ordered Bi‐dimensional C60 Arrays

Much of the research effort concerning the nanoscopic properties of clays has focused on its mechanical applications, for example, as nanofillers for polymer reinforcement. To broaden the horizon of what is possible by exploiting the richness of clays in nanoscience, herein we report a bottom‐up approach for the production of hybrid materials in which clays act as the structure‐directing interface and reaction media. This new method, which combines self‐assembly with the Langmuir–Schaefer technique, uses the clay nanosheets as a template for the grafting of C₆₀ into a bi‐dimensional array, and allows for perfect layer‐by‐layer growth with control at the molecular level. In contrast to the more‐common growth of C₆₀ arrays through nanopatterning, our approach can be performed under atmospheric conditions, can be upscaled to areas of tenths of cm², and can be applied to almost any hydrophobic substrate. Herein, we report a detailed study of this approach by using temperature‐dependent X‐ray diffraction, spectroscopic measurements, and STM.     

Surfaces de la classe VII0 admettant un champ de vecteurs

Résumé. Nous montrons qu'une surface de la classe VII₀ avec b ₂ > 0 sur laquelle existe un champ de vecteurs non trivial contient exactement b ₂ courbes rationnelles. Il s'ensuit par un théorème de I. Nakamura qu'une telle surface se déforme en une surface de Hopf primaire éclatée. Ce résultat contribue ? la classification des surfaces complexes compactes avec champs de vecteurs. Received: August 6, 1998     

A New Supramolecular Tetraruthenated Cobalt (II) Porphyrazine Displaying Outstanding Electrocatalytical Performance in Oxygen Evolution Reaction

A new supramolecular electrocatalyst for Oxygen Evolution Reaction (OER) was synthesized from a central multibridging cobalt tetrapyridylporphyrazine (CoTPyPz) species by attaching four [Ru(bpy)₂Cl]⁺ groups. Both CoTPyPz and the tetraruthenated cobalt porphyrazine species, TRuCoTPyPz, form very homogenous molecular films just by dropcasting their methanol solutions onto GCE electrodes. Such films exhibited low overpotentials for O₂ evolution, e.g., 560 e 340 mV, respectively, displaying high stability, typically exceeding 15 h. The kinetic parameters obtained from the Tafel plots showed that the peripheral complexes are very important for the electrocatalytic activity. Hyperspectral Raman images taken along the electrochemical process demonstrated that the cobalt center is the primary active catalyst site, but its performance is enhanced by the ruthenium complexes, which act as electron-donating groups, in the supramolecular system.     

Eco-Friendly Synthesis of an Oxovanadium(IV)-bis(abietate) Complex with Antimicrobial Action

The search for less expensive and viable products is always one of the challenges for research development. Commonly, the synthesis of coordination compounds involves expensive ligands, through expensive and low-yield routes, in addition to generating toxic and unusable residues. In this work, the organic ligand used is derived from the resin of a reforestation tree, Pinus elliottii var. elliottii. The synthesis method used Pinus resin and an aqueous solution of vanadium(III) chloride at a temperature of 80 °C. The procedure does not involve organic solvents and does not generate toxic residues, thus imparting the complex formation reaction a green chemistry character. The synthesis resulted in an unprecedented oxovanadium(IV)-bis(abietate) complex, which was characterized by mass spectrometry (MS), chemical analysis (CHN), vibrational (FTIR) and electronic spectra (VISIBLE), X-ray diffraction (XRD), and thermal analysis (TG/DTA). Colorimetric studies were performed according to the CIELAB color space. The structural formula found, consisted of a complex containing two abietate ligands, [VO(C₂₀H₂₉O₂)₂]. The VO(IV)-bis(abietate) complex was applied against microorganisms and showed promising results in antibacterial and antifungal activity. The best result of inhibitory action was against the strains of Gram-positive bacteria S. aureus and L. monocytogenes, with minimum inhibitory concentration (MIC) values of 62.5 and 125 μmol L⁻¹, respectively. For Gram-negative strains the results were 500 μmol L⁻¹ for E. coli; and 1000 μmol L⁻¹ for Salmonella enterica Typhimurium. Antifungal activity was performed against Candida albicans, where the MIC was 15.62 μmol L⁻¹, and for C. tropicalis it was 62.5 μmol L⁻¹. According to the MFC analysis, the complex presented, in addition to the fungistatic action, a fungicidal action, as there was no growth of fungi on the plates tested. The results found for the tests demonstrate that the VO(IV)-bis(abietate) complex has great potential as an antimicrobial and mainly antifungal agent. In this way, the pigmented ink with antimicrobial activity could be used in environments with a potential risk of contamination, preventing the spread of microorganisms harmful to health.     

Hydrogen bonding networks in gabapentin protic pharmaceutical salts: NMR and in silico studies

Hydrogen bonds (HBs) play a key role in the supramolecular arrangement of crystalline solids and, although they have been extensively studied, the influence of their strength and geometry on crystal packing remains poorly understood. Here we describe the crystal structures of two novel protic gabapentin (GBP) pharmaceutical salts prepared with the coformers methanesulfonic acid (GBP:METHA) and ethanesulfonic acid (GBP:ETHA). This study encompasses experimental and computational electronic structure analyses of ¹H NMR chemical shifts (CSs), upon in silico HB cleavage. GBP:METHA and GBP:ETHA crystal packing comprise two main structural domains: an ionic layer (characterized by the presence of charge-assisted ⁺NH_GBP⋯ O⁻_METHA/ETHA HB interactions) and a neutral layer generated in a different way for each salt, mainly due to the presence of bifurcated HB interactions. A comprehensive study of HB networks is presented for GBP:METHA, by isolating molecular fragments involved in distinct HB types (NH⋯ O, OH⋯ O, and CH⋯ O) obtained from in silico disassembling of an optimized three-dimensional packing structure. Formation of HB leads to calculated ¹H NMR CS changes from 0.4 to ~5.8 ppm. This study further attempts to assess how ¹H NMR CS of protons engaged in certain HB are affected when other nearby HB, involving bifurcated or geminal/vicinal hydrogen atoms, are removed.     

New integral LEM formulae applied to the nonlinear bar

The linear equivalence method (LEM), introduced by [Bull. Math. Soc. Sci. Math. de la Roumanie 24 (72) (1980) 4417; An. Univ. Bucure ti, ser. Matematica 31 (1982) 75] to get solutions of nonlinear ODEs, was used so far to get differential type representations. New LEM representations of integral type are presented here and used for the study of the nonlinear elastic bar; a good approximating formula for the rotation of the cross-section at the bar end is also obtained, in case of a simply supported bar. A parallel old–new results is made by means of a programming code.     

Corrigendum and addendum to my paper concerning Kummer extensions with few roots of unity

This note presents corrections and additions to my paper (J. Number Theory 41 (1992) 322-358).     

Spectroscopic characterization and electrocatalytical activity of tetrapyridylporphyrins intercalated into hydrated vanadium(V) oxide

The intercalation ofmeso-tetrapyridylporphyrins into hydrated vanadium(V) pentoxide has been studied using X-ray diffraction; FTIR, electronic and Mössbauer spectroscopy; cyclic voltammetry and spectroelectrochemistry. The intercalation compound containing iron tetrapyridylporphyrin exhibits pronounced electrocatalytical activity in the reduction of molecular dioxygen, reflecting an enhanced reactivity of the catalyst in a confined medium.     

Linkage isomerism,kinetics and electrochemistry of ruthenium-edta complexes of benzotriazole

The [RuIII(edta)(benzotriazole)]− complex has been investigated in aqueous solution, by means of cyclic voltammetry, stopped-flow kinetics and spectroelectrochemistry. The formation reaction, starting from [RuIII(edta)H2O]− and benzotriazole, leads essentially to the N(1) coordinated isomer. In the case of the RuII species, the products exhibit an intramolecular isomerization equilibrium involving the N(1) and N(2) binding sites, with K12=0.33. A complete set of acid/base and association constants has been obtained for the RuII and RuIII complexes. The data are coherent with theoretical calculations, reflecting the importance of π-backbonding interactions in the reduced species. This revised version was published online in June 2006 with corrections to the Cover Date.