Combined intra-intermolecular criss-cross cycloaddition of a new fluorinated unsymmetrical allenylazine with alkynes

The reaction of a new fluorinated unsymmetrical allenylazine with dimethyl acetylenedicarboxylate and phenylacetylene affords the combined intra-intermolecular criss-cross cycloaddition products, 2,3-disubstituted-1,10-diazatricyclo[5.2.1.0^4,10]deca-2,6-diene derivatives. The products contain three fused five-membered rings with two nitrogen atoms within an unsaturated heterocyclic system. The structures were assigned using 2D NMR correlations and in the case of the phenylacetylene adduct by X-ray structure analysis.     

Molecular beam measurements and Monte Carlo simulations of the kinetics of N2O decomposition on Rh(111) single-crystal surfaces

The kinetics of N2O decomposition on Rh(111) single-crystal surfaces were investigated both experimentally by isothermal molecular beam measurements and theoretically using a Monte Carlo algorithm. The present work was directed to the understanding of two unusual observations derived from our previous work on this system, namely, (1) the lower rates for N2O decomposition seen at higher reaction temperatures, and (2) the lower total nitrogen yields and final oxygen surface coverages that accompany that behavior. Experimentally, it was determined here that after the rhodium surface is rendered inactive by N2O decomposition at high (520 K) temperatures, significant activity is still possible at lower (350 K) temperatures. The Monte Carlo simulations explain these observations by assuming that the surface sites required for the activation of adsorbed N2O increase in size with increasing reaction temperature.     

Quantum effects in liquid water and ice: model dependence

This paper explores the influence of choice of potential model on the quantum effects observed in liquid water and ice. This study utilizes standard rigid models and a more formal context for the rigid-body centroid molecular dynamics methodology used to perform the quantum simulations is provided. Quantum and classical molecular dynamics simulations are carried out for liquid water and ice Ih at 298 and 220 K, respectively, with the simple point charge/extended and TIP4P-Ew water models. The results obtained for equilibrium and dynamical properties are compared with those recently reported on TIP4P [L. Hernandez de la Pena and P. G. Kusalik, J. Chem. Phys. 121, 5992 (2004); L. Hernandez de la Pena et al., J. Chem. Phys 123, 144506 (2005)]. For the liquid, an energy shift of about 8% and an average molecular uncertainty of about 11 degrees were found independently of the water model. The self-diffusion coefficient consistently increases by more than 50% when going from the classical to the quantum system and quantum dynamics are found to reproduce the experimental isotopic shifts with the models examined. The ice results compare remarkably well with those previously reported for the TIP4P water model; they confirm that quantum effects are considerable and that the quantum mechanical uncertainty and the energy shifts due to quantization are smaller in ice than in liquid water. The relevance of these findings in the context of the construction of water models is briefly discussed.     

Synthesis of 4-aminotropones from [(sulfinyl or sulfonyl)methyl]-substituted p-quinamines

An efficient synthesis of 4-aminotropones has been achieved in excellent yields by simple treatment of 4-amino-4-[(p-tolylsulfinyl)methyl]-2,5-cyclohexadienones (p-quinamines) with NaH. The method allowed regiocontrolled access to 3-methyl, 5-methyl- and 3,5-dimethyl-substituted derivatives starting from p-quinamines with adequate substituents at the cyclohexadienone moiety and/or at the carbon linked to the sulfur function. The p-quinamines in turn were easily accessible from N-Boc p-anisidines (Boc=tert-butoxycarbonyl) by electrochemical oxidation in MeOH to quinone imine monoketals, followed by addition of a alpha-lithium sulfinyl carbanion to the imino group, and ketal hydrolysis. Oxidation of the sulfoxide gave the sulfonyl-substituted p-quinamines that, upon basic treatment, behave similarly. The p-quinamine 55 and bis-p-quinamine 56, resulting in the addition of the anion derived from dimethyl sulfone to the p-quinonimine ketal 14, also gave the 4-aminotropone. The mechanism involves the initial formation of a alpha-sulfonyl carbanion, which intramolecularly attacks the cyclohexadienone giving a norcaradiene-like enolate intermediate, the evolution of which through a ring-expansion process, pushes off a methyl sulfinate anion or SO2. This efficient process fulfils the criteria of atom economy. The introduction of a proline substituent in the nitrogen of the starting p-quinamine allowed the synthesis of an enantiopure 4-aminotropone, the asymmetric Diels-Alder reactions of which with maleimide occurred in a highly endo and pi-facial diastereoselective manner.     

Determination of levofloxacin in pharmaceutical formulations and urine at reduced graphene oxide and carbon nanotube-modified electrodes

Journal of Solid State Electrochemistry - In this paper, we compare reduced graphene oxide (RGO) electrode with multi-walled carbon nanotubes (MWCNT) as modifiers for the sensitive detection of...     

Epoxy-silica/clay nanocomposite for silver-based antibacterial thin coatings: structure and ionic mobility

Journal of Solid State Electrochemistry - A novel material was developed using sol-gel chemistry and an environmental-friendly grafting process of clay nanoparticles. In a previous work of our...     

σ-Aromaticity-Induced Stabilization of Heterometallic Supertetrahedral Clusters [Zn6Ge16]4− and [Cd6Ge16]4−

In this work, the largest heterometallic supertetrahedral clusters, [Zn₆Ge₁₆]⁴⁻ and [Cd₆Ge₁₆]⁴⁻, were directly self-assembled through highly-charged [Ge₄]⁴⁻ units and transition metal cations, in which 3-center–2-electron σ bonding in Ge₂Zn or Ge₂Cd triangles plays a vital role in the stabilization of the whole structure. The cluster structures have an open framework with a large central cavity of diameter 4.6 Å for Zn and 5.0 Å for Cd, respectively. Time-dependent HRESI-MS spectra show that the larger clusters grow from smaller components with a single [Ge₄]⁴⁻ and ZnMes₂ units. Calculations performed at the DFT level indicate a very large HOMO–LUMO energy gap in [M₆Ge₁₆]⁴⁻ (2.22 eV), suggesting high kinetic stability that may offer opportunities in materials science. These observations offer a new strategy for the assembly of heterometallic clusters with high symmetry.