24 IPR isomers of fullerene C84: Cage deformation as geometrical characteristic of local strains

The structures of 24 IPR‐isomers of C₈₄ fullerene with distributed single, double and delocalized bonds are presented. Obtained results are fully supported by DFT quantum‐chemical calculations of electronic and geometrical structures of these isomers. Two reasons of instability of fullerene molecules are their radical origin and/or high local strain. Distortion of pentagons as well as hexagons with alternating single and double bonds is the most significant geometrical parameter reflecting local strain of a molecule. These distortions are measured as maximal dihedral angles of those cycles and reach 20 degrees in mostly deformed hexagons and pentagons. In contrast high values of dihedral angles in hexagons with delocalized π‐bonds are typical for stable isomers. Other geometric parameters such as valence angles, sums of valence angles and dihedral angles between approximate planes of fused rings have no marked influence on stability. The development of strain‐related criteria for fullerene stability will be helpful in the prediction which isomers might potentially be observable in experiment. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Acyclic tautomers in crystalline carbohydrates: the keto forms of 1-deoxy-1-carboxymethylamino-D-2-pentuloses (pentulose-glycines)

NMR and X-ray diffraction studies on acyclic carbohydrate keto tautomers of N-(1-deoxy-d-erythro-2-pentulos-1-yl)- and N-(1-deoxy-d-threo-2-pentulos-1-yl)glycines (ribulose-glycine, 1 and xylulose-glycine, 2), are reported. In aqueous solutions, both 1 and 2 exist as a tautomeric mixture, with the beta-furanose as a major form, followed by the alpha-furanose and the acyclic keto tautomer. Both 1 and 2 crystallize as zwitterions in the acyclic keto form. Solid-state 13C NMR spectra reveal the existence of two crystallographically independent molecules in 2 but only one in crystalline 1. The structure of 2 was solved by X-ray diffraction; in the crystal, two conformational isomers, 2a and 2b in a 1:1 ratio, were identified. The conformers are packed in stacks of similar molecules, with a system of intermolecular hydrogen bonds involving all hydroxyl, ammonium, and carboxyl groups. The structural data indicate that the sugar portion of acyclic 2 adopts conformations similar to those proposed for the parent d-xylulose.     

Photochromism of side-chain liquid crystal polymers containing spironaphthoxazines

Side-chain liquid crystal polyacrylates and polysiloxanes containing different photochromic spironaphthoxazine side groups were synthesized. Thermodynamic, spectral and kinetic properties of the polymers were investigated. The structure of the mesophase is discussed.     

Magnetic anisotropy engineering in square magnetic elements

Square magnetic elements with side in the 100–500 nm range have been fabricated using the focused ion beam (FIB) milling technique from a 10 nm thick, single-crystal Fe film, epitaxially grown on MgO(0 0 1). Thanks to the good crystal quality of the film, magnetic elements with well-defined magnetocrystalline anisotropy have been prepared, while the fine control of the size and shape of the magnets allows for the effective engineering of the anisotropic behavior of the magnetostatic energy that determines the so-called configurational anisotropy. Micromagnetic calculations and experiments show that the angular dependence of the transverse susceptibility has a strong dependence on the material parameters as well as on the static applied field. This allows the effective engineering of the total anisotropy of the magnets.     

Assessment of amplitude modulation in environmental noise measurements

This paper introduces a method to assess the parameters of amplitude modulation as applicable to environmental noise monitoring tasks. It is based on the analysis of time histories of sound pressure levels correlated with a reference cosine signal. The method brings accurate results in situations where the time history does not exhibit a clear modulation pattern or the signal-to-noise ratio is poor. These features make the suggested technique attractive for practical implementation.     

Oxide‐Supported IrNiOx Core–Shell Particles as Efficient,Cost‐Effective,and Stable Catalysts for Electrochemical Water Splitting

Active and highly stable oxide‐supported IrNiO_x core–shell catalysts for electrochemical water splitting are presented. IrNi_x@IrO_x nanoparticles supported on high‐surface‐area mesoporous antimony‐doped tin oxide (IrNiO_x /Meso‐ATO) were synthesized from bimetallic IrNi_x precursor alloys (PA‐IrNi_x /Meso‐ATO) using electrochemical Ni leaching and concomitant Ir oxidation. Special emphasis was placed on Ni/NiO surface segregation under thermal treatment of the PA‐IrNi_x /Meso‐ATO as well as on the surface chemical state of the particle/oxide support interface. Combining a wide array of characterization methods, we uncovered the detrimental effect of segregated NiO phases on the water splitting activity of core–shell particles. The core–shell IrNiO_x /Meso‐ATO catalyst displayed high water‐splitting activity and unprecedented stability in acidic electrolyte providing substantial progress in the development of PEM electrolyzer anode catalysts with drastically reduced Ir loading and significantly enhanced durability.