Study of Pt and Rh based supported catalysts modified with tetrabutyltin for the selective hydrogenation of 4-methoxyacetophenone

Catalysts based on Pt and Rh modified with Sn(C₄H₉)₄ were studied in the hydrogenation of 4-methoxyacetophenone. The selectivity to 1-(4-methoxyphenyl)ethanol was close to 100% at Sn/(Pt,Rh) = 1.0, however the catalytic activity decreased drastically. With respect to the balance between activity and selectivity the catalyst PtSnOM (Sn/Pt=0.4) showed the best performance.     

Comment on the validation of continuum electrostatics models

A validation based on solvation energies (vacuum to water transfer) is not sufficient to justify the use of approximated models of electrostatics to rank ligand/protein complexes. A full validation should be based on energies in solution, i.e., solvation plus vacuum Coulomb energies, because of the anticorrelation between solvation and vacuum energies. The energy in solution is the relevant quantity in simulations of biological macromolecules and complexes. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1533–1536, 1999     

Ueber kolloides Chlorophyll und über einige kolloide Chlorophyllderivate

Ohne Zusammenfassung     

Studying Natural Buckyballs and Buckybowls in Fossil Materials

Buckyballs (fullerenes) were first reported over 30 years ago, but still little is known regarding their natural occurrence, since they have so far only been found at sites of high‐energy incidents, such as lightning strikes or meteor impacts, but have not been reported in low‐energy materials like fossil fuels. Using ultrahigh‐resolution mass spectrometry, a wide range of fullerenes from C₃₀ to C₁₁₄ was detected in the asphaltene fraction of a heavy crude oil, together with their building blocks of C_10nH₁₀ stoichiometry. High‐level DLPNO‐CCSD(T) calculations corroborate their stability as spherical and hemispherical species. Interestingly, the maximum intensity of the fullerenes was found at C₄₀ instead of the major fullerene C₆₀. Hence, experimental evidence supported by calculations show the existence of not only buckyballs but also buckybowls as 3‐dimensional polyaromatic compounds in fossil materials.     

Emissive metallomesogens based on 2-phenylpyridine complexes of iridium(III)

Preparation of Ir(III) complexes using anisotropic 2,5-di(4-alkoxyphenyl)pyridine ligands leads to emissive, liquid-crystalline complexes containing bound Cl and dimethyl sulfoxide. Using analogous poly(alkoxy) ligands allows the preparation of bis(2-phenylpyridine)iridium(III) acac complexes, which are also mesomorphic. The observation of liquid crystallinity in octahedral complexes of this type is without precedent.     

Theoretical modeling of enzyme reactions: the thermodynamics of formation of compound 0 in horseradish peroxidase

In this paper, by using the perturbed matrix method (PMM) in combination with basic statistical mechanical relations both based on nanosecond time-scale molecular dynamics (MD) simulations, we quantitatively address the thermodynamics of compound 0 (Cpd 0) formation in horseradish peroxidase (HRP) enzyme. Our results, in the same trend of low-temperature experimental data, obtained in cryoenzymology studies indicate that such a reaction can be described essentially as a stepwise spontaneous process: a first step mechanically constrained, strongly exothermic proton transfer from the heme-H2O2 complex to the conserved His42, followed by a solvent-protein relaxation involving a large entropy increase. Critical evaluation of PMM/MD data also reveals the crucial role played by specific residues in the reaction pocket and, more in general, by the conformational fluctuations of the overall environment in physiological conditions.     

Febantel: looking for new polymorphs

The aim of this work was to search for new polymorphic forms of febantel, an anthelminthic drug of great present interest for the veterinary industry. Solvent-based recrystallization, thermal and mechanical treatments and spray drying were chosen to discover new solid forms. The solids obtained were physicochemically characterized by thermal techniques (DSC and TG), FTIR spectroscopy, laboratory and synchrotron X-ray powder diffraction and scanning electron microscopy. Our work leads to obtain a new solid form never described in the literature. In particular, the new polymorph was obtained by the anti-solvent method and the crystallization from isopropanol. The experimental conditions of crystallization favorable to the formation of the highest amount of the new solid phase were selected. The new phase shows a thermal, spectroscopic and diffractometric behavior unique. Furthermore, the preliminary structure investigation suggests two possible crystal systems: an orthorhombic or a monoclinic one, with really comparable lattice parameters and cell volume. Measurements put into evidence that the new phase is a metastable polymorph that is in monotropic relationship with the stable and known form.

     

Synthesis of new (−)-menthylgermanium derivatives and its use in heterogeneous bimetallic catalysis

The syntheses and physical properties of tri-(−)-menthylgermanium chloride (2), tri-(−)-menthylmethylgermanium (5), and tri-(−)-menthylgermanium hydride (6) are reported. The preparation of a bimetallic catalyst derived from 5 and Pt supported on SiO₂ and its use in the enantioselective catalytic hydrogenation of acetophenone is also reported.     

Long-term durability study of perfluoropolymer membranes in low humidification conditions

This paper reports a study on the understanding of the performance decrease mechanisms of polymer electrolyte fuel cells under critical operating conditions. In order to investigate the durability of perfluorosulfonate membranes at low humidification conditions, long-term fuel cell tests have been carried out. Results evidenced a strong effect of low relative humidity on the commercial polymer membrane lifetime. Prolonged dehydration of the membranes led to a decrease of the three-dimensional reaction zone due to the ionomer degradation in the catalytic layer and a continuous loss of material in the membrane evidenced by a thickness decrease. The last effect provoked a collapse of the electrode structure.