Identification of metastable states in peptide's dynamics

A recently developed spectral method for identifying metastable states in Markov chains is used to analyze the conformational dynamics of a four-residue peptide valine-proline-alanine-leucine. We compare our results to empirically defined conformational states and show that the found metastable states correctly reproduce the conformational dynamics of the system.     

Thermal behavior of partially hydrogenated polydienes by <Emphasis Type="Italic">p</Emphasis>-toluenesulfonylhydrazide

The hydrogenation of natural rubber (NR), polybutadiene (BR), and styrene-butadiene (SBR) rubbers with different microstructures was performed by a diimide hydrogenation agent generated in situ by a non-catalytic method [1–3]. Many properties of the material depend considerably on variables such as degree of hydrogenation and proportions of vinyl or phenyl units. The mobility of the hydrogenated chain was investigated by differential scanning calorimetry (DSC) and the results confirm the relationship between the degree of hydrogenation and chain flexibility. The flexibility of a high cis-1,4 BR hydrogenated sample, was significantly changed and a melting point (T _m) was detected after a certain degree of hydrogenation. Thermal stability was investigated by thermogravimetric analysis (TG) and an increase was found, but, the thermal resistance was influenced by the presence of the byproduct p-toluenesulfinic acid. Oxidation stability was investigated by chemiluminescence analysis and it improved with hydrogenation.     

Interaction of hydrogen with RuO2(110) surfaces: activity differences between various oxygen species

The interaction of hydrogen with RuO(2)(110) surfaces was studied by means of thermal desorption and vibration spectroscopies. The stoichiometric surface exposes two types of coordinatively unsaturated atoms: double-bonded O-bridge and five-fold-bonded Ru-cus, while at the O-rich surface the Ru-cus atoms are covered with single-bonded O-cus. On the stoichiometric RuO(2)(110) surface at 90 K, H(2) either adsorbs molecularly on Ru-cus sites or dissociates and forms with O-bridge an H(2)O-like surface group. If, in addition, also O-cus is present at the surface, hydrogen interacts exclusively with this species forming H(2)O-cus. This demonstrates that hydrogen reacts much more readily with O-cus than with O-bridge as expected from the reduced bond order and smaller binding energy of O-cus. It is furthermore shown that at surface temperatures below 90 K free coordinatively unsaturated Ru-cus sites are needed to activate the incoming H(2) molecules prior to any reaction with O-cus or O-bridge. Generally, Ru-cus sites play a key role for reactions of a number of molecules at the RuO(2)(110) surface. These findings are supported by recent DFT-based calculations but are at variance with other reports.     

Enantioselective syntheses of ring-C precursors of vitamin B12. Substrate control. A novel Si-assisted elimination of vinyl bromides

Homochiral ring-C precursors 34 of Vitamin B(12) have been prepared by Ireland-Claisen rearrangement of allyl esters 32, followed by a novel Si-assisted elimination of HBr. [reaction: see text]     

Photoemission from matrix-isolated nickel atoms

UV photoelectron spectra from Ni atoms isolated in a xenon matrix at 9 K have been measured for the first time using Hell (40 8 eV). Two peaks have been found at 2.8 and 4.6 eV below E_F, which are interpreted as being due to different d⁸s¹ final states of the Ni ion. including a relaxation shift of 2.0 eV. The existence of atomic Ni species in the matrix has been verified by in situ optical absorption spectra.