Beiträge zur Struktur und Chemie der Wollfaser

Ohne Zusammenfassung11. Mitteilung aus der Reihe Struktur und Reaktionsfäahigkeit der Wollfaser. 10. Mitteilung vgl. E. Elöd, H. Nowotny und H. Zahn, Klepzigs Textilzeitschrift45, 663 (1942).     

Study of CVD diamond C(100) by X-ray absorption spectroscopies

Surface sensitive x-ray absorption fine structure measurements were carried out near the carbon K-edge on chemical vapor deposited (CVD) diamond and natural diamond. Utilizing different methods, namely near edge and extended x-ray absorption fine structure measurements (NEXAFS and EXAFS), features were found in the spectra which were attributed to non-diamond coordination fractions, such as bulk C-H bonds, graphite-like and more diamond-like coordinated amorphous carbon domains. Both techniques show that the non-diamond fractions consist mainly of diamond-like amorphous carbon.     

Computational and conformational evaluation of FTase alternative substrates: insight into a novel enzyme binding pocket

Protein farnesyltransferase (FTase) is an important anticancer drug target. In an effort to develop isoprenoid diphosphate-based FTase inhibitors, striking variations have been observed in the ability of conservatively modified analogues to bind to the enzyme. For example, 2Z-GGPP is an alternative substrate with high binding affinity, while GGPP is not an alternative substrate. Using the availability of high-resolution FTase crystal structures, we have used pharmacophore and docking studies to elucidate a new binding pocket for isoprenoid analogues. The unique conformations between the first two isoprene units of 2Z-GGPP, but not GGPP, allows 2Z-GGPP to exploit this new binding pocket. The discovered conformation allows the molecule to adopt a reactive conformation while placing hydrophobic groups within the predominately hydrophobic binding pocket. This computational finding is supported by NMR studies on (13)C-labeled 2Z-farnesol, which confirm that the computationally predicted conformation is also favored in solution. These discoveries suggest that ligand conformational flexibility may be an important design consideration for the development of both inhibitors and alternative substrates of FTase.     

Die Bestimmung kleiner Mengen Sehwefel

Analytical and Bioanalytical Chemistry -     

Monitoring the ordering in biomolecular films on vicinal silicon surfaces by reflectance difference/anisotropy spectroscopy

DNA base molecules, adenine, thymine, guanine, and cytosine may be employed as charge transport molecules in biomolecular electronic devices. Their electronic properties are comparable with those of inorganic wide bandgap materials, e.g. GaN with the absorption onset in the near ultra-violet (UV) range. A recent field effect transistor study based on a modified DNA base revealed that the prototype bio-transistor gives rise to a better voltage gain compared to one based on carbon nanotubes (CNTs) [G. Mauricio, P. Visconti, V. Arima, S. D’Amico, A. Biasco, E. D’Amone, R. Cingolani, R. Rinaldi, Nanoletters 3 (2003) 479]. Here, in situ reflectance difference/anisotropy spectroscopy (RDS/RAS) is employed under ultra-high vacuum (UHV) conditions for monitoring the growth of DNA base molecules on vicinal hydrogen passivated Si(1 1 1) surfaces. Such vicinal substrates consisting of steps and terraces may serves as suitable templates for molecular ordering. Indeed, RDS/RAS measurements reveal information about molecular ordering of DNA bases induced by the density of steps on silicon surfaces. All four molecules, however, behave differently on the vicinal substrates. The first transition dipole moments corresponding to adenine and thymine molecules align mainly perpendicular to the step edge direction while for guanine and cytosine they align parallel to this direction, however, only in very thin layers. The RDS/RAS signal of the guanine and cytosine layers with thicknesses above 20 nm saturates due to a loss of ordering at higher coverages. Additionally, time-resolved RDS/RAS measurements at the silicon E₂ (4.25 eV) critical point (CP) demonstrate the sensitivity to the biomolecular/inorganic interface formation.     

The Role of Substitutional Defects in Order/Disorder Phenomena of OH− Ions in Hydroxyapatite

We report on density functional quantum mechanical calculations of hydroxyapatite. The central focus is dedicated to the local arrangement of hydroxide ions in proximity of defects originating from substituting OH^? by F^? or O^2? ions. At ambient conditions the preferred structure of bulk hydroxyapatite exhibits an ordering of OH^? ions oriented in rows along the [001] direction. From zero Kelvin geometry optimizations the orientation inversion of a hydroxide ion was found to be disfavored by 0.165 eV. This picture changes dramatically when replacing one of the OH^? ions by a fluoride ion. The preferred hydroxide ion arrangement next to the F^? defect was identified as an OH^?··F^?··HO^? constellation, which implies the orientation inversion of one of the neighboring hydroxide ions. An analogous phenomenon was observed for O^2? defects.