The molecular orientation of para-sexiphenyl on Cu(110) and Cu(110) p(2x1)O.

Controlling the molecular growth of organic semiconductors is an important issue to optimize the performance of organic devices. Conjugated molecules, used as building blocks, have an anisotropic shape and also anisotropic physical properties like charge transport or luminescence. The main challenge is to grow highly crystalline layers with molecules of defined orientation. The higher the crystallinity, the closer these properties reach their full intrinsic potential, while the orientation determines the physical properties of the film. Herein we show that the molecular orientation and growth can be steered by the surface chemistry, which tunes the molecule-substrate interaction. In addition, the oxygen reconstruction of the surface, demonstrates the flexibility of the organic molecules to adopt a given surface corrugation and their unique possibility to release stress by tilting.     

Template‐Free Galvanic Nanostructuring of Gold Electrodes for Sensitive Electrochemical Biosensors

Gold nanostructuring of smooth gold disk‐electrodes has been performed by electrodeposition. FE‐SEM images indicate a strongly enlarged electrochemically active surface of the modified electrodes. This could be approved by the gold oxide reduction peak in cyclic voltammetry. The electrodes were also applied for sequence‐specific DNA detection. For this, complementary single stranded capture probes were immobilized on the electrodes and consecutively hybridized with complementary and noncomplementary [OsO₄(bipy)]‐labeled DNA targets. We found that intermediate dehybridization steps did not decrease the sensitivity for the specific target. Moreover, the surface modification increased the voltammetric signal by an approx. factor of 9. Further, an enhanced linear calibration range was observed. The presented simple nanostructuring process holds great promise for many electrochemical sensor applications.     

“Small and beautiful” – The novel structures and phases of nano-oxides

Low-dimensional oxide nanostructures supported on well-defined metal surfaces raise scientific interest both on a fundamental level and for potential technological applications. These systems may be regarded as artificially created hybrid materials with novel emergent properties, supporting new concepts of geometrical structure, electronics and magnetism, complex phase diagrams and particular chemical reactivity. The coupling of the oxide nano-phase to the metal support surface by electronic and elastic interactions together with the low dimensionality aspects are at the origin of the particular behaviour of these hybrid structures. By way of prototypical examples, this Prospective article highlights some of the novel properties of nano-oxides and, as a side aspect, comments on the aesthetics of their structural motifs.     

Determination of accessible amino groups on surfaces by chemical derivatization with 3,5-bis(trifluoromethyl)phenyl isothiocyanate and XPS/NEXAFS analysis

The determination of amino groups on surfaces capable of binding biomolecules is important for the understanding and optimization of technologically relevant coupling processes. In this study, three different types of amino-functionalized model surfaces, amino thiolate on Au, amino siloxane on Si, and polyethylene (PE) foils and films reacted with 1,2-diaminoethane (DAE) were derivatized with 3,5-bis(trifluoromethyl)phenyl isothiocyanate. Subsequently, these samples were analyzed by chemical derivatization X-ray photoelectron spectroscopy (CD-XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). The determination of amino groups by this analytical approach allows gaining insight into the availability of groups on surfaces that can actually serve as attachment sites for biomolecules in technical applications. In the case of the amino thiolate on Au, almost 90% of the expected amino groups were detected by CD-XPS. Investigation of the amino siloxane films revealed lower yields for the derivatization reaction in the order of 30%. The lowered reaction yields are thought to be due to interactions between the amino siloxane’s amino and silanol groups or the underlying substrate, making them inaccessible to the derivatization agent. The aminated PE samples are characterized by a complex surface chemistry and structure, and reaction yields of the derivatization reaction cannot be unequivocally derived. However, 1–3% of the total carbon atoms in the surface layer were found to be bound to amino groups accessible to the derivatization agent. It can be concluded that, depending on the detailed character of the investigated amino-terminated surface, the amount of amino groups accessible to CD-XPS can be substantially lower than the total amount of amino groups present at the surface.     

Local structure of amorphous ice as revealed by O K-edge EXAFS.

The oxygen K-edge extended X-ray absorption fine structure (EXAFS) spectrum of an ice film prepared by deposition of water vapor on a substrate at 100 K was measured in the surface-sensitive Auger yield mode. Five distinct peaks are revealed in the Fourier transform spectrum of the EXAFS data. The peaks are attributed to O-H bonds (with overlapping contributions from intramolecular covalent and intermolecular hydrogen bonds) as well as to intermolecular O...O scattering paths in the distance range of 1-7 A. The pattern of the longer O...O distances resembles that of a high-pressure crystalline modification of ice (ice II).     

Trivalent‐Intermediate Valent Cerium Ordering in CeRuSn – A Static Intermediate Valent Cerium Compound with a Superstructure of the CeCoAl Type

New equiatomic stannide CeRuSn was synthesized from the elements by arc‐melting. CeRuSn was investigated by X‐ray powder and single crystal diffraction: C2/m, a = 1156.1(4), b = 475.9(2) and c = 1023.3(4) pm, β = 102.89(3)°, wR2 = 0.0466, 1229 F² values and 38 variables. CeRuSn adopts a superstructure of the monoclinic CeCoAl type through a doubling of the subcell c axis. In the superstructure two crystallographically independent cerium sites occur. Based on the interatomic distances the two sites can be assigned to trivalent Ce2 and intermediate valent Ce1. This trivalent‐intermediate valent cerium ordering is underlined by magnetic susceptibility measurements χ_m(T): below 150 K χ_m, measured with decreasing temperature, follows a Curie‐Weiss law χ_m = C_m/(T–θ_p) giving C_m = 0.38 emuK/mol as Curie constant per CeRuSn mol; a value showing that only half of the cerium atoms are trivalent in CeRuSn (C_m = 0.807 emuK/mol for one free Ce³⁺ ion). A remarkable feature of the CeRuSn structure are the short Ce1–Ru1 (233 pm) and Ce1–Ru2 (246 pm) distances. The crystal chemistry of CeRuSn is discussed on the basis of a group‐subgroup scheme.     

Studies on the chiral recognition of peptide enantiomers by neutral and sulfated beta-cyclodextrin and heptakis-(2,3-di-O-acetyl)-beta-cyclodextrin using capillary electrophoresis and nuclear magnetic resonance

The separation of dipeptide and tripeptide enantiomers using a neutral single isomer cyclodextrin (CD) derivative, heptakis-(2,3-di-O-acetyl)-beta-CD (DIAC-beta-CD), was investigated with respect to the amino acid sequence applying standard separation conditions. With only one exception the DD-enantiomers migrated faster than the LL-stereoisomers. Separations obtained for the same set of peptides using beta-CD and the sulfated single isomer derivatives heptakis-(2,3-di-O-acetyl-6-sulfo)-beta-CD (HDAS-beta-CD) and heptakis-6-sulfo-beta-CD (HS-beta-CD) revealed identical enantiomer migration order in the presence of the 2,3-disubstituted derivatives DIAC-beta-CD and HDAS-beta-CD. In contrast, reversed migration sequence was found for beta-CD and HS-beta-CD compared to DIAC-beta CD and HDAS-beta-CD indicating the importance of the substitution pattern on the wider rim of the CD cavity on the chiral recognition of the peptide enantiomers by the CDs. Nuclear magnetic resonance (NMR) experiments indicated different complexation modes between the enantiomers and the CDs depending on the presence of acetyl substituents on the wider rim of the CD torus. Thus, the CD-induced chemical shifts observed in samples containing Ala-Phe or Ala-Tyr and beta-CD or HS-beta-CD were consistent with an inclusion of the aromatic moiety into the CD cavity. Although the CD-induced chemical shifts in the presence of DIAC-beta-CD and HDAS-beta-CD did not allow direct conclusions on the complexation mode they substantially differed from those observed in the presence of 2,3-unsubstituted CDs indicating different structures of the peptide-CD complexes.