Conductance measurements of individual polypyrrole nanobelts.

We present here a study on the electrical conduction properties of individual polypyrrole nanobelts by using conductive atomic force microscopy and discuss a general effect while probing soft materials. A length-dependent analysis demonstrates that the tip could induce local defects into the polymer structure and, thus diminishes the electrical conduction.

Interaction between ALOX5AP-SG13S114A/T and COX-2-765G/C increases susceptibility to cerebral infarction in a Chinese population.

We made a case-control study to investigate a possible association between ALOX5AP-SG13S114A/T, COX-2-765G/C, and COX-1-50C/T polymorphisms with cerebral infarction in a Chinese population. A total of 411 cases with cerebral infarction were included; 411 controls matched for age, gender, and risk factors were also selected. The ALOX5AP-SG13S114A/T (rs10507391), COX-2-765G/C (rs20417), and COX-1-50C/T (rs3842787) polymorphisms were determined using PCR-RFLP. The generalized multifactor dimensionality reduction method was employed to detect gene-gene interactions. Based on single-gene analysis, there were no significant differences in the genotype and allele frequency distributions of ALOX5AP-SG13S114A/T, COX-2-765G/C, and COX-1-50C/T between the cerebral infarction group and controls. However, in those cases carrying ALOX5AP-SG13S114AA as well as COX-2-765CC, the risk of cerebral infarction increased significantly by 2.84 times (95%CI = 1.324-6.543). The single-gene ALOX5AP-SG13S114A/T, COX-2-765G/C, and COX-1-50C/T polymorphisms appear not to be associated with the development of cerebral infarction in Chinese populations. However, the interaction between ALOX5AP-SG13S114AA and COX-2-765CC apparently increases susceptibility to cerebral infarction.

Manipulating surface diffusion ability of single molecules by scanning tunneling microscopy.

The bonding of single diferrocene [Fc(CH(2))(14)Fc, Fc = ferrocenyl] molecules on a metal surface can be enhanced by partial decomposition of Fc groups induced by the tunneling current in scanning tunneling microscopy. Although the isolated intact molecule is mobile on the terrace of Cu(110) at 78 K, the modified molecule is immobilized on the terrace. Calculations based on density functional theory indicate that the hollow site of the Cu(110) surface is the energetically favorable adsorption site for both ferrocene and the Fe-cyclopentadienyl complex, but the latter one possesses a much higher binding energy with the substrate.

Patterned nucleation control in vacuum deposition of organic molecules.

We report a generally applicable method to pattern organic molecules on mesoscopic scales. In our method, organic molecular beam deposition was conducted on substrate surfaces prepatterned with materials to which the organic molecules have larger binding energies in comparison to the substrate. Fully uniform nucleation control at these predefined locations can be achieved by an appropriate selection of the growth parameters including temperature and deposition rate. The physical mechanisms involved are studied by Monte Carlo simulations and stand in good agreement with the experimental findings.

Selective nontemplated adsorption of organic molecules on nanofacets and the role of bonding patterns.

A key element of functionalizing nanocrystals with organic molecules is the nontemplated selective adsorption of different molecules on different facets. Here we report scanning-tunneling-microscopy images of perylene-3,4,9,10-tetracarboxylic-dianhydride and 2,5-dimethyl-N,N'-dicyanoquinonediimine on silver, demonstrating selective adsorption on different facets. We also report first-principles calculations that account for the data and show that bonding, which controls selectivity, occurs via the end atoms, while the molecule's midregion arches away from the substrate. The results are also consistent with data that have been interpreted in terms of bonding via the midregion.

Role of lateral alkyl chains in modulation of molecular structures on metal surfaces.

We use low energy electron diffraction, scanning tunneling microscopy, first-principles density-functional theory, and molecular mechanics calculations to analyze the adsorption and growth of quinacridone derivatives (QA) with alkyl chains of 4 and 16 carbon atoms on a Ag(110) substrate. Surprisingly, we find that the alkyl chains determine the orientation of the molecular overlayers. While the interaction of QA and the Ag substrate is primarily due to chemical bonding of oxygen to the silver substrate, determining the molecular orientation and preferred adsorption site, the intermolecular arrangement can be adjusted via the length of alkyl chains. We are thus able to fabricate uniform QA films with very well controlled physical properties.

Structure of a fusion peptide analogue at the air-water interface, determined from surface activity, infrared spectroscopy and scanning force microscopy.

We have investigated a point mutant of the HIV-1 fusion peptide in a compressed monolayer at the air-water interface. A variety of surface sensitive techniques were applied to study structural features under conditions mimicking the hydrophobic/hydrophilic environment of a biomembrane. Possible partitioning into the aqueous bulk phase and molecular areas were examined by surface activity based mass conservation plots. This shows that the peptide is practically fully accumulated in the interface. Secondary structure and orientation was analyzed by means of polarized infrared reflectivity. Brewster angle microscopy and scanning force microscopy contributed nanostructural images. At low surface pressures the molecules form anti-parallel beta-sheets lying flat on the interface. Upon a moderate increase of the lateral pressure a flat beta-turn structure appears with inter- and intramolecular H-bonds. We also observed aggregates forming fingerprint-like structures with a diameter of approximately double the hydrophobic length of a beta-turn conformation. Beyond approximately 18 mN m(-1) the beta-turns straighten up. The lowest measured tilt angle was 45 degrees at 36 mN m(-1).

Domain structures in langmuir-blodgett films investigated by atomic force microscopy.

Investigations of phase-separated Langmuir-Blodgett films by atomic force microscopy reveal that on a scale of 30 to 200 micrometers, these images resemble those observed by fluorescence microscopy. Fine structures (less than 1 micrometer) within the stearic acid domains were observed, which cannot be seen by conventional optical microscopic techniques. By applying the force modulation technique, it was found that the elastic properties of the domains in the liquid condensed phase and grains observed within the liquid expanded phase were comparable. Small soft residues in the domains could also be detected. The influence of trace amounts of a fluorescence dye on the micromorphology of monolayers could be detected on transferred films.