Peptide sequence mediated self-assembly of molybdenum blue nanowheel superstructures

The precise control over the formation of complex nanostructures, e.g. polyoxometalates (POMs), at the sub-nanoscale is challenging but critical if non-covalent architectures are to be designed. Combining biologically-evolved systems with inorganic nanostructures could lead to sequence-mediated assembly. Herein, we exploit oligopeptides as multidentate structure-directing ligands via metal-coordination and hydrogen bonded interactions to modulate the self-assembly of POM superstructures. Six oligopeptides (GH, AH, SH, G₂H, G₄H and G₅H) are incorporated into the cavities of Molybdenum Blue (MB) POM nanowheels. It is found that the helicity of the nanowheel can be readily switched (Δ to Λ) by simply altering the N-terminal amino acid on the peptide chain rather than their overall stereochemistry. We also reveal a delicate balance between the Mo-coordination and the hydrogen bonds found within the internal cavity of the inorganic nanowheels which results in the sequence mediated formation of two unprecedented asymmetrical nanowheel frameworks: {Mo₁₂₂Ce₅} and {Mo₁₂₆Ce₄}.

Peptide sequence can be used to control the self-assembly and structures of nanoscale molybdenum blue polyoxometalate (POM) wheel-shaped clusters.     

Role of thiol‐disulfide exchange in episulfide polymerization

Episulfide polymerization offers a number of features that are uncommon in other ring‐opening anionic mechanisms. Besides the negligible sensitivity to water, the most distinctive and novel one is likely to be the role of disulfides, which may act both at the levels of chain transfer and end‐capping, producing polymers that feature both terminal and internal disulfides. In this article, we have qualitatively studied the kinetics of chain transfer and measured the thiolate–disulfide exchange equilibrium constants. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2233–2249, 2008     

Theoretical study of the performance for short channel carbon nanotube transistors with asymmetric contacts

We have simulated short channel carbon nanotube field-effect transistors with asymmetric source and drain contacts using a coupled mode space approach within the non-equilibrium Green's function framework. The simulated results show that the asymmetric conduction properties under positive and negative drain-to-source voltages are caused by the asymmetric Schottky barriers to carriers at the source and drain contacts. Under negative drain-to-source voltages, hole and electron conduction are dominated by thermionic emission and tunneling through the Schottky barrier, respectively, leading to the different subthreshold behaviors of the hole and electron conduction. With increasing channel length, short channel effects can be suppressed effectively and ON/OFF ratio can be improved.     

Redetermination of the X-ray structure of nitroxylcobalamin: base-on nitroxylcobalamin exhibits a remarkably long Co-N(dimethylbenzimidazole) bond distance

The X-ray structures of three new crystals of nitroxylcobalamin (NOCbl) have been determined. Unlike our earlier reported structure in which NOCbl was partially oxidized (L. Hannibal, C. A. Smith, D. W. Jacobsen and N. E. Brasch, Angew. Chem., Int. Ed. 2007, 46, 5140), the O atom of the nitroxyl ligand is located in a single position with a N=O bond distance of 1.12-1.14 ?, consistent with a double bond. The Co-N-O angle is in the 118.9-120.3 ? range. The α-axial Co-N(dimethylbenzimidazole) (Co-NB3) bond distance is a remarkable 2.32-2.35 ? in length, ~0.1 ? longer than that reported for all other cobalamin structures. The change in the Gibbs free energy for the base-on/base-off equilibrium now correlates extremely well with the Co-NB3 bond distance, as observed for other cobalamins.     

Role of disorder and anharmonicity in the thermal conductivity of silicon-germanium alloys: a first-principles study

The thermal conductivity of disordered silicon-germanium alloys is computed from density-functional perturbation theory and with relaxation times that include both harmonic and anharmonic scattering terms. We show that this approach yields an excellent agreement at all compositions with experimental results and provides clear design rules for the engineering of nanostructured thermoelectrics. For Si(x)Ge(1-x), more than 50% of the heat is carried at room temperature by phonons of mean free path greater than 1 μm, and an addition of as little as 12% Ge is sufficient to reduce the thermal conductivity to the minimum value achievable through alloying. Intriguingly, mass disorder is found to increase the anharmonic scattering of phonons through a modification of their vibration eigenmodes, resulting in an increase of 15% in thermal resistivity.     

Scalable InP integrated wavelength selector based on binary search

We present an InP monolithically integrated wavelength selector that implements a binary search for selecting one from N modulated wavelengths. The InP chip requires only log(2)N optical filters and log(2)N optical switches. Experimental results show nanosecond reconfiguration and error-free wavelength selection of four modulated wavelengths with 2 dB of power penalty.     

Crystalline misfit-angle implications for solid sliding

For the contact of two finite portions of interacting rigid crystalline surfaces, we compute the pinning energy barrier dependency on the misfit angle and contact area. This simple model allows us to investigate a broad contact-size and angular range, thus obtaining the statistical properties of the energy barriers opposing sliding for a single asperity. These data are used to generate the distribution of static frictional thresholds for the contact of polycrystals, as in dry or even lubricated friction. This distribution is used as the input of a master equation to predict the sliding properties of macroscopic contacts.