We demonstrate that nanotubular networks formed by enzyme-triggered self-assembly of Fmoc-L3 (9-fluorenylmethoxycarbonyl-tri-leucine) show significant charge transport. FT-IR, fluorescence spectroscopy and wide angle X-ray scattering (WAXS) data confirm formation of beta-sheets that are locked together viapi-stacking interactions. Molecular dynamics simulations confirmed the pi-pi stacking distance between fluorenyl groups to be 3.6-3.8 A. Impedance spectroscopy demonstrated that the nanotubular xerogel networks possess minimum sheet resistances of 0.1 MOmega/sq in air and 500 MOmega/sq in vacuum (pressure: 1.03 mbar) at room temperature, with the conductivity scaling linearly with the mass of peptide in the network. These materials may provide a platform to interface biological components with electronics.

We have performed classical molecular dynamics to study the properties of a water-miscible and a water-immiscible room-temperature ionic liquid when mixed with small quantities of water. The two ionic liquids consist of the same 1-ethyl-3-methylimidazolium ([EMIM]) cation combined with either the boron tetrafluoride ([BF(4)]) or bis(trifluoromethylsulfonyl)imide ([NTf(2)]) anion. It is found that, in both ionic liquids, water clusters of varying sizes are typically hydrogen bonded to two anions with the cation playing a minor role. We also highlight the difficulties of obtaining dynamic quantities such as self-diffusion coefficients from simulations of such viscous systems.

ABSTRACT:For the first time a potential based on high-rank atomic multipole moments computed according to quantum chemical topology (QCT) has been used in molecular dynamics simulations. Completing earlier work on the performance of this QCT potential on small gas-phase van der Waals complexes we now focus on the liquid structure of water. Other than the parameter L, which keeps track of the rank of the electrostatic interaction, the current QCT potential contains only two adjustable parameters of the Lennard-Jones type. A system of 216 water molecules was simulated including long-range interactions represented by a high-rank multipolar Ewald summation. High-order multipolar interactions (L ϭ 5) are essential to recover the typical features of a liquid-like structure. Liquid simulations at five different temperatures showed a maximum in the density and a temperature profile that agrees fairly well with experiment. The density of simulated water at 300 K and 1 atm is about 0.1% off the experimental value, while the calculated potential energy of the liquid is within 3% of the experimental result. The experimental value of the self-diffusion coefficient is underestimated by 35%. The value of C p is overestimated by 40% and the thermal expansion coefficient ␣ by 37%. The calculated correlation coefficients between the calculated QCT profile and the experimental profile of g OO (r), g OH (r), and g HH (r) are 0.976, 0.970, and 0.972, respectively.

The homogeneous-shear (HS} technique has been used extensively to study shear How, but it uses artificial methods to remove the viscous heat generated. In reality the viscous heat is removed from the system by conduction out through the boundaries. This inevitably leads to characteristic gradients in temperature, density, and shear rate. While at low shear rates these effects may be neglected, and the use of HS justified, at high shear rates they certainly cannot, and doubts remain as to the validity of HS in this regime. In this study we make careful comparisons between HS and a more-realistic slidingboundary method. HS gives very similar results when conditions corresponding to different regions within the sliding system are used. The use of HS simulations at shear rates where energy is generated at a rate faster than can be realistically removed by any natural process is called into question.PACS number(s): 47.50.+d, 47.25.Ei, 44.90.+c, 66.20.+d

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