Epitaxial growth of pentacene on alkali halide surfaces studied by Kelvin probe force microscopy.

In the field of molecular electronics, thin films of molecules adsorbed on insulating surfaces are used as the functional building blocks of electronic devices. Control of the structural and electronic properties of the thin films is required for reliably operating devices. Here, noncontact atomic force and Kelvin probe force microscopies have been used to investigate the growth and electrostatic landscape of pentacene on KBr(001) and KCl(001) surfaces.

Modeling of the Chiroptical Response of Chiral Amino Acids in Solution Using Explicit Solvation and Molecular Dynamics.

Molecular dynamics (MD) simulations and TDDFT linear response computations were employed to model the molar rotations of the zwitterionic forms of glycine, alanine, proline, and phenylalanine in aqueous solution. The MD simulations inherently take into account averaging the chiroptical response of different amino acid conformers and also allow the effects from vibrational distortions and explicit solvent perturbations on the optical rotation to be modeled. The results show that the chiroptical response correlates strongly to the conformations of these molecules relative to their carboxylate functional groups.

Ab Initio and Density Functional Theory Modeling of the Chiroptical Response of Glycine and Alanine in Solution Using Explicit Solvation and Molecular Dynamics.

We investigate ways in which simple point charge (SPC) water models can be used in place of more expensive quantum mechanical water molecules to efficiently model the solvent effect on a solute molecule's chiroptical responses. The effect that SPC waters have on the computed circular dichroism of a solvated glycine molecule are comparable to, albeit somewhat weaker than, that of quantum mechanical waters at the coupled cluster CC2 level of theory. The effects of SPC waters in fact correlate better with QM-CC2 waters than quantum mechanical waters computed with density functional theory (DFT) methods, since they do not promote spurious charge transfer excitations that are a known deficiency with most popular density functionals.

Computational modeling of the optical rotation of amino acids: a new look at an old rule for pH dependence of optical rotation.

The molar rotation of a solution of a natural alpha amino acid is changed in the positive direction by addition of a strong acid. Three decades ago, an attempt to rationalize this old rule, named for Clough, Lutz, and Jirgensons (CLJ), was made by assigning circular dichroism octants for overlapping carbonyl n to pi* transitions. Modern quantum chemical methods allow us to take a new look at this phenomenon.

Calculation of circular dichroism spectra from optical rotatory dispersion, and vice versa, as complementary tools for theoretical studies of optical activity using time-dependent density functional theory.

A comparison of two theoretical methods based on time-dependent density functional theory for the calculation of the linear dispersive and absorptive properties of chiral molecules has been made. For this purpose, a recently proposed computational method for the calculation of circular dichroism (CD) spectra from the imaginary part of the optical rotation parameter has been applied to six rigid organic molecules. The results have been compared to the CD spectra obtained from the rotatory strengths and from the Kramers-Kronig transformation of optical rotatory dispersion (ORD) curves.

Time dependent density functional theory modeling of specific rotation and optical rotatory dispersion of the aromatic amino acids in solution.

Time Dependent Density Functional Theory (TDDFT) along with the COnductor-like Screening MOdel (COSMO) has been applied to model the specific rotation at 589.3 nm and the optical rotatory dispersion (ORD) of the aromatic amino acids phenylalanine, tyrosine, histidine, and tryptophan. Solution structures at low, neutral, and high pH were determined.

Hydrogen desorption exceeding ten weight percent from the new quaternary hydride Li3BN2H8.

Mobile applications of hydrogen power have long demanded new solid hydride materials with large hydrogen storage capacities. We report synthesis of a new quaternary hydride having the approximate composition Li(3)BN(2)H(8) with 11.9 wt % theoretical hydrogen capacity.

Time dependent density functional theory modeling of chiroptical properties of small amino acids in solution.

Time dependent density functional theory (TDDFT) and the conductor-like screening model (COSMO) of solvation were used to model the specific rotation and optical rotatory dispersion (ORD) of alanine, proline and serine solutions. Zwitterionic, cationic and anionic forms of amino acids were investigated and the results compared with experimental literature data obtained in neutral, acidic and basic conditions, respectively. It was found that TDDFT consistently underestimated the electronic excitation energies of the molecules, leading to calculated optical rotations that are of the correct sign but somewhat larger in magnitude than those of experiment.