Abstract.Following recently published study of Prezhdo and coworkers (JPC Letters, 2014, 5, 4129-4133), we report a systematic investigation of how monovalent and divalent ions influence valence electronic structure of graphene. Pure density functional theory is employed to compute electronic energy levels. We show that LUMO of an alkali ion (Li + , Na + ) fits between HOMO and LUMO of graphene, in such a way tuning the bottom of the conduction band (i.e. band gap). In turn, Mg 2+ shares its orbitals with graphene. The corresponding binding energy is ca. 4 times higher than in the case of alkali ions. The reported insights provide inspiration for engineering electrical properties of the graphene containing systems.

For first time surfactant-like peptide (SLP) based membranes were investigated by full atomistic molecular dynamics simulations. Two different classes of membranes were simulated to quantify the impact of both nonpolar tail and hydrophilic head on the membrane properties. Structural analysis in terms of planar RDFs, density mass profiles, and 2D thickness maps was performed to evaluate the influence of the hydrophobic tail and hydrophilic head in the membrane structural pattern. Unlike what is observed in case of SLP membrane, a lipid membrane has low and short-range local ordering that imposes a significant difference between the two types of membranes. While the lipid membrane interactions are mainly van der Waals for the SLP membrane, both contributions are relevant. This result indirectly implies lower conformational flexibility of SLP and, therefore, their lower potential for live systems. On the basis of the pattern of structuring the membrane in equilibrium, we classified roughly into three different types: (a) those uniform and well ordered, with small variations in thickness and without water inside and therefore no flaw in the hydrogen bond network, (b) those with appreciable variations in structure, with fixed small holes that act as pores for water confinement and defects in the hydrogen bonding network, and (c) a group that has the same properties of the group (a) but present an undulating surface rather than a planar surface.

Surfactant-like peptide (SLP) based nanostructures are investigated using all-atomistic molecular dynamics (MD) simulations. We report structure properties of nanostructures belonging to the ANK peptide group. In particular, the mathematical models for the two A3K membranes, A6K nanotube, and A9K nanorod were developed. Our MD simulation results are consistent with the experimental data, indicating that A3K membranes are stable in two different configurations: (1) SLPs are tilted relative to the normal membrane plane; (2) SLPs are interdigitated. The former configuration is energetically more stable. The cylindrical nanostructures feature a certain order of the A6K peptides. In turn, the A9K nanorod does not exhibit any long-range ordering. Both nanotube and nanorod structure contain large amounts of water inside. Consequently, these nanostructures behave similar to hydrogels. This property may be important in the context of biotechnology. Binding energy analysis-in terms of Coulomb and van der Waals contributions-unveils an increase as the peptide size increases. The electrostatic interaction constitutes 70-75% of the noncovalent attraction energy between SLPs. The nanotubular structures are notably stable, confirming that A6K peptides preferentially form nanotubes and A9K peptides preferentially form nanorods.

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Electronic properties of graphene quantum dots (GQDs) constitute a subject of intense scientific interest. Being smaller than 20 nm, GQDs contain confined excitons in all dimensions simultaneously. GQDs feature a non-zero band gap and luminescence on excitation. Tuning their electronic structure is an attractive goal with technological promise. In this work, we apply density functional theory to study the effect of neutral ionic clusters adsorbed on the GQD surface. We conclude that both the HOMO and the LUMO of GQDs are very sensitive to the presence of ions and to their distance from the GQD surface. However, the alteration of the band gap itself is modest, as opposed to the case of free ions (recent reports). Our work fosters progress in modulating electronic properties of nanoscale carbonaceous materials.