Guilherme Colherinhas

The Band Gap of Graphene Is Efficiently Tuned by Monovalent Ions

Small monovalent ions are able to polarize carbonaceous nanostructures significantly. 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 the lowest unoccupied molecular orbital (LUMO) of an alkali ion (Li(+), Na(+)) fits between the highest occupied molecular orbital (HOMO) and LUMO of graphene, in such a way as to tune 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 that in the case of alkali ions. The reported insights provide inspiration for engineering electrical properties of the graphene-containing systems.

Molecular dynamics study of surfactant-like peptide based nanostructures.

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.

Versatile interactions of boron fullerene B80 with gas molecules

Stable all-boron fullerene B80 supplements a family of elemental cage molecules. These molecules may initiate a drastic rise to intriguing new chemistry. The principal stability of B80 was recently demonstrated using photoelectron spectroscopy. We report the systematic investigation of different aspects of B80 interactions with small gas molecules—such as carbon dioxide, molecular hydrogen, hydrogen sulfide, hydrogen fluoride, ammonia and sulfur dioxide—employing density functional theory. We found peculiar interactions between B80 and ammonia resulting in the formation of a weak boron–nitrogen covalent bond in one of their local-minimum configurations. Hydrogen fluoride maintains a weak hydrogen bond with B80. The boron fullerene was found to be strongly polarizable, with its electron density distribution changing significantly even in the presence of low-polar gases. The binding energies of the gas molecules to B80 are generally in direct proportion to their dipole moments. Valence bands are predominantly localized on B80. According to the present findings, one of the prospective applications of B80 in future may be gas capture and separation.

Assessing the interaction between surfactant-like peptides and lipid membranes

Atomistic molecular dynamics simulations were used to study the interaction of AnK peptides (with n = 3, 6 and 9) in contact with two different types of lipid membranes, DPPC and DPPG. PMF calculations and their decomposition into enthalpic and entropic components allowed a detailed thermodynamic analysis of the energy profile associated with the adsorption and penetration of the peptides through the lipid membranes. Our simulations indicated a drastic difference between the interactions of the peptides with both membranes. For the peptide A6K the interaction with the DPPG and DPPC membranes were −222 kJ mol−1 and −16 kJ mol−1, respectively. PMF for the DPPC membrane did not show any minimum in the interface region, that is, no favorable interaction with its surface. On the other hand, the interaction with the DPPG membrane showed a clear minimum near the surface. This minimum, although shallow, −10 kJ mol−1, indicates that the adhesion of the AnK peptides on the surface of the DPPG membranes is a favorable process.

Solvent effects on the electrical and magnetic spectroscopic properties of azo-enaminone derivatives in methanol and in water

We have investigated the solvent effects on the nonlinear and spectroscopic optical properties of some azo-enaminone molecules in the gas phase and in methanol and water solutions. Using the sequential Monte Carlo/Quantum Mechanics (S-MC/QM) approach, we have included the polarization of the solute due to the solvent medium. We have carried out TD-CAM-B3LYP/6-311++G(2d,2p) theoretical calculations for the electronic transitions. Solvatochromic deviations up to 25 nm in solution were observed for azo-enaminones in enol forms. Our CAM-B3LYP/6-311+G(d) calculations have indicated that the βHRS values may increase up to 100% when compared with the respective gas phase results. The magnetic signature of oxygen atoms was significantly affected by the inclusion of solvation effects.

GIAO-DFT-NMR characterization of fullerene-cucurbituril complex: the effects of the C 60 @CB[9] host-guest mutual interactions

AbstractMagnetic shielding constants for an isolated fullerene C60, cucurbituril CB[9], and the host-guest complex C60@CB[9] were calculated as a function of separation of the monomers. Our results in the gas phase and water indicate a significant variation of the magnetic properties for all atoms of the monomers in the complex and after liberation of fullerene C60 from the interior of the CB[9] cavity. The interaction between the two monomers results in a charge transfer that collaborates with a redistribution of electron density to deshield the monomers. Graphical AbstractNMR spectroscopy alteration on C60@CB[9] host-guest mutual interactionsᅟ

Storing Energy in Biodegradable Electrochemical Supercapacitors

The development of green and biodegradable electrical components is one of the main fronts of research to overcome the growing ecological problem related to the issue of electronic waste. At the same time, such devices are highly desirable in biomedical applications such as integrated bioelectronics, for which biocompatibility is also required. Supercapacitors for storage of electrochemical energy, designed only with biodegradable organic matter would contemplate both aspects, that is, they would be ecologically harmless after their service lifetime and would be an important component for applications in biomedical engineering. By means of atomistic simulations of molecular dynamics, we propose a supercapacitor whose electrodes are formed exclusively by self-organizing peptides and whose electrolyte is a green amino acid ionic liquid. Our results indicate that this supercapacitor has a high potential for energy storage with superior performance than conventional supercapacitors. In particular its capacity to store energy was estimated to be almost 20 times greater than an analogue one of planar metallic electrodes.