Current Physical Chemistry - Volume 6, Issue 1, 2016

We have generated models of nanotubes by selecting atoms from the unit cells of TiO2 crystals (rutile and anatase) in specific planes, i.e., the plane (101) for anatse and the plane (110) for rutile. Using a programming language created in shell bash we designed clusters of titanium dioxide nanotubes with different lengths and diameters. The structures generated were submitted to quantum mechanical calculations using the semi-empirical PM7 method, HF and DFT methods with the 6-31g and 6-311G basis sets. The clusters were optimized and the one with the most stable structures were those with the largest diameters. The best models, i.e. the most stable structures, were the anatase nanotube of molecular formula [[(TiO2)4]20]3 and the rutile nanotube with molecular formula [[(TiO2)2]13]3. Comparing the relative free energies of the structures with the same number of atoms we concluded that the anatase nanotubes had a greater stability in comparison with the rutile nanotubes. Calculations of the DFT energy gaps yields values between 2.0 and 2.5 eV, characteristic of semiconductors and in agreement with experiment.

Structural and electronic properties of TiO2, S and Mo doped TiO2 anatase were investigated by means of Density Functional Theory with the B3LYP hybrid functional. Calculated structural and electronic properties of TiO2 show good agreement with experimental and theoretical predictions. Structural property reveals that the unit cell volume for doped TiO2 is controlled by the ionic radius of the dopant. Density of States and Band Structure results indicate the band-gap narrowing from creation of midgap states instead of band-gap widening resulting in an enhancement of photocatalytic behavior in comparison to TiO2.

The aim of this study is to investigate the properties related to peptide inhibitors of replication of Dengue virus type 2, predict whether these compounds exhibit pharmacokinetic properties (absorption, distribution and toxicology) and propose new drug candidates with better properties (physicochemical, toxicological and pharmacokinetic). Fifteen inhibitors of nonstructural protein 3 (NS3) were selected, i.e. the most active in the database of Binding DB, based on the value of Ki. From this study for the development of new potential NS3-protease inhibitor candidates for the Dengue virus type 2 treatments; we described that modifications achieved satisfactory results because three molecules showed improvements in some properties relative to the reference compound, which was the most active. However, the inhibitor that stood out in ADME/Tox calculations among the 15 inhibitors was compound 11, which is better absorbed by oral administration, showing an improvement in the absorption in the intestine, remaining inactive in the central nervous system (CNS). This compound is not carcinogenic for mice in toxicological analysis, yielding a potential drug candidate inhibitor of nonstructural protein 3 (NS3) for Dengue type 2.

Parkinson's disease (PD) is a debilitating disease that affects the elderly. With the availability of treatment it has become possible to maintain good functional mobility for years, increasing life expectancy of the treated patients. Levodopa is the main form of pharmacological treatment, and is administered along with dopamine agonists monoamine oxidase B inhibitors (MAO-B). However, the use of these agonists causes various side effects. MAO-B is an enzyme that catalyzes the oxidative deamination of neurotransmitters such as dopamine, serotonin, norepinephrine, and epinephrine. This enzyme is thus an important therapeutic target for the treatment of PD. Consequently, in this study we computationally designed new inhibitors of MAO-B compounds as future drug candidates for the treatment of PD. We present three proposals where the changes were made from the compound that had the best results in activity/docking among the inhibitors found in the BindingDB. The compounds were then assessed for their physicochemical properties, biological activity and synthetic accessibility. The results suggest that the three proposals could be promising inhibitors of MAO-B.

The effects of Ba doping on structural, electronic and optical properties of crystalline wurtzite-ZnO were analyzed by DFT/B3LYP calculations. The substitution of Zn atoms causes an increase of lattice parameters and small variation of unit cell angles. Likewise, the doping changes the optical properties, reducing the band-gap by 0.2 eV and modifying the associated wavelength to the visible spectrum range. In electronic properties, the number of charge carriers for pure and doped materials were also evaluated and it was verified for both materials that the number of electrons are higher than holes; therefore, the doping does not change the ZnO electronic nature, an n-type semiconductor. After the doping process, the ferroelectric properties monitored through the ionic bond character, dielectric constants and polarizability show a good improvement.

Methodologies based on rolling a sheet of graphene were used to design, program and investigate single and double wall silicon carbide zigzag and armchair nanotubes (SiCNTs). For each combination of models we start by investigating details such as type of conformations, diameters, lengths, energy levels and number of atoms. We are thus able to separate groups of isomers based on these properties. We subsequently made calculations with one hundred single wall and twenty double wall armchair and zigzag SiCNTs using semi-empirical AM1, MNDO, HF and DFT with 3-21g and 6-31g basis sets. The semi-empirical, ab-initio and DFT models indicate similar trends. These results may be of interest for workers with limited computational resources. We investigated the stability between isomers of zigzag and armchair with different geometries. We also investigated the effects of radial and vertical growth of nanotubes on stability, geometries, band gaps and charges. These calculations also indicated that the larger and longer configurations are more stable. The average bond distances with single wall indicated values of ~ 1.70 Â in the center of the tube with variations at the extremities. Analysis of the diameters indicates that the armchair configurations are more symmetric than the zigzag. The analysis of |HOMO-LUMO| indicates variations tending to regions of metallic and semiconductor materials. The Mulliken charges are more symmetric for the armchair configurations. Results of the variation of energy with the double wall indicate similar results as for the single wall nanotubes.