Current Physical Chemistry - Volume 6, Issue 2, 2016

Nanotubes investigated in this work were designed from the (110) crystal planes of GaAs using a set of matrix transformations and the experimental cell parameters of zinc blend GaAs, preserving the stoichi-ometry and symmetry of the (110) plane. Authors performed calculations with semi-empirical PM7 and HF and DFT/B3LYP methods. The geometries of GaAs nanotubes indicated greater stability when compared with the crystal plane (110) without curvature. The stability of these geometries correlates with the number of formative basic units, geometries of the crystal planes and diameter of nanotubes. These parameters also in-fluence the electronic properties of these materials. The more stable geometries indicate semiconductor char-acter. Our calculations yield energy gaps of 1.45 and 1.89 eV in agreement with experiment (1.42 eV).

The organic Light Emitting Diodes (OLEDs) have been attracting considerable interest due to low cost of production and their use in producing flexible electronic materials. Poly [2-methoxy-5-(20-ethylhexyloxy)-1,4-phenylene] vinylene (MEH-PPV) is one of the most interesting materials that can be applied as OELDs due to its electroluminescent characteristic in the visible region of the electromagnetic spectrum. Poly (3,4 ethylenedioxithiophene) (PEDOT) has been investigated for applications in flexible organic solar cells. Computational chemistry methods are good tools for molecular investigation of organic semiconductors because of the possibility to compare molecular geometries and electronic properties for better understanding of charge mobility as a function of geometrical parameters that can be modified. In this work, we present a semi-empirical study for MEH-PPV and PEDOT systems using three methodologies, PM6, PM7 and RM1 to study the stabilization energy and gap energy behavior with chain length. The results showed that PM6 methodology better describes the chain length for both systems, where heavy atom energy become stable from certain monomeric units for MEH-PPV and PEDOT chain length. Furthermore, by PM6 methodology, gap energy produces asymptotic behavior with chain length, with closer agreement with experimental results than other methodologies. In addition, PM6 methodology provides the best geometry for large oligomers, proving the ability of this methodology to produce good results for organic semiconductor systems.

Quantitative structure-activity relationship (QSAR) studies are tools used in the design of new drugs, as illustrated by the development of the antibacterial agent norfloxacin and the acetylcholinesterase inhibitor donepezil. Here we demonstrate that the use of 2-D and 3-D descriptors, in association with classical physicochemical descriptors, was suitable to predict the antibacterial activities of sulfonamides and can be used to design new, chemically accessible, and, putatively, more active compounds. The use of freely availa-ble software and web servers makes this protocol a useful and easily implementable pedagogical resource, providing to pharmacy and chemistry students a practical experience with important issues regarding the use of QSAR in drug design.

FeGeO;3 has been investigated theoretically to understand the structure for this ilmenite-type perovskite. A theoretical DFT based study B3LYP exchange-correlation functional has given structural and electronic properties of this new polymorph. The structural parameters are in agreement with experimental results and show that the FeO;6 and GeO;6 octahedral are distorted by the Jahn-Teller effect that is spread along the crystalline structure from the Fe-O-Ge-O-Fe intermetallic connection. Bulk-Modulus results suggest an instability above 33 GPa and electronic results suggest that this polymorph of FeGeO;3 is a potential candidate for electro-optical applications due to the band-gap of 3.41 eV.

Molecular dynamic modeling of the nonlocal dielectric response of liquid water predicts a so-called "overscreening effect" which means an oscillating behavior of the electrostatic potential around the charged species. Calculations of the ion solvation energy for such a medium within the framework of the Born model of the ion charge distribution (its localization on the external surface of the ion cavity) result in values strongly exceeding even the solvation energy for the local-dielectric model of the surrounding medium, which is known as overestimating the experimental data for alkali ions. In this context it was a surprising result [J. Chem. Phys., 1996, 104, 1524] that a sufficiently broad distribution of the ion charge along the radial coordinate might lead to a strong diminution of the predicted solvation energies, up to their proximity to experimental values. Our actual study has been carried out to uncover the physical origin of this enormous reduction of the solvation energy for this model which combines the overscreening effect in the solvent response and a smeared out distribution of the ion charge. It has demonstrated that the shift of the charge density of the ion from the cavity's surface inside the cavity (in particular, with its smearing out along the radial coordinate) may only result in a further increase of the solvation energy. It means that a strong reduction of its predicted values allowing one to achieve their proximity to experimental data for alkali ions can only be achieved owing to the ion charge spreading out of the cavity, with its penetration into the solvent.

The structural properties and phase behavior of ionic networks embedded in polymer solutions are investigated using the Random Phase Approximation first introduced by de Gennes in polymer physics. The partial structure factors which are accessible by small angle neutron scattering are given in terms of the bare structure factors expressing the architecture of the polymer species and the interactions combining both excluded volume and long range electrostatic effects. It is found that the polyelectrolyte behavior characterizing the cross linked ionic network is tempered by linear chains present in the solution even though they are neutral and exert only shorter range excluded volume interactions. This finding was confirmed consistently by analyzing the scattering curves under a variety of conditions. The scattering peak at a finite wave vector qm shifts to higher values both with added salt and linear chains concentrations. Analysis of the phase behavior and effective thermodynamic interactions indicates an enhanced contraction of the network as more chains are added to the solution. While electrostatic charges tend to stabilize the system, the presence of linear chains promotes deswelling and phase separation processes. This analysis was developed from the q = 0 limit for the macro phase transition and q = qm for the micro phase reminiscent of ionic systems. The phase diagram covering both transition lines indicates clearly that the linear polymer favors the phase separation on both macroscopic and microscopic scales.

Two boride layers having different kinds of microstructure are formed on the surface of industrial high chromium steel (13 and 25% Cr) samples during their interaction with boron powder at 850–950ºC and reaction times 3600–43200 s (1–12 h). In the case of 13% Cr steel, the outer layer bordering boron consists of the FeB phase, whereas the inner layer adjacent to the solid substrate consists of the Fe2B phase. Each layer is a homogeneous phase. It is a microstructure of the first kind. With 25% Cr steel, each of boride layers is two-phase. The outer layer comprises the FeB and CrB phases, while the inner layer the Fe2B and Cr2B phases. It is a microstructure of the second kind. Both boride layers on both steels are characterized by a profound texture. Growth kinetics of boride layers obeys a parabolic relation. Boride layers with the microstructure of the second kind exhibit a much higher dry abrasive wear resistance than those with the microstructure of the first kind.

Aggregation of gold nanoparticles in gold colloidal solutions can be induced via the addition of an aminosilane or a change in pH. This aggregation may affect the optics, morphology and stability of these nanomaterials. Therefore, thoroughly detailing the changes will serve as a reference for individuals manipulating these parameters, especially in the field of biomedical applications and diagnostics. A systematic study utilizing several concentrations ranging from 48 mM to 475 mM of 3-aminopropyl triethoxysilane were utilized throughout the duration of the study. Ultraviolet–visible absorption spectra and photoluminescence emissions were monitored as a function of concentration and time. In addition, scanning electron and transmission electron microscopy images were taken to study the morphology. To quantify the extent of aggregation, the Nanotrac Wave (a dynamic light scattering technique) was used to determine size and size distribution of aggregates. This study demonstrates the degree to which an aminosilane could impact the stability, optics and morphology of gold nanoparticles in colloidal solutions. Ultraviolet–visible absorption spectra display systematic and extensive red shifts from 500 nm to 650 nm as the test parameters were changed. Morphology studies indicate that red shifts are largely associated with aggregation of nanoparticles as opposed to particle growth. With the addition of 3-aminopropyl triethoxysilane, the photoluminescence of the gold nanoparticles also increases as a function of concentration and time. This paper also comments on opportunities for misinterpretation of data results while using 3-aminopropyl triethoxysilane.

Metal cations that are exchanged in zeolites are generally characterized by a low coordination number and can adsorb more than one small molecule. For instance, Cu+ ions exchanged in ZSM-5 (and in other zeolites) can bind, at low temperature, up to three CO and up to two NO molecules. Although mixed aqua-carbonyl complexes are easily formed, here we show that no mixed carbonyl-nitrosyl species are produced. Instead, NO adsorption on Cu-ZSM-5 with pre-formed Cu+-CO species leads to formation of dicarbonyls and dinitrosyls according to the reaction: 2 Cu+-CO + 2 NO 130;® Cu+(CO)2 + Cu+(NO)2. The role of the ligand and the nature of the bond formed on the production of mixed ligand complexes are discussed.