Current Physical Chemistry - Volume 4, Issue 1, 2014

In this paper, we report a detailed structural and electronic characterization of PbMoO4 crystals by using a conventional hydrothermal (CH) method. The samples were characterized by X-ray diffraction (XRD), Fourier transform Raman (FT-Raman), field-emission gun scanning electron microscopy (FEG-SEM) and photoluminescence (PL) measurements. In addition, first-principles quantum mechanical calculations based on the density functional theory were employed in order to understand the band structure and density of states for the PbMoO4. Analysis of both theoretical and experimental results allows to rationalize the role of order-disorder effects in the observed green PL emissions in these ordered powders.

We have used the periodic quantum-mechanical method with density functional theory at the B3LYP hybrid functional level in order to study the doping of SnO2 with pentavalent Sb⁵⁺. The 72-atom 2x3x2 supercell SnO2 (Sn24O48) was employed in the calculations. For the SnO2:4%Sb , one atom of Sn was replaced by one Sb atom. For the SnO2:8%Sb, two atoms of Sn were replaced by two Sb atoms. The Sb doping leads to an enhancement in the electrical conductivity of this material, because these ions substitute Sn⁴⁺ in the SnO2 matrix, leading to an electronic density rise in the conduction band, due to the donor-like behavior of the doping atom. This result shows that the bandgap magnitude depends on the doping concentration, because the energy value found for SnO2:4%Sb was 2.8eV whereas for SnO2:8%Sb it was 2.7eV. It was also verified that the difference between the Fermi level and the bottom of the conduction band is directly related to the doping concentration.

Room temperature photoluminescence (PL) of SrSnO3: Fe³⁺ perovskites synthesized by the polymeric precursor method was evaluated. The amount of carbonate decreased with increasing temperature, as shown in the XRD patterns and the IR spectra. According to the IR spectra, the splitting of the ν1 band indicated that clusters with different symmetries were formed, especially in samples doped with 20 mol % of Fe³⁺. PL at different regions was observed, indicating that different defects are present in the structure. For samples calcined at 400 ºC, a yellow emission was observed indicating a higher short-range disorder. Increasing the calcination temperature to 700 ºC led to a change in the emission region to green or blue. This behavior was assigned to a higher short range ordering also suggested by the increase in the band gap value.

Heterogeneous ribonucleoprotein K (hnRNP K) is a constitutive protein found in nucleus, cytoplasm and mitochondria of cells and interacts with diverse molecules involved in gene expression and signal transduction. Its over expression is associated with the development of prostate, breast and colorectal cancer types. The binding to nucleotides is the main interaction that triggers biological activity and is mediated by its three K homology (KH) domains. Trying to optimize a benzimidazole and a phenylbenzamide derivatives, already reported as hnRNP K ligands, and generate novel ligand candidates with potential anticancer activity, bioisosteric replacements were suggested in the molecular groups able to perform polar interactions with R40 and R59, the main residues of KH3 domain responsible for nucleotide recognition. The top-ranked fragments from BROOD database regarding interaction with the protein, and also steric and electrostatic similarity with query fragments, were selected as potential bioisosters. The novel fragments when inserted in the benzimidazole and phenyilbenzamide derivatives could interact with R40 or R59 by hydrogen bond or ionic interaction. Some of the selected fragments show toxicophoric groups able to induce hepatotoxicity, carcinogenicity and chromosome damage. In this way, the bioisosters without classical toxicophoric groups should be prioritized for synthesis of novel lead compounds, generating diversity in the continuous search of effective and safer anticancer drugs.

An intracellular hallmark of Alzheimer Disease (AD) is accumulation of hyperphosphorylated tau as tangles of paired helical filaments (PHF). A significant advance in understanding tau’s behaviour isolated came when it was recognized that the protein contains isolated short peptide motifs, embedded in an otherwise hydrophilic environment, which have a high tendency for beta-structure and aggregation, forming the core of the PHF. In a recent work, we used the smallest fragment responsible for aggregation, the hexapeptide 306VQIVYK311, in order to investigate with molecular dynamics simulations possible binding modes of the tau protein fragment with respect to an active flavonoid, which would be responsible for the inhibitory process of aggregation of tau. Considering such results, we have used in this work a selected pharmacophoric model and carried out a pharmacophore-based virtual screening with the purpose of designing novel potential Tau aggregation inhibitors. An initial set of 96 compounds was selected, of which 86 are unpublished regarding Tau anti-aggregation activity and the other 10 compounds are reported as Tau ligands. Prediction of biological activity and pharmaceutical properties indicated four tiophene derivatives as promising Tau aggregation inhibitors for Alzheimer’s disease treatment.

Zirconia (ZrO2) is of great importance as a support for systems where high ionic conductivity and mechanical stability are required. Doping/defects have a significant effect on the physical properties of this oxide by stabilizing the most symmetric phases, increasing the ionic conductivity and possible facilitating three phase interconnections in solid oxide fuel cells (SOFCs). Although Zirconia in its pure form exhibits different structures at high temperatures when it is alloyed with other oxides the high temperature cubic polymorph can be stabilized to temperatures low enough for fuel cell applications. Although there has been tremendous technological investment to obtain better materials, we are still far from an optimum solution. We start in this work with theoretical calculations as a support/participation in the search for more appropriate materials that will make this important technology viable in a wide range of applications in the near future. The calculations were performed in the framework of Density Functional (DFT) pseudopotential theory using the Projector Augmented Wave (PAW) with various approximations to the exchange-correlation functional. We investigate structural, electronic/band structure, density of states and charge densities for pure zirconia taking into consideration as well different dopants, their concentrations as well as vacancies for the various polymorphs with interest in fuel cell electrolyte applications.

The electronic and structural properties and elastic constants of the wurtzite phase of GaN, was investigated by computer simulation at Density Functional Theory level, with B3LYP and B3PW hybrid functional. The electronic properties were investigated through the analysis of the band structures and density of states, and the mechanical properties were studied through the calculus of the elastic constants: C11, C33, C44, C12, and C13. The results show that the maximum of the valence band and the minimum of the conduction band are both located at the Γ point, indicating that GaN is a direct band gap semiconductor. The following constants were obtained for B3LYP and B3PW (in brackets): C11 = 366.9 [372.4], C33 = 390.9 [393.4], C44 = 99.1 [96.9], C12 = 143.6 [155.2], and C13 = 107.6 [121.4].

The electronic structures and spectroscopic properties of a series of trans-dioxoosmium(VI) complex ions [OsO2(L)4]z (L = CN, z = 2- (1); L = CO, z = 2+ (2); L = CCH, z = 2- (3)) were investigated using quantum chemistry methods. The geometrical structures of the complexes were fully optimized at the B3LYP level for the ground state and the CIS level for the lower-lying excited state with the LANL2DZ basis sets with two f-type (for Os) and two d-type (for C, N, and O) polarization functions, respectively. The calculations revealed that the bond lengths of Os=O in the excited state are elongated relative to those in the ground state for the three complexes. The calculation results show that the dipole-allowed absorptions of the three complexes are in the region of λ >230 nm. The high energy absorptions at 353 nm for 1, 359 nm for 2, and 314 nm for 3 are mainly assigned as π (CN)→π*(Os=O), px(O)→σ*(Os-CO), and π(CC)→π*(Os=O), respectively. Whereas the lower-lying absorptions at 531 nm and 475 nm for 1 and 3, respectively, are originated from metal centered d-d transition combined with ligand (CN and CCH) to ligand (O) charge transfer character, but that at 413 nm for 2 due to [px,y(O)→π(dxz,yz-px,y)(Os=O)]. The phosphorescence was calculated with the TD-DFT method based on the optimized geometry structure in the excited state. The calculated phosphorescence at 617 nm 638 nm and 553 nm originate from 3[(π*(Os=O))1(Os(dxy)+π(CN/CCH))1] and 3[(π*(Os=O))1(pz(O))1] excited states for 1/3 and 2, respectively. The phosphorescence energies are in the order of 2>1>3, therefore the emission can be influenced and tuned by the attached ligands.

TiO2 and SnO2 have the (P42/mnm) rutile structure with close lattice parameters and are extensively used in technological applications due to catalytic and optical properties. These properties can dependend on the surface directions and surface energy. It is of interest to estimate which directions are appropriate or energetically more favorable. Mathematical expressions often used in the literature to estimate the surface energy in oxides are based on a direct relationship between surface and bulk energies. However, for other workers the solid growth direction is represented only in the surface energy term (Esurf), whereas the bulk energy factor (Ebulk) has no influence of the solid growth direction. The latter term (Ebulk) is important for surface growth direction of a solid because both surface and bulk can grow in the same direction. This objective of our work is to investigate the influence of the bulk energy term (Ebulk), traditionally used in the literature, as well as the supercell energy term (Esupercell) representing the influence of the bulk growth direction on the surface energy of the solid.

The fullerenes are of considerable theoretical and experimental interest indicating numerous optical and electrical properties with many important potential technological applications. The transfer and withdrawal of electrons from the neutral species of C70 results in redistribution of charges, modifications of multiplicities, electronic energy levels and their band gaps. We use semi-empirical and ab initio methods to investigate the energy levels and stability of C70 as a function of charge and multiplicity.

We have used docking, virtual screening, pharmacophore modeling, molecular interaction fields, molecular dynamics and pharmacokinetic-toxicity analyses in order to propose novel potential CDK2 inhibitors for cancer treatment. We also have proposed molecular modifications of known inhibitors and evaluated them with respect to pharmacodynamic and pharmacokinetic-toxicity properties. Four proposals have been selected and they indicate new and improved polar and hydrophobic interactions with the enzyme, as well as good pharmacotherapeutic profiles.

Influence of mechanical dispersion and exposure to air on hydrogen-sorption properties and thermal stability of β-MgH2 synthesized by two different methods, namely through direct hydriding in gaseous medium and by reactive mechanical alloying, is studied employing thermodesorption spectroscopy and X-ray photoelectron spectroscopy. It is established that the temperature of the beginning of desorption of the β-MgH2 phase of the composite synthesized through direct hydriding in gaseous medium depends upon exposure to air after its synthesis. Exposure of the sample to air for 20 min (for more than 5 h) increases the temperature of decomposition of the β-MgH2 phase from 360 to 375 oC (from 360 to 440 oC). Following dispersion of the composite in the ball mill decreases the decomposition temperature of the hydride phase from 440 to 340 oC. Exposure of the dispersed composite to air for 5 h and even for several days does not increase the decomposition temperature of the MgH2 phase. Significant role of the surface state in increase of the decomposition temperature (and thermal stability) due to exposure to air of MgH2 hydride derived by hydriding of magnesium powder in gaseous medium is revealed. It is found that dispersion of the hydride in the ball mill reduces the temperature of decomposition of the MgH2 phase.

Aggregation of proteins has a close association with amyloidoses and a number of neurodegenerative diseases like Alzheimer’s, Parkinson’s, Huntington’s and Prion’s. Aggregation also demands special attention at some point or the other, in the life time of a protein, starting from refolding, to its shipping and storage. A lucid understanding of the underlying mechanism is a must for the development of strategies for the prevention of unwanted aggregation. In this review, we present an extensive report on various models proposed for the mechanistic understanding of this phenomenon. In addition, we discuss the different structural, kinetic and thermodynamic tools used (a) to differentiate between the possible mechanisms of aggregation and (b) to determine various thermodynamic and kinetic parameters associated with various stages of the aggregation processes. Structural tools include methods to characterize/identify the conformations of proteins that are prone to aggregation (β-sheet conformer) and type of aggregation. Kinetic tools include methods to characterize time course of the reaction and the concentration, temperature and pressure dependences of aggregation. Finally, thermodynamic treatment of kinetic data may be used to determine energy barriers associated with different steps. A survey of the literature shows that different mathematical models have been applied for analysis of different proposed mechanisms of aggregation, each giving an estimate of the different steps involved. Thus, combining of physical and analytical tools could make it possible to identify the various parameters associated with each step of the aggregation process - something we have described in this review.

In this review paper, have been investigated three novel crystal structures of three molecules with carbazole substituents as the electron-donor group. These molecules, 2-(phenyl)-3-(N-ethyl-(3'-carbazolyl))acrylonitrile (I), 2-(3''- pyridyl)-3-(N-ethyl-(3'-carbazolyl))acrylonitrile (II), and 2-(4-pyridyl)-3-(N-ethyl-(3´-carbazolyl))acrylonitrile (III) in their structure, possess the electron-donor carbazole moiety, a -CN group attached to the double bond, and a phenyl or a pyridine function at the meta- or para-position. It was revealed with the help of single crystal diffraction X-ray analysis that there exists no difference in the crystal system, because all the compounds were crystallized in monoclinic system with space group P21/c. For determining the effect of the position of the nitrogen atom substitution on the crystal properties, has been analyzed and contrasted the molecular packing in a single crystal with that of other previously reported carbazole derivatives. The double bond bearing N-ethylcarbazole,–CN, phenyl or pyridine groups was observed to impart sufficient polarity in order to show slipped π-stacking aggregation in the solid state, affecting the compounds in the solid state and consequently affecting their fluorescence properties. The substitution at the para position was reported to exhibit more multiple C-H...π interactions as well as an interesting and unexpected short contact distance between adjacent N...N molecules those brought a conformational change resulting in an edge-to-face alignment in the molecules and affecting the best relative photoluminescence efficiency of the sample.