JOURNAL OF PHYSICAL AND THEORETICAL CHEMISTRY
Year:2011 | Volume:8 | Issue:3|Papers Count:12

For better understanding of conformational stability of the dipeptide model HCO–Gly–L–Leu–NH2, ab initio and DFT computations at HF/6-31G (d), 6-311++G (d, p) and B3LYP/6-31G (d) levels of theory were carried out. Geometry optimization of the dipeptide within the leucine (Leu) side chain angles (X1¸X2) resulted in three stable conformations as followings: anti-anti, the most stable one, (X1=180o, X2=180o), Gauche (+) - trans (X1=60o, X2=210o) and 270o-Gauche (-) (X1=270o, X2= 300o). The thermodynamic properties E, H, G, and S by changing dihedral angles Y1 (D1) and F1 (D11) of glycine (Gly), Y2 (D6), and F2 (D4) of Leu and keeping the SC dihedral angles of the anti--anti conformer were obtained by frequency calculations at the same levels. The calculations indicate that the BB has the highest stability bearing Y1 (D1) =180o, F1 (D11) =180o, Y2 (D6) =150o, and F2 (D4) =210o.

Calixarenes are a readily available and important class of macrocycles in supramolecular chemistry. Calixarenes have generated considerable interest due to their basket shaped structure and as useful building blocks to synthesize selective receptors for the guest species, notably alkali, alkaline earth, lanthanide and transition metal cations. In this work studied on the complexing properties of a para-sulfonato-calix [4] arene (C28H24O16S4) with alkali metal cations. The complexation properties of para-sulfonato- calix [4] arene were studied by Hartree Fock method. The complexes showed different properties for the different cations, depending on the cations and the position of the substituents grafted on the ligand.

Density functional theory (DFT) calculations have been performed to investigate the properties of carbon decorated (C-decorated) models of boron nitride (BN) nanocones. To this aim, the apex and tip of nanocone have been substituted by the carbon atoms to represent the C-decorated models. The results indicated that dipole moments and energy gaps could reveal the effects of C-decorations on the properties of BN nanocones. Computations of quadrupole coupling constants (Qcc) for boron-11 and nitrogen-14 of the optimized structures have indicated that those boron and nitrogen atoms close to the C-decorated regions detect the most significant effects of C-decorations. Moreover, these atoms could play dominant role in determining the properties of the C-decorated BN nanocones.

The complexation of sodium molybdate with para-sulfonatocalix [4] arene was studied in the temperature range from 20 to 40oC and pH=5.8 by spectroscopic method in water solution. The stability constants of complexes were calculated by the multiwavelength analysis of spectral data using SQUAD program. The equilibrium constant, spectroscopic data, molar absorptivities and concentrations of all species were adequately optimized by program when the chemical model with 1: 1 stoichiometry was considered in the calculation. The extracted values of molar absorptivities and concentration profile of the formed complex were reported. The logarithms of the stability constants of complexes were calculated to be 3.672, 3.143, 2.986, 2.555, and 2.333 at 20, 25, 30, 35 and 40oC respectively.

In recent years there has been considerable interest in the structures, energies and thermodynamics of (GaN)4 clusters and it is the subject of many experimental and theoretical studies because of their fundamental importance in chemical and physical process. All calculation of this study is carried out by Gaussian 98. Geometry optimization for (GaN)4 nanocluster are be fulfilled at B3LYP, B1LYP and LSDA levels of theory with LANL2DZ basis set. Calculated are accomplished at 298 K. The structures, energetic and thermodynamic properties and vibrational spectra will be discussed.

The Density Functional Theory (DFT) and the Natural Bond Orbital (NBO) calculations based method B3LYP/6-31G* were carried out to study the interaction of carbon nanotube (8, 0) with nitrobenzene in two situations perpendicular and parallel. Formation energies of compounds, charges, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) and the HOMO-LUMO band gap were calculated. The parallel direction is more stable than the perpendicular direction. The lower HOMO-LUMO gaps confirm this stability.

Hydrothermal synthetic were studied for the preparation of coordination polymeric material based on Ag (I) and 4, 4´-bipy. A polymeric compound [Ag (4, 4´-bipy)].NO3, (I), was prepared and structurally characterized by single crystal X-ray diffraction. Compound I (91% yield) was isolated from the reaction of AgNO3 with 4, 4´-bipy in 2: 1 molar ratio. In compound I, each silver (I) is linked to two nitrogens of different but symmetry-equivalent 4, 4´-bipy units in a nearly linear coordination to form extended chains.

Hydrogels are introduced to modern medicine as novel materials suitable for a variety of biomedical applications. Studying hydrogels as novel biomaterials has become a fast-developing and exciting research field during the last two decades. These interesting biomaterials have found a wide range of application including contact lenses, vehicles for drug delivery and scaffold in tissue engineering and protein delivery systems. Traditionally hydrogels are formed by chemical crosslinking of water-soluble polymers or by polymerization of water-soluble monomers. However, these cross-linking methods lack biocompatibility with fragile molecules like pharmaceutical proteins and living cells. In all types of applications, the biocompatibility of hydrogels is the most important factor to be considered. Many newly developed hydrogels are designed to gel spontaneously under physiological conditions. In these systems, hydrogel formation occurs in situ, at the site of injection, without the aid of potentially toxic or denaturizing cross-linking agents. This review paper presents the chemical nature and biomedical applications of hydrogels.

In this study, the adsorption of thallium (III) ion from aqueous solutions onto modified ZnO nanopowder as a fairly low cost adsorbent has been investigated in batch mode. It was found that modification of the adsorbent was essential for obtaining the significant adsorption percentage. The adsorbent modified by sodium phosphate solution. The effect of experimental parameters such as initial pH of solution, contact time, adsorbent dosage, thallium initial concentration and temperature was studied. The results showed that the adsorption percentage was dependent on this parameters specially pH. The successful adsorption percentage of thallium (III) ion obtained at 25±1oC was 92.2-92.6%. The equilibrium data could be well described by the Freundlich isotherm but its fitting by Langmuir model was not so successful. Separation factor, RL, values showed that modified ZnO nanopowder were favorable for the sorption of thallium (III) ion.

In this investigation we synthesized NaX-Nanozeolite by hydrothermal crystallization conditions. These nanoparticles were prepared at different conditions in a temperature controlled shaker. The synthesized zeolites were characterized by instrumental analysis methods, such as X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The observed results showed particle size between 20 to100 nm. Then we examined the influence of different parameters on particle size such as reaction time, temperature and agitation. Crystallization with shaking at 60oC for 2 days was the best conditions for synthesis of NaX-Nanozeolite.

The photocatalytic degradation of betamethasone sodium phosphate was investigated in aqueous suspensions of zinc oxide nanoparticular with diameter size 20 nm under a variety of conditions. Different parameters such as irradiation time, the amount catalyst (0.12–0.8 g L-1), initial concentration of drug (10–50 mgL-1) and initial pH values (ranging from 3 to 11) were investigated in the presence of various electron acceptors. It was observed that 0.44 gL-1 of photocatalyst is the optimum value for photocatalyst dosage. In the most favorite conditions, the degradation efficiency was obtained 30gL-1 for betamethasone sodium phosphate. Finally, the kinetics process was studied and the photodegradation rate of betamethasone sodium phosphate was found to obey pseudo-first-order kinetics equation represented by the Langmuir–Hinshelwood model.