Journal of Physical and Theoretical Chemistry
Volume:8 Issue: 3, Autumn 2011

For better understanding of conformational stability of the dipeptide model HCO—Gly—L—Leu—NH2,ab initio and DFT computations at HF/6-31G(4 6-311++G(d,p) and B3LYP/6-31G(d) levels oftheory were carried out. Geometry optimization of the dipeptide within the leucine (Leu) side chainangles (x2 ,x2) resulted in three stable conformations as followings: anti-anti, the most stable one,(Xi = 180°, x2 = 180°), Gauche (+)-trans (xi= 60°, x2 = 210°) and 270°-Gauche (-)(x4 = 270°, x2 =3001. The thermodynamic properties E, H, G, and S by changing dihedral angles '111 (DO and (Di(D11) of glycine (Gly), ‘1J2 (D6), and (62 (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 indicatethat the BB has the highest stability bearing 'P I (DO = 180°, (1:11 (D11 ) = 180°, T2 (D6) = 150°, and 02(D4) = 210°.

Calixarenes are a readily available and important class of macrocycles in supramolecularchemistry. Calixarenes have generated considerable interest due to their basket shaped structureand 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 complexingproperties of a para-sulfonato-calix [4] arene (C281424016S4) with alkali metal cations. Thecomplexation 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 andthe position of the substituents grafted on the ligand.

Density functional theory ,(DFT) calculations have been performed to investigate the properties ofcarbon decorated (C-decorated) models of boron nitride (BN) nanocones. To this aim, the apex andtip of nanocone have been substituted by the carbon atoms to represent the C-decorated models. Theresults indicated that dipole moments and energy gaps could reveal the effects of C-decorations onthe properties of BN nanocones. Computations of quadrupole coupling constants (Qcc) for boron-IIand nitrogen-14 of the optimized structures have indicated that those boron and nitrogen atoms closeto the C-decorated regions detect the most significant effects of C-decorations. Moreover, theseatoms 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 thetemperature range from 20 to 40 °C and pH = 5.8 by spectroscopic method in water solution. Thestability constants of complexes were calculated by the multiwavelength analysis of spectral datausing SQUAD program. The equilibrium constant, spectroscopic data, molar absorptivities andconcentrations of all species were adequately optimized by program when the chemical modelwith 1:1 stoichiometry was considered in the calculation. The extracted values of molarabsorptivities and concentration- profile of the formed complex were reported. The logarithms ofthe stability constants of complexes were calculated to be 3.672, 3.143, 2.986, 2.555, and 2.333at20, 25, 30, 35and 40 °C 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 theirfundamental importance in chemical and physical process. All calculation of this study is carried outby Gaussian 98. Geometry optimization for (GaN)4 nanocluster are be fulfilled at B3LYP, B1LYPand LSDA levels of theory with LANL2DZ basis set. Calculated are accomplished at 298 K. Thestructures, energetic and thermodynamic properties and vibrational spectra will be discussed.

The Density Functional Theory (DFT) and the Natural Bond Orbital (NBO) calculations basedmethod B3LYP/6-31G* were carried out to study the interaction of carbon nanotube (8,0) withnitrobenzene 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 morestable than the perpendicular direction. The lower HOMO-LUMO gaps confirm this stability.

Hydrothermal synthetic were studied for the preparation of coordination polymeric material basedon Ag (I) and 4, 4"-bipy. A polymeric compound [Ag (4, 4'-bipy)].NO3. (I), was prepared andstructurally characterized by single crystal X-ray diffraction. Compound 1(91% yield) was isolatedfrom the reaction of AgNO3 with 4, 41bipy in 2:1 molar ratio. In compound I. each silver (I) islinked to two nitrogens of different but symmetry-equivalent 4, 4"-bipy units in a nearly linearcoordination to form extended chains.

Hydrogels are introduced to modem medicine as novel materials suitable for a variety ofbiomedical applications. Studying hydrogels as novel biomaterials has become a fast-developingand exciting research field during the last two decades. These interesting biomaterials have found awide range of application including contact lenses, vehicles for drug delivery and scaffold in tissueengineering and protein delivery systems. Traditionally hydrogels are formed by chemical crosslinkingof water-soluble polymers or by polymerization of water-soluble monomers. However,these cross-linking methods lack biocompatibility with fragile molecules like pharmaceuticalproteins and living cells. In all types of applications, the biocompatibility of hydrogels is the mostimportant factor to be considered. Many newly developed hydrogels are designed to gelspontaneously 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 ZnOnanopowder as a fairly low cost adsorbent has been investigated in batch mode. It was found thatmodification of the adsorbent was essential for obtaining the significant adsorption percentage. Theadsorbent modified by sodium phosphate solution. The effect of experimental parameters such asinitial pH of solution, contact time, adsorbent dosage, thallium initial concentration and temperaturewas studied. The results showed that the adsorption percentage was dependent on this parametersspecially pH. The successful adsorption percentage of thallium (III) ion obtained at 25±1°C was 92.2-92.6%. The equilibrium data could be well described by the Freundlich isotherm but its fitting byLangmuir model was not so successful. Separation factor, RL, values showed that modified ZnOnanopowder 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. Thesynthesized zeolites were characterized by instrumental analysis methods, such as X-raydiffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) andtransmission electron microscopy (TEM) techniques. The observed results showed particle sizebetween 20 to100 nm. Then we examined the influence of different parameters on particle sizesuch as reaction time, temperature and agitation. Crystallization with shaking at 60°C for 2 dayswas the best conditions for synthesis of NaX-Nanozeolite.

The photocatalytic degradation of betamethasone sodium phosphate was investigated in aqueoussuspensions 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 LH), initialconcentration of drug (10-50 mgLjand initial pH values (ranging from 3 to II) were investigatedin the presence of various electron acceptors. It was observed that 0.44 gL-I of photocatalyst is theoptimum value for photocatalyst dosage. In the most favorite conditions, the degradationefficiency was obtained 30gL-I for betamethasone sodium phosphate. Finally, the kinetics processwas studied and the photodegradation rate of betamethasone sodium phosphate was found to obeypseudo-first-order kinetics equation represented by the Langmuir-Hinshelwood model.