Journal of Physical and Theoretical Chemistry
Volume:5 Issue: 1, Spring 2008

The 1, 3-bis(trimethyl silyl)ether of p-tert-butyl calix[4]arene, Rt-Bu)Ca1ixTMS21112, has beensynthesized and used as a dianionic ligand for "Sn". The complex of [(t-Bu)Ca1ixTMS2]Snexhibits exo and endo isomerism. The structural properties of [(Rp)Ca1ixTMS2]Sn, (Rpara= H,CH3, t-Bu) and the inter conversion of exoendo isomers were investigated by using of SCF-MOPM3 method.

Enzymes catalyze many biological reactions. The rates of chemical reaction in the presence ofenzymes are, in some cases, accelerated more than 10 orders of magnitude relative to thecorresponding rates in solution.In this paper a comparison between optimized structures of two enzyme molecules in aspect ofenergy and dipole moment in different conditions including presence of metallic ion, withoutmetallic ion and in the presence of substrate molecule was performed. The stabilizing effect ofmetallic ion is clearly seen. The calculations were performed with three basis sets: 6-31G, 6-31G*and 6-31G** and 6 different solvents and in vacuum. We conclude that the addition of polarizedfunctions to basis sets cause to create higher energy level of system.

The present work reports a kinetic spectrophotometric method for the determination of traceamounts of sulphite that is based on inhibitory effect of sulphite on the oxidation of Methyleneblue (MB) in acidic media. The reaction is followed spectrophotometrically by monitoring thedecrease in absorbance of MB at 664 nm with a fixed time of 0.5-4.5 minutes. It was found thatsulphite exert a strong inhibitory effect on this reaction. The method is applicable in the range of0.05-120 mg L-1 sulphite and the lower limit of detection is 0.04 mg L-1 (3o). The relativestandard deviation for 6 replicated determinations was 0.9 and 0.5 % for 4.0 and 20.0 mg L-1,receptively. This method was successfully applied for the determination of sulphite in realsamples.

Bond-Order Conservation-Morse Potential (BOC-MP) method is used to carry out the calculationon the CO2+ H20 system. One of the best catalysts for methanol synthesis in catalytic reductionof CO2 with H2O is Cu/ZnO/A1203 whose surface is supported by with some amount of Pd orGa. Reduction of CO2 with H20 on Cu will result in methanol formation; while on Ni will lead tomethane formation. In the mechanism of methanol synthesis from CO2+ H20 on Cu, the formate(HCOO) hydrogenation step is rate-determining step and in the mechanism of methane synthesison Ni, carbon hydrogenation is rate-determining step. The kinetic of each proposed mechanism isinvestigated.

The synthesis and properties of new monoazo dyes derived from the diazonium salts of paminobenzoic acid, 3-trifluoromethyl aniline , 4-trifluoromethyl aniline are considered .Theprepared compounds were characterized by UV-Visible , FT-IR and H NMR spectroscopictechniques . The effect of varying solvent upon the absorption ability of p-amino benzoic acidcoupled with 4,4 —diethyl aniline , aniline ethanol, 2 — naphthol and 2,4 -dihydroxy benzene wasexamined.

P53 is one of the gene that has important role in human cell cycle and in the human cancers too.Models of codon substitution make it possible to separate mutational biases in the DNA fromselective constraints on the protein, and offer a great advantage over amino acid models forunderstanding the evolutionary process of proteins and protein-coding DNA sequences. In thiswork, we investigated about CUA codon in exon5 of p53 that has mutated to CCA codon.We studied solvent effects on CUA codon by theoretical method, because the most of biologicalsystems studied in solution and solvents have essential role in mutation of genes. Five solventsconsist of acetone, ethanol, methanol, DMSO and water are predicated using ab initio method.Also, indirect (Au ind) solvent effects are obtained and NMR shielding tensors (ppm) have beencomputed with the continuous set of the gauge independent atomic orbital (GIAO) method.

Using UV-VIS spectrophotometric method, the formation constant for interaction of Fe2+(aq) ion with L-Alaninewas experimentally studied at pH = 4.1 ± 0.01 (50mM of potassium hydrogen phthalate buffer), ionic strengthof 0.1M potassium nitrate and at 5 different temperatures 15,20, 25,30 and 35 T. The optical absorption spectraof mixtures containing considered cation and L-Alanine were analyzed by using SQUAD software, in order toobtain the formation constant and the stoichiometry of respect complex. The best fitting of our results showedthe 1:2 complex respect to the studied system (Fe2+00 + L-Alanine) is formed. Regarding the value of formationconstants at different temperatures and using Van' t Hoff equation, it is possible to calculate the respectivethermodynamic functions of formation such as AG', An' , AS', ... of the studied complex.

DFT and QTAIM computations have been performed on numbers of pure nitrogen cluster speciesi.e. Nn (n = 4, 6) for investigating the structure and bonding. This study is critical since thesemolecules have been nominated as the good synthetic targets of High Energy Materials (HEM).0nthe other hand the decomposition mechanism is closely depends on the bonding pattern. Thislatter concept was searched via modem theory of Atoms in molecules (QTAIM) since theconventional methods were found to be incapable for describing the structure and bond in theseatomic clusters.

In this research complexation of dioxovanadium(V) with nitrilotriacetic acid (NTA) at differentionic strengths (0.1 to 1.0 mol dm-3) of sodium perchlorate as supporting electrolyte and pH rangeof 1.00-2.50 at 25 °C has been investigated by a combination of potentiometric and UVspectrophotometric measurements. Stability constants of two species, V0211L- and VO2H2L havebeen calculated. Ionic strength dependence semi-empirical parameters for the dissociation andstability constants were derived on the basis of extended Debye-Htickel type equation.

The discovery of mesoporous molecular sieves, MCM-41, which possesses a regular hexagonalarray of uniform pore openings, aroused a worldwide resurgence in this field. This is not onlybecause it has brought about a series of novel mesoporous materials with various compositionswhich may find applications in catalysis, adsorption, and guest-host chemistry, but also it hasopened a new avenue for creating of the zeotype materials. This paper presents a comprehensiveoverview of recent advances in the field of MCM-41. Adsorption of drug molecules such asPseudeoephedrine hydrochloride onto mesoporous molecular sieves (MCM-41) from aqueoussolution has been investigated systematically using batch experiments in this study. Resultsindicate that Pseudeoephedrine hydrochloride adsorption is initially rapid and the adsorptionprocess reaches a steady state after 2 min. The adsorption isotherms are well described by theLangmuir model. Based on the results, it suggests that the adsorption is primarily brought about byhydrophobic interaction between drug molecules and MCM-41 surface.