Journal of Physical and Theoretical Chemistry
Volume:1 Issue: 2, Summer 2004

Tin(II)-ion-selective electrode consisting of dibenzo-18-crown-6 (DB18C6) as an ionophore inPVC matrix was developed. The influences of membrane composition, selectivity, response time,reversibility and temperature on the electrode performance were investigated. The electrodeshowed a near Nernstian response for Sn2+ ions over a concentration range from 1.0× 10-6 – 1.0× 10-2 M with a slope of 27.5 ± 0.6 mV per concentration decade in a acidic solution (pH=1). Thelimit of detection was 8.0 × 10-7 M. It has a relatively fast response time and can be used for atleast 3 months without any divergence in potentials. The isothermal temperature coefficient of thiselectrode amounted to 0.0012 V/ °C. The stability constant (log Ks) of the Sn(II) – DB18C6complex was determined at 25 °C by potentiometric titration in mixed aqueous solution.

The hydration of biomolecules is vitally important in molecular biology, so in this paper thesolvation energy and radial distribution function of DNA bases have been calculated by theMonte Carlo simulation.The geometries of isolated Adenine, Guanine, Cytosine, and Thyminehave been optimized using 6-31+G(d,p) basis function sets. These geometries then will be used inthe Monte Carlo calculation of the DNA bases in water.We have used TIP3 model for water andOPLS for nucleic acid bases. The computed solvation energy have Good agreement with the othercomputational data Radial distribution function of O and N atoms of Adenine, Guanine, Cytosine,and Thymine which have been computed and the results have been compared with other availabledata observed for these molecules. The Monte Carlo simulation also has been performed by theCHARMM39, 40 program in the same conditions and the results of two procedures have beencompared.

A quantum chemical study of the corrosion inhibition properties of some organic inhibitormolecules, pyridine, 2-picoline, 3-picoline, 4-picoline, 2, 4-lutidine at the aluminum surface inhydrochloric acid (HCl) was carried out. The models of the inhibitors adsorption on the Al-surfacewere optimized with the HF and B3LYP level using the 6-31G and LANL2DZ basis sets fromthe program package Gaussian 98 (A.7 Public Domain version). Based on the calculated resultsthe compound was adsorbed on the metal surface mainly in their protonated forms. In the Alsurfaceis transferred to the inhibitor and organic inhibitor is adsorbed at the Al-surface in aninclined state.

The binding data for interaction of a homologous series of n-alkyl sulfates with alkyl chainlengths from C8 to C12 with insulin were analyzed on basis of Hill equation for two classes ofbinding sites .The intrinsic Gibbs free energies were calculated and resolute on basis ofelectrostatic and hydrophobic contributions The estimation of these contributions reveals themajor role of electrostatic interactions on first binding set and the minor one in the second.

In this research some mathematical calculations has been explained on the “ +VO2 +glycylglycine” system and some equations has been deduced to determine the stability constants ofthe equilibrium models including MLH+, ML and ML2H species (while M+ ≡ +2 VO , H2L+ ≡protonated glycylglycine and MLH+, ML and ML2H represent the considered complexes). Thecalculations are based on some relations between variation of absorbance (in the UV-vis region)and hydrogen ion concentration. The absorptivities and stability constants of complexes could beobtained from the intercept and slope of resulting linear equations. According to this approach thecomplexes refer to “ +VO2 + glycylglycine” system has been investigated in aqueous solutions ationic strength 0.5mol dm-3 sodium perchlorate at 250C ( ± 0.1); and a combination ofpotentiometric and spectrophotometric (UV-vis) method was used.

We have performed quantum-chemical ab initio in various basis sets at the Hartree-Fock andB3LYP levels for Adenine and Thymine with the program GAUSSIAN98. The Dipole,Quadrupole, Octapole and Hexadecapole moments and primitive in nine basis sets for thesemolecules are presented. The most stabilized forms of these molecules are observed in 6-311++G** basis set. We have evaluated coefficient hybridation of bonds and occupancy orbital,donor and acceptors. NBO calculations show that hybridation of coefficient and occupancy inseveral basis sets is different.

In this research oxidation kinetic panceuo.s (P.S) by S2O8-2 at the presence of AgNO3 ascatalyst was studied.The method was spectrophotometer following absorption spectrum (P.S) inwave length of 518 nm. After improving the condition such as PH, P.S concentration, K2S2O8concentration, ionic strength, temperature, rate constant, activation energy, constant frequency,order reaction and thermo dynamical values as ΔH#, ΔS#, ΔG# for catalyst and non catalyst weredetermined.The results show that oxidation rate P.S by means of S2O8-2 would be increased by theaddition of AgNO3 and silver ion would function as a positive catalyst in this reaction.

Equilibria of the reaction of molybdenum(VI) with L-aspartic acid (Asp) and L- Glutamic acid(Glu) have been studied by spectrophotometric measurements in mixed solvent systems at an ionicstrength of 0.2 mol/dm3 sodium perchlorate, employed (15, 20, 25, 30± 0.1°C) at pH ranges of 3.2to 5.5 with a high ratio of ligand to metal. The stability constants of the complexes and theresulting free energy changes are presented. The effect of solvent systems on protonation andcomplexation are discussed. Linear relationships are observed by plotting logK versus 1/D , whereK and D show stability and dielectric constants, respectively.

The interaction of Magnesium hydrate at the phosphate oxygen atom of the pyrimidine nucleotides (CMP,UMP,dTMP) were studied at the Hartree-Fock level Theory. We used LANL2DZ basis set for Mg and 6-31g* basis set for atoms.The basis set superposition error (BSSE) begins to converge for used Method/basis set. The gauge-invariant atomic orbital (GIAO) method and the continuous-set-of-gauge-transformation (CSGT) procedure were employed to calculate isotropic atomic shielding of the nucleotides using density functional theory at the B3LYP/6-31g** . These calculations yield molecular geometries in good agreement with available experimental data.