Journal of Physical and Theoretical Chemistry
Volume:6 Issue: 2, Summer 2009

It seems that the general applicability of the quantum theory of atoms in molecules (QTAIM) oncharacterizing the bonded interactions is still questionable even afier 30 years since its formulation. Fordemonstrating the generality of bonding schemes in QTA IM, ea( isomers were chosen as the modelsystems and the results from molecular charge density analysis and vibrational normal modes werecompared to each other. It was demonstrated that the mathematical properties of the elements of moleculargraph, derived from charge density analysts, have (m excellent correlation with the properties of thevibrational normal modes. The excellent correlation among four different indices of chemical bond i.e. internuclear distances, th.QTAIM bond orders (q)

Thermal denaturation of p-Iactoglobulin type B in the absence and pteNcno: of g arious concentrations oftrehalo5e, sucrose and sork toles sugar osmolytes and twlyols were nuyoured hy monitoring changes in theabsorption coefficients at pH 2.0. These measurements gave aliss, or I. mpdpDint of denaturation), Al-fis(enthalpy change at Ty). and ACp (consttun-pressure heal capaciit eh.iltgtii under a gisen solvent conditionUsing these valuer of Ali,, rs, and AC, , AG D° (Gibbs Dieu:, chantiet was determined at a givenconcentration of each sugar. Ii has been obsessed that each sugar glafili se. the 13-lac toglob B m ternsof 3. and AGna. The temperature that corresponds to rtmirntim proiv in Rahflits.. Is is increased G thepresence of these osmulytes. The same rend was also obsessed for fir,. the temperanirc corresponding tonun eat-haler change of denaturation.

We have evaluated the NMR shielding tensors for active site of oxidized ayurin Azurin is classified to atype I copper protein with ET functionality. We have computed NMR shielding tensor at .133LYP and IDlevels by usum 6-3IG basis set in the gas phase and in different solvents such as water, HMSO,Nitromethane, methanol, ethanol, acetone ,dicholoroethane. These solvents represent a wide range ofsolvent properties from thc point of view of polarity as well as hydrogen bonding inleraction,The NNWshielding tensors were calculated using the :CIAO and CSOT methods. Our results reveal that NIvMchemical shielding parameters are strongly affected by inducing different solvent media Regarding to our graphs of ow, , tau do, i.I versus a. the largest cru, values obtained in ethanol and water for Cuatom whereas file smallest one belonged to DMSO. It is interesting to note that the opposite trend havebeen observed for asymmetry parameters OffAlso, calculations at the HF in CSGT and GIA0 methods have shown bat molecular geometry andshielding properties an better than the other methods. laIlLYR in CIAO mid CSGT methods.

The prtnonation constant values of tryptophan were studied at 25 C. different ionic strengths. 0.1-1.0 moldm", and various ionic media of NaCIO, and N4N01, using a combination of spectrophotometrie andpotentiometric techniques. The general vend for the two protonation con Slant Vai net of tryptophan is in theorder of NaC104 > NaNO3 in different ionic media. The dependence of protonation constants on ionicstrength and ionic media were taken into account; using a Debye-Huckel type equation (molarconcentration scale) and the SIT (specific ion interaction theory) approach (udal concentration scale).Differences in protonation constants in thc various supporting electrolytes were also interpreted anddiscussed.

Theoretically predictionq of the solvent effects of I - pentadecanoyl - 2 -docosahexaennyl - Sn - glycerol3 - phosphocholin have been studied using 'Jamey-lock quantiun chemical approximation and STD - 30basis set within the Onsager Self-Consistent Reaction field (SCRS') model All optimized conformers of I -pentadecanoyl - 2 -docosahexaenoyI - Sn - glycerol 3 - phosphocholin as well as their total relativeenergies in terms of the most stable conformer in as phase and different solvent media such as water.ethanol. methanol and IMISO have been calculated. According to the obtained resulLz the I - pentadecanoyl- 2 - docosahexaeneyl - Sn - glycerol - 3 - phosphocholin configuration has the most neeative energyvalues and then has been found to be the most stable conformer. In this aspect the gaph of relative energyvalues versus dielectric. constants (c) as well as Ln (I /c) of employed solvents has been plotted and theobserved trend has been analyzed.For further investigation, the effect of solvent's polarity on the dipole moments of 1-pentadecanoyl - 2 -docosahexaenoyl - Sn - glycerol - 3 - phosphocholin in various solvent media have been reported andcompared with the gas phase. We would like to note that the dipole moment variations revealed that thevalues or the computed dipole moment seems to he solvent - dependent because this property is closelyrelated to the en viromnental effects the greatest dipole moment brings more stability which is underinfluence of solvation

In this research the interaction of Pyrene (Cullm) as a polycyclic aromatic hydrocarbon with human serumalbumin (HSA) has been investigated. Variations of UV-Vis spectrum of Prene can help us to investigatethe changes that are ereated in protein structure. Pyrene in insoluble in water and soluble in acetic acid.mixture of acetic acid and water and in organic solvents such as methanol. UV-Vis spectrum of Pyrene hasthree strong bands at 308,349 and 433 on'. A series of UV-Vis titration experiments were earned out basedon titration of a given amount of Pyrene with ESA at various pH. phosphate buffer and differenttemperatures. 1 he titration spectrum were analyzed at each temperature using SQUAD program and basedon 1:1, I:2 and 2:1 models. Results indicated that formed complex between Pyrene and ESA is I:I. Allthermodynamic parameters of complex formation including AG", AH', AS' and formation constant ofcomplex (K) were calculated and results showed that the process is endothermic and entropy driven. Thisissue shows the predornmant role of hydrophobic forces in inleraction between Pyrene and ESA.Investigating the effect of increasing the ionic strength on absorption spn, ram of Pyrene-HSA complexalso confirms the results of thermodynamic studies. Using the changes in the structure of absorptionspectrum of Pyrene in water. plasma of human blood and in a buffer solution of ESA, we could indicatethat Pyrene in Mood plasma is concentrated in hydmphilic micro phases of plasma proteins and lipid.

The structure and relative stability of Molybdata-Phosphonic Acid (MP) Complex in different solventshave been carried out using Density Functional Theory (DP[) methods. The methods me used forcalculations are B3LYP and 83PW91. that have been studied in two series of basis sets: D95"and 6-31+0(cl,p) for hydrogen and oxygen atoms; LANL2OZ for Mn and Phosphorus. Predicted geometw and relativestability are discussed. Equilibritun geometry in the ground electronic state energy has been calculated forLt complex. The best results for energeto and geometrical grotmd state in different of used solvents wereobtained with Becke3LYP calculations.

Topological indices are one of the oldest and most widely used descriptors in Quantitative StructureProperties Relationvhips (QSPR). Amongst the topological indices used a,s descriptors in QSPIC., the Wienerindex is by far the most popular index. as it has been shown that the Wiener index has a strong correlationwith the chemical propenies of the compound.In this study, the relationship between some of the Wiener index in contrast to the electric moments andenergy (klma]) of some armchair polyher. carbon nanotubes ThAter[2p, g] with same circumference [216and various length [g] an: presented. The results are performed by use of the Gaussian 98 program P theRestricted Hamee-fock RUE) levels with the 3-210 basis set.

The potential energy hyper surfaces (FES) of the unimolecular rearrangements of a) Nitromethane itei totrans acknitromethane b) nitrometharie (/) to methyl nitrite (3) and c) naromethane decomposition tomethyl and nitrogen dioxide were searched using the ab !nth° MP2 method. Split valence 6-310(d.p) basisset was used for geometry optimizations, frequency and 1RC computations along each reaction pan. Theenergy barrier for the decomposition path or nitremethane was found to be 87.8 kcal/mot net newlydetermined transition state. The nitromeihane to methyl nitrite bent bight was previously determined tohe the 70.5 kealimol. which is 17.3 kcal/mol less than nat of the nitromethane decomposition path repottedin WE won. Using these data it was possible for the first time to explain the experimentally observed pathof nitromethane decomposition

A theoretical study of the kinetic and mechanism of intramoleccha cychcation of (1)-undeca-7,8-dien-2-yne was performed using MT methods at B3LYP and B3PW91 levels of theory using 6-311g, 6-311C.6-31 IGs*, 6-31I+G, 6-31 I4-SG and 6-3114H-Gs* basis seo. Equilibrium molecular geometries andharmonic vibrational frequencies of the reaccint, transition state and product wens calculated. Theconsidered rate constants and activation thermodynamic parameters were eak saluted. It wa.s demonstratedthat the obtained results for all calculations were nearly independent to basis sets at 83 PW91 I e el.These calculations showed that the reaction proceeds through asynchronous concerted mechanism,