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دسترسی آزاد مقاله
1 - Investigation of solvent effect on the active site energy of Carbonic Anhydrase and Ribonucleotide Reductase
M. Heshmat S. Saki M. Khaleghian S. Irani M. MonajjemiEnzymes 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 o چکیده کاملEnzymes 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. پرونده مقاله -
دسترسی آزاد مقاله
2 - Rationalizing the Strength of Hydrogen-Bonded of Molybdate-Phosphonic acid Complex (1:2): Density Functional Theory Studies
Mohammad Hossein Ghorbani Hossein AghaeiThe relative stability of hydrogen-bonded of Molybdate-Phosphonic Acid (MPA) complex (1:2) ingas phase has been carried out using Density Functional Theory (DFT) methods. The methods are usedfor calculations are B3LYP, BP86 and B3PW91 that have been studied in two serie چکیده کاملThe relative stability of hydrogen-bonded of Molybdate-Phosphonic Acid (MPA) complex (1:2) ingas phase has been carried out using Density Functional Theory (DFT) methods. The methods are usedfor calculations are B3LYP, BP86 and B3PW91 that have been studied in two series of basis sets: D95**and 6-31+G(d,p) for hydrogen and oxygen atoms; LANL2DZ for Mo and Phosphorus. Predictedhydrogen-bond geometry and relative stability are discussed. Equilibrium geometry in the groundelectronic state energy has been calculated for 1:2 complex. The best results for energetics and geometryof the ground state was obtained with BP86 calculations. پرونده مقاله -
دسترسی آزاد مقاله
3 - Quantum Chemistry Study & Evaluation of Basis Set Effects on Prediction of Amino Acids Properties:
M. Monajjemi M. Karimkhan M. R. Gholami A. Ziglari K. Zare S. AfsharnezhadThe potential energy surface of gaseous glycine determined years ago in the ab initio B3LYP/6-311++G** calculations is composed of thirteen stable conformers. We performed the ab initiomolecular orbital calculations as the starting point to carry out a force field and n چکیده کاملThe potential energy surface of gaseous glycine determined years ago in the ab initio B3LYP/6-311++G** calculations is composed of thirteen stable conformers. We performed the ab initiomolecular orbital calculations as the starting point to carry out a force field and normal coordinatecalculation on the most stable conformer of non-zwitterionic glycine [conformer (I)]. Thecalculations were carried out at different levels of theory using two methods, namely, the Hartree-Fock (HF) and the Möller-Plesset second order perturbation (MP2) method (including electroncorrelation), and using the Pople’s basis sets, namely, STO-nG (n=2, 3 and 6), 3-21G, 6-21G, 6-31G, 6-311G and also cc-pVnZ to obtain HF limit. This different basis sets accompanied with thedifferent combinations of diffuse and polarization functions were used. Each level of theory, withno symmetry restrictions, did fully optimization of neutral glycine. The atomic chargedistributions were obtained using the Mulliken population analysis. The structural characteristicssuch as the total energies, the complete optimized geometrical parameters including bond lengths,normal and torsion angles, as well as dipole moments, rotational constants, atomic chargedistributions, vibrational frequencies and IR intensities of the equilibrium conformation of glycinein gas phase were calculated at a wide range of the levels of theory -as mentioned above- and theresults were compared together and with HF limit and the experimental data to examine thereliability of the applied basis sets and to introduce the most efficient ones. We also assayed howthe strength of internal H-bonds depended on the variant parameters of basis set via the calculatedatomic charges. پرونده مقاله -
دسترسی آزاد مقاله
4 - Theoretical Study of electronic Structure of [CoF6]3" Complex embedded in Nano-Ring
Mehrnoosh Khaleghian Majid MonajjemiDensity functional theory calculations (DFT), as well as hybrid methods (B3LYP) for Bi8N18-[CoF6]3- complexhave been carried out to study the non-bonded interaction. The geometry of the 1313N18 has been optimized atB3LYP method with EPR-II basis set and geometry of the چکیده کاملDensity functional theory calculations (DFT), as well as hybrid methods (B3LYP) for Bi8N18-[CoF6]3- complexhave been carried out to study the non-bonded interaction. The geometry of the 1313N18 has been optimized atB3LYP method with EPR-II basis set and geometry of the [CoF6]3 have been optimized at B3LYP method withDe12-TZVP basis set and Stuttgart RSC 1997 Effective Core Potential. The electromagnetic interactions of the[CoF6]3- molecule embedded in the B13N18 nano ring have been investigated at B3LYP and total atomic charges,spin densities, dipole moment and isotropic Fermi coupling constants parameters in different loops and bonds ofthe B15N18-[CoF613- system have been calculated. Also NBO analysis such as electronic delocalization betweendonor and acceptor bonds has been studied by DFT method. Then we have been investigated the lowestunoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) for the lowestenergy have been derived to estimate the structural stability of the Bi8N18-[CoF6]3- system. The Gaussianquantum chemistry package is used for all calculations. پرونده مقاله -
دسترسی آزاد مقاله
5 - Theoretical study of structure spectral properties of Tacrine as Alzheimer drug
Leila Pishkar Parisa R. Jamaat Somayeh MakaremTacrine (9-amino-1,2,3,4-tetrahydroacridine) as a reversible inhibitor of acetylcholinesterase (AChE),was the first drug for the symptomatic treatment of Alzheimer’s disease (AD). NMR structuredetermination still presents some considerable challenges: the method i چکیده کاملTacrine (9-amino-1,2,3,4-tetrahydroacridine) as a reversible inhibitor of acetylcholinesterase (AChE),was the first drug for the symptomatic treatment of Alzheimer’s disease (AD). NMR structuredetermination still presents some considerable challenges: the method is limited to systems ofrelatively small molecular mass, data collection times are long, data analysis remains a lengthyprocedure, and it is difficult to evaluate the quality of the final structures but calculation of a structureitself has become extremely rapid, and new labeling methods have significantly improved bothspectral quality and automated analysis, whilst rigorous standards and data formats affordcompatibility of different software packages. In this theoretical study, we used HF and DFT (BLYP,B3LYP) method for chemical shift nucleus magnetic resonance DFT-NMR. The basis set used were631G, 631G** and 6-31G++. The results show a reasonably good correlation between calculatedand experimental chemical shifts. Agreement of experiment and calculated data suggesting thatstudies of drug structures can be pursued with some degree of confidence with this level of theory. پرونده مقاله
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