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Search Results: 1 - 10 of 1405 matches for " DFT Calculations "
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Quantum-Chemical Description of Influence of the R-Groups on Formation of Peptide Bond  [PDF]
Jumber Kereselidze, Marine Kvaraia, George Mikuchadze
Computational Molecular Bioscience (CMB) , 2014, DOI: 10.4236/cmb.2014.42004
Abstract: The description of influence of the R-groups on formation of the peptide bond by quantum-chemical method of density functional theory (DFT) is carried out. The criterion of probability of formation of the peptide bond has been constructed. In particular it is shown that the propensity to formation of the peptide bond is increased as a result of 1) decrease of the CO and NH bond orders (PCO and PNH) and of activation energy (ΔE#), 2) increase of OH and CN bond orders (POH and PCN), 3) exothermic property of this reaction (ΔE < 0).
DFT Calculations for Corrosion Inhibition of Ferrous Alloys by Pyrazolopyrimidine Derivatives  [PDF]
Nuha Ahmed Wazzan, Fatma Mohamed Mahgoub
Open Journal of Physical Chemistry (OJPC) , 2014, DOI: 10.4236/ojpc.2014.41002

The inhibition performance of 5-tolyl-2-phenylpyrazolo[1,5-c] pyrimidine-7(6H)thione (Tolyl), 5-tolyl-2-pheenylpyrazolo [1,5-c]pyrimidine-7(6H)one (Inon) was investigated as corrosion inhibitors using density functional theory (DFT) at the B3LYP/6-31 + G(d,p) level of theory. The calculated quantum chemical parameters correlated to the inhibition efficiency are: the highest occupied molecular orbital energy(EHOMO), the lowest unoccupied molecular orbital energy (ELUMO), the energy gap (ΔEL-H), dipole moment (μ), ionization energy (Ι), electron affinity (Α), absolute electronegativity (χ), absolute hardness (η), absolute softness (σ), the fraction of electron transferred (ΔN), and the total energy (Etot) which were calculated. The local reactivity has been analyzed through the Fukui function and local softness indices in order to compare the possible sites for nucleophilic and electrophilic attacks. The success of DFT calculations in predicting the inhibition efficiency was assessed.

A Comparative Study on the Structural and Vibrational Properties of Two Potential Antimicrobial and Anticancer Cyanopyridine Derivatives  [PDF]
María J. Márquez, María B. Márquez, Pablo G. Cataldo, Silvia A. Brandán
Open Journal of Synthesis Theory and Applications (OJSTA) , 2015, DOI: 10.4236/ojsta.2015.41001
Abstract: 2-Hydroxy-4,6-dimethylpyridine-3-carbonitrile and 2-chloro-4,6-dimethylpyridine-3-carbonitrile compounds have been studied from a theoretical point of view in order to know their structural and vibrational properties in gas and aqueous solution phases by means of Density Functional Theory (DFT) calculations. The stable structures in both media were optimized by using the hybrid B3LYP/6-31G* method and the solvent effects in aqueous solution were studied by using the integral equation formalism of the polarizable continuum model (IEFPCM) employing the selfconsistent reaction field (SCRF) method. Detailed vibrational analyses for both compounds in the two phases were performed combining the DFT calculations with Pulay’s Scaled Quantum Mechanics Force Field (SQMFF) methodology. The different interactions for both compounds were analyzed by means of the bond orders, atomic charges, solvation energies, dipole moments, molecular electrostatic potentials and force constants parameters. The nature of the interactions was studied by using different descriptors.
Synthesis, Crystal Structure and Infrared Characterization of Bis(4-dimethylamino-pyridinium) Tetrachlorocuprate  [PDF]
Mahjouba Ben Nasr, Frédéric Lefebvre, Chérif Ben Nasr
American Journal of Analytical Chemistry (AJAC) , 2015, DOI: 10.4236/ajac.2015.65044
Abstract: The chemical preparation, crystal structure and spectroscopic characterization of a novel organic-inorganic hybrid material, bis(4-dimethylaminopyridinium) tetrachlorocuprate, have been reported. This compound crystallizes in the monoclinic system in space group C2/c and cell parameters a = 12.4356 (18), b = 12.0901 (17), c = 14.094 (2) Å, β = 115.303 (2)°, Z = 4 and V = 1915.8 (5) Å3. In the title salt, (C7H11N2)2CuCl4, both 4-dimethylaminopyridinium cations are protonated at their pyridine N atoms. The geometry of the CuCl2-4 ions is intermediate between tetrahedral and square planar. The atomic arrangement can be described by an alternation of inorganic layers built up by tetrachlorocuprate anions and organic layers formed by 4-dimethylaminopyridinium cations. The organic layers are located in sandwich between the inorganic layers. The anionic and cationic layers are held together by N-H···Cl and C-H···Cl hydrogen bonds into a three-dimensional network. The individual cations are π-π stacked with their neighbors at a distance of 3.7622 (5) Å. The vibrational absorption bands were identified by infrared spectroscopy and DFT calculations allowed their attribution.
Site Selectivity of One Hydroxyl Group Bonded on the Surface of Finite (5, 0) Zigzag Carbon Nanotube  [PDF]
Afshin Abbasi, Hossein Mostaanzadeh, Reza Safari, Ebrahim Honarmand
Computational Chemistry (CC) , 2017, DOI: 10.4236/cc.2017.51001
Abstract: We have investigated the stability, geometrical structure, electronic properties and vibrational spectra of different isomers of hydroxylate (5, 0) zigzag carbon nanotube (CNT) with 60 C atoms and 10 hydrogen (C60H10) by using all-electron density-functional-theory (DFT) methods. Stable arrangements of these molecules were found by means of full geometry optimizations using B3LYP/6-31G(d) level of theory. From symmetrical point of view, four isomers of HO-C60H10 are possible when -OH bonds to the surface. We observed that the molecular properties strongly depend on the position of bonded hydroxyl group on the surface of CNT.
Dipole Moments of the Bioactive Constituents Present in Flutab Drug by Ab-Initio Calculations  [PDF]
Raghad Alajlani, Amal Alssadi
Open Journal of Physical Chemistry (OJPC) , 2019, DOI: 10.4236/ojpc.2019.94013
Abstract: Many of the technology and computational chemistry applications are used to study drugs and their biological effects. Flutab® drug contains Paracetamol, Diphenhydramine and Pseudoephedrine. Ab-initio calculations were performed at DFT/B3LYP and HF methods with three basis sets, namely, STO-3G, 3-21G, and 6-31G(d) in order to calculate the dipole moments of the three constituents of Flutab® drug. The Diphenhydramine compound was found to be the most stable constituent, with the lowest value of dipole moment.
Unsynchronized resonance of covalent bonds in the superconducting state
Costa, Marconi B. S.;Bastos, Cristiano C.;Pav?o, Antonio C.;
Journal of the Brazilian Chemical Society , 2012, DOI: 10.1590/S0103-50532012000700015
Abstract: dft calculations performed on different cluster models of cuprates (laba2cu3o6.7, la1.85sr0.15cuo4, yba2cu3o7, tlba2ca2cu3o8.78, hgba2ca2cu3o8.27), metallic systems (nb3ge, mgb2) and the pnictide lao0.92f0.08feas made evident the occurrence of unsynchronized resonance of covalent bonds in the superconducting state, as predicted by pauling′s resonating valence bond (rvb) theory. for cuprates, the unsynchronized resonance involves electron transfer between cu atoms accompanied by a decrease in the charge of the la, sr, y and ca atoms. for mgb2, electron transfer occurs in the mg layer, while the b layer behaves as charge reservoir. for nb3ge, unsynchronized resonance occurs among the ge atoms, which should be responsible for charge transfer. for lao0.92f0.08feas, the results suggest that both la-o and fe-as layers are involved in the mechanism of superconductivity. the identification of unsynchronized resonances in these systems provides evidence which supports rvb as a suitable theory for high-temperature superconductivity (high-tc).
A DFT/ECP-Small Basis Set Modelling of Cisplatin: Molecular Structure and Vibrational Spectrum  [PDF]
Nicolay I. Dodoff
Computational Molecular Bioscience (CMB) , 2012, DOI: 10.4236/cmb.2012.22004
Abstract: A DFT conformational and vibrational analysis of a single molecule of cisplatin (cis-[Pt(NH3)2Cl2]) was performed by means of PW91 functional and LANL08 ECP basis set for the Pt atom. 3-21G and 3-21G* Basis sets were used for the remaining atoms. All the initially chosen conformations were found to converge to the global minimum conformation of C2v symmetry with H atoms lying in the coordination plane and pointing to the Cl atoms. The computational results were compared with the newest experimental structural data and with the vibrational spectroscopic data for cisplatin, obtained by other workers. The chosen level of theory was found to describe satisfactory the molecular structure (r. m. s. of the relative deviations ≤ 6%) and the harmonic vibrational frequencies (r. m. s. of the relative deviations ≤ 5%) of cisplatin.
Spectroscopic Evaluation of the Molecular Structures of di-μ-Chlorobis(1,5-Cyclooctadiene) Iridium (I) and Rhodium (I) Complexes  [PDF]
Saheed A. Popoola, Abdulaziz A. Al-Saadi
Journal of Applied Mathematics and Physics (JAMP) , 2015, DOI: 10.4236/jamp.2015.32021

Vibrational and H-NMR spectroscopic studies on di-μ-chlorobis(1,5-cyclooctadiene) of iridium(I) and rhodium (I) complexes have been carried out. In addition, the two D2h and D2 structures for both complexes have been fully optimized. It was expected from the single-molecule vapor-phase density functional theory (DFT) calculation that the D2 structure is more stable by 5 - 6 kcal/mol. While spectroscopic analysis study confirms that in the solid phase, the two complexes retain the higher D2h symmetry. The vibrational wavenumbers of certain modes associated to free 1,5-cyc- looctadiene were observed to be shifted to lower values upon coordination with rhodium or iridium metals. It was also found theoretically that the metal-olefin interaction is slightly more pronounced for iridium metal.?

Photochemical Reactions of Microcystin-LR Following Irradiation with UV Light  [PDF]
Yoshihiro Mizukami
Open Journal of Physical Chemistry (OJPC) , 2016, DOI: 10.4236/ojpc.2016.64008
Abstract: Photochemical reactions of microcystin-LR, a toxic compound produced by some blue green algae, were investigated. Ultraviolet absorption of microcystin-LR was assessed. Time-dependent density functional theory (TDDFT) calculations indicated that absorption peak at 238 nm was mainly due to excitation of electrons from the linear chain structure Adda of microcystin-LR. Irradiation of microcystin-LR with UV light resulted in the reduction of the 238 nm absorption peak and the appearance of a new peak at 300 nm. Density functional theory (DFT) and TDDFT calculations with a model molecule suggested that this 300 nm peak was due to tricyclo-Adda microcystin-LR, an intermediate in photochemical reactions of microcystin-LR. Analysis of the rate of this photochemical reaction showed that it was a first order reaction.
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