Search results for "DFT CALCULATION"

Structure Sensitivity of 2‐Methyl--butyn-2-ol Hydrogenation on Pd: Computational and Experimental Modeling

2014

Integrated experimental and theoretical study on the phase transition and photoluminescent properties of ZrO2:xTb3+ (x=1, 2, 4 and 8 mol %)

2021

Abstract Zirconia (ZrO2) has been intensively studied as an important ceramic material, and numerous technological applications have been found. The present work deals with synthesizing and characterizing the phase transition (cubic vs tetragonal) and photoluminescence emissions of ZrO2:xTb3+ (x = 1,2,4 and 8 mol%). The samples formed by the complex polymerization were thoroughly characterized for physicochemical properties such powder by X-ray diffraction (XRD), and Raman and diffuse reflectance spectroscopies. First-principle calculations at the density functional theory level were performed to complement and rationalize the experimental results. An energy transfer mechanism which promote…

Novel meso-substituted porphyrins: Synthesis, characterization and photocatalytic activity of their TiO2-based composites

2009

Abstract Two series of novel meso-substituted porphyrins, namely 5,10,15,20-tetra[4-(3-phenoxy)-propoxy]phenyl porphyrin, the structural analogue 5,10,15,20-tetra[2-(3-phenoxy)-propoxy]phenyl porphyrin and their Co(II) Cu(II) and Zn(II) complexes were synthesized. The compounds were characterized using various spectroscopic techniques and their molecular structure was proposed based on density functional theory calculations. The diverse properties of the porphyrin derivatives result from the different stereochemistry of the particular substituents at the meso site on the macrocycle and are controlled also by the coordinated metal. The 1H NMR spectrum of the free-base porphyrin showed a comp…

Synthesis and electronic aspects of tetrahydrobenzothienopyrimidine derivatives

2015

Abstract The chemistry of thiophenes, pyrimidines, triazolopyrimidines and benzothiophenes has drawn much attention because of their biological activities. Their interesting properties are connected with their complex π-electron delocalisation effects. Herein the synthesis, crystal and molecular structures at 100 K and DFT calculated structures of three tetrahydrobenzothienopyrimidine derivatives are reported i.e. 4-hydrazino-5,6,7,8-tetrahydro[1]benzothieno[2,3-d]pyrimidine which was a substrate for 2-phenyl-8,9,10,11-tetrahydro[1]benzothieno[3,2-e][1,2,4]triazolo[1,5-c]pyrimidine and 3-methyl-9,10,11,12-tetrahydro-2H-[1]benzothieno[2′,3′:4,5]pyrimido[1,6-b][1,2,4]triazin-2-one. Moreover t…

DFT and experimental studies on structure and spectroscopic parameters of 3,6-diiodo-9-ethyl-9H-carbazole

2015

The first report on crystal and molecular structure of 3,6-diiodo-9-ethyl-9H-carbazole is presented. Experimental room-temperature X-ray and 13C chemical shift studies were supported by advanced theoretical calculations using density functional theory (DFT). The 13C nuclear magnetic shieldings were predicted at the non-relativistic and relativistic level of theory using the zeroth-order regular approximation (ZORA). Theoretical relativistic calculations of chemical shifts of carbons C3 and C6, directly bonded to iodine atoms, produced a reasonable agreement with experiment (initial deviation from experiment of 44.3 dropped to 4.25 ppm). The changes in ring aromatic character via simple harm…

Molecular modeling and experimental studies on structure and NMR parameters of 9-benzyl-3,6-diiodo-9H-carbazole

2015

A combined experimental and theoretical study has been performed on 9-benzyl-3,6-diiodo-9H-carbazole. Experimental X-ray (100.0 K) and room-temperature 13C NMR studies were supported by advanced density functional theory (DFT) calculations. The non relativistic structure optimization was performed and the 13C nuclear magnetic shieldings were predicted at the relativistic level of theory using the Zeroth Order Regular Approximation (ZORA). The changes in the benzene and pyrrole rings compared to the unsubstituted carbazole or the parent molecules were discussed in terms of aromaticity changes using the harmonic oscillator model of aromaticity (HOMA) and the nucleus independent chemical shift…

The influence of substitution in the quinoxaline nucleus on 1,3-dipolar cycloaddition reactions

2013

The reaction mechanism of 1,3-dipolar cycloadditions of both symmetric and unsymmetric benzo-condensed diazines with a nitrilimine dipole, to give two different mono- and bis-cycloadducts, in tetrahydrofuran (THF) solution, was studied by DFT calculatio ns. The results obtained show that each 1,3-dipolar cycloaddition reaction always proceeds by a two steps mechanism, in which the first intermediate shows only one covalent bond between the beta carbon of the nitrilimine and the aromatic nitrogen of the diazine molecule. The structure and energy content of the two transition states of the two cycloaddition steps, in the case of the unsymmetric benzo-condensed diazine, nicely explains why the…

Reactivity of antitumor coinage metal-based N-heterocyclic carbene complexes with cysteine and selenocysteine protein sites

2021

Abstract The reaction of the antitumor M(I)-bis-N-heterocyclic carbene (M(I)-NHC) complexes, M = Cu, Ag, and Au, with their potential protein binding sites, i.e. cysteine and selenocysteine, was investigated by means of density functional theory approaches. Capped cysteine and selenocysteine were employed to better model the corresponding residues environment within peptide structures. By assuming the neutral or deprotonated form of the side chains of these amino acids and by considering the possible assistance of an external proton donor such as an adjacent acidic residue or the acidic component of the surrounding buffer environment, we devised five possible routes leading to the binding o…

The influence of solvent on conformational properties of peptides with Aib residue—a DFT study

2017

The conformational propensities of the Aib residue on the example of two model peptides Ac-Aib-NHMe (1) and Ac-Aib-NMe2 (2), were studied by B3LYP and M06-2X functionals, in the gas phase and in the polar solvents. To verify the reliability of selected functionals, we also performed MP2 calculations for the tested molecules in vacuum. Polarizable continuum models (PCM and SMD) were used to estimate the solvent effect. Ramachandran maps were calculated to find all energy minima. Noncovalent intramolecular interactions due to hydrogen-bonds and dipole attractions between carbonyl groups are responsible for the relative stabilities of the conformers. In order to verify the theoretical results,…

Reactivity of dialkoxydibutylstannanes toward carbon dioxide: A DFT study of electronic and steric effects

2012

Abstract DFT calculations were performed for the reaction of CO 2 with the monomeric species, R′ 2 Sn(OR) 2 , (R = R′ = CH 3 ; R = CH 3 , CH 2 CH 3 , CH(CH 3 ) 2 , R′ =  n -Bu) for assessing the role of electronic and steric effects in the kinetics and thermodynamics of CO 2 insertion into Sn–OR bonds. The reaction pathways are exothermic and involve the successive insertion into the two Sn–OR bonds. The driving force for insertion is ascribed to a charge-transfer between the HOMO of the complexes, mainly localized on the oxygen atom of the alkoxy ligands, and the LUMO of CO 2 . Interestingly enough, the energy barrier of the second insertion is much lower by around 27 kJ mol −1 , and quite…