Time filter

Source Type

Arabieh M.,Computational Chemistry Laboratory | Khodabandeh M.H.,Shahid Beheshti University | Karimi-Jafari M.H.,University of Tehran | Platas-Iglesias C.,University of La Coruna | Zare K.,Shahid Beheshti University
Journal of Rare Earths

We reported a quantum mechanical study of the complexes formed between Sm3+ and the bisphosphonate ligand pamidronate in aqueous solution. According to available experimental pKa values pamidronate was expected to exist in aqueous solution, at physiologically relevant pH, in its di- and tri-protonated forms (denoted by H3L and H2L). The most stable structures of the ligands and Sm3+ complexes were found by using a detailed analysis of the conformational space with semiempirical and DFT methods. The results showed that both H2L and H3L bisphosphonates acted as a tridentate ligands in their complexes with Sm3+. The addition of explicit water molecules to the coordination sphere of the metal not only gave different coordination numbers for H2L and H3L complexes (CN=9 and 10), but also provided different trends in stabilization energies. The results highlighted the importance of considering not only an explicit first coordination shell, but also a second hydration shell, for an adequate description of this type of complexes in aqueous solution. © 2015 The Chinese Society of Rare Earths. Source

Gomis L.,Cheikh Anta Diop University | Faye I.G.,Cheikh Anta Diop University | Diallo S.,Cheikh Anta Diop University | Tall M.S.,Cheikh Anta Diop University | And 4 more authors.
Physica Scripta

The quadrupole, monopole and dipole generalized oscillator strengths (GOSs) as a function of momentum transfer are respectively calculated for these 3p6 → 3p5 (4p, 5p, 6p) and 3p6 → 3p5 (4s, 5s, 6s) transitions. Configuration interaction (CI) and random phase approximation with exchange (RPAE) methods are used in the determination of these GOS, in the length and velocity forms. The code of Hibbert has been used to generate the wavefunctions from which a partial of argon GOSs are been computed. The present work has reduced the gap between the absolute values of the theoretical calculations of GOSs and those of the experimental results of Zhu et al for the quadrupole excitations to 3p5 (4p, 5p). The profile of our quadrupole GOS 3p6 → 3p55p transition agrees well with the experimental result of Zhu. The best agreement (0.7%) is observed between the (length) first maximum position and the experimental one for the quadrupole GOS 3p6 → 3p54p transition. The present velocity GOS minimum position for the dipole excitation in 3p6 → 3p54s and the calculated velocity GOS maximum position of the monopole 3p6 → 3p54p transition are in good agreement with the experimental observations (differences of 1.82% and 3.08%, respectively). Correlation effects decrease with increasing of the excited state principal quantum number and have no great influence on the extrema positions. © 2016 The Royal Swedish Academy of Sciences. Source

Arabieh M.,Shahid Beheshti University | Arabieh M.,Computational Chemistry Laboratory | Karimi-Jafari M.H.,University of Tehran | Ghannadi-Maragheh M.,Computational Chemistry Laboratory
Journal of Molecular Modeling

Extensive DFT and ab initio calculations were performed to characterize the conformational space of pamidronate, a typical pharmaceutical for bone diseases. Mono-, di- and tri-protic states of molecule, relevant for physiological pH range, were investigated for both canonical and zwitterionic tautomers. Semiempirical PM6 method were used for prescreening of the single bond rotamers followed by geometry optimizations at the B3LYP/6-31++G(d,p) and B3LYP/6-311++G(d,p) levels. For numerous identified low energy conformers the final electronic energies were determined at the MP2/6-311++G(2df,2p) level and corrected for thermal effects at B3LYP level. Solvation effects were also considered via the COSMO and C-PCM implicit models. Reasonable agreement was found between bond lengths and angle values in comparison with X-ray crystal structures. Relative equilibrium populations of different conformers were determined from molecular partition functions and the role of electronic, vibrational and rotational degrees of freedom on the stability of conformers were analyzed. For no level of theory is a zwitterionic structure stable in the gas-phase while solvation makes them available depending on the protonation state. Geometrically identified intramolecular hydrogen bonds were analyzed by QTAIM approach. All conformers exhibit strong inter-phosphonate hydrogen bonds and in most of them the alkyl-amine side chain is folded on the P-C-P backbone for further hydrogen bond formation. [Figure not available: see fulltext.] © 2012 Springer-Verlag. Source

Karimi-Jafari M.H.,Computational Chemistry Laboratory | Maghari A.,University of Tehran | Farjamnia A.,Computational Chemistry Laboratory | Farjamnia A.,University of Tehran
Journal of Physical Chemistry A

In this work, for the first time, an analytical four-dimensional representation for the intermolecular potential of the N2-CO dimer is constructed from ab initio calculations. The most stable structure of dimer is found to be a distorted T-shape conformation with CO forming the top and N 2 the leg of T. Important structures of the dimer are characterized, and surprisingly, it is found that in contrast with general assumptions, the potential energy surface of the N2-CO dimer has a single symmetry unique minimum. The energy profile of a minimum energy path that connects two T-shaped saddle points to the minimum structure is derived. Important structures are characterized along this path to represent the concerted internal rotation of monomers within the complex. The second virial coefficient is calculated from the fitted PES, and reasonable agreement is found with recent experimental results. © 2011 American Chemical Society. Source

Karimi-Jafari M.H.,Computational Chemistry Laboratory | Ashouri M.,Computational Chemistry Laboratory
Physical Chemistry Chemical Physics

Based on definition of angular central moments, a quantitative measure is proposed for comparative assessment of the anisotropy of different intermolecular potential energy surfaces at different intermolecular distances. Angular spreadness, skewness and peakedness are three features of anisotropy that are used here to describe the distribution of values of interaction energy around its isotropic component. In agreement with qualitative interpretations, the proposed measure exhibits a sharp change in the R-dependent pattern of anisotropy at an intermediate distance where the repulsive forces on the average overcome the attractive ones. The R-dependence of anisotropy of available N2-N2 potentials is examined in comparison with bare ab initio data and considerable discrepancies are found at distances shorter than the onset of repulsion. It is shown that the full experimentally derived potentials with simplified functional forms do not reproduce the correct anisotropy of interaction energy. © 2011 the Owner Societies. Source

Discover hidden collaborations