Theoretical B3LYP Study on Electronic Structure of Contrast Agent Iopamidol

Nonionic low-osmolar contrast agents are thought about safe for intravenous or intra-arterial administration. Iopamidol is one of the contrast agents used for diagnostic clinical computed tomography (CT) protocols last four decades years. The molecular structure of Iopamidol was calculated by the B3LYP density functional model with the LANL2DZ basis set by the Gaussian program. The natural bond orbital analysis in terms of the hybridization of atoms and the electronic structure of the title molecule have been analyzed by using the data obtained from the quantum chemical results. First-order hyperpolarizability (βtot), the dipole moment (μ) and polarizability (α) and anisotropic polarizability (Δα) of the molecule have been reported. HOMO and LUMO energies and parameters related to energies, and dipole moment, polarizability and hyperpolarizability show minor dependences on the solvent polarity. The hardness of Iopamidol decreases with increasing solvent polarity. The stability of the Iopamidol contrast agent with the hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital analysis. In addition, thermodynamic properties were obtained in the range of 200–1000 K.

Energy, orbital and structural stacking landscape of a purine homodimer system

The multidimensional study, combining the extensive calculations of potential energy surfaces for the parallel-displaced configurations and methods such as energy decomposition and natural bond orbital analysis, has been carried out. The resulted data give an energy, orbital and structural landscapes of this biologically essential system. The balance of the two energy sources, electrostatic and dispersion, is clearly visible. The obtained results, taken as a whole, provide an insight into the hierarchy of intermolecular interactions in the purine system, together with their sources.

Theoretical investigations on the HOMO–LUMO gap and global reactivity descriptor studies, natural bond orbital, and nucleus-independent chemical shifts analyses of 3-phenylbenzo[d]thiazole-2(3H)-imine and its para-substituted derivatives: Solvent and substituent effects

Natural bond orbital analysis, salvation, and substituent effects of electron-releasing (–CH3, –OH) and electron-withdrawing (–Cl, –NO2, –CF3) groups at para positions on the molecular structure of synthesized 3-phenylbenzo[ d]thiazole-2(3 H)-imine and its derivatives in selected solvents (acetone, toluene, and ethanol) and in the gas phase by employing the polarizable continuum method model are studied using the M06-2x method and 6-311++G(d,p) basis set. The relative stability of the studied compounds is influenced by the possibility of intramolecular interactions between substituents and the electron donor–acceptor centers of the thiazole ring. Furthermore, atomic charges, electron density, chemical thermodynamics, energetic properties, dipole moments, and nucleus-independent chemical shifts of the studied compounds and their relative stability are considered. The dipole moment values and the highest occupied molecular orbital–lowest unoccupied molecular orbital energy gaps reveal different charge-transfer possibilities within the considered molecules. Finally, natural bond orbital analysis is carried out to picture the charge transfer between the localized bonds and lone pairs.

Quantum chemical topology and natural bond orbital analysis of M–O covalency in M(OC6H5)4 (M = Ti, Zr, Hf, Ce, Th, Pa, U, Np)

VXC(M,O): the exchange–correlation metric quantifies covalency between M and O atomic basins in M(OC6H5)4 (M = Ti, Zr, Hf, Ce, Th, Pa, U, Np).

Atmospheric reactions of glyoxal with NO2 and NH2 radicals: Hydrogen abstraction mechanism and natural bond orbital analysis

Glyoxal can be important in atmospheric chemistry in terms of its ability to convert to secondary organic aerosols. In this study, the glyoxal-breaking reaction by two atmospheric active radicals, NO2 and NH2, has been investigated at the B3LYP and M06-2X levels in connection with 6-311++G(d,p) basis set. The formation of the most stable adducts from glyoxal with NO2/NH2 radical requires two hydrogen atom transfers. The accuracy of the predicted mechanisms in describing the hydrogen transfers was confirmed by atoms-in-molecules calculations and natural bond orbital analysis. The calculated results predict that hydrogen transfer process in both reactions at the M06-2X level is favourable from the kinetic and thermodynamic points of view. In the natural bond orbital analysis, the stabilization energy, E(2), delocalization corrections, at the B3LYP level is much higher than the same results at the M06-2X level (nearly twice). The activation thermodynamic parameters show that the first steps of the two reactions have lower barrier energy than the second steps. The Gibbs free energy values estimate that adducts of both the reactions at the mentioned method are spontaneous. The whole reaction of glyoxal + NH2 is more favourable than the whole reaction of glyoxal + NO2. The rate constants were calculated for the mentioned pathways using transition state theory for bimolecular steps and the fitted equations are reported.

Conformational preference and cationic structure of 2-methylpyrazine by VUV-MATI spectroscopy and natural bond orbital analysis

Alkylpyrazines, which are well-known as aromatic substances and traditional medicines, are interesting molecular systems, and their methyl conformations result in unique structural and dynamical properties.