DFT computational studies on rotation barriers, tautomerism, intramolecular hydrogen bond, and solvent effects in 8‐hydroxyquinoline

Abstract

Intramolecular hydrogen binding interactions in 8-hydroxyquinoline, both in its zwitterionic tautomer and in the rotamer without the intramolecular hydrogen bond (IHB), have been computed using the B3LYP and MPW1K density functionals. The rotation of the OOH bond and intramolecular proton transfer reactions were studied theoretically. The following theory levels have been applied: B3LYP/6-31G(d,p), B3LYP/6-311ϩϩG(d,p), MPW1K/6-311ϩϩG(d,p), and MPW1K/6-311ϩϩG(2d,3p)//MPW1K/6-311ϩϩG(d,p). Natural bond orbital (NBO) analysis has also been carried out. The effect of medium (benzene, chloroform, tetrahydrofuran, 1,2-dichloroethane, acetone, water) was simulated using the self-consistent reaction field (SCRF) method within the framework of the polarizable continuum model (PCM), at the MPW1K/6-311ϩϩG(d,p) level. The evolution of geometry, relative energies, heights of rotation (around the OOH bond) and tautomerization barriers, IHB energies, and ⌬G(solv) have been systematically investigated. The results obtained have shown the failure to neglect some changes of the above characteristics in polar media with respect to the gaseous phase. The series of stability of the forms under study in the gaseous phase remains the same in solution. Thus, in spite of the important role of the solvent electrostatic effects, the intrinsic stability of those species overcomes the solvent effects.

Electronic structure of planar-quasicycled organic molecules with intramolecular hydrogen bond

“…As for the molecules XXXIX, XL, the tendencies in IHB effect on the electron structure of molecules revealed in the present work coincide with those found at the higher theory levels: B3LYP/6-31G(d,p), B3LYP/6-31+G(2d,2p), B3LYP/6-311++G(d,p), MPW1K/6-31+G(2d,2p), MPW1K/6-311++G(d,p), MPW1K/6-311++G(2d,3p)//MPW1K/6-311++G(d,p), BH&HLYP/6-311++G(d,p), G96LYP/6-311++G(d,p), including the use of natural bond analysis (NBO). 18,19 The latter testificies to the correctness of the results of the present work.…”

“…17 That theory level (HF/6-311G(d,p) is sufficient for the overview of tendency in electron density redistribution on the IHB formation in the series of compounds. Such a statement is confirmed by the computations at higher theory levels for 8-hydroxyquinoline 18 The charges on atoms of the molecular system I-XLI, with IHB as well as of the reference compounds (another conformers of the molecules and the corresponding para isomers), were obtained within the framework on the analysis of orbital occupancies by Mulliken. 20 The electron distribution in molecule defines its dipole moment.…”

DFT studies of the bonding mechanism of 8-hydroxyquinoline and derivatives on the (111) aluminum surface

“…63,64 The pK a values of 8-HQ in aqueous solutions at 20 1C are 5.13 (NH + /N) and 9.89 (ÀOH/O À ). The obtained geometrical information for the a 8-HQ free molecule (calculated in vacuum, bond lengths presented in Table 1, bending angles and torsional angles not detailed here) were in good agreement with experimental results, 62 and other calculations [63][64][65] presented in the literature. In highly basic solutions the 8-HQ molecule can be present in the dehydrogenated form and we also studied the adsorption on Al(111) of the dehydrogenated 8-HQ molecule that is a radical species.…”

“…62 Depending on the nature of the solvent, the 8-HQ molecule can be present under the a form (with intramolecular hydrogen bonding), b form (without intramolecular hydrogen bonding) and tautomeric form (see Fig. 63,64 The pK a values of 8-HQ in aqueous solutions at 20 1C are 5.13 (NH + /N) and 9.89 (ÀOH/O À ). This latter form is supposed to be present in polar solvents.…”

Voltammetric analysis of nitroxoline in tablets and human serum using modified carbon paste electrodes incorporating mesoporous carbon or multiwalled carbon nanotubes

“…57 The pH ZPC of MC has been reported at 5.34. So, at pH < pK a1 , a repulsive interaction between positively charge nitrogen of hydroxyquinoline moiety [48][49][50][51] and positively charged MC surface may be present leading to relatively small peak current. So, at pH < pK a1 , a repulsive interaction between positively charge nitrogen of hydroxyquinoline moiety [48][49][50][51] and positively charged MC surface may be present leading to relatively small peak current.…”