Theoretical Study of Molecular Structure, Tautomerism, and Geometrical Isomerism of Moxonidine:  Two-Layered ONIOM Calculations

Abstract

The geometries of various tautomers and rotamers of moxonidine in both anionic and protonated forms were optimized using the two-layered ONIOM(B3LYP 6-311+G(d,p): AM1) method. The calculations showed that, in agreement with experiments, moxonidine exists in a more stable imino tautomer. The tautomer containing the amino group is less stable by about 19 kJ/mol. The computed stable conformation for the moxonidine species is characterized by the pyrimidine and imidazolidine rings being in the mutual gauche conformation to one another. In contrast to the parent neutral molecule of moxonidine, ionization caused considerable geometric changes in the anions compared to the neutral species. In the neutral form and anion of the parent drug, an intramolecular hydrogen bond stabilizes the structure and makes the most stable conformations more planar. The primary protonation site is the imidazolidine part of drug. The proton affinity of moxonidine was computed to be −1004 kJ/mol. The moxonidine base was found to be less lipophilic than the base of parent clonidine.

An ONIOM investigation on anion recognition of alkali–metal complexes with diurea calix[4]arene receptor

“…Two-layered ONIOM (B3LYP/6-31G(d):AM1) was therefore employed throughout this work for geometry optimization of the present hostguest investigation. The reliability of the ONIOM(B3LYP/ 6-31G(d):AM1) method used in a similar system has been discussed in the literature [40,41]. The real and model systems used in the two-layered ONIOM(MO:MO) calculations for the hosts and host-guest interaction models are shown in Fig.…”

Theoretical study of conversion reactions of ketone to hydroxyalkylene in cluster models of zeolite H-ZSM-5

“…S2 (Supplementary data). The energies computed at the B3LYP/6-31G(d) for 3T (3T-DFT) and 5T (5T-DFT) cluster models and the ONIOM2(B3LYP/6-31G(d):AM1) [53,54] for 50/3T model have been carried out with the zero-point vibration energy corrections.…”

Theoretical Study of Gas-Phase Acidities of Selected Angiotensin-Converting Enzyme Inhibitors

“…2. It has been shown [27][28][29][30][31][32] that the integrated MO approach, ONIOM, provides an ideal method for the accurate calculations of large systems. For such molecules accurate calculations are often too expensive and out of reach.…”