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The ambident reactivity of small-sized XAHs (X=H, F, Cl, Br, CH3, and A=S, Se, Te) molecules towards the imidazole molecule (IMZ) has been investigated using wave function (MP2) and Density Functional Theory (B3LYP, B3LYP-D3). Molecular electrostatic potentials (MEPs) and frontier molecular orbitals of monomers are computed to rationalise the regioselectivity of IMZ towards XAHs. The chemical bonding of each complex is described in the framework of the quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) paradigms. The symmetry-adapted perturbation theory (SAPT) is employed to assess the physical nature of the interactions. Our findings suggest that XAHs mainly bind to IMZ through H-bonding and chalcogen-bonding interactions of weak to moderate strength, with binding energies ranging from −3.1 to −17.6 kcal/mol at the MP2/aug-cc-pVDZ(-PP) level. Topological QTAIM descriptors reveal all H-bonds between IMZ and XAHs to be purely noncovalent contacts, while chalcogen bonds of halogenated XAHs (X = F, Cl, Br) show a partial covalent character. SAPT2 calculations indicate that both H-bonded and chalcogen-bonded complexes are mainly stabilised by electrostatic interactions. Insights drawn from this study are expected to constitute the bedrock for further investigations about noncovalent interaction between middle to big-sized chalcogen-containing molecules and imidazole derivatives. [ABSTRACT FROM AUTHOR]

Temozolomide was paired with guanine, 6-selenoguanine, and 6-thioguanine, as well as the SH tautomer of the latter. The potential energy surface of each heterodimer was searched for all minima, using Dispersion-Corrected Density Functional Theory and MP2 methods. Among the dozens of minima, three categories were observed. Stacked geometries place the aromatic systems of the two molecules parallel to one another, while the two systems are roughly perpendicular to one another in a second category. Also found are coplanar structures held together by H-bonds. Dispersion proves to be a dominating attractive force for the stacked structures, less so for perpendicular, and smallest for the coplanar dimers. Geometries and energetics are relatively insensitive to S and Se substitution, but tautomerization reverses relative stabilities of different geometries. [ABSTRACT FROM AUTHOR]

B3LYP, B3LYP-D3 and MP2 calculations are used to predict the preferred site of binding of HCl to temozolomide (TMZ). Binding energies, bond length perturbations, and infrared spectra of the various heterodimers indicate that the O-atom of the terminal amide group is the preferred attack site. The interaction is strong with binding energy of roughly 30 kJ mol −1 . The molecular electrostatic potential surrounding TMZ is consistent with this preference, but is unable to fully account for the energetic ordering of the other minima. [ABSTRACT FROM AUTHOR]

Highlights: [•] All possible binding sites of TMZ with water are considered, and binding energies evaluated. [•] The terminal amide group represents the strongest binding site, with water bound by 40kJ/mol. [•] The global minimum is cyclic, with water acting as simultaneous proton donor and acceptor. [•] Molecular electrostatic potential (MEP) and Natural Bond Orbital (NBO) data aid in understanding the binding preferences. [ABSTRACT FROM AUTHOR]