Unveiling Bifunctional Hydrogen Bonding with the Help of Quantum Chemistry: The Imidazole-Water Adduct as Test Case

Abstract

The ubiquitous role of water and its amphiprotic nature call for a deeper insight into the physical–chemical properties of hydrogen-bonded complexes formed with building blocks of biomolecules. In this work, the semiexperimental (SE) approach combined with the template model (TM) protocol allowed the accurate determination of the equilibrium structure of two isomeric forms of the imidazole-water complex. In this procedure, the integration of experiment (thanks to a recent rotational spectroscopy investigation) and theory is exploited, also providing the means of assessing the reliability and accuracy of different quantum-chemical approaches. Overall, this study demonstrated the robustness of the combined SE-TM approach, which can provide accurate results using affordable quantum-chemical methods. Finally, the structural and energetic characteristics of these complexes have been examined in detail and compared with those of analogous heterocycle–water adducts, also exploiting energy decomposition analyses.

Spectroscopic Characterization of 3-Aminoisoxazole, a Prebiotic Precursor of Ribonucleotides

“…The average relative difference on the rotational constants was found to be about 0.1%, while the discrepancies for quartic centrifugal distortion and nitrogen quadrupole coupling constants are larger, but on average are below 5%. This agreement is in line with the literature on this topic [ 43 , 49 , 50 , 51 , 52 , 53 ]. Owing to the inclusion in the fit of both a - and b -type transitions, all rotational constants have been accurately determined: the resulting relative error is about 2 parts per 10 million, while a precision of 2 parts per 10 thousand has been obtained for the quartic centrifugal distortion constants.…”

Development and Validation of a Parameter-Free Model Chemistry for the Computation of Reliable Reaction Rates

“…27−31 More recently, an improved variant (referred to as the jun-Cheap scheme, jChS) has been introduced, which, thanks to the use of the "june" partially augmented basis set of the "calendar" family, 32 provides very accurate results also for noncovalent interactions. 33,34 On these grounds, in this paper, we provide a comprehensive benchmark of the jChS model chemistry for several classes of reactions for which accurate reference results are available or have been purposely computed. Together with electronic energies, we analyze also zero point energies, thermal contributions to enthalpies and entropies, and overall reaction rates computed for elementary reactions in the framework of the master equation (ME) approach based on the ab initio transition-state theory (AITSTME).…”

Stacked but not Stuck: Unveiling the Role of π→π* Interactions with the Help of the Benzofuran–Formaldehyde Complex

“…For the isomer I, the availability of a large set of rotational constants (eleven isotopologues for the u = 1 state) allows the determination of a semi-experimental (SE) equilibrium structure (r e SE ) [37] by exploiting the SE approach in combination with the template model (TM) approach, [38] which are both detailed in the SI. Briefly, the structures of the BZF and FA frames within the complex have been accurately determined using the TM approach starting from the r e SE values of the isolated fragments.…”