Abstract
We describe an experimental and quantum chemical study for the accurate determination of the conformational space of small molecular systems governed by intramolecular non-covalent interactions. The model systems investigated belong to the biological relevant aminoalcohol's family, and include 2-amino-1-phenylethanol, 2-methylamino-1-phenylethanol, noradrenaline, adrenaline 2-aminoethanol, and N-methyl-2-aminoethanol. For the latter molecule, the rotational spectrum in the 6–18 and 59.6–74.4 GHz ranges was recorded in the isolated conditions of a free jet expansion. Based on the analysis of the rotational spectra, two different conformational species and 11 isotopologues were observed and their spectroscopic constants, including 14N-nuclear hyperfine coupling constants and methyl internal rotation barriers, were determined. From the experimental data a structural determination was performed, which was also used to benchmark accurate quantum chemical calculations on the whole conformational space. Atom in molecules and non-covalent interactions theories allowed the characterization of the position of the intramolecular non-covalent interactions and the energies involved, highlighting the subtle balance responsible of the stabilization of all the molecular systems.
Highlights
The essential chemical and biological processes of molecular transport and recognition are determined by the shape of molecules and the weak interactive forces between them
The combined experimental and theoretical study of the conformational space of the small and flexible MAE molecule studied in the isolated phase, allowed the understanding of the driving forces and factors influencing its stability
The analysis performed in the isolated phase shows that the two lowest energy conformations are strongly stabilized by an intermolecular OH···N hydrogen bonds (HB) that was structurally characterized and energetically quantified
Summary
The essential chemical and biological processes of molecular transport and recognition are determined by the shape of molecules and the weak interactive forces between them. A study of the conformational landscapes and the non-covalent interactions in isolated systems or small molecular complexes is necessary to understand the influence of these factors on the mechanisms of transport and drug-receptor interaction (Robertson and Simons, 2001), as well as reactivity and catalysis (Sohtome and Nagasawa, 2012; Hanoian et al, 2015). From the chemical point of view, the combination of donor and acceptor groups in the same molecule stabilizes molecular conformations involving intramolecular HB either of OH···N or NH···O type (Penn and Curl, 1971) while, from a biological point of view, one can note that many natural products contain the aminoalcohol functionality (Robertson and Simons, 2001)
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