9-Ethyladenine: Mechanochemical Synthesis, Characterization, and DFT Calculations of Novel Cocrystals and Salts

Abstract

Liquid-assisted grinding and solvent crystallizations have been undertaken to prepare salts and cocrystals of the modified nucleobase 9-ethyladenine with several carboxylic acids. The new solid forms have been characterized by X-ray powder and single-crystal diffraction, attenuated total reflectance Fourier transformed infrared spectroscopy, and thermal methods. From single-crystal structures we have observed that the length of the alkyl chain in the carboxylic acid prevents a canonical self-assembly for the longest coformer. Moreover, density functional theory (DFT) calculations combined with the quantum theory of “Atoms-in-Molecules” QTAIM have been performed to analyze the different binding modes of adenine and the energetic features of the complexes. In particular, the interaction energies of several adenine dimers and trimers, and also the hydrogen bonds with carboxylic acids interacting with Watson–Crick and Hoogsten faces of adenine, have been computed and compared.