Chiral recognition in self-complexes of diketopiperazine derivatives
The chiral discrimination in the self-association of 2,5-diketopiperazines derivatives has been studied using density functional theory (DFT) methods. Hence, clusters from dimers to tetramers have been considered. We have found a variety of linear and cyclic structures depending on the geometry of the monomers. In general, the heterochiral dimers (RR:SS or SS:RR) are more stable than the homochiral ones (RR:RR or SS:SS) with slight energetic differences. Nevertheless, most of the larger clusters (trimers and tetramers) show changes in stability, the homochiral cyclic structures being favored due to the better geometry of the hydrogen bond and/or the higher number of interactions. Some interesting correlations between the hydrogen bond geometrical descriptors and theoretical parameters obtained from the Natural Bond Orbital analysis (NBO), Natural energy decomposition analysis (NEDA), and the Atoms in Molecules theory (AIM) have been found. The chiral discrimination in the recognition process of these self-complexes has been evaluated. In addition, evidence of cooperative effects has been observed.