On the applicability of functional-group symmetry-adapted perturbation theory and other partitioning models for chiral recognition - the case of popular drug molecules interacting with chiral phases

Association Complexes of Calix[6]arenes with Amino Acids Explained by Energy-Partitioning Methods

Intermolecular complexes with calixarenes are intriguing because of multiple possibilities of noncovalent binding for both polar and nonpolar molecules, including docking in the calixarene cavity. In this contribution calix[6]arenes interacting with amino acids are studied with an additional aim to show that tools such as symmetry-adapted perturbation theory (SAPT), functional-group SAPT (F-SAPT), and systematic molecular fragmentation (SMF) methods may provide explanations for different numbers of noncovalent bonds and of their varying strength for various calixarene conformers and guest molecules. The partitioning of the interaction energy provides an easy way to identify hydrogen bonds, including those with unconventional hydrogen acceptors, as well as other noncovalent bonds, and to find repulsive destabilizing interactions between functional groups. Various other features can be explained by energy partitioning, such as the red shift of an IR stretching frequency for some hydroxy groups, which arises from their attraction to the phenyl ring of calixarene. Pairs of hydrogen bonds and other noncovalent bonds of similar magnitude found by F-SAPT explain an increase in the stability of both inclusion and outer complexes.

Ab Initio Study of Chiral Discrimination in the Glycidol Dimer

Chiral discrimination, the ability of a chiral molecule to exhibit different weak intermolecular interactions than its mirror image, is investigated for dimers of oxiranemethanol (glycidol). In this regard, high-level ab initio calculations were performed to study the chiral recognition effects in the homochiral and heterochiral dimers of glycidol. Fourteen dimer structures, seven homochiral and seven heterochiral, were studied: they all feature two intermolecular O-H···O hydrogen bonds. These structures have been determined with the second-order Møller-Plesset perturbation theory (MP2) using the aug-cc-pVTZ basis set and verified to pertain to actual local minima. The benchmark interaction energy values were computed using MP2 extrapolated from the aug-cc-pVQZ and aug-cc-pV5Z bases with a higher-level correction from a coupled-cluster calculation in the aug-cc-pVTZ basis. The global minimum structure is a homochiral one, with the two hydrogen bonds forming a part of a ring with eight heavy atoms. A similar heterochiral structure has a binding energy smaller by about 0.6 kcal/mol. The largest diastereomeric energy difference is about 1.0 kcal/mol. Further insight into the origins of chiral discrimination was provided by symmetry-adapted perturbation theory (SAPT) and a functional-group SAPT (F-SAPT) difference analysis to investigate the direct and indirect effects of two -H/-CH₂OH substitutions leading from an achiral ethylene oxide dimer to the chiral glycidol dimer. Last but not least, harmonic frequency shifts relative to a noninteracting glycidol molecule were calculated and analyzed for all conformations to get insight into the origins of chiral discrimination. It is found that the largest frequency shifts are related to the effect of hydrogen bonding on the O-H stretch mode, the stability of the ring involving both hydrogen bonds, and the transition between two nonequivalent minima of the glycidol molecule.

Description of Chiral Complexes within Functional-Group Symmetry-Adapted Perturbation Theory-The Case of (S/R)-Carvone with Derivatives of (-)-Menthol

Symmetry-adapted perturbation theory (SAPT) and functional-group SAPT (F-SAPT) are applied to examine differences in interaction energies of diastereoisomeric complexes of two chiral molecules of natural origin: (S/R)-carvone with (-)-menthol. The study is extended by including derivatives of menthol with its hydroxy group exchanged by another functional group, thus examining the substituent effect of the interaction and the interaction differences between diastereoisomers. The partitioning of the interaction energy into functional-group components allows one to explain this phenomenon by the mutual cancellation of attractive and repulsive interactions between functional groups. In some cases, one can identify dominant chiral interactions between groups of atoms of carvone and menthol derivatives, while in many other instances, no major interaction can be distinguished and the net chiral difference results from subtle near cancellation of several smaller terms. Our results indicate that the F-SAPT method can be faithfully utilized for such analyses.