Supramolecular chemistry in the gas phase
One of the most important goals of the supramolecular chemistry is the construction of artificial receptors, which can mimic enzyme activity and selectivity and are applicable to asymmetric synthesis. To shed more light on the intrinsic factors governing enantiodiscrimination by cyclochiral receptors, we used inherently chiral resorcin[4]arenes as model system. Nano-electrospray ionization (nano-ESI)-Fourier transform ion cyclotron resonance mass spectrometry was the experimental method of choice to investigate the effect of cyclochirality of rccc-2,8,14,20-tetra-n-decyl-4,10,16,22-tetra-O-methylresorcin[4]arene as host molecule (hereafter named M) on the enantiodiscrimination of a number of chiral bidentate and tridentate aromatic and aliphatic biomolecules as guest molecules (hereafter named A). Formation of diastereomeric proton-bound [M•H•A]+ complexes was invertigated by nano-ESI mass spectroscopy of solutions containing an equimolar amount of quasi-enantiomers (M) together with the chiral guest (A) and the subsequent measurement of the rate of the A substitution by the attack of several achiral and chiral amines B. In general, the heterochiral complexes react faster than the homochiral ones, except when A is an aminoalcoholic neurotransmitter whose complexes, beyond that, exhibit the highest enantioselectivity. The kinetic results were further supported by both collision-induced dissociation experiments on some of the relevant [M2•H•A]+ three-body species and Density functional theory (DFT) calculations performed on the most selective systems.
C. Fraschetti, M. C. Letzel, M. Paletta, J. Mattay, M. Speranza, A. Filippi, M. Aschic and A. B. Rozhenko, J. Mass. Spectrom. 2012, 47, 72–78.