Collect. Czech. Chem. Commun. 2009, 74, 275-297
Published online 2009-02-14 09:22:56

Gas-phase structure and relative stability of proton-bound homo- and heterochiral clusters of tetra-amide macrocycles with amines

Caterina Fraschetti, Marco Pierini*, Claudio Villani, Francesco Gasparrini, Antonello Filippi and Maurizio Speranza*

Dipartimento di Chimica e Tecnologie del Farmaco, Universita “La Sapienza”, 00185 Roma, Italy


The structure, stability, and CID pattern of proton-bound homochiral and heterochiral complexes, formed in the gas phase by the combination of two molecules of a chiral macrocyclic tetra-amide and an amine B, i.e. CH3NH2, (CH3)2NH, or (S)-(–)-1-phenylethylamine, have been examined by ESI-ITMS-CID mass spectrometry. With B = CH3NH2, the CID pattern is characterized by the predominant loss of B, accompanied by a much less extensive release of one tetra-amide molecule. With (S)-(–)-1-phenylethylamine, loss of a tetra-amide molecule efficiently competes with loss of B. Finally, with (CH3)2NH, loss of a tetra-amide molecule predominates over loss of B. No appreciable isotope and chiral guest configuration effects have been detected in the fragmentation of the homochiral complexes. A distinct configurational effect has been appreciated in the CID of the homo- and the heterochiral complexes with all amines used. The results of this study have been discussed in the light of semi-empirical computational evidence. The differences in the CID patterns of the homo- and the heterochiral complexes have been rationalized in terms of structural factors and of the basicity of amine B.

Keywords: Diastereoselectivity; Collision-induced dissociation; Supramolecular isomers; Amines; Chiral clusters; Mass spectrometry; Gas-phase chiral recognition.

References: 25 live references.