Hydrogen-bonding interactions in gas-phase polyether/ammonium ion complexes

Abstract

Hydrogen bonds are among the most important interactions involved in selective complexation in host-guest chemistry. In this study a variety of hydrogen-bonded crown ether/ammonium ion complexes are generated in the gas phase by association reactions between an amine substrate and a polyether, one of which is initially protonated, and stabilized by many collisions in the chemical ionlzation source of a triple quadrupole mass spectrometer or in a quadrupole ion trap. The nature of the hydrogen-bonding interactions of the ion complexes are evaluated by comparison of their collision-activated dissociation spectra. After collisional activation, those complexes that are weakly bound dissociate to form intact protonated polyether molecules and/or ammonium ions by simple cleavages of the hydrogen-bond association interactions. In contrast, those complexes strongly bound by multiple hydrogen bonds dissociate not only to the protonated polyether and/or ammonium ions but also by extensive covalent bond cleavage of the protonated ether skeleton.This latter type of dissociation behavior suggests that the polyether/ammonium ion complexes may be sufficiently strongly bound that surpassing the high barrier to decomposition results in formation of internally excited polyether molecules that may then undergo subsequent fragmentation by skeletal cleavages. Moreover, complexes involving multiple hydrogen bonds may have slower dissociation kinetics, allowing competition from fast dissociation processes that have substantial energy barriers.

Electrospray ionization mass spectrometry with in-source collision-induced dissociation of monensin factors and related metabolites

“…Several recent studies utilizing tandem quadrupole and quadrupolar ion trap mass spectrometry have investigated various crown and acyclic ethers as model host compounds and have described extensively the interactions of these factors in gas phase polyether/ammonium ion com- plexes. [25][26][27] These researchers consistently report effective hydrogen-bonding between ammonium ions and the polyether host oxygens as comprising the predominant binding interactions in the complexes investigated. Polyether molecules offering numerous sites for complexation of ammonium ions by multiple hydrogen-bonding interactions indicated the formation of strongly bound, internally excited complexes that offered high energy barriers to decomposition, thus resulting in the observed skeletal covalent bond cleavages.…”

Solution vs. gas phase relative stability of the choline/acetylcholine cavitand complexes

“…On the other hand, mass spectrometry has been shown to be a reliable tool for the exploration of host-guest systems 8,[27][28][29][30] and the determination of thermochemical data. 8,[31][32][33][34] For instance the preferential capture of the acetylcholine ions by a 3iPO phosphonate cavitand (see Fig. 1) has been recently observed by Electrospray Mass Spectrometry (ESI-MS) and corroborated by NMR experiments.…”

Molecular recognition and supramolecular chemistry in the gas phase

“…The formation of multiple hydrogen bonds between NH 4 þ and crown ethers provides binding energies large enough for a skeletal cleavage of the host to compete to some extent with ligand loss (Liou et al, 1994). In collision-induced dissociation (CID) experiments, the fragmentation pathways of such complexes were studied at different collision energies (Maleknia & Brodbelt, 1993).…”