Photodissociation of Non-Covalent Peptide-Crown Ether Complexes

Highly chromogenic 18-crown-6-dipyrrolylquinoxaline coordinates primary amines of peptides, forming non-covalent complexes that can be transferred to the gas-phase by electrospray ionization. The appended chromogenic crown ether facilitates efficient energy transfer to the peptide upon ultraviolet irradiation in the gas phase, resulting in diagnostic peptide fragmentation. Collisional-activated dissociation and infrared multiphoton dissociation of these non-covalent complexes result only in their disassembly with the charge retained on either the peptide or crown ether, yielding no sequence ions. Upon UV photon absorption the intermolecular energy transfer is facilitated by the fast activation timescale of ultraviolet photodissociation (<10 ns) and by the collectively strong hydrogen bonding between the crown ether and peptide, thus allowing effective transfer of energy to the peptide moiety before disruption of the intermolecular hydrogen bonds

Synthetic ditopic receptors

A small. but emerging field of topical interest in supramolecular chemistry is ion-pair recognition, in which a host simultaneously binds both cationic and anionic guests. Details of these receptors. which combine, for example, crown ethers and calixarenes for cation complexation, with Lewis acid centers, pyrroles, amides or urea groups for anion recognition, will be discussed. The predicate of this approach, successfully achieved in certain instances, is that the binding of one guest ion can induce electrostatic and conformational changes in the host, thereby enhancing the complexation of the counter ion