Structures and Binding Energies of Noncovalent Complexes of Peptidomimetic Protonated Nitrogen Bases with 18-Crown-6

摘要

Protein structure is one of the keys to understanding function or malfunction in biological systems at the molecular level. Methods using agents that selectively bind to peptides and proteins through complexation enable rapid identification and characterization of protein sequence, structure, and function. For example, selective noncovalent adduct protein probing (SNAPP) utilizes noncovalent recognition of basic amino acid residues, and in particular lysine residues, by 18C6 to monitor changes in protein structure. In this study, absolute 18C6 affinities of six model protonated bases are determined by guided ion beam tandem mass spectrometry. The model bases examined in the present study include: imidazole (IMID), 4-methylimidazole (4MeIMID), n-butylamine (NBA), 1,5-diamino pentane (DAP), isopropylamine (IPA) and methylguanidine (MGD). The kinetic-energy-dependent cross sections for collision-induced dissociation (CID) of six (18C6)H~(+)(B) complexes are analyzed using an empirical threshold law to extract absolute 0 and 298 K bond dissociation energies (BDEs) after accounting for the effects of multiple collisions, kinetic and internal energy distributions of the reactants, and unimolecular dissociation lifetimes.