Reactions of angiotensin ions with hydroiodic acid

The kinetics of HI attachment to gaseous angiotensin-related ions were dete rmined in a quadrupole ion trap mass spectrometer. The (M + H)(+) and (M 2H)(2+) ions of peptides with sequences of DRVYIHPFHL, NRVTVHPFHL, and RVYI HPFHL and the (M + H)(+) ions of DRVYIHPF and NRVYVHPF and their respective methyl esters were studied. For many of the ions studied here, multiple re active conformations were resolved by their differing reactivities. The kin etics of the attachment of HI to the singly charged ions are consistent wit h structural models that are generated by molecular mechanics calculations, which suggest a high degree of intraionic interactions between the protona tion site and other basic sites in the ion. The incorporation of HI can als o disrupt the inherent intraionic interactions in the ions, which is not on ly reflected in the reaction kinetics, but also consistent with the interac tions suggested by the molecular mechanics simulations. These results confi rm that HI attachment kinetics can be used as a probe of three dimensional ion structure and provide important new information regarding the utility o f this molecular probe. (Int J Mass Spectrom 202 (2000) 299-313) (C) 2000 E lsevier Science B.V.