The kinetics of attachment of hydroiodic acid to gaseous protonated bradykinin, des-Arg(1)-bradykinin, des-Arg(9)-bradykinin, and their respective methyl esters are reported. Rate constants range from 9.3 x 10(-11) cm(3)-s(-1) for attachment of hydroiodic acid to the (M + H)(+) ion of bradykinin to much less than 3 x 10(-12) cm(3)-s(-1) for a slow-reacting component of a population of (M + H)(+) ions derived from des-Arg(9)-bradykinin. In the cases of the (M + 2H)(2+) ions from bradyErinin and the (M + H)(+) ions from des-Arg(9)-bradykinin, the rate data could not be fit with a single rate constant, indicating the presence of at least two non-interconverting ion populations. For the (M + 2H)(2+) ions, it was demonstrated that the two reacting structures could be induced to interconvert upon gentle activation. The attachment sites are the most basic neutral sites of the molecule, viz., arginine and the N-terminus in the case of bradykinin and its analogues. A simple picture is proposed to estimate the rate constant for hydroiodic acid attachment to a fully exposed neutral basic site. The picture is based upon the assumption that a significant degree of proton transfer from hydroiodic acid to the attachment site occurs and therefore estimates that the capture radius is the distance at which the endoergicity of the proton-transfer reaction is just compensated for by the Coulomb attraction of the ion pair. Storage of the ions in the presence of deuterioiodic acid (DI) showed evidence for hydrogen/deuterium exchange. Two competing mechanisms can lead to H/D exchange, one of which involves initial DI attachment to a neutral basic site. However, experimental evidence suggests that the gas phase H/D exchange reactions result primarily from a "relay-type" mechanism proposed for similar systems reacting with D2O. These results provide important new information to facilitate the use of hydroiodic acid attachment kinetics and H/D exchange kinetics using DI as chemical probes of three-dimensional gaseous polypeptide ion structure.