Protonated clusters of ammonia and adipic acid were initially generated using the LTQ system. It was quickly noted that protonated adipic acid and its water-loss product are readily generated as well, as shown in Figure . Isolation of the protonated ammonia-adipic acid cluster yielded a substantial fraction of protonated adipic acid, and CID of the cluster produced a 1:1 yield of protonated adipic acid. Under ordinary solution-phase conditions, the pKa to add an additional proton to fully protonated adipic acid is expected to be significantly lower than the pKa of ammonia. The generated protonated adipic acid suggests that, in the cluster configuration, adipic acid serves as a better base than ammonia. We hypothesized that this is due to a confinement effect affecting the relative acidity of the protonated site. Similar deprotonated dicarboxylic acid anions have been shown to form ring structures featuring a shared proton linking the two carboxylate moities, and we proposed a similar structure in which an ammonium or proton is shared between the carbonyls of the two protonated carboxylic acid groups.