A review of gas-phase H/D exchange experiments: The protonated arginine dimer and bradykinin nonapeptide systems

Some recent gas-phase H/D exchange experiments are discussed. These experiments are carried out using an electrospray ionization-fast flow tube technique. Some of the goals are: (1) deducing site-specific rate constants; (2) learning about conformers and isomers of biomolecules; (3) understanding H/D exchange mechanisms. The experimental technique, and its advantages and disadvantages are reviewed, by comparison with other methods such as FT-ICR. The different methods of analyzing the data are described including a newly developed algorithm for extracting site-specific rate constants. The examples of bradykinin (singly and doubly protonated) and the proton bound dimer of arginine are discussed in some detail. Both systems are known to exist as gas-phase salt-bridge structures in which two arginines are protonated and a carboxyl group is deprotonated yielding an ion-zwitterion configuration: + - +. Some internal inconsistencies between H/D exchange results for ND3 with the two systems are pointed out. (C) 2004 Elsevier B.V. All rights reserved.