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Gas phase H/D exchange kinetics: DI versus D2O.
T G Schaaff1, J L Stephenson, S A McLuckey
1Chemical and Analytical Sciences Division, Oak Ridge National Laboratory, Tennessee 37831-6365, USA.
Journal of the American Society for Mass Spectrometry
|February 26, 2000
Summary
Gas phase H/D exchange reactions reveal two distinct bradykinin ion populations. Deuterium iodide (DI) shows faster exchange than deuterium oxide (D2O) due to acidity and bond length differences.
Area of Science:
- Chemical Kinetics
- Mass Spectrometry
- Gas-Phase Ion Chemistry
Background:
- Bradykinin is a peptide hormone involved in various physiological processes.
- Gas-phase ion-molecule reactions are crucial for understanding peptide structure and reactivity.
- Hydrogen/deuterium (H/D) exchange is a powerful technique for probing ion structures.
Purpose of the Study:
- To investigate the gas-phase H/D exchange reactions of bradykinin (M + 3H)3+ ions.
- To identify and characterize different reactive populations of bradykinin ions.
- To compare the reactivity of deuterium oxide (D2O) and deuterium iodide (DI) as H/D exchange probes.
Main Methods:
- Utilized a quadrupole ion trap mass spectrometer to monitor H/D exchange reactions.
- Employed D2O and DI as chemical probes for H/D exchange with bradykinin ions.
- Analyzed reaction kinetics to determine the presence of distinct ion populations.
Main Results:
- Observed two noninterconverting reactive gas-phase ion populations of bradykinin (M + 3H)3+.
- Found that H/D exchange with DI proceeds faster than with D2O.
- Kinetics support the proposed 'relay mechanism' for gas-phase H/D exchange.
Conclusions:
- Gas-phase bradykinin ions exist in at least two distinct conformational states at room temperature.
- The observed differences in exchange rates are attributed to the gas-phase acidity and bond characteristics of the chemical probes.
- The 'relay mechanism' effectively explains the H/D exchange behavior of protonated peptides.