Michael Dürr oral presentation (OB4-Fri1-1-1)
H/D exchange in oligopeptides followed in real time by means of cluster induced desorption/ionization mass spectrometry
1 Institute of Applied Physics - Justus Liebig University Giessen, Heinrich-Buff-Ring 16, 35392 Giessen, Germany
2 Bruker Daltonik GmbH, Fahrenheitstr. 4, 28359 Bremen, Germany
In biochemistry, H/D exchange (HDX) is widely used, among others, to probe protein structures and their dynamics. HDX has been successfully analyzed by means of mass spectrometry, however, real-time measurements are difficult to be performed with standard techniques such as ESI or MALDI. Here we use desorption/ionization induced by neutral clusters (DINeC) for real-time monitoring of HDX in oligopeptides which gives full access to the kinetics of the exchange process and the relevant time constants as well as their dependence on the chemical nature of the functional groups involved.
In DINeC, the SO2 clusters impacting on the surface both provide the energy for desorption of the analyte molecules as well as they serve as a transient matrix due to the high dipole moment of SO2. Thus the desorption process takes place at comparably low cluster energies (< 1eV/molecule) and even fragile analytes are desorbed without any fragmentation .
For the HDX experiments, mass spectra of angiotensin II as well as of various porphyrines, which were used as reference systems, were recorded by means of DINeC-MS. Exposure to D2O led to a broadening of the isotopic pattern and a continuous shift towards higher m/z values. Quantitative evaluation of the spectra and their evolution with increasing D2O dose revealed the full exchange kinetics of the deuteration process up to the highest degree of deuteration possible. The results were modeled by means of Monte Carlo simulations. For modeling HDX in angiotensin II, at least three different rate constants were necessary; in comparison with the reference systems, they could be assigned to three different types of functional groups present in angiotensin II.
The results demonstrate localized quantification of exchange rates in the molecule by means of DINeC-MS. As the experiments were performed both with bulk samples as well as for isolated molecules adsorbed on Au surfaces, they furthermore show in more general the capability of DINeC for real-time monitoring of complex surface reactions.
 Gebhardt et al., Angew. Chem. Int. Ed. 48, 4162 (2009); Portz et al., J. Chem. Phys. 146, 134705 (2017).