Do proteins denature during droplet evolution in electrospray ionization?

The experiments described in this paper were designed to address the question of whether proteins undergo denaturation on the millisecond timescale of the phase transition in electrospray ionization. The experiments show that it is relatively difficult to induce a change in charge in selected proteins by the application of heat to electrosprayed droplets during their transfer from atmospheric pressure to the vacuum of the mass spectrometer. These findings indicate that the net heat transfer to the droplets is insufficient for denaturation given the short lifetime of the droplets in the heated tube (0.6 ms or less) and provide a partial explanation as to why the charge distribution characteristic of a protein in equilibrium in solution is to some extent preserved into the gas phase. Our findings lead us to suggest general guidelines for improving the information about solution protein conformation and non-covalent associations obtained by electrospray ionization mass spectrometric measurements.