Direct Extraction and Ionization of Intact Proteins from Aqueous Environment Using Desorption by Impulsive Vibrational Excitation.

The molecular analysis of proteins and their complexes directly from aqueous environment using mass spectrometry (MS) remains a significant challenge. Here, we demonstrate the direct extraction and ionization of intact proteins (ubiquitin and the tetrameric beta-galactosidase complex) from pure aqueous environment using Ionization via Desorption by Impulsive Vibrational Excitation (I-DIVE). We show that this process, when coupled directly to MS, produces intact gas-phase ions of proteins with charge states beyond the lower limit of native electrospray ionization MS. We propose a new mechanism for charge state formation under aqueous conditions via laser-induced proton liberation. Driven by the transient superheating and heat-induced proton release of water, this mechanism exploits the temperature pH dependence of water as a source of protonation for gas-phase detection and characterization of biological macromolecules and their assemblies.