Abstract: Tt was found that N-diisopropyloxyphosphoryl alanine (DIPP-Ala) could form adduct with hen egg white lysozyme (HEWL) as shown in electrospray ionization mass spectroscopy (ESI-MS), but the non-phosphorylated alanine couldn’t. The capability for formation of DIPP-Ala dimmer was more stronger than that of alanine. It suggested that a specific non-covalent complex was formed in the solution phase and could be transferred to the gas phase via electrospray ionization (ESI). The results implied that phosphorylated alanine possessed relatively stronger affinities for protein and formed non-covalent complexes with protein more easily than alanine. Using Tripos force field, molecular mechanics calculation on DIPP-Ala dimmer showed that such non-covalent adduct formation was due to the inter-molecular hydrogen bond.

Key words: ESI-MS, Intermolecular hydrogen bond, Molecular dynamic simulation