Adduct formation and energy redistribution in UV and IR matrix-assisted laser desorption ionization

摘要

Abstract: Molecular dynamics calculations were carried out to follow the first 100 ps of the plume formation in matrix-assisted laser desorption ionization (MALDI). Two specific issues were addressed: the desorption of guest species in the form of matrix adducts and some distinctive features of infrared (IR) MALDI. Co-desorption of guest and matrix ions in the form of an adduct was studied using positive substance P ions surrounded by sinapinic acid anions. Upon laser heating the surface layers of the matrix underwent phase transition and the adduct was transferred into the gas phase without decomposition. IR-MALDI was studied using succinic acid as a matrix in combination with triglycine guest molecules. The IR laser induced desorption process was modeled by coupling the succinic acid O-H bond to an external 900 K heat bath. The energy redistribution within the matrix molecules themselves and the transfer between the matrix and guest molecules resulted in an increase of the system temperature. The kinetic temperature of the matrix reached plateau at approximately 670 K within a few ps. The temperature of the guest molecule increased on a slower time scale and during the calculation the values remained several hundred K below the O-H vibrational temperature. The liftoff velocity of the guest species (approximately 300 m/s) was similar to the values obtained in our previous calculations for different matrices and excitation methods. !19