Matrix-Guest Energy Transfer in Matrix-assisted Laser Desorption

Abstract

Molecular dynamics was used to analyze energy transfer rates between matrix and guest molecules in matrix-assisted laser desorption allowing for a large number of internal degrees of freedom. The effect of initial matrix temperature jump on internal energy equilibration times and on guest limiting temperatures has been studied on a model system comprising a pyridine-3-carboxylic acid matrix and leucine enkephalin (Tyr-Gly-Gly-Phe-Leu) guest molecule. It appears that the energy transfer rates between matrix and guest molecules depend on the initial matrix temperature jump. The initial matrix temperature of 900 K leads to incomplete desorption, whereas at 1500 K complete desorption and the formation of an energy-transfer bottleneck was observed. Following the guest center-of-mass at different initial matrix temperatures indicates that in the case of 1500 K and 3000 K the desorption process is complete, whereas at 900 K the guest molecule stays near the matrix surface. In the case of complete desorption deeper embedding of the guest molecules leads to somewhat lower guest limiting temperatures. Uniformly higher limiting temperatures are observed for higher laser irradiance and the increase in burial depth leads to more complete equilibration between the two species. © 1997 John Wiley & Sons, Ltd.