Mechanism of Ionization in Matrix-Mechanism of Ionization in Matrix-Assisted Laser Desorption Ionization Assisted Laser Desorption Ionization

(MALDI):(MALDI):How does proton transfer occurHow does proton transfer occurAjax Group

http://pslc.ws/mactest/maldi.htm

Joshua P. Layfield Jordan C. VincentDesiree M. Bates Ashley K. Tucker

Sara E. Ray Ron C. Estler

MALDI OverviewMALDI Overview•MALDI is a soft ionization technique that has revolutionized high-molecular weight mass spectrometry •Technique used to measure the molecular weights of a number of systems

•Proteins•Polysaccharides •Glyco-lipids•Synthetic Polymers

•Nobel Prize Awarded to Fenn and Tanaka in 2002 for the development of soft ionization techniques

http://www.magnet.fsu.edu/education/tutorials/tools/ionization_maldi.html

AdvantagesAdvantages Used for Disease Used for Disease

DiagnosisDiagnosis Able to Ionize Large Able to Ionize Large

moleculesmolecules Accurate / Rapid Accurate / Rapid

AnalysisAnalysis Fast TechniqueFast Technique

MALDI OverviewMALDI OverviewDisadvantagesDisadvantages

Lack of ReproducibilityLack of Reproducibility– Sample Hot SpotsSample Hot Spots

Lack of proper Matrix Lack of proper Matrix MoleculesMolecules

Poor Fundamental Poor Fundamental Understanding of the Understanding of the MechanismMechanism

Lack of Rational Lack of Rational DesignDesign

Cluster IonizationCluster Ionization– Ionization occurs after desorption Ionization occurs after desorption

from the matrix from the matrix – Proton transfer occurs in the gas-Proton transfer occurs in the gas-

phase or in small matrix clustersphase or in small matrix clusters

Proposed MechanismsProposed Mechanisms

PhotoionzationPhotoionzation– Multiple matrix molecule photon Multiple matrix molecule photon

absorptionabsorption– Energy transferred to the analyte in Energy transferred to the analyte in

the solid-phase or the gas-phasethe solid-phase or the gas-phase

Proposed MechanismsProposed Mechanisms

MethodsMethods Run a MD canonical Run a MD canonical

simulation (CHARMM) to simulation (CHARMM) to determine the general determine the general structure of the matrix structure of the matrix protein interactionsprotein interactions

Optimize the structures of Optimize the structures of potentially relevant potentially relevant matrix/analyte matrix/analyte conformations using conformations using electronic structure theoryelectronic structure theory

Study the energetics of the Study the energetics of the proton transfer reactions proton transfer reactions using intrinsic-reaction-using intrinsic-reaction-coordinate electronic coordinate electronic structure studies for a test structure studies for a test set of amino acid/benzoic set of amino acid/benzoic acid derivativesacid derivatives

MethodsMethods

Future ChallengesFuture Challenges Move beyond pure molecular mechanicsMove beyond pure molecular mechanics Investigate other possibilities for matrix Investigate other possibilities for matrix

moleculesmolecules Move beyond the gas phase for the MD Move beyond the gas phase for the MD

simulationssimulations Testing new matrix molecules for Testing new matrix molecules for

predictive recommendations to predictive recommendations to experimentalists experimentalists

Special Thanks…Special Thanks…