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Title: Probing gas phase biomolecules with femtosecond lasers
Author: Duffy , Martin Joseph
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2013
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The use of intense, femtosecond laser pulses to ionise and f fragment gas phase biomolecules, for mass spectrometry purposes, was investigated. Research into new biomolecule volatilisation techniques is one which has had much recent success with the development of MALDI and ES1. In this thesis, laser Induced Acoustic Desorption (LIAD) was implemented and characterised for its ability to produce cool, neutral bimolecular targets in the gas phase. The standard activation technique (CID) in mass spectrometry often provides incomplete sequence information. Research into activation techniques is aimed at producing more complete sequence information and elucidation of fragmentation mechanisms. Results obtained with 800 nm femtosecond pulses and the peptides Leu-leu-Tyr and Ala-Phe show that a wider range of fragments are formed compared to CID. By using 267 nm pulses, when aromatic amino acids are present, it is seen that parent ion production dramatically increases. N-terminal immonium ions are produced when the charge resides on the nn orbital at the N-terminal. When using 267 nm pulses ionisation is localised at the C-terminus, but still a significant contribution due to the immonium ion was witnessed. This indicates that the charge had migrated to the N-terminal. To study the electronic dynamics further, a pump-probe scheme that uses fragment ratios to track the charge location was implemented. An initial one colour (800 nm) pump-probe experiment on phenylalanine showed no evidence of dynamics within the statistical limits. However, this experiment provides a platform to two colour pump-probe schemes, which promise future success in witnessing charge transfer in a biomolecule.
Supervisor: Not available Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available