Mass spectrometry is a powerful tool that has become a popular method for the analysis of biological molecules, such as proteins and sugars. A challenge when dealing with biological molecules is that there can be many gas phase conformations of the same molecule, and these conformations may fragment differently. It can also be difficult to differentiate structural isomers. Ion mobility spectrometry (IMS) utilizes a uniform electric field and a buffer gas to separate ions based on their collisional cross sectional area. This enables the separation of conformations and structural isomers. Ultraviolet (UV) photodissociation can then be used to deposit a large but well-defined amount of energy into these ions, producing informative high-energy photofragments that can be used for elucidating the ion's structure.
A new hybrid instrument consisting of an IMS drift tube, a linear ion trap mass spectrometer, and a 157 nm fluorine (F2) laser was constructed. This instrument was used to probe the gas phase structure of the pentapeptide RVVPV and the b2 ions of several tripeptides (most notably HAP). While these experiments did not reach a definitive conclusion, they illuminated the need for several instrument improvements. These improvements included the need for higher resolving powers and the ability to photodissociate the ions before they enter the linear ion trap. This can be accomplished by interfacing the laser so it is orthogonal to the IMS drift tube.
A fundamental study of the 157 nm photofragmentation of arginine containing dipeptides was performed on a time of flight-time of flight mass spectrometer (TOF-TOF) and on an ion trap mass spectrometer. In addition to the expected a-, d-, x-, and v- type ions, it was found that both the C-terminal and N-terminal arginine dipeptides produced other fragments involving multiple homolytic cleavages. The formulae of a series of high-energy C-terminal arginine dipeptide fragments from 180-200 Da were determined using an accurate internal mass calibration of the TOF-TOF mass spectra. Additionally, it was observed that there is a tendency for amino acid side chains to cleave between their beta and gamma carbons, producing vn+14 and mn+13 ions.
|Advisor:||Reilly, James P.|
|Commitee:||Clemmer, David E.|
|School Location:||United States -- Indiana|
|Source:||MAI 51/03M(E), Masters Abstracts International|
|Subjects:||Molecular biology, Biochemistry|
|Keywords:||Ion mobility spectrometry, Mass spectrometry, Peptides, Photodissociation, Photofragmentation, Proteins|
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