LASER ION-BEAM PHOTODISSOCIATION STUDIES OF MODEL AMINO-ACIDS AND PEPTIDES
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abstract
Visible (458-514.5 nm) and UV (333385 nm) photodissociation of the [M + H]+ ions of dinitroDhenyl (DNP) derivatized amino acids and peptides is reported. Photoexcitation of the DNP peptides by a visible photon results in fragmentation of the peptide chain with little fragmentation within the chromophore. Conversely, UV photoexcitation of the DNP peptides results in fragmentation of the chromophore as well as the peptide chain, but loss of NO or NO2 (within the chromophore) often dominates the photofragment ion spectrum. These results are rationalized with particular emphasis on energy-selective dissociation channels of large ionic systems. DNP-leucine and DNP-isoleucine [M + H]+ can be differentiated on the basis of photodissociation reactions which yield distonic radical cations. The rate of dissociation of photoexcited ions of DNP peptides is shown to decrease with increasing molecular weight (degrees of freedom). Lastly, comparisons between photodissociation and collision-induced dissociation as a structural probe are presented. 1989, American Chemical Society. All rights reserved.
