Rapid peptide fragmentation without electrons, collisions, infrared radiation, or native chromophores

Ultraviolet photodissociation of peptides followed by mass analysis has several desirable advantages relative to other methods, yet it has not found widespread use due to several limitations. One shortcoming is the inefficiency with which peptides absorb in the ultraviolet. This issue has a simple solution and can be circumvented by the attachment of noncovalent adducts that contain appropriate chromophores. Subsequent photoactivation of the chromophore leads to vibrational excitation of the complex and eventually to fragmentation of the peptide. Herein, the energetics that control the efficiency of this process are examined as a function of the characteristics of both the peptide and the noncovalently attached chromophore. Fragmentation efficiency decreases with increasing peptide size and is also constrained by the binding energy of the noncovalent adduct. The optimum chromophore should have excellent absorption at the excitation wavelength and a low luminescence quantum yield. It is demonstrated that a naphthyl based 18-crown-6 adduct is ideally suited for attaching to a variety peptides and fragmenting them following absorption of 266 nm light. Potential applications and limitations of this methodology are discussed.