Photolysis of the peptide bond at 193 and 222 nm

Ultraviolet (UV) light is a well-established tool for fragmenting peptides in vacuum. This study investigates the fragmentation of peptides using 193 and 222 nm light in aqueous solution. Changes in the absorption spectra of solutions of the model dipeptide glycylglycine are monitored using a combination of real-time in situ transmission measurements and UV-Vis spectroscopy to report peptide bond scission following UV irradiation. Irradiation by a broadband ultraviolet light source flattens the absorbance peak centered near 193 nm, indicating cleavage of peptide bonds. Irradiation with low-intensity, monochromatic 193 and 222 nm light enabled measurements of the single-photon quantum yield of peptide bond scission, found to be (1.50 ± 0.12)% at 193 nm and (0.16 ± 0.03)% at 222 nm. These findings indicate that peptides may be fragmented in solution prior to emission into a mass spectrometer for new types of single-molecule analyses. The susceptibility of peptide bonds to ultraviolet radiation also suggests limited lifetimes for peptides on the early Earth's surface, which are relevant to theories of the origins-of-life, and suggests a role for protein damage in explanations of the germicidal effect of 222 nm light exposure.