pH dependency of photolabile protection groups used for applications in dynamic structural biology

Photolabile protection groups (PPGs) are important tools in biophysical experiments and allow light-induced spatial and temporal control of compound release. Photocaged substrates are recently driving new experiments in dynamic structural biology, in particular time-resolved serial crystallography (TR-SX) at XFELs and synchrotrons. PPGs are seldom characterized in aqueous conditions, despite their application in biological experiments. Several common PPGs exhibit a strong pH dependency of their absorption spectrum and extinction coefficient, which needs to be considered in experimental planning. We report here the static pH dependent photophysical properties (key absorption bands and corresponding extinction coefficients) of four common PPGs as initial guide for planning time-resolved experiments in dynamic structural biology.