Following the Ca²⁺ roadmap to photocaged complexes for Zn²⁺ and beyond

The first photocaged complexes appeared in the mid-1980s specifically to complement the ongoing work studying intracellular Ca(2+) signaling with fluorescent probes. Recently, the field of biological inorganic chemistry has focused increasingly on the homeostasis mechanisms and possible signaling functions of transition metal ions like Mn(2+), Fe(2+), Cu(+) and Zn(2+). Development of fluorescent sensors for imaging studies has been a very active area of research; however the corresponding chemical tools for delivering metal ions have received less interest. Using the roadmap provided by Ca(2+) predecessors, we describe how new photocaged complexes are being developed, and highlight some of the obstacles that must be overcome to investigate an emerging area in metal ion biology with different requirements.