Inorganic elements, including d-block metals and diverse p-block members, are essential catalytic cofactors of fundamental importance in biology. Preference for covalent bonding or the sheer over-abundance of potential ligands in biological fluids ensures these elements are found either bound to or coordinated within biological macromolecules. These elements shape local chemical environment and determine reactivity availability of biometals across cellular environments. Traditionally, characterisation of specific metal-ligand species requires isolation of the complex, necessitating disruption of biological systems despite the attendant risk of mismetallation and loss of biochemical context. Despite the confounding potential of typical preparation methodologies, the tools available to study biological coordination chemistry in situ have remained limited. Explosion of high-energy-resolution fluorescence detection techniques in X-ray spectroscopy coupled with the synergy between synchrotron-based X-ray fluorescence microscopy (XFM) and X-ray absorption near edge structure (XANES) spectroscopy represent powerful analytical approaches for studying bioinorganic chemistry.
Demand to study this suit of elements has encouraged the creation of a new beamline at the Australian Synchrotron. The Medium Energy X-ray Spectroscopy (MEX) beamline will use X-rays in the “medium” energy range of 1.5 to 14 keV to bridge between existing instruments that currently operate at higher, “hard” (>5 keV), lower, "soft" (<2 keV), energy ranges. MEX will offer unique opportunities for synchrotron-based X-ray spectroscopy in the life sciences. In particular access to K-edges of sulphur through selenium offer opportunities to study local structure, speciation, and chemistry of many important biological compounds, structures and processes. Due to a scarcity of optimized facilities many exciting scientific questions remain to be explored in this energy regime. Such measurements also involve unique experimental challenges.
Using examples and highlighting particular techniques this presentation will introduce MEX to the Australian microscopy and microanalysis community with a particular focus on µMEX, MEX's scanning X-ray microprobe.