Applications of "Tender" Energy (1-5 keV) X-ray Absorption Spectroscopy in Life Sciences.

The "tender" energy range of 1 to 5 keV, between the energy ranges of most "hard" (>5 keV) and "soft" (<1 keV) synchrotron X-ray facilities, offers some unique opportunities for synchrotron- based X-ray absorption fine structure spectroscopy in life sciences. In particular the K absorption edges of Na through Ca offer opportunities to study local structure, speciation, and chemistry of many important biological compounds, structures and processes. This is an area of largely untapped science, in part due to a scarcity of optimized facilities. Such measurements also entail unique experimental challenges. This brief review describes the technique, its experimental challenges, recent progress in development of microbeam measurement capabilities, and several highlights illustrating applications in life sciences.