Studying biological coordination chemistry: a useful role for low latency, energy-dispersive photon counting XRF detectors
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Date
2016-02-04
Journal Title
Journal ISSN
Volume Title
Publisher
Australian Microscopy and Microanalysis Society
Abstract
Day to day cellular function is fundamentally dependent on electron transfer reactions mediated by transition metals, often iron and/or copper. The
biological consequences of this metal-catalysed redox chemistry arise from biochemical context generated via the multi-scale organisation of
biological systems, i.e. the local concentration of metal → the nature of the donor atoms and bonding environment within the ligand → the location
and abundance of the ligand within the cell → the suite of metal-ligand complexes comprising a cell’s metallome → the differences between one
cell’s instance of it’s metallome compared to another within and between tissues. Biochemical insight must be anchored to the structural biology of
the cell. In this view, understanding metallobiology requires us to interrogate the coordination environment of biological metal-ligand complexes in
situ, and the lack of suitable probes limits our appreciation for the role metallobiology plays in health and disease. Ideally, such probes must exhibit
extremely high specificity, sensitivity, and spatial resolution; requirements met by scanning X-ray fluorescence microscopy (XFM) and X-ray Emission
Near Edge Structure (XENES).
Advances in energy-dispersive detector technology have enormously enhanced the efficiency and speed of data acquisition when performing XFM
and XENES measurements. When using the Maia detector system installed at the Australian Synchrotron XFM beamline the distribution of
biometals can be mapped at rates in excess of 3 M pix / hr. This speed reduces imaging dose whilst maintaining counting statistics. Exploiting these
technical advances we have undertaken a multi-pronged assault on characterising elemental distribution and speciation in a variety of whole-
organism biological systems, including Caenorhabditis elegans and Drosophila melanogaster. We have utilised projective elemental mapping and 3D visualisations of elemental distributions to assess the distribution of chemical speciation through XENES imaging and tomography. The
complementarity of these studies demonstrates that volumetric chemical speciation is achievable with the right instrumentation and approach to
measurement but projective imaging can still provide a window into fundamental biological processes. Opportunities and challenges associated
with visualizing in situ biometal speciation will be discussed.
Description
Keywords
Chemistry, Photons, Metals, Iron, Copper, Redox reactions, Ligands, Bonding, Fluorescence spectroscopy, Tomography
Citation
James, S., de Jonge, M., McColl, G., Burke, R., Paterson, D., Howard, D., & Hare, D. (2016). Studying biological coordination chemistry: a useful role for low latency, energy-dispersive photon counting XRF detectors. Paper presented to ACMM24 : Australian Conference on Microscopy and Analysis : Melbourne Convention and Exhibition Centre, 31 Jan-4 Feb 2016. (pp. 29-30).