Synchrotron-Based X-Ray Spectroscopy Techniques Enable Exploration of Metal Interactions in Biological and Biogeochemical Systems. Top and Bottom Left: Understanding the structure of the copper-dependent integral membrane metalloenzyme in methanotrophic bacteria that converts methane to methanol. Top right: Extended X-ray absorption fine structure (EXAFS) reveals the structure of the active site of a nitrogenase enzyme that converts dinitrogen (N2) to bioavailable ammonia (NH3), which is a fundamental step in the biogeochemical nitrogen cycle. Bottom right: Geogenic CO2 exhalations are excellent natural laboratories for studying the behavior of copper in soil. The natural gradients found in redox conditions and in soil organic matter enable interacting processes to be disentangled. [All images copyrighted. See credit information at bottom of page.]
Synchrotron-based X-ray spectroscopy techniques provide a powerful and synergistic toolkit to explore metal interactions within biological and biogeochemical systems and with the environment. These interactions can be observed on molecular scales to genomics-controlled mesoscales and include local environmental phenomena such as elemental uptake, catalytic behavior, storage, and bioavailability. The synchrotron-based X-ray spectroscopy suite encompasses standard and high-resolution X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES), extended X-ray absorption fine structure (EXAFS), and resonant inelastic X-ray scattering (RIXS).
Synchrotron-based X-ray spectroscopy techniques can probe how metalloproteins enable catalytic reactions like CO2 reduction and methane formation and how trace elements are involved in metabolism. They can also shed light on molecular transformations occurring in biogeochemical systems and processes by answering questions such as how the redox state and bonding description of a particular element evolve under various conditions and over time.
Instruments can be tuned to a specific element, providing complementary geometric and electronic structure information about the element and its nearest neighbors. The ability to probe one or more element independently under a variety of sample conditions allows detailed characterization of the chemistry in complex multifaceted systems. U.S. Department of Energy X-ray spectroscopy facilities can probe phosphorus through higher-atomic-number elements and enable structural dynamics studies on time scales into the sub-millisecond regime.
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Row 1, Image 1: Reprinted with permission from Elsevier from Sirajuddin, S., et al. 2014. "Effects of Zinc on Particulate Methane Monooxygenase Activity and Structure," Journal of Biological Chemistry 289, 21782–794. DOI: 10.1074/jbc.M114.581363. Copyright 2014.
Row 1, Image 2: Reprinted with permission from Elsevier from Flores, R. M. 2014. “Chapter 3 - Origin of Coal as Gas Source and Reservoir Rocks,” In Coal and Coalbed Gas, 97-165. Ed. R.M. Fores, Elsevier. ISBN: 9780123969729, DOI: 10.1016/B978-0-12-396972-9.00003-3.
Row 1, Image 3: Reprinted with permission from Van Stappen, C., et al. 2019. "Spectroscopic Description of the E1 State of Mo Nitrogenase Based on Mo and Fe X-ray Absorption and Mössbauer Studies," Inorganic Chemistry 58, 12365. DOI: 10.1021/acs.inorgchem.9b01951. Further permissions related to the material excerpted should be directed to the American Chemical Society.
Row 2, Image 1 and 2: Reprinted with permission from Elsevier.from Ro, S. Y., et al. 2018. "From Micelles to Bicelles: Effect of the Membrane on Particulate Methane Monooxygenase Activity," Journal of Biological Chemistry 293, 10457. DOI: 10.1074/jbc.RA118.003348.
Row 2, Image 3: Reprinted with permission from Mehlhorn, J., et al. 2018. "Copper Mobilization and Immobilization along an Organic Matter and Redox Gradient—Insights from a Mofette Site," Environ. Sci. Technol. 52, 13698. DOI: 10.1021/acs.est.8b02668. Copyright 2018 American Chemical Society.
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