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Most bacteria require iron to grow, yet soluble forms of iron are largely not available to microbes due to a combination of low solubility of ferric ion in the environment and sequestration in proteins and enzymes in living organisms. Microbes therefore compete for iron in various ways, including by production of siderophores, which are ligands with a high affinity for ferric ion and which facilitate transport of Fe(III) into and within bacteria. This review summarizes our work on the classes of siderophores isolated from open ocean isolates, including suites of amphiphilic siderophores that vary in the nature of the fatty acid appendages, photoreactive Fe(III)-siderophore complexes as a result of coordination to -hydroxy carboxylic acid groups, and a new series of tris catechol siderophores.
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This content will become publicly available on September 19, 2026
Coordination Chemistry of an Emerging Group of Diazeniumdiolate Siderophores: Crystal Structures of M(III)-Gramibactin (M= Fe and Ga)
To overcome iron starvation, microorganisms often produce siderophores—chelators with high affinity and selectivity for Fe(III). The recent discovery of the siderophore gramibactin garnered significant interest, as it added the C-diazeniumdiolate as a new Fe(III)-binding group in siderophores. Gramibactin is a mixed ligand siderophore, comprised of two graminine residues harboring the diazeniumdiolate donors and a β-hydroxy-aspartate donor. Diazeniumdiolate siderophores have so far evaded crystallographic characterization and few structures of synthetic diazeniumdiolate complexes are reported. To address the gap in structural information, the complexes K[M(III)-gramibactin] (M= Fe and Ga) were prepared, crystallized and their structures solved by X-ray diffraction (XRD). The four Fe-O bond lengths in the two diazeniumdiolates are quite similar, ranging from 1.978 Å to 2.059 Å, indicating an equal contribution in bonding. In contrast, the differing Fe-O bond lengths in β-hydroxy-aspartate reflect the relative donor strengths of the carboxylate (1.997 Å) and alkoxide (1.902 Å) groups. Gramibactin coordinates Fe(III) in a Δ-configured distorted octahedral geometry. The diamagnetic nature of Ga(III) is often leveraged in NMR studies to infer the solution structure of the corresponding Fe(III)-siderophores, which are assumed to be identical. The structural similarity of Ga(III)- and Fe(III)-gramibactin is striking and represents the first crystallographic verification of the assumed isostructural relationship between a Ga(III)- and an Fe(III)-siderophore. By providing concrete evidence, this study promotes Ga(III) as a reliable proxy for Fe(III) in siderophore complexes, with implications for solution structure determination of siderophores and design of Ga(III)-siderophore-based theranostics.
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- Award ID(s):
- 2108596
- PAR ID:
- 10643676
- Publisher / Repository:
- ACS
- Date Published:
- Journal Name:
- Journal of the American Chemical Society
- Volume:
- 147
- Issue:
- 39
- ISSN:
- 0002-7863
- Page Range / eLocation ID:
- 36007 to 36015
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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