Ferric stability constants of representative marine siderophores: Marinobactins, aquachelins, and petrobactin

Guangping Zhang, Shady A. Amin, Frithjof C. Küpper, Pamela D. Holt, Carl J. Carrano, Allson Butler

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The coordination of iron(III) to the marine amphiphilic marinobactin and aquachelin siderophores, as well as to petrobactin, an unusual 3,4-dihydroxybenzoyl siderophore is reported. Potentiometric titrations were performed on the apo siderophore to determine the ligand pK a values, as well as the complex formed with addition of 1 equiv of Fe(III). The log K ML values for Fe(III)-marinobactin-E and Fe(III)-aquachelin-C are 31.80 and 31.4, respectively, consistent with the similar coordination environment in each complex, while log K ML for Fe(lll)-petrobactin is estimated to be about 43. The pK a of the β-hydroxyaspartyl hydroxyl group was determined to be 10.8 by 1H NMR titration. 13C NMR and IR spectroscopy were used to investigate Ga(III) coordination to the marinobactins. The coordination-induced shifts (CIS) in the 13C NMR spectrum of Ga(III)-marinobactin-C compared to apo-marinobactin-C indicates that the hydroxamate groups are coordinated to Ga(III); however, the lack of CISs for the carbons of the β-hydroxyamide group suggests this moiety is not coordinated in the Ga(III) complex. Differences in the IR spectrum of Ga(lll)-marinobactin-C and Fe(III)-marinobactin-C in the 1600-1700 cm -1 region also corroborates Fe(III) is coordinated to the β-hydroxyamide moiety, whereas Ga(III) is not coordinated.

Original languageEnglish (US)
Pages (from-to)11466-11473
Number of pages8
JournalInorganic Chemistry
Issue number23
StatePublished - 2009

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry


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