title: Ferric stability constants of representative marine siderophores: marinobactins, aquachelins, and petrobactin.
abstract: 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(III)-petrobactin is estimated to be about 43. The pK(a) of the beta-hydroxyaspartyl hydroxyl group was determined to be 10.8 by (1)H NMR titration. (13)C NMR and IR spectroscopy were used to investigate Ga(III) coordination to the marinobactins. The coordination-induced shifts (CIS) in the (13)C 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 beta-hydroxyamide group suggests this moiety is not coordinated in the Ga(III) complex. Differences in the IR spectrum of Ga(III)-marinobactin-C and Fe(III)-marinobactin-C in the 1600-1700 cm(-1) region also corroborates Fe(III) is coordinated to the beta-hydroxyamide moiety, whereas Ga(III) is not coordinated.
authors.affiliation: Department of Chemistry and Biochemistry, University of California Santa Barbara, California 93106-9510, USA.
authors.forename: Guangping
authors.initials: G
authors.lastname: Zhang
authors.forename: Shady A
authors.initials: SA
authors.lastname: Amin
authors.forename: Frithjof C
authors.initials: FC
authors.lastname: Küpper
authors.forename: Pamela D
authors.initials: PD
authors.lastname: Holt
authors.forename: Carl J
authors.initials: CJ
authors.lastname: Carrano
authors.forename: Alison
authors.initials: A
authors.lastname: Butler
mesh_terms: D001549:Benzamides / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D009842:Oligopeptides / Q000737:chemistry*; D010169:Palmitic Acids / Q000737:chemistry*; D017262:Siderophores / Q000737:chemistry*
chemical_list: D001549:Benzamides; D005290:Ferric Compounds; D009842:Oligopeptides; D010169:Palmitic Acids; D017262:Siderophores; C547048:aquachelin-C; C521124:marinobactin E; C450699:petrobactin