title: Ti(IV) and the Siderophore Desferrioxamine B: A Tight Complex Has Biological and Environmental Implications.
abstract: The siderophore desferrioxamine B (DFOB) binds Ti(IV) tightly and precludes its hydrolytic precipitation under biologically and environmentally relevant conditions. This interaction of DFOB with Ti(IV) is investigated by using spectro-potentiometric and spectro-photometric titrations, mass spectrometry, isothermal titration calorimetry (ITC), and computational modeling. The data from pH 2-10 suggest two one-proton equilibria among three species, with one species predominating below pH 3.5, a second from pH 3.5 to 8, and a third above pH 8. The latter species is prone to slow hydrolytic precipitation. Electrospray mass spectrometry allowed the detection of [Ti(IV) (HDFOB)]2+and [Ti(DFOB)]+; these species were assigned as the pH < 3.5 and the 3.5 < pH < 8 species, respectively. The stability constant for Ti(IV)-DFOB was determined by using UV/vis-monitored competition with ethylenediaminetetraacetic acid (EDTA). Taking into consideration the available binding constant of Ti(IV) and EDTA, the data reveal values of log β111= 41.7, log β110= 38.1, and log β11-1= 30.1. The former value was supported by ITC, with the transfer of Ti(IV) from EDTA to DFOB determined to be both enthalpically and entropically favorable. Computational methods yielded a model of Ti-DFOB. The physiological and environmental implications of this tight interaction and the potential role of DFOB in solubilizing Ti(IV) are discussed.
authors.affiliation: Department of Chemistry, Temple University , Philadelphia, Pennsylvania 19122-6081, United States.
authors.forename: Kayleigh E
authors.initials: KE
authors.lastname: Jones
authors.affiliation: Department of Chemistry, Yale University , New Haven, Connecticut 06520-8107, United States.
authors.forename: Kathleen L
authors.initials: KL
authors.lastname: Batchler
authors.affiliation: Department of Chemistry, Temple University , Philadelphia, Pennsylvania 19122-6081, United States.
authors.forename: Célia
authors.initials: C
authors.lastname: Zalouk
authors.affiliation: Department of Chemistry, Temple University , Philadelphia, Pennsylvania 19122-6081, United States.
authors.forename: Ann M
authors.identifier: http://orcid.org/0000-0002-5943-5493
authors.initials: AM
authors.lastname: Valentine
mesh_terms: D003676:Deferoxamine / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D011789:Quantum Theory; D017262:Siderophores / Q000737:chemistry*; D014025:Titanium / Q000737:chemistry*
chemical_list: D017262:Siderophores; D014025:Titanium; D003676:Deferoxamine