Search

The obligate human pathogen Haemophilus influenzae utilizes a siderophore-independent (free) [Fe.sup.3+] transport system to obtain this essential element from the host iron-binding protein transferrin. The hFbpABC transporter is a binding protein-dependent ABC transporter that functions to shuttle (free) [Fe.sup.3+] through the periplasm and across the inner membrane of H. influenzae. This investigation focuses on the structure and function of the bFbpB membrane permease component of the transporter, a protein that has eluded prior characterization. Based on multiple-sequence alignments between permease orthologs, a series of site-directed mutations targeted at residues within the two conserved permease motifs were generated. The hFbpABC transporter was expressed in a siderophore-deficient Escherichia coli background, and effects of mutations were analyzed using growth rescue and radiolabeled [sup.55][Fe.sup.3+] transport assays. Results demonstrate that mutation of the invariant glycine (G418A) within motif 2 led to attenuated transport activity, while mutation of the invariant glycine (G155A/V/E) within motif 1 had no discernible effect on activity. Individual mutations of well-conserved leucines (L154D and LAI7D) led to attenuated and null transport activities, respectively. As a complement to site-directed methods, a mutant screen based on resistance to the toxic iron analog gallium, an bFbpABC inhibitor, was devised. The screen led to the identification of several significant hFbpB mutations; V497I, I174F, and $475I led to null transport activities, while S146Y resulted in attenuated activity. Significant residues were mapped to a topological model of the hFbpB permease, and the implications of mutations are discussed in light of structural and functional data from related ABC transporters.

A study was conducted to investigate the iron release process from various forms of holo-ferric binding protein (FbpA), Fe(sub 3+)-FbpA-X, during the course of a chelator competition reaction using EDTA and Tiron. The results reaffirm the contribution of the synergistic anion to the FbpA iron transport process as the anion, in addition to playing a facilitative role in iron binding, and further establishes the synergistic anions as crucial players in periplasmic Fe(super 3+) transport in gram-negative bacteria.

Manganese/ligand association dynamics are studied using a series of structurally related anionic phosphorous ester ligand probes. It is revealed that probe/water solvent interactions must be significantly weakened in order to form the outer-sphere complex that leads to ligand substitution.

Spectrophotometry, potentiometry, and cyclic voltammetry are used to characterize the aqueous chelation equilibria and solution coordination chemistry of iron with exochelin MS. The exochelin MS is a hexadentate trihydroxamate siderophore.

Ionophore-siderophore host-guest assemblies composed of 18-crown-6 and ferrioxamine B,benzo-18-crown-6 and ferrioxamine B and cis-syn-cis-dicyclohexno-18-crown-6 and ferrioxamine B are successfully crystallized. These structures are determined by single-crystal x-ray diffraction.

The combination of experimental and theoretical methods, allowed unraveling the magnetic properties of the novel cationic tungsten(IV) complexes in solid state and in solution. The presented methodology provides strong guidelines for future studies in the field of solution and solid-state magnetochemistry.

The Fe(III) chelation chemistry of exochelin MN was explored in aqueous solution. The thermodynamic and the spectroscopic properties of the Fe(III)-complexes were unique as the coordination of Fe(III) by ExoMN involved a rare beta-hydroxyhistidine moiety.

Research has been conducted on saccharide-based ferrichrome analogue. The coordination chemistry of this analogue has been investigated, and the results are reported.

Research has been conducted on the L-lysinehydroxamic acid. The iron(III) coordination chemistry of this acid, kinetics, thermodynamics and chelation/dechelation process mechanisms have been investigated and the details are reported.

Research has been conducted on the saccharide-based enterobactin analogues. The synthesis of these analogues has been carried out and their pK (sub)a values, Fe(III) binding constants and aqueous solution speciation determined by the spectrophotometric and potentiometric titration techniques have been investigated and reported.

Research has been conducted on the methyl phosphite and methylethyl phosphate. Results indicate that these compounds may be used as probes of the paramagnetic metal ion reactivities toward the inner shell coordination exchange without the studies of the variable temperatures.

Research has been conducted on the host-guest supramolecular assembly formation constants which involve siderophore ferrioxamine B second-sphere complexation caused by the lariat ether carboxylic acid host in wet chloroform. Results indicate that these constants have been obtained from the liquid-liquid extractions at pH values.

Research has been conducted on the reaction of ferrioxamine B with 1,10-phenanthroline. The results of the spectrophotometric measurement of this reaction demonstrate that it gives a ternary intermediate complex in the aqueous solutions including M sodium dodecyl sulfate.

Results describe the effects of chloride, bromide, and nitrate ions on the ligand dissociation kinetics of tetradentate and bidentate (hydroxamato)iron(III) complexes. Data reveal a marked rate enhancement with chloride ion at relatively low concentrations with the effects of bromide and nitrate being lot slower.

Electron mass spectrometric analyses of solution of dihydroxamate siderophore alcaligin and thodotorulic acid complexes and synthetic dihydroxamic acids reveal that the ligands contain multiple tris- and bis-chelated mono- and di-Fe(III) species. Data suggest that the relative concentration of the components is dependent on pH and Fe/L ratio.

Linear synthetic dihydroxamic acids ([CH3N(OH)C=O)}(sub 2)(CH2)(sub n), H2L(super n)) with short (n= 2) and long (n = 8) hydrocarbon-connecting chains form mono- and dinuclear complexes with Fe(III) in aqueous solution. The existence of multiple pathways and the additional liability that they afford the dissociating Fe(II), may play a major role in dihydroxamate siderophore mediation of Fe bioavailability and may be a rationale for their biosynthesis, despite the higher environmental ligand concentrations required for complete Fe(III) chelation relative to their hexadentate counterparts.

Thermodynamic parameters (DELTAH, DELTAS, and DELTAG) were determined by microcalorimetry for second-sphere host-guest complexation between ferrioxamine B and various cyclic ethers in chloroform. Trends in DELTAH and DELTAS with changes in host and guest structure are attributed to host-guest complex formation, as solvation effects were determined to be insignificant (DELTAC(sub p) = 0).