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Project: Isolation and Photophysical Characterization of Pyoverdine Compounds from Pseudomonas Bacteria
The pyoverdines will be purified by solid-phase extraction and analyzed by LC/MS, primarily to determine purity and molecular mass. We will then investigate the ground- and excited-state photophysical properties of these pyoverdines, and their complexes with a range of metals including VIII/V, CrIII, MnII/III, FeIII, CoII, and NiII, over a pH range of 4-10. These efforts include measuring excitation and emission spectra of the free pyoverdines, and their 1:1 metal complexes, along with the fluorescence lifetimes, excited-state (transient) absorption spectra, and excited-state quenching by a series of electron transfer quenchers. These data will be used, along with the ground state redox potentials of the pyroverdines and pyroverdine-metal complexes obtained from cyclic and square-wave voltammetry, to obtain excited state redox potentials and map the excited state energy and electron transfer behavior of the complexes. Results from these studies are critical to the incorporation of pyroverdine chelates into a fluorescence-based molecular recognition scheme. Further work will measure the stability constants of the pyoverdine-metal complexes and quantify the accessibility of the metal cation in the metal-pyoverdine complex. This work will involve isolation and purification of the pyoverdine compounds and spectroscopic characterization of the pyoverdines and their metal-complexes. Students will learn a number of laser spectroscopy techniques, as well as chromatography (HPLC) and standard (absorbance, fluorescence) spectroscopic methods. |
Pyoverdines are yellow-green, water soluble, fluorescent pigments produced by fluorescent Pseudomonas spp., and related genera, as iron chelators (siderophores) and transporters.142 The peptide chain –Pep– consists of 6-12 amino acids and is highly variable amongst species, even amongst strains, both in number and type of residues. Pyoverdines produced by environmental isolates of several Pseudomonas bacteria are being investigated as potentially novel molecular recognition systems for metal ions. The pyoverdine binds the metal ion in an octahedral geometry via the catechol moiety and two bidentate amino acid residues in the peptide chain. Preliminary efforts at Oak Crest have focused on collecting UV-vis absorption and fluorescence spectra of pyoverdines in the supernatant produced by iron-limited cultures from our library of axenic Pseudomonads.