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    Solution and Interfacial Characterization of Rhamnolipid Biosurfactant from P.aeruginosa ATCC 9027

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    Author
    Lebron-Paler, Ariel
    Issue Date
    2008
    Keywords
    bioremediation
    biosurfactant
    P.aeruginosa
    rhamnolipids
    Advisor
    Pemberton, Jeanne E.
    Committee Chair
    Pemberton, Jeanne E.
    
    Metadata
    Show full item record
    Publisher
    The University of Arizona.
    Rights
    Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
    Abstract
    Rhamnolipid biosurfactants are investigated to determine their role in biological processes, and for discovery of novel, more biocompatible applications in areas related to medicine, agriculture, and environment. Fundamental understanding of the physical and chemical properties of rhamnolipids is needed. Thus, systematic studies on solution and interfacial properties on rhamnolipids from P.aeruginosa ATCC 9027 were undertaken. A purification protocol was developed and a thorough qualitative and quantitative speciation analysis was performed with high performance liquid chromatography-mass spectrometry (HPLC-MS), nuclear magnetic resonance (NMR) spectroscopy and HPLC with evaporative light scattering detection (ELSD). Acid-base properties of the mixture of 30 monorhamnolipid congeners, including both saturated and unsaturated species, were characterized at concentrations below and above the CMC at fixed ionic strength using potentiometry and attenuated total reflectance-Fourier transform infrared (ATRFTIR) spectroscopy. A pKₐ of 4.3 was found for concentrations below 50 μM and a pKₐ of 5.6 above 100 μM. The pKₐ is dictated by aggregation in solution. Molecular areas of monorhamnolid monolayers at the air-water interface are strongly influenced by protonation state, and increase from 31 to 109 Ų/molecule as pH increases from 4 to 8.5 and as ionic strength decreases. Adsorption isotherms of monorhamnolipids on γ-Al₂O₃ were investigated as a function of pH using ATR-FTIR spectroscopy and Frumkin model fits, from which K(ads) values of 1.20 (± 0.10) x 10⁵ M⁻¹ at pH 4.0, 2.14 (± 0.51) x 10⁴ M⁻¹ at pH 6.3 and 1.31 (± 0.09) x 10³ M⁻¹ at pH 8.6 were obtained. Interaction parameters were positive at all pH values. Cooperative adsorption is driven by hydrophobic interactions (physisorption) at any pH including hydrogen bonding and electrostatic interactions. Chemisorption was also observed at high pH values. Formation constants for monorhamnolipid-Pb²⁺ and monorhamnolipid-Cd²⁺ complexes were determined using differential pulse polarography in the low μM concentration range. A modified Lingane equation was developed to account for monorhamnolipid adsorption on the Hg surface. β values for adsorbed metal complexes are ~10^3.2 and ~10^0.8 for Pb²⁺ and Cd²⁺, respectively, compared to previously published β values of 10^8.58 and 10^6.89, respectively. Evidence for 1:1 and 2:1 monorhamnolipid-metal complexes was provided by electrospray ionization-mass spectrometry.
    Type
    text
    Electronic Dissertation
    Degree Name
    Ph.D.
    Degree Level
    doctoral
    Degree Program
    Chemistry
    Graduate College
    Degree Grantor
    University of Arizona
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