Interfacial and Solution Characterization of Rhamnolipid Biosurfactants and their Synthetic Analogues

Persistent Link:
http://hdl.handle.net/10150/217062
Title:
Interfacial and Solution Characterization of Rhamnolipid Biosurfactants and their Synthetic Analogues
Author:
Wang, Hui
Issue Date:
2011
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 (RL) biosurfactants have been considered "green" alternatives to synthetic surfactants. Here, systematic studies of monorhamnolipids (mRLs) and their synthetic analogues are performed to characterize their interfacial and solution behaviors as surfactants. Chemical structure-surface activity relationships of rhamnolipids were probed using surface tension measurements on RLs and a series of their synthetic analogues designed by "truncation modification." Based on our study on RLs and the rationally-designed RL analogues, the key structural factor responsible for the excellent surface activity performance of rhamnolipids is the presence of the rhamnose moiety in the headgroup. As a result, rhamnopyranosides (RhEs), the simplest surfactants with a rhamnose moiety in the headgroup, show surface activity comparable to the bioproduced mRLs. The purified mixture of mRLs harvested from Pseudomonas aeruginosa ATCC 9027 was mixed with a nonionic surfactant Tween-20 (TW) and studied by surface tension measurements at pH 8. The experimental values of CMC show deviation from the theoretical values predicted by ideal solution theory, which is hypothesized to be due to a shape change from rod-shaped to spherical as the mole fraction of TW is increased. The hypothesis about the shape change is supported by dynamic light scattering results, regular solution theory, and packing parameter theory. Polarization modulated-infrared reflection-absorption spectroscopy (PM-IRRAS) has been used to characterize the orientation of the synthetic rhamnolipid Rha-C18-C18 at the air-water interface. Although rhamnolipids exhibit pH-dependent micellization, their orientation at the air-water interface is not affected by pH. The average tilt angle of their alkyl chains is determined to be ~45° at a surface pressure π = 40 mN/m which decreases to 36° when Pb²⁺ is present in the subphase. Assisted by molecular modeling, the packing of mRLs at the air-water interface is believed to be dominated by the packing of their large hydrophilic headgroups. Finally, the adsorption isotherm of mRLs on hydrophobic polyethylene surfaces was generated by ATR-FTIR from solutions of different pH, which were then fit to a Frumkin adsorption model to yield the thermodynamic adsorption parameters, the adsorption equilibrium constant and the interaction parameter. mRLs strongly adsorb to d-PE, and the adsorption is pH dependent.
Type:
text; Electronic Dissertation
Keywords:
mixed surfactant system; PM-IRRAS; rhamnolipid; surface tension; Chemistry; biosurfactant; critical micelle concentration
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Chemistry
Degree Grantor:
University of Arizona
Advisor:
Pemberton, Jeanne E.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleInterfacial and Solution Characterization of Rhamnolipid Biosurfactants and their Synthetic Analoguesen_US
dc.creatorWang, Huien_US
dc.contributor.authorWang, Huien_US
dc.date.issued2011-
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © 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.en_US
dc.description.abstractRhamnolipid (RL) biosurfactants have been considered "green" alternatives to synthetic surfactants. Here, systematic studies of monorhamnolipids (mRLs) and their synthetic analogues are performed to characterize their interfacial and solution behaviors as surfactants. Chemical structure-surface activity relationships of rhamnolipids were probed using surface tension measurements on RLs and a series of their synthetic analogues designed by "truncation modification." Based on our study on RLs and the rationally-designed RL analogues, the key structural factor responsible for the excellent surface activity performance of rhamnolipids is the presence of the rhamnose moiety in the headgroup. As a result, rhamnopyranosides (RhEs), the simplest surfactants with a rhamnose moiety in the headgroup, show surface activity comparable to the bioproduced mRLs. The purified mixture of mRLs harvested from Pseudomonas aeruginosa ATCC 9027 was mixed with a nonionic surfactant Tween-20 (TW) and studied by surface tension measurements at pH 8. The experimental values of CMC show deviation from the theoretical values predicted by ideal solution theory, which is hypothesized to be due to a shape change from rod-shaped to spherical as the mole fraction of TW is increased. The hypothesis about the shape change is supported by dynamic light scattering results, regular solution theory, and packing parameter theory. Polarization modulated-infrared reflection-absorption spectroscopy (PM-IRRAS) has been used to characterize the orientation of the synthetic rhamnolipid Rha-C18-C18 at the air-water interface. Although rhamnolipids exhibit pH-dependent micellization, their orientation at the air-water interface is not affected by pH. The average tilt angle of their alkyl chains is determined to be ~45° at a surface pressure π = 40 mN/m which decreases to 36° when Pb²⁺ is present in the subphase. Assisted by molecular modeling, the packing of mRLs at the air-water interface is believed to be dominated by the packing of their large hydrophilic headgroups. Finally, the adsorption isotherm of mRLs on hydrophobic polyethylene surfaces was generated by ATR-FTIR from solutions of different pH, which were then fit to a Frumkin adsorption model to yield the thermodynamic adsorption parameters, the adsorption equilibrium constant and the interaction parameter. mRLs strongly adsorb to d-PE, and the adsorption is pH dependent.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectmixed surfactant systemen_US
dc.subjectPM-IRRASen_US
dc.subjectrhamnolipiden_US
dc.subjectsurface tensionen_US
dc.subjectChemistryen_US
dc.subjectbiosurfactanten_US
dc.subjectcritical micelle concentrationen_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineChemistryen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorPemberton, Jeanne E.en_US
dc.contributor.committeememberSaavedra, S. Scotten_US
dc.contributor.committeememberWysocki, Vicki H.en_US
dc.contributor.committeememberGlass, Richarden_US
dc.contributor.committeememberLichtenberger, Dennisen_US
dc.contributor.committeememberPemberton, Jeanne E.en_US
All Items in UA Campus Repository are protected by copyright, with all rights reserved, unless otherwise indicated.