Potentiometric and spectroscopic determination of the acid dissociation constant of monorhamnolipid in aqueous solution

ANYL 65

Ariel Lebrón-Paler, alpaler@email.arizona.edu1, Jeanne A. Pemberton1, Bridget A. Becker, babecker@ku.edu2, and Cynthia K. Larive, clarive@ucr.edu2. (1) Department of Chemistry, University of Arizona, 1306 East University Boulevard, Tucson, AZ 85721, (2) Department of Chemistry, University of California, Riverside, Riverside, CA 92521
The anionic biosurfactant rhamnolipid produced by Pseudomonas aeruginosa has been proposed as a biocompatible technology for remediation of organic and metal-contaminated soil environments. Characterization of the intrinsic molecular properties of such molecules in aqueous solution is extremely important to understand the mechanism of interaction within the resulting molecular assembly and to develop predictive insight about factors affecting their fate and transport in environmental systems. In this work, the monorhamnolipid form of the biosurfactant produced by P.aeruginosa ATCC 9027 was isolated and the pKa of the carboxylic acid group moiety was determined below and above the critical micelle concentration (CMC). Results will be presented from potentiometry and two independent spectroscopic techniques, NMR and ATR-FTIR spectroscopy. A minimum pKa of 4.3 at concentrations where premicellar and, presumably, small micellar molecular aggregates form was obtained. This value shifts to higher values as the level of assembly aggregation becomes more complex. Implications of these findings will be discussed.
 

General Papers
7:00 PM-9:00 PM, Sunday, 10 September 2006 Moscone Center -- Hall D, Poster

Division of Analytical Chemistry

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006