Jeanne Pemberton, Raina Maier, Robin Polt, Maria-Teresa Velez, Robert Bates (University of Arizona) and Jani Ingram (Northern Arizona University) are jointly supported to study the fundamental surface and interfacial chemistry of biosurfactants, particularly the rhamnolipids, siderolipids, surfactins and sophorolipids. Synthetic analogues to the microbially-produced biosurfactants will also be studied. The project will incorporate chemical synthesis, surface and interface analysis, theory and modeling, as well as a microbiology component to study the biosynthetic pathways and molecular environments that influence which biosurfactants are made under what conditions. Biosurfactants are known to aggregate in solution at low concentrations and exhibit powerful surfactant activity at both liquid and solid surfaces. Each individual biosurfactant can have remarkably different properties, because their interactions are driven by the interplay of van der Waals forces, dipole-dipole interactions, and solvation effects. Biosurfactants will be characterized in solution using light scattering, the vibrational spectroscopies, NMR spectroscopy, mass spectrometry and surface tension measurements, while biosurfactant assemblies at interfaces and on surfaces will be characterized using a combination of the vibrational spectroscopies and atomic force microscopy.

This project is funded through the Collaborative Research in Chemistry Program (CRC) and the Office of Multidisciplinary Activities in the Directorate for Mathematical and Physical Sciences. Biosurfactants have potential applications in industrial, medical, pharmaceutical and environmental applications. This interdisciplinary research project will be used as a platform to improve the recruitment and participation of underrepresented students, especially Hispanics and Native Americans, in scientific careers in chemistry and environmental science. This award provides collaborative training and research opportunities for K-12 teachers and students, and undergraduate and graduate students at both institutions.

Project Report

Intellectual Merit Today’s commercial markets for amphiphilic molecules, including surfactants, emulsifiers, wetting control agents, drug and gene delivery agents, microencapsulents, nanoparticle growth agents, cleaning products, and food and cosmetic additives, are mostly comprised of materials prepared by chemical synthesis from petroleum-based starting materials. However, many such synthetic amphiphiles are known to be acutely toxic and can exhibit high persistence in water supplies and soil after deposition. Indeed, increasing global regulatory pressure and consumer interest are driving the amphiphile markets to seek "greener" alternatives to such systems. Naturally-occurring biosurfactants that are biosynthesized by and can be extracted from animals, plants and bacteria are one class of alternative materials that are currently receiving widespread attention as suitable replacements for synthetic amphiphiles. Biosurfactants are known to aggregate in solution at low concentrations and exhibit powerful surfactant activity at both liquid and solid surfaces. The structural intricacy of these materials is magnified further upon realization that they are produced as complex mixtures of up to 40 congeners in which the hydrophilic head groups are fairly conserved and the hydrophobic tail groups have considerable variation. Component congeners within these complex mixtures can have remarkably different properties, because their interactions are driven by a complex interplay of weak forces that have yet to be fully explored. These studies combined the expertise of an environmental microbiologist (Dr. Raina M. Maier), a synthetic chemist (Dr. Robin L. Polt) and an analytical chemist (Dr. Jeanne E. Pemberton), all of the University of Arizona, to elucidate the fundamental surface and interfacial chemistries of naturally occurring, individual congeners of these surfactants as well as carefully-chosen (e.g. aided by modeling and dynamics studies) synthetic analogues with specific molecular attributes. Interfacial and surface studies were undertaken at air-liquid interfaces and at oxide, metal, and polymer surfaces and were supplemented by solution aggregation studies. Complementing this effort were studies geared to discovery of new biosurfactants and to the assessment of how to achieve biosynthetic control of each biosurfactant class through modification of the biosynthetic pathways and molecular environment in which the bacteria grown. The ultimate goal was to generate microbial systems capable of producing in large quantities of specific biosurfactant congeners that possess desirable surface and interfacial characteristics for a given application. Additionally, we sought to develop efficient, cost-effective strategies to chemically synthesize these biosurfactants in larger quantities than can be readily attained by biosynthetic routes. We achieved significant progress on each of these goals during the award period. First, we comprehensively defined the complex mixture of surfactants that comprise the native mixture of monorhamnolipids harvested from Pseudomonas aeruginosa ATCC 9027 and extensively characterized their air-water interface and solution aggregation properties. We developed synthesis procedures for flavolipids and monorhamnolipids and successfully extended the monorhamnolipid synthesis to a broader range of glycolipid molecules. Broader Impacts The ubiquity of surfactants as essential chemicals and their massive industrial use, coupled with emerging concerns about their long-term environmental impacts, present a compelling opportunity for advances in molecular design and synthesis of green surfactants. Widespread interest in these issues supports exploration of all viable alternatives to meet the increasing demands of the global surfactant market, predicted to reach $40B annually by 2018. This work has contributed patentable innovations to the marketplace, including new glycolipid surfactants with the potential for tailorable properties as well as green and sustainable synthetic strategies. This effort has additionally provided important new insight into biosurfactant structure-function relationships that could drive future advances in molecular design. This effort also had considerable broader impact through its education and outreach activities. This inherently interdisciplinary effort provide a platform to provide inter-disciplinary training opportunities to the broad spectrum of researchers, from postdoctoral researchers through high school students, involved with this project. Noteworthy in the broader impacts area is our success at incorporating 27 undergraduate students, 14 high school teachers and 17 high school students in research associated with this grant. Evidence of the desirability of this type of research as a training vehicle is the employment outcomes of the students who have worked on it; indeed, student training is the most important conduit for "technology transfer" from this effort. As recent examples of these outcomes for students/postdoctoral researchers involved in this project, one is helping to start a small company, GlycoSurf LLC, based on technology developed from this research, one is employed by Procter & Gamble, one was recently hired as a Research Scientist at Sion Power, one is employed by a small chemical company (CF Industries) in Mississippi, one is an educator at Point Loma Nazarene University in San Diego, one is employed by Exxon Mobile, one is the recipient of an NSF Graduate Fellowship based on his work on this grant, and several students are completing their PhD degrees in their respective programs at the University of Arizona.

National Science Foundation (NSF)
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Zeev Rosenzweig
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University of Arizona
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