Laboratory for Entropy Driven Research
Background and Projects
Our research probes the non-covalent intermolecular interactions that control the self-assembly of surfactant molecules (also known as soaps, detergents, and in biology, phospholipids) in solution. Surfactants spontaneously assemble into micelles and form a variety of aggregate structures such as spherical and rod-like micelles, lamellar and cubic mesophases, and reverse micelles in oil/water mixtures. The results from our research program are leading to new models for the balance of forces controlling aggregate self-assembly, antioxidant distributions in emulsions and someday perhaps, protein organization in membranes. Surfactant solutions wash your dishes, clean your clothes, and some assemble into vesicles that organize cell function. The forces responsible for self-assembly are the same ones that drive protein coiling and the formation of biological membranes. The forces controlling these interactions are weak, on the order of the strengths of hydrogen bonds or less, and include hydration, polarization, Van der Waals, electrostatic and ion specific interactions. The contributions of each to the balance of forces controlling self-assembly are still not understood.
Our primary research tool for investigating the properties of self-assembled surfactant aggregates is a chemical trapping reaction using a hydrophobic arenediazonium ion probe that associates very strongly with surfactant aggregates and is chemically trapped by water, alcohols, urea and peptide bonds, halide ions and other weakly basic nucleophiles. This reaction provides estimates of the molarities of water, counterions, and other weakly nucleophile molecules in the interfacial regions and provides new insight into changing interfacial concentrations with changing aggregate structures, for example, the transition for spherical to rod-like micelles. We also use, UV/VIS, NMR, light scattering, chemical kinetics to probe the aggregates, and periodically synthesize new molecules.
Typical Experimental Work
The exact type of experiments that are done depends upon the particular project, but most projects include: measuring product yields from the chemical trapping reaction. This work requires separation and identical of the products by HPLC, which means products synthesized independently and characterized by 1H NMR, IR, UV and sometimes other methods such as measurement of rate constants for dediazoniation by spectrometry. Once the products are identified, chemical trapping reactions are carried out in surfactant solutions over a wide range of compositions and concentrations to determine the change in product yields determined by HPLC with solution composition followed by correlation of interfacial composition with published changes in aggregate structure. The antioxidant projec requires measurement of observed rate constants of reactions between the arenediazonium ion and antioxidants in emulsions to determine the effect of emulsion composition on antioxidant distributions. The protein project is in early development and will combine the trapping reaction with HPLC and mass spectrometry as well as product identification as described above.
The most important qualification for an undergraduate student to work in our group is a strong interest in participating chemical research. Our projects are primarily physical chemistry in nature, but an understanding of introductory organic chemistry is important. Students with one semester of P. Chem. lab and lecture are better prepared for the type of projects that we do than those without. However, undergraduates who have finished one-year introductory organic chemistry and sometimes even high school students have successfully worked in our laboratory.