Lawrence W. Potts

 
Students working with Professor Potts are investigating synthetic polymers and their chemical and physical interactions at a variety of surfaces. We are particularly interested in acrylic, amide, and imide polymers and their chemical interactions with surfaces of minerals such as apatite (bones and teeth), aluminum silicates (clays and micas), oxides of titanium, vanadium, and tungsten (in ceramics), and silver oxides. Since proteins have carboxylic acid groups (like acrylic polymers) and amide groups (like polyamides such as nylon), we hope that simple synthetic polymers will help up understand more about how to enhance adhesion of proteins to surfaces. Our major analytical tools are infrared spectroscopy (Nicolet Magna 560 FTIR) and proton and carbon NMR spectroscopy (Varian 2000 300 MHz instrument).

There are currently three major projects: 
 

• Thermal synthesis of amino acid polymers
  There is considerable interest in polymers made by heating dicarboxylic amino acids such as aspartic acid and glutamic acid in the absence of oxygen. Heating causes dehydration, and can lead to products such as polyamides. We originally undertook a synthesis of polyaspartic acid to create an extremely simple and regular peptide oligomer (a short polymer) for use in chemisorption studies of polyimides and polyamides on acidic metal oxide surfaces such as tungsten and vanadium. Our successful synthesis and characterization of polyaspartic acid and its intermediate forms led us to try the polymerization of glutamic acid. We have isolated (but not yet characterized) what appears to be a thermoplastic and elastic intermediate in this synthesis. We will continue to investigate this novel material using spectroscopic methods, separation methods such as size-exclusion chromatography, and pull-testing experiments.
   
• Chemisorption of glutamate oligomers onto mineral and metal oxide surfaces
  We have designed and successfully synthesized an 8-unit oligomer of glutamic acid. Computerized molecular modeling tells us that the repeat distance of carboxylic acid groups in this synthetic oligomer will closely match the repeat distance of calcium ion sites in the mineral, hydroxy apatite ("HA," the mineral in bones and teeth). We anticipate that chemical bonding between our new peptide and an HA surface should be quite strong, as a consequence of the close fit, and that we might be able to learn more about how proteins and enzymes bind to such surfaces.
   
•  A new high vacuum plasma-treatment system 
  A recent grant from the National Science Foundation helped us to purchase equipment to build and maintain two high vacuum systems, one for vapor deposition of metals, and the other for plasma cleaning and controlled oxidation of surfaces. These systems are used in conjunction with a new scanning tunneling microscope, also a component of the grant. Recently we have found that short-term treatment with water plasma will leave a oxidized film (a few molecular layers) on polystyrene.  Longer plasma treatment leads only to ablation, and no apparent oxidation of the surface. We hope to move on to investigate polymers such as polyvinylpyridine and polyethylene terepthalate.