Research Statement
Luis G. Rosa
My past and current research efforts have focused on the multidisciplinary area of experimental soft condensed matter physics, with particular emphasis on surface characterization and gas-surface chemistry of polymer surfaces and organic self assemble monolayer.
I have specialized in surface science novel approaches in order to investigate these generally more fragile and complex organic surfaces. Surface sensitive angle resolved electron photoemission spectroscopy and inverse photoemission spectroscopy can be used to obtain the electronic band structure, molecular orientation, and Fermi level placement of organic polymer surfaces and organic self assembled monolayers. These techniques have traditionally provided detailed information on the basic physics underlying the device properties of organic diodes and transistors.
Organic electronics are not the only application for organic thin films. Small gas particle interactions with organic polymer surfaces are a good stage for gas sensitive devices with a variety of applications. Thermal desorption, angle resolved thermal desorption spectroscopy can be used to scrutinize the gas-surface interactions of water molecules and a ferroelectric organic polymer surface, providing information on desorption energies, identification of adsorption sites, molecular orientation of adsorbate-surface bond and its dependence on coverage or number of water molecules. This is more or less the same way that historically surface science has been carried out on single crystal of metal surfaces, but the opportunities abound in the study of organic surface both at the most fundamental level of physics (such as identifying novel phase transitions at surfaces) and also with an eye towards a number of applications in piezo-electric devices, high energy density storage and “printable” devices, sensors, and OLED’s.
Lately I have been involved in the characterization of thiol self assembled monolayers by using atomic force microscopy (AFM). Nanografting or nanolithography have facilitated the comparison and characterization of various molecular properties; friction, conductivity and height or structure profiles are obtained from such patterned surfaces.
Such a combination of experimental approaches has proven to be a route to providing fundamental information on the physics and possible device applications of organic layers. I would like to continue using the tool box of surface science approaches to identify scientific issues which required the production of well order or crystalline organic surfaces, characterization of such surfaces and device applications. Some examples of research projects that I would like to pursue are:
Growth of protein self assembled monolayers or spontaneous self assembling of design proteins with terminal groups that will chemically bind to a surface. The goal of such approach will be to obtain crystalline or well ordered surface structure assemblies of proteins. Helix bundle proteins and similar systems are suitable for the growth of order self assemble monolayer1,2. Having a crystalline or well ordered structure will allow surface science tools box of techniques like x-ray diffraction, infrared spectroscopy, UV circular dichroism, UV absorption spectroscopy, etc. to be used on the characterization of this protein self assemble surface. I hope to identify that electron localization does not always occur, and that organic systems when bound to surfaces can adopt chiral structures not available to the free molecule.
Proteins can be grouped in a broad range of functional classes: structural proteins, which provided structure rigidity in larger structures such as cells; transport proteins, which control the flow of material across cellular membranes; regulatory proteins, which act as a sensor and switches to control protein activity and gene function; signaling proteins, including cell surface receptors and other proteins that transmit external signals; and motor proteins, which causes motion. Transport, regulatory and signaling protein functions usually involves the biding of small molecules or atoms for example: CO, water, glucose, retinal and atomic ions (for example Ca+, Cl-, Na+). The dynamics and function is not always clear at the most fundamental level as temperature effects on electronic structure, and the details of electronic structure are often not investigated by the biology community.
Growing well order or quasi crystalline surfaces composed by assembling of proteins will provide the opportunity to bind a specific molecule to the proteins which composes the surface and the possibility of designing proteins that bind such molecules. Main goal of achieving such a surface will be characterization of the small molecule-protein binding (docking) physical chemistry3,4; absorption energetic and kinetics are example of the physics obtained from the absorption of molecules to protein assemble monolayers. Such study will be complemented with characterization of surface structure and electronic structure. Information that will be correlated to absorption binding sites, molecular orientation and possibly structural changes, since a wide range of proteins function depends on structural conformational changes.
1. Wackerbarth, H., Tofteng, A.P., Jensen, K.J., Chorkendorff, I., Ulstrup, J. Langmuir 22, 6661-6667, 2006.
2. Hu, Y., Das, A., Hecht, M.H., Scoles, G. Langmuir 21, 9103-9109, 2005.
3. Cao, W., Christian, J.F., Champion, P.M., Rosca, F., Sage, J.T., Biochemistry 40, 5728-5737, 2001.
4. Schmidt, M., Nienhaus, K., Pahl, R., Krasselt, A., Anderson, S., Parak, F., Nienhaus, G.U., Srajer, V., Proceedings of the National Academy of Sciences of the United States of America 102, 11704-11709, 2005.