Nonlinear optics of chiral surface systems

The second order nonlinear optical technique, second harmonic generation (S HG), has characteristics desirable in studying biological surfaces: it has extreme surface specificity and submonolayer sensitivity; it is useful for studying buried aqueous interfaces; and it is sensitive to chirality. The p roperty of chirality can serve as an important marker for conformations of proteins, for example. In order to better understand SHG from chiral surfac es, we have performed in-depth studies on model monolayer systems in which the chirality can be controlled. Differential SHG signals from chiral surfaces are recorded using right and left circularly polarized incident light. We show that chiral information f rom the surface is conveyed through this SHG process. This study focuses on the model protein system, cytochrome c, adsorbed on various self-assembled mono- and hi-layers at the solid/liquid interface. SHG-CD signals are show n to be related to the oxidation state of the protein and are utilized to o bserve changes in this feature of the protein in situ at surfaces of varyin g chemical properties.