Diffractive optics-based nonlinear spectroscopy: application to the study of deterministic protein motion

Summary form only given. Biological systems constantly transduce various forms of chemical energy into functions in which the inherent response of the system operates at the edge of stability. Excursions from the stability region lead to denaturation; whereas small fluctuations about the stability point lead to highly correlated responses that behave in a deterministic fashion with respect to the function of the system. Exactly how is the bond energy directed in such a complex system and how has the system evolved to minimize entropic losses in conversion efficiency? We have used the oxygen binding heme proteins as model systems for studying the coupling of reaction forces to functionally relevant motions; i.e., structural transitions important to the self regulation of oxygen binding and transport. Since the forces involved become spatially distributed over an enormous number of degrees of freedom, the net relative motions can be exceedingly small (<.1 /spl Aring/). A very sensitive method is needed to detect these motions and the time resolution must be sufficient to follow from the very first events of bond breaking to full relaxation. The use of diffractive optics for the implementation of heterodyne detected grating spectroscopy has recently been demonstrated. The diffractive optic also generates tilted phase fronts to provide true femtosecond time resolution in noncollinear geometries. This approach has sufficient time resolution and sensitivity to follow the mass displacement, as connected through changes in the material index of refraction, to address this issue.