[29] Analysis of optical activity spectra of turbid biological suspensions

This chapter outlines a method for analyzing the optical activity spectra of turbid biological suspensions. It provides a brief description of the theoretical principles and equations relating the optical activity of a scattering suspension to the intrinsic optical activity of the molecules composing the scattering particle, as for example the measured spectra of a membrane suspension and the corresponding solution spectra of the proteins making up the membranes. The chapter shows the separation of scattering and absorption flattening effects, which will be useful in recognizing the various contributions to the spectra as well as in the interpretation of partially corrected experimental spectra measured with a spectropolarimeter capable of collecting the scattered light. In addition, the practical application of the relevant equations with illustrative examples for turbid suspensions of proteins and cell membranes is discussed in the chapter. There are two general types of optical activity experiments: (a) those where the biopolymer structure and solution spectra are known and an understanding of the turbid suspension spectra is desired and (b) those where only the experimental suspension spectra are known to determine the intrinsic particle or solution optical activity and to learn about the macromolecular structure, as in cell membrane suspensions. In both cases, a functional relation between suspension and particle optical activity is required.