LD spectroscopy of natural and synthetic biomaterials

The structural characterization of biomaterials is challenging because they are usually too large for NMR or high resolution mass spectrometry and not well-enough structured for X-ray crystallography. Structural characterization and kinetic analysis for such systems thus has to proceed by collecting complementary data from a wide range of different techniques. This tutorial review describes how linear dichroism, a polarized absorbance spectroscopy technique applied to oriented molecular systems, can be used to provide useful data on biomaterials. In particular LD can provide information about relative orientations of sub-units of biomaterials and orientations of the whole biomaterial with respect to an orientation axis. An outline of linear dichroism and a summary of the artifacts to be avoided are followed by a description of how Couette flow linear dichroism has been used for a range of biomaterial systems including: DNA; DNA:ligand systems; cytoskeletal fibrous proteins; synthetic protein fibres; membrane proteins in liposomes; bacteriophage; carbon nanotubes; and peptidoglycan systems.