The Interpretation of Infrared Dichroism in Fibrous Protein Structures

The increasing use of infrared dichroism measurements in studying the molecular structure of fibrous proteins necessitates a critical examination of its interpretation. Relationships between transition moment direction and dichroic ratio are derived for perfectly and imperfectly oriented fibers, and the effects of reflection losses, form dichroism, and convergence are considered. Uncertainties in the assignment of the transition moment directions associated with the principal vibrations of the —CO·NH— group are discussed.