Conformational disorder in lipid bilayer systems is commonly measured with reference to the intensity of the 1130 cm⁻¹ Raman band. However, estimates of the concentration of gauche bonds may vary by a factor of six according to the model used to relate intensity and concentration. In an effort to narrow the wide range in these estimates, we have measured the intensity of the 1130 cm⁻¹ band of crystalline n-C₂₁H₄₄ in its orthorhombic and hexagonal phases. On transition to the hexagonal phase, the intensity of the 1130 cm⁻¹ band is much reduced. It is assumed that the observed intensity reduction results from the introduction of gauche bonds whose number can be independently estimated from other features in the Raman and infrared spectra. From these measurements we conclude that the intensity of the 1130 cm−1 band is not linearly related to the concentration of gauche bonds and that a disproportionately large decrease in the 1130 cm⁻¹ band intensity results from the introduction of a low concentration of gauche bonds. Thus previous estimates of gauche bond concentrations based on the assumption of a linear relation have tended to greatly overestimate the gauche bond concentration. These results derived from experiment are in accord with those of Pink et al. (Pink, D.A., Green, T.J. and Chapman, D. (1980) Biochemistry 19, 349–356) derived from theory.
Biochimica et Biophysica Acta (BBA) - Biomembranes684, no. 1: 111–116.