Conformation‐dependent Raman bands of phospholipid surfaces. 3—head group Ortho‐phosphate stretching vibrations

TLDR: In this article, the results of Raman temperature and solvent studies of diethyl phosphate are reported and are found to be in good agreement with the conclusions obtained from the normal coordinate analyses.

Abstract: Vibrational frequencies of diethyl phosphate were calculated for rotamers for which the dihedral angle about the PO and CO bonds varied. The frequencies predicted for the symmetric and antisymmetric OPO stretches, the symmetric and antisymmetric ionic PO2− stretches, and the CC stretches are found to be sensitive to the PO and CO dihedral angles. The results of Raman temperature and solvent studies of diethyl phosphate are reported and are found to be in good agreement with the conclusions obtained from the normal coordinate analyses. Frequencies of diethyl phosphate rotamers having the geometries of crystalline glycerophosphorylcholine (GPC), crystalline GPC CdCCl2, and amorphous GPC CdCl2 were calculated and compared to the Raman spectra of these phospholipid head group models. The normal coordinate analyses are in good agreement with Raman spectra. These results indicate that the observed frequencies of phosphate group vibrations may be compared to the normal coordinate analyses of diethyl phosphate rotamers to monitor conformation in phospholipid head groups (and other organic ortho -phosphates). The Raman symmetric OPO stretch bandwidth may be used to monitor rotational freedom or broadening due to the distribution of differing conformations.