FT-IR spectroscopy for exposing the CH vibrational bands from the polar parts of phospholipids

Lipids as an important class of chemical and, in particular, biochemical compounds have been largely characterised by a number of structural and thermodynamic methods in the past. An in-depth application of vibrational spectroscopy as one of the powerful methods in this field, however, hampered from the fact that the C–H absorption bands of relevant moieties situated in the polar part of lipids are hidden by the overlapping C–H bands arising from the overwhelming majority of respective moieties situated in the apolar region, i.e. in the lipid chains. For the sake of overcoming this lack, we have excogitated a set of deuterated derivatives of 1,2-dimyristoyl-sn-glycerophosphocholine tailor-made such as to disentangle all the CH and CH2 unities present, and studied these substances as well as methylphosphocholine as a lipid headgroup model in the solid state by means of FT-IR spectroscopy. The data are considered in terms of assessing the usability of the material, especially with respect to the observed IR bands due to the minor components. Isotopic shift factors are regarded and assignments for the different species are proposed and discussed.