Experimental measurement of the strength of a C alpha-H...O bond in a lipid bilayer

Due to the apolar nature of the lipid bilayer, the weak Calpha-H...O H-bond is thought to contribute significantly toward the stability of transmembrane helical bundles such as glycophorin A (GPA). Here for the first time we measured the strength of such a bond, using vibrational frequency shifts of a dimeric and nondimeric variants of GPA containing a Gly CD2 label. Although the resulting estimated bond strength of 0.88 kcal/mol is relatively weak, several such bonds could contribute significantly toward bundle stabilization.