Experimental Measurement of the Strength of a Cα-H⋯O Bond in a Lipid Bilayer

Due to the apolar nature of the lipid bilayer, the weak Cα-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.