Proton magnetic resonance spectroscopic studies of the interaction of ubiquinone‐10 with phospholipid model membranes

Abstract

Proton magnetic resonance spectra of ubiquinone‐10 and ubiquinone‐10 dispersed with dipalmitoylglycero‐phosphocholine or egg phosphatidylcholine in aqueous medium have been obtained. The dispersions are in the form of multilamellar liposomes as judged by ³¹P‐NMR spectra and the thermal history of the samples have ensured that ubiquinone not incorporated into the phospholipid structure only gives rise to a broad‐line NMR proton spectrum. A high‐resolution proton spectrum of ubiquinone is observed with upfield shifts of the O‐methyl protons of the benzoquinone rings, indicating close proximity of the molecules but with an arrangement different from the pure liquid ubiquinone. Spectra obtained in the presence of the lanthanide shift reagents, dysprosium fluorooctanedionate and Dy(NO₃)₃, which have a preferred location in the hydrophobic and hydrophilic domains, respectively, of ubiquinone/phospholipid codispersions, are consistent with the partitioning of ubiquinone into a hydrophobic phospholipid environment remote from the aqueous phase. The type of arrangements of ubiquinone that could be accomodated within bilayers of phospholipid are discussed.