Figure shows the correlation between the 2 H -/( 13 C -+ 12 C -) and C -/( 13 C -+ 12 C -) ratio for each labeling scheme. The 2 H - /( 13 C -+ 12 C -) ratio tracks the amount of 2 H-labeled lipid in the bilayer, while the 13 C -/( 13 C -+ 12 C -) ratio tracks the amount of C-labeled lipid in the bilayer. Figure demonstrates that the correlation between the ratios is a function of both the location of the isotopic label and the overall composition of the bilayer. The ternary mixture containing both 2 H31-POPC and 13 C18-POPC shows a positive correlation between lipid concentrations. Conversely, the ternary mixture containing 2 H31-POPC and 13 C18-DSPC displays a clear negative correlation between the concentrations of the two components. These trends can be attributed to preferential interactions between 13 C18-POPC and 2 H31-POPC and unfavorable interactions between 13 C18-DSPC and 2 H31-POPC within ternary bilayers. These interactions are depicted schematically in the cartoons shown in Figure .