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A largevariety of data exists on lipid phase behavior; however,it is mostly in nonbuffered systems over nonbiological temperatureranges. We present biophysical data on lipid mixtures of dioleoylphosphatidylcholine(DOPC), dioleoylphosphatidylethanolamine (DOPE), and lysophosphatidylcholine(LysoPC) examining their behaviors in excess water and buffer systemsover the temperature range 4–34 °C. These mixtures arecommonly used to investigate the effects of spontaneous curvatureon integral membrane proteins. Using small-angle X-ray scattering(SAXS) and 31P NMR, we observed lamellar and vesicle phases,with the buffer causing an increase in the layer spacing. Increasingamounts of DOPE in a DOPC bilayer decreased the layer spacing of themesophase, while the opposite trend was observed for increasing amountsof LysoPC. 31P static NMR was used to analyze the DOPC:LysoPCsamples to investigate the vesicle sizes present, with evidence ofvesicle budding observed at LysoPC concentrations above 30 mol %.NMR line shapes were fitted using an adapted program accounting forthe distortion of the lipids within the magnetic field. The distortionof the vesicle, because of magnetic susceptibility, varied with LysoPCcontent, and a discontinuity was found in both the water and buffersamples. Generally, the distortion increased with LysoPC content;however, at a ratio of DOPC:LysoPC 60:40, the sample showed a levelof distortion of the vesicle similar to that of pure DOPC. This impliesan increased flexibility in the membrane at this point. Commonly,the assumption is that for increasing LysoPC concentration there isa reduction in membrane tension, implying that estimations of membranetension based on spontaneous curvature assumptions may not be accurate. [ABSTRACT FROM AUTHOR]