In order to study the temperature dependence of the crystallization process of C30d inside DMPC membranes, we first performed 1 H NMR measurements on mixtures of nondeuterated C30 and DMPC with per-deuterated acyl tails (DMPC-d54). The measurements were performed under MAS at a spinning rate of 5 kHz. This allowed us to record the 1 H NMR signal of the n-alkane alkyl protons during a temperature sweep. At the MAS frequency used, the 1 H alkyl peaks can only be resolved if the alkane is in a liquid state; in the crystalline and rotator phase the peaks are broadened beyond detection due to significantly reduced chain mobility and consequent increase of the 1 H homonuclear dipolar cou- plings. For the rotator phase, this observation is similar to lipid gel-phases, where reduced mobility results in increased dipole-dipole interactions and T 2 relaxation rates . Figure shows the results of such measurements. In Figure , the alkyl chain region of the 1 H spectrum is plotted with decreasing temperature, and the low-temperature spectrum of DMPC-d54/water is included for comparison. The normalized spectrum integrals upon heating/cooling of C30 in bulk and in the membrane are plotted in Figure . The melting of bulk C30 is indicated by a strong signal increase between 64 and 67 • C, which corresponds to the expected melting temperature of about 65 • C (from the rotator to the liquid phase) . In the subsequent cooling runs, the signal intensity decreases between approx. 65 and 60 • C. According to Sirota et al., the liquid-to-rotator transition of C30 is similar to, but slightly below, it's melting temperature . More precisely, since they also found a transition between the RIV and RIII rotator phases at 63.9-64.4 • C, the liquidto-rotator transition of C30 should lie between 64 and 65 • C. We'd like to note here that, since the 1 H NMR experiments were conducted under MAS, a temperature gradient of a few degrees exists within the samples. This gradient broadens the observed transitions and obstructs a more accurate comparison with literature values. Still, Figure shows that C30 in a DMPC-d54 membrane behaves notably different from bulk C30: The apparent melting process starts earlier, at approx. 50 • C, and continues until about 62 • C, after which the signal increases sharply. This two-step process becomes even more evident in the cooling runs, were we first observe a fast decay similar to the bulk sample, followed by a second process between 55 and 45 • C. Based on these results alone, there are two possible explanations for this two-step melting/crystallization process. One is that it is possible that the initial, fast drop of 1 H intensity upon cooling corresponds to bulk C30 that is not incorporated into the lipid membranes; the slower drop of intensity (at lower temperatures) would then correspond to crystallization of alkane molecules incorporated in the lipid bilayers. An alternative explanation is that both transitions relate to mixed C30, where one component behaves similar to bulk alkane while the other is more strongly associated with the lipid. In fact, this lipid-associated component may not even crystallize, but only adopt a rotator phase/gel-like state in combination with the lipid acyl tails.