# Assessment of DPPC Liposome Disruption by Embedded
## 3 Results
### DSC Measurements  
To complete the above presented fluorescence probe results with thermodynamic and thermotropic information as enthalpy, temperatures, and cooperativities of the main phase transition, we applied the DSC method. Figure 7 presents the thermograms obtained during DSC measurements of DPPC with embedded TM. For pure DPPC, the DSC scan shows the main phase transition peak with a maximum at 42.35 \({}^{\circ}\)C and a small peak at 35 \({}^{\circ}\)C, ascribed to the pretransition, which occurs from the gel to the ripple phase. Figure 7 shows that embedded TM at 2, 5, or 10 mol% into DPPC influences the DSC curves of these mixtures. Increasing TM concentration is gradually broadening the main transition peak, lowering the T\({}_{\text{m}}\) temperature and lowering the intensity of the whole trace. Moreover, the measured thermograms became unsymmetrical by forming shoulders toward lower temperatures. The pretransition peak disappears from the trace at TM presence, even at 2 mol%. The incorporation of 20 mol% of TM led to the disappearance of DSC traces, indicating a complete fluidization of the membrane. The cooperativity parameter, calculated from DSC results, decreased from 803 for pure DPPC to 287 at 10 mol% of TM, indicating an increasing disorder in the bilayer. Figure 6: Anisotropy values versus TM and Toc concentrations in the gel phase at 25 \({}^{\circ}\)C and in the liquid crystalline phase at 48 \({}^{\circ}\)C: (a) DPH; (b) TMA–DPH. Figure 7: (a) DSC measurements (black lines), with fitted components (green, red and blue lines), ofmxtures of DPPC with TM at 0, 2, 5, and 10 mol% (please notice changing heat flow scale values on abscissas); (**b**) plots of the essential thermodynamic parameters versus TM concentration calculated from the DSC thermograms: temperatures of the main transition (T\({}_{\text{m}}\)), half-width of the peak \(\Delta\)T\({}_{1/2}\), enthalpy of the phase transition (\(\Delta\)H\({}_{\text{m}}\)) and cooperativity unit (CU). Presence of TM in liposomes generates multicomponent DSC endotherm. Fitting procedures have shown that those traces are consisting of two or three new peaks, indicating the presence of at least two thermal processes (Figure 7a). Positions of maxima and intensities of deconvolved peaks depend on TM concentration. All fitted peaks are wider compared to pure DPPC, and those appearing with increasing TM concentrations are shifted towards lower T\({}_{\text{m}}\). The new bands with a maxima at 42.15 \({}^{\circ}\)C and 39.5 \({}^{\circ}\)C at 2 mol% are relatively small compared to the main peak transition, whereas at 5 mol%, those bands dominate with negligible participation of the main transition peak. Additionally, we observed the formation of another shoulder at 37.5 \({}^{\circ}\)C. At 10 mol%, the total disappearance of the main peak occurs, whereas the other bands still exist but with much lower intensity. The data presented in Figure 7a indicate that recorded DSC traces of the TM-containing DPPC liposomes can be correctly simulated as a summation of three components. Such results suggest that the DPPC bilayer mixtures with TM may contain at least two populations of domains with different melting temperatures. Figure 7b presents a multiplot with the measured and calculated parameters derived from the DSC scans as the temperature of the main transition peak T\({}_{\text{m}}\), the width of the transition at half-peak height \(\Delta\)T\({}_{1/2}\), the enthalpy of the phase transition \(\Delta\)H\({}_{\text{m}}\), and the cooperativity unit CU plotted against TM concentrations. The decreasing values of T\({}_{\text{m}}\), the \(\Delta\)H\({}_{\text{m}}\), CU, and increasing \(\Delta\)T\({}_{1/2}\) indicate a structural modification of DPPC introduced with increasing concentrations of TM. This last parameter indicates a progressing disappearance of cooperativity, which is clearly shown on this plot for the CU parameter.