Thermotropic phase behaviour of mixed liposomes of archaeal diether and conventional diester lipids
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The phase behaviour and phase stability of mixed liposomes prepared from diether polar lipids isolated from thermophilic Archaea and from conventional diester dipalymitoyl-l-α-phosphatidylcholine (DPPC) at different molar ratios were investigated by differential scanning calorimetry. The permeability of these mixed liposomes was investigated as a function of temperature, by measuring the fluorescence emission intensity for the release of calcein in the temperature range from 20 to 98 °C. Our data show that diether polar lipids isolated from hyperthermophilic Archaea can form mixed liposomes with synthetic α-DPPC. Liposomes prepared from pure archaeal lipids do not show the characteristic gel-to-liquid crystalline phase transition characteristics of DPPC liposomes in the temperature range from 0 to 100 °C. In the presence of 5 mol% archaeal lipids in mixed α-DPPC liposomes, the temperature of the phase transition decreases and the broadness of the peak increases, although the enthalpy change (ΔH) of the phase transition is not significantly influenced. At molar ratios of archaeal lipids greater than 50 mol% in these mixed liposomes, the typical gel-to-liquid crystalline phase transition disappears, which indicates that the lipids are predominantly in the liquid crystalline state. At ratios of archaeal lipids greater than 50 mol% in these mixed liposomes, their permeability for anionic calcein is the same as for liposomes made from 100 mol% archaeal lipids, across the whole temperature range.
KeywordsArchaeal lipids Dipalymitoyl-l-α-phosphatidylcholine Differential scanning calorimetry Phase behaviour Liposome Calcein release
The authors would like to express their gratitude for financial support from the Slovenian Research Agency through the P4-0121 research programme and the J2-3639 project.
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