Black S G, Dixon G S
Biochemistry. 1981 Nov 10;20(23):6740-4. doi: 10.1021/bi00526a033.
The gel to liquid-crystal phase transition in dimyristoylphosphatidylcholine liposomes was studied with 0.4-Hz ac calorimetry. The ac heat capacity on heating scans exhibited a peak in the vicinity of 23.9 degrees C with a full width at half-maximum of 0.15-0.20 degrees C. The enthalpy change was 4.8 kcal/mol, in good agreement with conventional differential scanning calorimetry. On cooling scans, the peak shifted to lower temperature by 0.1-0.5 degrees C, the width increased to 0.25-0.40 degrees C, and the apparent enthalpy change was only 40% of that observed on heating. Both the heating and cooling heat capacities were stable for at least 20 min in quasi-isothermal conditions. Following a 1 h anneal at 10 degrees C, the heating scans were quite reproducible. The results have been interpreted in terms of the nucleation and subsequent annealing of small ordered domains in the bilayer on freezing the acyl chains. No peak associated with the pretransition was observed, as expected since the relaxation time for the degrees of freedom the produce the pretransition is much longer than the period of the 0.4-Hz temperature wave.
采用0.4赫兹交流量热法研究了二肉豆蔻酰磷脂酰胆碱脂质体从凝胶态到液晶态的相变。加热扫描时的交流热容在23.9摄氏度附近出现一个峰值，半高宽为0.15 - 0.20摄氏度。焓变为4.8千卡/摩尔，与传统差示扫描量热法的结果吻合良好。冷却扫描时，峰值温度降低0.1 - 0.5摄氏度，宽度增加到0.25 - 0.40摄氏度，表观焓变仅为加热时的40%。在准等温条件下，加热和冷却热容至少20分钟内保持稳定。在10摄氏度下退火1小时后，加热扫描结果具有很好的可重复性。这些结果可以用酰基链冻结时双层中有序小区域的成核及随后的退火来解释。未观察到与预转变相关的峰值，正如预期的那样，因为产生预转变的自由度的弛豫时间远长于0.4赫兹温度波的周期。
