van Osdol W W, Johnson M L, Ye Q, Biltonen R L
Department of Biochemistry, University of Virginia School of Medicine, Charlottesville 22908.
Biophys J. 1991 Apr;59(4):775-85. doi: 10.1016/S0006-3495(91)82290-1.
The relaxation kinetics of the gel to liquid-crystalline transition of five phosphatidylcholine (DC14PC to DC18PC) bilayer dispersions have been investigated using volume perturbation calorimetry, a steady-state technique which subjects a sample to sinusoidal changes in volume. Temperature and pressure responses to the volume perturbation are measured to monitor the relaxation to a new equilibrium position. The amplitude demodulation and phase shift of these observables are analyzed with respect to the perturbation frequency to yield relaxation times and amplitudes. In the limit of low perturbation frequency, the temperature and pressure responses are proportional to the equilibrium excess heat capacity and bulk modulus, respectively. At all temperatures, the thermal response data are consistent with a single primary relaxation process of the lipid. The less accurate bulk modulus data exhibit two relaxation times, but it is not clear whether they reflect lipid processes or are characteristic of the instrument. The observed thermal relaxation behavior of all multilamellar vesicles are quantitatively similar. The relaxation times vary from approximately 50 ms to 4 s, with a pronounced maximum at a temperature just greater than Tm, the temperature of the excess heat capacity maximum. Large unilamellar vesicles also exhibit a single relaxation process, but without a pronounced maximum in the relaxation time. Their relaxation time is approximately 80 ms over most of the transition range.
利用体积扰动量热法研究了五种磷脂酰胆碱（DC14PC至DC18PC）双层分散体从凝胶态到液晶态转变的弛豫动力学，这是一种稳态技术，使样品受到体积的正弦变化。测量对体积扰动的温度和压力响应，以监测向新平衡位置的弛豫。针对扰动频率分析这些可观测量的幅度解调及相移，以得出弛豫时间和幅度。在低扰动频率极限下，温度和压力响应分别与平衡过量热容和体积模量成正比。在所有温度下，热响应数据与脂质的单一初级弛豫过程一致。不太准确的体积模量数据呈现出两个弛豫时间，但尚不清楚它们是反映脂质过程还是仪器的特征。所有多层囊泡观察到的热弛豫行为在数量上相似。弛豫时间从约50毫秒到4秒不等，在略高于Tm（过量热容最大值的温度）的温度下有一个明显的最大值。大单层囊泡也表现出单一弛豫过程，但弛豫时间没有明显的最大值。在大部分转变范围内，它们的弛豫时间约为80毫秒。
