Caffrey M, Fanger G, Magin R L, Zhang J
Department of Chemistry, Ohio State University, Columbus 43210.
Biophys J. 1990 Sep;58(3):677-86. doi: 10.1016/S0006-3495(90)82410-3.
The dynamics and mechanism of the premelting (L beta'-P beta') and main transitions (P beta'-L alpha) in fully hydrated dipalmitoylphosphatidylcholine were examined by low-angle time-resolved x-ray diffraction (TRXRD) using microwave radiation to effect uniform, internal sample heating. Equilibrium and dynamic aspects of the transitions were investigated. The dynamic studies involved applying a temperature jump of sufficient amplitude to effect the two transitions sequentially. Our findings are as follows. (a) Microwave radiation has proven useful as a means for implementing rapid and uniform internal heating in temperature-jump studies of lipid-phase transition kinetics. (b) Heating rate can be controlled by adjusting microwave power setting. (c) The thermal expansion coefficient of the three lyotropic phases follows the sequence L beta' not equal to O greater than P beta' much greater than L alpha. (d) Regardless of temperature-jump amplitude and sample heating rate the P beta' phase was always in evidence as an intermediate between the L beta' and L alpha phases. (e) The degree of development of the P beta' phase was inversely proportional to temperature-jump amplitude and heating rate. (f) The shortest transit time recorded for the combined L beta'-P beta', and P beta'-L alpha transitions was less than 1 s. (g) Upon cooling from the L alpha phase the onset of the chain disorder/order transition was apparent as a dramatic change of slope in the scattering angle vs. time plot which is interpreted as arising from sample heating by the latent heat of the transition. (h) Based on the shape of the low-angle diffraction pattern of the P beta' phase the P beta'-L alpha transition appears to be reversible with no evidence of metastability as was observed in the slow scan TRXRD measurements of Tenchov et al. (1989. Biophys. J. 56:757-768).
利用微波辐射实现样品内部均匀加热，通过低角度时间分辨X射线衍射（TRXRD）研究了完全水合的二棕榈酰磷脂酰胆碱中预熔解（Lβ'-Pβ'）和主要转变（Pβ'-Lα）的动力学及机制。对转变的平衡和动力学方面进行了研究。动力学研究包括施加足够幅度的温度跃变以依次实现这两个转变。我们的研究结果如下：（a）在脂质相转变动力学的温度跃变研究中，微波辐射已被证明是实现快速且均匀内部加热的有效手段。（b）加热速率可通过调整微波功率设置来控制。（c）三种溶致相的热膨胀系数顺序为Lβ'≠O＞Pβ'≫Lα。（d）无论温度跃变幅度和样品加热速率如何，Pβ'相始终作为Lβ'和Lα相之间的中间相出现。（e）Pβ'相的发展程度与温度跃变幅度和加热速率成反比。（f）记录到的Lβ'-Pβ'和Pβ'-Lα联合转变的最短过渡时间小于1秒。（g）从Lα相冷却时，链无序/有序转变的开始表现为散射角与时间曲线斜率的急剧变化，这被解释为是由转变潜热导致的样品加热引起的。（h）基于Pβ'相低角度衍射图案的形状，Pβ'-Lα转变似乎是可逆的，没有如Tenchov等人（1989年，《生物物理杂志》56:757 - 768）在慢扫描TRXRD测量中观察到的亚稳性证据。
