Studies of structural fluctuations of complex systems by transient hole-burning

我们开发的时间分辨光谱空穴燃烧光谱是一种很好的方法，使我们能够直接观察各种材料在很宽的温度和时间范围内的平衡构象波动。我们将该方法的时间分辨率提高到10ns，并将其应用于汞溴染料和锌取代肌红蛋白的水-甘油混合物中。研究发现，在150 ~ 300 K温度范围内，空穴质心的时间依赖关系可以用一个拉伸的指数函数来表示，波动的相关时间服从Vogel-Fulcher定律。与染料溶液相比，蛋白质溶液中的时间行为是非指数性的，对温度的依赖性也弱得多。已经直接证明，蛋白质分子的构象动力学强烈地依赖于其周围环境的构象动力学，并且蛋白质的玻璃化转变是由溶剂的冻结控制的。所得结果可以用层次约束动力学模型很好地解释。我们还比较了天然类和熔化球状细胞色素c之间的构象动力学。此外，我们还发现，除了时间分辨光谱烧孔外，还可以利用极化光谱确定肌红蛋白和细胞色素c在不均匀加宽吸收带中的Qx和Qy波段的光谱形状。

The time-resolved spectral hole-burning spectroscopy we have developed is an excellent method that enables us directly to observe the equilibrium conformational fluctuations in various materials over wide temperature and time ranges. We have improved the temporal resolution of this method to 10 ns, and applied it to merbromin dye and zinc-substituted myoglobin in a water-glycerol mixture. It has been found that the time dependence of the barycenter of the hole is expressed by a stretched exponential function and that the correlation time of the fluctuation obeys the Vogel-Fulcher law over the 150-300 K temperature range. The time behavior is much more non-exponential and much weakly dependent on temperature in protein solutions compared with dye solutions. It has been directly demonstrated that the conformational dynamics of a protein molecule is strongly dependent on that of its surroundings, and the glass transition of the protein is governed by the freezing of the solvent. Whole the obtained results have been found to be explained well by a hierarchically constrained dynamics model. We have also compared the conformational dynamics between native-like and moltenglobule-like cytochrome c. Further, it has been shown that the spectral shapes of the Qx and Qy bands of myoglobin and cytochrome c, which are buried in the inhomogeneously broadened absorption bands, can be determined using polarization spectroscopy in addition to the time-resolved spectral hole-burning.