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

我们发展的时间分辨光谱烧孔光谱是一种很好的方法，它使我们能够在很宽的温度和时间范围内直接观察各种材料的平衡构象涨落。我们已将该方法的时间分辨率提高到10 ns，并将其应用于水-甘油混合物中的水银染料和锌取代肌红蛋白。结果表明，在150-300K温度范围内，空穴质心的时间依赖关系用伸长的指数函数表示，涨落的关联时间服从伏格尔-富勒定律。与染料溶液相比，蛋白质溶液中的时间行为更具非指数性，对温度的依赖性更弱。已经直接证明了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。总体而言，所获得的结果被发现可以很好地用分层约束的动力学模型来解释。我们还比较了天然类细胞色素c和类熔球状细胞色素c的构象动力学，进一步表明，肌红蛋白和细胞色素c的Qx和Qy带的光谱形状除了时间分辨的烧孔光谱外，还可以用偏振光谱来确定，它们隐藏在非均匀展宽的吸收带中。

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.