Massari Aaron M, Finkelstein Ilya J, Fayer Michael D
Department of Chemistry, Stanford University, Stanford, California 94305, USA.
J Am Chem Soc. 2006 Mar 29;128(12):3990-7. doi: 10.1021/ja058745y.
Spectrally resolved infrared stimulated vibrational echo spectroscopy is used to measure the fast dynamics of heme-bound CO in carbonmonoxy-myoglobin (MbCO) and -hemoglobin (HbCO) embedded in silica sol-gel glasses. On the time scale of approximately 100 fs to several picoseconds, the vibrational dephasing of the heme-bound CO is measurably slower for both MbCO and HbCO relative to that of aqueous protein solutions. The fast structural dynamics of MbCO, as sensed by the heme-bound CO, are influenced more by the sol-gel environment than those of HbCO. Longer time scale structural dynamics (tens of picoseconds), as measured by the extent of spectral diffusion, are the same for both proteins encapsulated in sol-gel glasses compared to that in aqueous solutions. A comparison of the sol-gel experimental results to viscosity-dependent vibrational echo data taken on various mixtures of water and fructose shows that the sol-gel-encapsulated MbCO exhibits dynamics that are the equivalent of the protein in a solution that is nearly 20 times more viscous than bulk water. In contrast, the HbCO dephasing in the sol-gel reflects only a 2-fold increase in viscosity. Attempts to alter the encapsulating pore size by varying the molar ratio of silane precursor to water (R value) used to prepare the sol-gel glasses were found to have no effect on the fast or steady-state spectroscopic results. The vibrational echo data are discussed in the context of solvent confinement and protein-pore wall interactions to provide insights into the influence of a confined environment on the fast structural dynamics experienced by a biomolecule.
光谱分辨红外受激振动回声光谱法用于测量嵌入硅溶胶 - 凝胶玻璃中的一氧化碳肌红蛋白（MbCO）和一氧化碳血红蛋白（HbCO）中血红素结合的CO的快速动力学。在大约100飞秒到几皮秒的时间尺度上，相对于水性蛋白质溶液，MbCO和HbCO中血红素结合的CO的振动退相明显更慢。血红素结合的CO所感知的MbCO的快速结构动力学比HbCO受溶胶 - 凝胶环境的影响更大。通过光谱扩散程度测量的较长时间尺度的结构动力学（几十皮秒），对于封装在溶胶 - 凝胶玻璃中的两种蛋白质与水溶液中的情况相同。将溶胶 - 凝胶实验结果与在水和果糖的各种混合物上获得的粘度依赖性振动回声数据进行比较表明，溶胶 - 凝胶封装的MbCO表现出的动力学相当于在粘度比纯水高近20倍的溶液中的蛋白质。相比之下，溶胶 - 凝胶中HbCO的退相仅反映粘度增加了2倍。发现通过改变用于制备溶胶 - 凝胶玻璃的硅烷前体与水的摩尔比（R值）来改变封装孔径对快速或稳态光谱结果没有影响。在溶剂限制和蛋白质 - 孔壁相互作用的背景下讨论了振动回声数据，以深入了解受限环境对生物分子经历的快速结构动力学的影响。
