We simulated an excited state proton transfer in green fluorescent protein by excited state ab initio dynamics, and examined the reaction mechanism in both the time and the frequency domain through a multi resolution wavelet analysis. This original approach allowed us, for the first time, to directly compare the trends of photoactivated vibrations to femtosecond stimulated Raman spectroscopy results, and to give an unequivocal interpretation of the role played by low frequency modes in promoting the reaction. We could attribute the main driving force of the reaction to an important photoinduced softening of the ring–ring orientational motion of the chromophore, thus permitting the tightening of the hydrogen bond network and the opening of the reaction pathway. We also found that both the chromophore (in terms of its inter-ring dihedral angle and phenolic C–O and imidazolinone C–N bond distances) and its pocket (in terms of the inter-molecular oxygen’s dihedral angle of the chromophore pocket) relaxations are modulated by low frequency (about 120 cm⁻¹) modes involving the oxygen atoms of the network. This is in agreement with the femtosecond Raman spectroscopy findings in the time-frequency domain. Moreover, the rate in proximity to the Franck Condon region involves a picosecond time scale, with a significant influence from fluctuations of nearby hydrogen bonded residues such as His148. This approach opens a new scenario with ab initio simulations as routinely used tools to understand photoreactivity and the results of advanced time resolved spectroscopy techniques.

中文翻译：

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通过激发态从头动力学在时间分辨频域中揭示绿色荧光蛋白质子穿梭机制†

我们通过激发态从头算动力学模拟了绿色荧光蛋白中的激发态质子转移，并通过多分辨率小波分析研究了时域和频域的反应机制。这种原创方法使我们第一次能够直接比较光激活振动的趋势与飞秒受激拉曼光谱结果，并对低频模式在促进反应中所起的作用给出明确的解释。我们可以将反应的主要驱动力归因于发色团环-环取向运动的重要光诱导软化，从而使氢键网络收紧并打开反应途径。我们还发现发色团（就其环间二面角和酚类 C-O 和咪唑啉酮 C-N 键距而言）及其口袋（就发色团口袋的分子间氧二面角而言）松弛由涉及网络氧原子的低频（约120 cm ^-1 ）模式调制。这与飞秒拉曼光谱在时频域的发现一致。此外，Franck Condon 区域附近的速率涉及皮秒时间尺度，受到附近氢键残基（例如 His148）波动的显着影响。这种方法开辟了一个新的场景，从头开始模拟作为理解光反应性和先进时间分辨光谱技术结果的常规工具。