Chromophore Dynamics in the PYP Photocycle from Femtosecond Stimulated Raman Spectroscopy

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• 作者：Mark Creelman ; Masato Kumauchi ; Wouter D. Hoff ; Richard A. Mathies
• 刊名：Journal of Physical Chemistry B
• 出版年：2014
• 出版时间：January 23, 2014
• 年：2014
• 卷：118
• 期：3
• 页码：659-667
• 全文大小：483K
• ISSN：1520-5207

文摘

Femtosecond stimulated Raman spectroscopy (FSRS) is used to examine the structural dynamics of the para-hydroxycinnamic acid (HCA) chromophore during the first 300 ps of the photoactive yellow protein (PYP) photocycle, as the system transitions from its vertically excited state to the early ground state cis intermediate, I₀. A downshift in both the C₇鈺怌₈ and C₁鈺怬 stretches upon photoexcitation reveals that the chromophore has shifted to an increasingly quinonic form in the excited state, indicating a charge shift from the phenolate moiety toward the C₉鈺怬 carbonyl, which continues to increase for 170 fs. In addition, there is a downshift in the C₉鈺怬 carbonyl out-of-plane vibration on an 800 fs time scale as PYP transitions from its excited state to I₀, indicating that weakening of the hydrogen bond with Cys69 and out-of-plane rotation of the C₉鈺怬 carbonyl are key steps leading to photoproduct formation. HOOP intensity increases on a 3 ps time scale during the formation of I₀, signifying distortion about the C₇鈺怌₈ bond. Once on the I₀ surface, the C₇鈺怌₈ and C₁鈺怬 stretches blue shift, indicating recovery of charge to the phenolate, while persistent intensity in the HOOP and carbonyl out-of-plane modes reveal HCA to be a cissoid structure with significant distortion about the C₇鈺怌₈ bond and of C₉鈺怬 out of the molecular plane.