Abstract：

Structure and dynamics of complex systems in condensed phase govern their functions which broadly impact biological and materials applications. However, a complete understanding of those processes is hindered by the availability of suitable tools that can resolve atomic motions on molecular timescales. We developed tunable femtosecond stimulated Raman spectroscopy (FSRS) in the mixed time-frequency domain^1-3 to investigate various photochemical events of organic chromophores in solution and proteins, capturing high-resolution molecular “movies” on ultrafast timescales.⁴ Resonance enhancement conditions for transient molecular species along multidimensional reaction coordinates are achieved with guidance from transient absorption.^5,6 This talk focuses on green fluorescent protein (GFP) chromophore as a versatile nanomachine that has enabled new insights into the photoinduced isomerization in solution,⁷ excited state proton transfer in protein matrix,^8,9 site-specific modification to achieve redder fluorescence emission¹⁰ and functional change of a calcium biosensor.¹¹ These new endeavors bridge the gap between structure and function of nanomachines and also generate the targeted design principles for improved functionalities, which has found wide applications across disciplines.^4,12

References:

    (1)     Liu, W.; Han, F.; Smith, C.; Fang, C. Ultrafast Conformational Dynamics of Pyranine during Excited State Proton Transfer in Aqueous Solution Revealed by Femtosecond Stimulated Raman Spectroscopy. J. Phys. Chem. B 2012, 116, 10535-10550.

    (2)     Wang, W.; Liu, W.; Chang, I.-Y.; Wills, L. A.; Zakharov, L. N.; Boettcher, S. W.; Cheong, P. H.-Y.; Fang, C.; Keszler, D. A. Electrolytic Synthesis of Aqueous Aluminum Nanoclusters and in situ Characterization by Femtosecond Raman Spectroscopy & Computations. Proc. Natl. Acad. Sci. U. S. A. 2013, 110, 18397-18401.

    (3)     Zhu, L.; Liu, W.; Fang, C. A Versatile Femtosecond Stimulated Raman Spectroscopy Setup with Tunable Pulses in the Visible to Near Infrared. Appl. Phys. Lett. 2014, 105, 041106.

    (4)     Fang, C.; Tang, L.; Oscar, B. G.; Chen, C. Capturing Structural Snapshots during Photochemical Reactions with Ultrafast Raman Spectroscopy: From Materials Transformation to Biosensor Responses. J. Phys. Chem. Lett. 2018, 9, 3253–3263.

    (5)     Liu, W.; Wang, Y.; Tang, L.; Oscar, B. G.; Zhu, L.; Fang, C. Panoramic Portrait of Primary Molecular Events Preceding Excited State Proton Transfer in Water. Chem. Sci. 2016, 7, 5484-5494.

    (6)     Liu, W.; Tang, L.; Oscar, B. G.; Wang, Y.; Chen, C.; Fang, C. Tracking Ultrafast Vibrational Cooling During Excited State Proton Transfer Reaction with Anti-Stokes and Stokes Femtosecond Stimulated Raman Spectroscopy. J. Phys. Chem. Lett. 2017, 8, 997–1003.

    (7)     Taylor, M. A.; Zhu, L.; Rozanov, N. D.; Stout, K. T.; Chen, C.; Fang, C. Delayed Vibrational Modulation of the Solvated GFP Chromophore into A Conical Intersection. Phys. Chem. Chem. Phys. 2019, 21, 9728-9739.

    (8)     Fang, C.; Frontiera, R. R.; Tran, R.; Mathies, R. A. Mapping GFP Structure Evolution during Proton Transfer with Femtosecond Raman Spectroscopy. Nature 2009, 462, 200-204.

    (9)     Oscar, B. G.; Liu, W.; Zhao, Y.; Tang, L.; Wang, Y.; Campbell, R. E.; Fang, C. Excited-State Structural Dynamics of a Dual-Emission Calmodulin-Green Fluorescent Protein Sensor for Calcium Ion Imaging. Proc. Natl. Acad. Sci. U. S. A. 2014, 111, 10191-10196.

    (10)   Chen, C.; Baranov, M. S.; Zhu, L.; Baleeva, N. S.; Smirnov, A. Y.; Zaitseva, S.; Yampolsky, I. V.; Solntsev, K. M.; Fang, C. Designing Redder and Brighter Fluorophores by Synergistic Tuning of Ground and Excited States. Chem. Commun. 2019, 55, 2537-2540.

    (11)   Tachibana, S. R.; Tang, L.; Wang, Y.; Zhu, L.; Liu, W.; Fang, C. Tuning Calcium Biosensors with a Single-Site Mutation: Structural Dynamics Insights from Femtosecond Raman Spectroscopy. Phys. Chem. Chem. Phys. 2017, 19, 7138-7146.

    (12)   Zhang, C.; Holoubek, J. J.; Wu, X.; Daniyar, A.; Zhu, L.; Chen, C.; Leonard, D. P.; Rodríguez-Pérez, I. A.; Jiang, J.-X.; Fang, C.; et al. ZnCl2 Water-in-Salt Electrolyte for Reversible Zn Metal Anode. Chem. Commun. 2018, 54, 14097–14099.