Ultrafast Structural Dynamics of Biomolecular Complexes Probed by Broadband Time-Resolved Circular Dichroism

Area of Science:

• Chemical Physics
• Biophysics
• Spectroscopy

Background:

• Chiral molecular dynamics are crucial for understanding biomolecular reaction mechanisms.
• The three-dimensional structure of molecules dictates reaction selectivity and efficiency.

Purpose of the Study:

• To develop a practical method for tracking absolute configuration changes in photoexcited biomolecules.
• To investigate the excited-state dynamics of bilirubin-human serum albumin (BR-HSA) complexes.

Main Methods:

• Combining ultrafast and broadband time-resolved circular dichroism (TRCD) spectroscopy.
• Applying exciton coupling theory to interpret spectroscopic data.
• Conducting a proof-of-principle experiment on BR-HSA complexes.

Main Results:

• Observed a sign inversion in excited-state CD spectra of BR-HSA complexes with a time constant of approximately 5 ps.
• Attributed the spectral sign reversal to a structural change from a ridge-tile to a stretched conformation.
• Demonstrated that the observed phenomenon is not a complete chirality inversion.

Conclusions:

• The developed TRCD method is effective for real-time probing of excited-state molecular dynamics.
• The study provides insights into the conformational changes of photoexcited biomolecules.
• Exciton coupling theory aids in understanding the observed spectral changes and structural dynamics.