Structural Flexibility and Electronic Tuning in N₅-Substituted Anionic Reduced Flavins: Implications for Flavoenzyme...

Area of Science:

• Biochemistry
• Physical Chemistry
• Computational Chemistry

Background:

• N5-substituted reduced flavins are crucial but understudied intermediates in flavoenzyme catalysis.
• Understanding their properties is key to advancing enzymatic and catalytic applications.

Purpose of the Study:

• To investigate the structural and electronic dynamics of N5-substituted anionic reduced flavin derivatives.
• To elucidate the factors governing their unique absorption properties and relaxation pathways.

Main Methods:

• Steady-state and ultrafast transient absorption spectroscopy.
• Density Functional Theory (DFT) and Time-Dependent DFT (TDDFT) simulations.

Main Results:

• N5-substituted flavins show distinct blue-shifted absorption bands (330 or 370 nm), unlike FADH-.
• HOMO orbital stabilization, not isoalloxazine ring bending, dictates absorption properties.
• Ultrafast spectroscopy reveals relaxation from various bend conformations to a planar state via a conical intersection.

Conclusions:

• Findings reshape the understanding of flavin photophysics and electronic reorganization.
• The N5 substituent modulates the conical intersection, influencing relaxation pathways.
• This work provides fundamental insights into flavoenzyme catalytic mechanisms.