Fermi resonance as a tool for probing peridinin environment

Area of Science:

• Biophysical Chemistry
• Spectroscopy
• Computational Chemistry

Background:

• Peridinin is a vital carotenoid pigment found in photosynthetic organisms.
• Peridinin plays crucial roles in light harvesting and photoprotection within peridinin-chlorophyll proteins (PCPs).
• Understanding peridinin's environment is key to elucidating its function in light-harvesting complexes.

Purpose of the Study:

• To investigate the vibrational signature of peridinin in various solvents.
• To utilize resonance Raman spectroscopy (RRS) and theoretical calculations to probe peridinin's molecular environment.
• To establish a spectroscopic method for differentiating peridinin molecules in distinct environments.

Main Methods:

• Combined experimental resonance Raman spectroscopy (RRS) with theoretical calculations (DFT).
• Analyzed the Fermi resonance between the lactonic C═O stretch and the C-H wag overtone.
• Employed a quasi-classical dynamical model of coupled oscillators to validate spectroscopic findings.

Main Results:

• Identified a Fermi resonance in peridinin's vibrational spectrum, sensitive to solvent polarity.
• Demonstrated that solvent polarity can tune the Fermi resonance, altering band intensity and splitting.
• Successfully assigned vibrational modes in the 800-1600 cm(-1) region, linked to polyene chain motion.

Conclusions:

• The Fermi resonance provides a powerful tool to differentiate peridinin environments, crucial for understanding PCPs.
• This spectroscopic approach offers insights into the photophysical roles of peridinin in different protein contexts.
• Reinterpretation of previous vibrational spectroscopic data in PCPs is now possible based on these findings.