Carotenoids: Importance in Daily Life-Insight Gained from EPR and ENDOR | JoVE Visualize

Carotenoids: Importance in Daily Life-Insight Gained from EPR and ENDOR

A Ligia Focsan¹, Nikolay E Polyakov^2,3, Lowell D Kispert⁴

¹Department of Chemistry, Valdosta State University, Valdosta, GA 31698 USA.

Applied Magnetic Resonance|March 29, 2021

View abstract on PubMed

Summary

Carotenoid radicals, including radical cations and neutral radicals, were studied using electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) methods. These techniques, combined with DFT calculations, help distinguish between these important antioxidant species.

Area of Science:

Biochemistry
Physical Chemistry
Spectroscopy

Background:

Carotenoids are vital antioxidants found in plants, algae, and bacteria, protecting against oxidative stress.
Dietary carotenoids offer health benefits to humans, acting as antioxidants.
Carotenoids are susceptible to oxidation, forming radical cations and neutral radicals.

Purpose of the Study:

To review and discuss carotenoid radicals, specifically radical cations and neutral radicals, studied using various physicochemical methods.
To differentiate between carotenoid radical cations and neutral radicals using advanced spectroscopic and computational techniques.
To elucidate electron and proton transfer processes involving carotenoids in both artificial and biological systems.

Main Methods:

Electron Paramagnetic Resonance (EPR) spectroscopy
Electron Nuclear Double Resonance (ENDOR) spectroscopy
Density Functional Theory (DFT) calculations
INDO calculations (for historical comparison)
EPR spin-trapping technique

Main Results:

Carotenoid radical cations and neutral radicals exhibit similar hyperfine couplings due to electron-proton interactions.
EPR and ENDOR, coupled with DFT, successfully distinguished between radical cation and neutral radical species.
DFT calculations predicted larger coupling constants for neutral radicals than for radical cations, correcting previous INDO misassignments.
Physicochemical studies elucidated electron and proton transfer processes in adsorbed carotenoids, with implications for aqueous solutions and biological systems.
EPR spin-trapping was used to analyze carotenoid inclusion complexes.

Conclusions:

Physicochemical characterization of carotenoid radicals provides a deeper understanding of their biological implications.
The study of carotenoid radical chemistry in artificial systems paved the way for investigating these species in vivo.
Understanding carotenoid radical behavior is crucial for their role in biological antioxidant defense mechanisms.