The Structure and Function of Quinones in Biological Solar Energy Transduction: A Cyclic Voltammetry, EPR, and Hyperfine Sub-Level Correlation (HYSCORE) Spectroscopy Study of Model Naphthoquinones

• Published in: The journal of physical chemistry. B Vol. 117; no. 24; pp. 7210 - 7220
• Main Authors: Coates, Christopher S, Ziegler, Jessica, Manz, Katherine, Good, Jacob, Kang, Bernard, Milikisiyants, Sergey, Chatterjee, Ruchira, Hao, Sijie, Golbeck, John H, Lakshmi, K. V
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 20.06.2013
• Subjects: Biological and medical sciences; Electrochemical Techniques; Electron Spin Resonance Spectroscopy; Electronic properties; Fundamental and applied biological sciences. Psychology; Hydrogen bonds; Mathematical models; Models, Molecular; Molecular biophysics; Molecular Structure; Naphthoquinones - chemistry; Photochemistry. Photosynthesis. Bioluminescence; Quinones; Quinones - chemistry; Radiation-biomolecule interaction; Solar Energy; Solvents; Spectroscopy; Tuning; Voltammetry; Solvent effect; Cyclic voltammetry; Continuous wave; Electronic structure; Quinone; Electron mobility; Electron paramagnetic resonance; Photosynthesis; Hydrogen bond
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp401024p

Quinones function as electron transport cofactors in photosynthesis and cellular respiration. The versatility and functional diversity of quinones is primarily due to the diverse midpoint potentials that are tuned by the substituent effects and interactions with surrounding amino acid residues in the binding site in the protein. In the present study, a library of substituted 1,4-naphthoquinones are analyzed by cyclic voltammetry in both protic and aprotic solvents to determine effects of substituent groups and hydrogen bonds on the midpoint potential. We use continuous-wave electron paramagnetic resonance (EPR) spectroscopy to determine the influence of substituent groups on the electronic properties of the 1,4-naphthoquinone models in an aprotic solvent. The results establish a correlation between the presence of substituent group(s) and the modification of electronic properties and a corresponding shift in the midpoint potential of the naphthoquinone models. Further, we use pulsed EPR spectroscopy to determine the effect of substituent groups on the strength and planarity of the hydrogen bonds of naphthoquinone models in a protic solvent. This study provides support for the tuning of the electronic properties of quinone cofactors by the influence of substituent groups and hydrogen bonding interactions.