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

Abstract

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.

Exploring Bio-inspired Quinone-Based Organic Redox Flow Batteries: A Combined Experimental and Computational Study

“…36 As the peak in CV measurement arises from the formation of a diffusion layer near the electrode surface, the smaller peak area of the second reduction process of NQ might be due to a resistive diffusion layer of quinone intermediate on the electrode surface (Figure S3). 37,38 In contrast, Figure 3A shows that NQ undergoes two successive oneelectron-transfer processes with almost equal capacities at a much lower rate of 0.05 C. In addition to the factor of the charge-discharge rate, different test environments may also lead to distinction in electron-transfer processes between CV measurements and battery tests of quinone.…”

Respiratory quinones in Archaea: phylogenetic distribution and application as biomarkers in the marine environment

“…Structural characterization and quantification of respiratory quinones facilitates the elucidation of microbial electron transport chains (Whittaker et al ., ; Stams and Plugge, ; Coates et al ., ). Similarly, interpretation of quinone profiles in environmental samples is facilitated by detailed description of quinone diversity in cultivated organisms (Collins and Jones, ; Hiraishi, ; Urakawa et al ., 2000; 2005).…”

Synthesis of Amino Acid–Naphthoquinones and In Vitro Studies on Cervical and Breast Cell Lines

“…In the last decades, some publications have been dedicated to finding an explanation for the formation of these intermediates in the synthetic mechanism, and their properties that have produced different compounds with a plethora of applications of biological importance and effects that involve intra- or intermolecular interactions. One of the principal effects of these compounds is the generation of reactive oxygen species (ROS), producing cytotoxicity in different cell lines [6,7,8,9,10,11,12,13]. ROS generation with naphthoquinones represents a challenge in the design of new active compounds, principally with anticancer effect.…”