Polyphenolic compounds as electron shuttles for sustainable energy utilization

Abstract

For renewable and sustainable bioenergy utilization with cost-effectiveness, electron-shuttles (ESs) (or redox mediators (RMs)) act as electrochemical “catalysts” to enhance rates of redox reactions, catalytically accelerating electron transport efficiency for abiotic and biotic electrochemical reactions. ESs are popularly used in cellular respiratory systems, metabolisms in organisms, and widely applied to support global lives. Apparently, they are applicable to increase power-generating capabilities for energy utilization and/or fuel storage (i.e., dye-sensitized solar cell, batteries, and microbial fuel cells (MFCs)). This first-attempt review specifically deciphers the chemical structure association with characteristics of ESs, and discloses redox-mediating potentials of polyphenolics-abundant ESs via MFC modules. Moreover, to effectively convert electron-shuttling capabilities from non-sustainable antioxidant activities, environmental conditions to induce electrochemical mediation apparently play critical roles of great significance for bioenergy stimulation. For example, pH levels would significantly affect electrochemical potentials to be exhibited (e.g., alkaline pHs are electrochemically favorable for expression of such electron-shuttling characteristics). Regarding chemical structure effect, chemicals with ortho- and para-dihydroxyl substituents-bearing aromatics own convertible characteristics of non-renewable antioxidants and electrochemically catalytic ESs; however, ES capabilities of meta-dihydroxyl substituents can be evidently repressed due to lack of resonance effect in the structure for intermediate radical(s) during redox reaction. Moreover, this review provides conclusive remarks to elucidate the promising feasibility to identify whether such characteristics are non-renewable antioxidants or reversible ESs from natural polyphenols via cyclic voltammetry and MFC evaluation. Evidently, considering sustainable development, such electrochemically convertible polyphenolic species in plant extracts can be reversibly expressed for bioenergy-stimulating capabilities in MFCs under electrochemically favorable conditions.

Kinetic insights into the peroxygenase activity of cellulose-active lytic polysaccharide monooxygenases (LPMOs)

“…In Nature 27 as well as in industrial applications [28][29][30] , LPMOs involved in lignocellulose degradation operate in redox-active environments where both potential co-substrates, O 2 and H 2 O 2 , as well as multiple compounds and/or enzymes interacting with these co-substrates, are present. For example, the secretomes of fungi growing on lignocellulosic biomass contain, next to LPMOs, a myriad of different enzymes including several H 2 O 2 -consuming enzymes like different peroxidases and peroxygenases 27 .…”

Interactive deciphering electron-shuttling characteristics of agricultural wastes with potential bioenergy-steered anti-COVID-19 activity via microbial fuel cells

“…Stably reversible profiles of ESs or gradually attenuated sketches of antioxidants from distinct herbal extracts could suggest whether such herbal extracts were sustainable or unendurable for bioenergy/biorefinery applications, respectively. As prior studies [ 39 , 40 ] revealed, comparison upon more than 20 species of refreshing medicinal herbs indicated that electroactive medicinal herbs- Syzygium aromaticum (Dıng xiang), Citrus reticulate (Chenpí) and Lonicera japonica (Jınyín hua) and Camellia green tea ( Camellia sinensis (L.) Kuntze) were the most electroactive medicinal herbs due to the greatest area and most significant redox potential peaks displayed in CV profiles. As recent novel findings disclosed [11] , chemicals bearing ortho or para dihydroxyl substituents on benzene ring and the flavonoid structure(s) would be the most favorable to mediate electron-shuttling features for bioenergy stimulation and antiviral “catalysis”.…”

Exploring community evolutionary characteristics of microbial populations with supplementation of Camellia green tea extracts in microbial fuel cells

“…In addition, the final solid/liquid ratio (S/L) was set as 5 g/50 mL to have identical basis for comparison. To have comparative assessment with prior studies, the deionized water and 80% methanol (MEOH) aqueous solutions were intentionally used as solvents of extraction at room temperature in total volume of 50 mL with continuous stirring for 12 h [33] , [34] , [35] . Supernatants of GT extracts were obtained via centrifugation at 13,000 rpm, 25 °C for 10 min.…”

“…As prior work indicated, different methods of extraction could result in different levels of antioxidant/ electron transfer capabilities (e.g., H 2 O extracted > EtOH extracted) [33] . Moreover, many medicinal herbs may not be appropriate to be extracted in low temperature, rather than at high temperature.…”