Biomimetic Approach to Confer Redox Activity to Thin Chitosan Films

Abstract

Electron transfer in biology occurs with individual or pairs of electrons, and is often mediated by catechol/o‐quinone redox couples. Here, a biomimetic polysaccharide‐catecholic film is fabricated in two steps. First, the stimuli‐responsive polysaccharide chitosan is electrodeposited as a permeable film. Next, the chitosan‐coated electrode is immersed in a solution containing catechol and the electrode is biased to anodically‐oxidize the catechol. The oxidation products covalently graft to the chitosan films as evidenced by electrochemical quartz crystal microbalance (EQCM) studies. Cyclic voltammetry (CV) measurements demonstrate that the catechol‐modified chitosan films are redox‐active although they are non‐conducting and cannot directly transfer electrons to the underlying electrode. The catechol‐modified chitosan films serve as a localized source or sink of electrons that can be transferred to soluble mediators (e.g., ferrocene dimethanol and Ru(NH3) 6Cl3). This electron source/sink is finite, can be depleted, but can be repeatedly regenerated by brief (30 s) electrochemical treatments. Further, the catechol‐modified chitosan films can i) amplify currents associated with the soluble mediators, ii) partially‐rectify these currents in either oxidative or reductive directions (depending on the mediator), and iii) switch between regenerated‐ON and depleted‐OFF states. Physical models are proposed to explain these novel redox properties and possible precedents from nature are discussed.

Enzymatic Writing to Soft Films: Potential to Filter, Store, and Analyze Biologically Relevant Chemical Information

“…Similar differences have been observed elsewhere for CVs of fi lms in which smaller amounts of grafted catechol (peak shape) were compared to those with larger levels of grafted catechol (sigmoidal shape). [ 41 ] Thus, the CV results in Figure 3 d are consistent with the previous explanation that ascorbate suppresses catechin's enzymatic grafting but accelerates resveratrol's enzymatic grafting.…”

“…One of the challenges in detecting phenolics from typical dietary sources (e.g., fruits) is that often these samples contain chitosan [ 41 ] fi lms are conducting (these fi lms cannot directly exchange electrons with the underlying electrode). Second, the electron transfer reactions are thermodynamically driven as illustrated by the redox-plot in Scheme 2 ; electrons can only be transferred to the fi lm from mediators that have a more negative redox potential or transferred from the fi lm to mediators that have a more positive redox potential.…”

“…[ 41,42 ] Typically, the fi lm's redox-activity is measured using electrochemical mediators that can diffuse through the fi lm and engage in redox-cycling reactions that transfer electrons between the fi lm and an underlying electrode. The scheme at the left in Scheme 2 shows the ferrocene dimethanol mediator (Fc) diffusing through the fi lm, being oxidized at the electrode and then being re-reduced by accepting electrons from the grafted catechol moieties.…”

Reversible Electroaddressing of Self‐assembling Amino‐Acid Conjugates

“…Electrochemical quartz crystal microbalance (EQCM) measurements were carried out on a CHI420a Electrochemical Analyzer (CH Instruments, Inc., Austin, TX) and the experimental procedure was described elsewhere. [ 63 ] For in situ EQCM experiments, the gold-coated crystal (working area: 0.205 cm 2 ) with 8 MHz resonating frequency served as the working electrode, Ag/AgCl as a reference electrode and Pt wire as a counter electrode. For ex situ QCM experiments, the frequency of the dried crystal before and after electrodeposition was measured in the air, and the difference of frequency ( Δ F ) was used to estimate the mass change using the Sauerbrey equation.…”

Effect of deproteination and deacetylation conditions on viscosity of chitin and chitosan extracted from Crangon crangon shrimp waste

“…Biological materials derived from chitin like chitosan films either alone or in blends with other polymers have found extensive technological applications in material engineering. Blending chitosan with sucrose, sorbitol, gelatin, pectin etc., is a promising approach in the field of food packaging for producing edible films useful for specific purposes [8][9][10]. Due to its chelating ability with metals and radioactive isotopes, lack of toxicity and biodegradability, chitosan has found another useful application as an adsorbent.…”