Studies investigating the influence of the length of linkers between redox-active moieties and peptide-based polymer backbones were conducted to advance fundamental knowledge toward the design and development of sustainably-sourced, recyclable, and degradable materials for energy applications. In this work, precursor polypeptides were synthesized through the ring-opening polymerizations of N-carboxyanhydrides decorated with varying lengths of alkylchloride side chain groups, followed by post-polymerization installation of the viologen moieties. Electrochemical interrogation of the viologen-based polypeptides provided estimates of the electron transfer rate constants, both heterogeneous (k⁰) and electron self-exchange (k_ex), the apparent diffusion coefficient (D_ap), and their device-based energy storage performance. For the first redox couple (viologen dication state to viologen radical-cation state), it was found that the rate of electron transfer among the pendant groups in all viologen-based polypeptides, k_ex, was not significantly impacted by linker length. In contrast, for the second redox couple (viologen radical-cation state to the neutral viologen), k_ex varied with linker length and was fastest during reduction from the viologen radical-cation state to the neutral viologen. Most interestingly, a linear relationship was identified between log(k⁰) and log(k_ex) with a slope of 1.85, indicating that electron transport in the viologen-based polypeptides followed most closely to Marcus–Hush theory with diffusion limitations or Laviron–Andrieux–Savéant (LAS) theory. Finally, the polypeptides were studied in lithium metal half cells to determine the relationship between k_ex and energy storage performance. The viologen-based polypeptide with the moderate length linker exhibited the highest capacity and lowest degree of swelling, but only moderate k_ex, demonstrating that the device performance was primarily influenced electrode swelling. Taken together, the viologen-polypeptide backbone dictated the mechanism of electron transfer, whereas the linker length could be used to alter the rate of electron transfer (k_ex). Balancing the rate of electron transfer (k_ex) and degree of swelling will be a major challenge to identify polymers for high performance energy storage devices.

中文翻译：

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具有不同侧基接头间距的含紫精多肽的电子传递动力学


进行了调查氧化还原活性部分和基于肽的聚合物骨架之间连接子长度影响的研究，以推进用于能源应用的可持续来源、可回收和可降解材料的设计和开发的基本知识。在这项工作中，通过用不同长度的烷基氯化物侧链基团装饰的 N-羧酐的开环聚合合成前体多肽，然后进行紫精部分的后聚合安装。基于紫精的多肽的电化学询问提供了电子传递速率常数的估计值，包括异质 （k⁰） 和电子自交换 （k_ex）、表观扩散系数 （D_ap） 及其基于器件的储能性能。对于第一对氧化还原对 （紫精定义状态到紫精自由基-阳离子状态），发现所有基于紫精的多肽中悬垂基团之间的电子转移速率 k_ex 不受接头长度的显着影响。相反，对于第二个氧化还原对（中性紫精的紫精自由基-阳离子态），k_ex 随接头长度的变化而变化，并且在从紫精自由基-阳离子状态还原到中性紫精状态的过程中最快。最有趣的是，在 log（k⁰） 和 log（k_ex） 之间确定了斜率为 1 的线性关系。85，表明基于紫精的多肽中的电子传递最接近于具有扩散限制的 Marcus-Hush 理论或 Laviron-Andrieux-Savéant （LAS） 理论。最后，在锂金属半电池中研究多肽，以确定 k_ex 与储能性能之间的关系。具有中等长度接头的基于紫精的多肽表现出最高的容量和最低的溶胀程度，但只有适度的 k_ex，表明器件性能主要受电极溶胀的影响。综上所述，紫精多肽骨架决定了电子转移的机制，而接头长度可用于改变电子转移速率 （k_ex）。平衡电子转移速率 （k_ex） 和膨胀程度将是确定用于高性能储能器件的聚合物的主要挑战。