Department of Chemistry, University of Utah , 315 S 1400, Salt Lake City, Utah 84112, United States.
Department of Chemistry and Biochemistry, Texas Tech University , Lubbock, Texas 79416, United States.
Anal Chem. 2017 Dec 19;89(24):13290-13298. doi: 10.1021/acs.analchem.7b03380. Epub 2017 Nov 28.
The need to immobilize active enzyme, while ensuring high rates of substrate turnover and electronic charge transfer with an electrode, is a centrally important challenge in the field of bioelectrocatalysis. In this work, we demonstrate the use of confocal Raman microscopy as a tool for quantitation and molecular-scale structural characterization of ionomers and proteins within biocatalytic membranes to aid in the development of energy efficient biofuel cells. A set of recently available short side chain Aquivion ionomers spanning a range of equivalent weight (EW) suitable for enzyme immobilization was investigated. Aquivion ionomers (790 EW, 830 EW and 980 EW) received in the proton-exchanged (SOH) form were treated with tetra-n-butylammonium bromide (TBAB) to neutralize the ionomer and expand the size of ionic domains for enzyme incorporation. Through the use of confocal Raman microscopy, membrane TBA ion content was predicted in calibration studies to within a few percent of the conventional titrimetric method across the full range of TBA: SO ratios of practical interest (0.1 to 1.7). Protein incorporation into membranes was quantified at the levels expected in biofuel cell electrodes. Furthermore, features associated with the catalytically active, enzyme-coordinated copper center were evident between 400 and 500 cm in spectra of laccase catalytic membranes, demonstrating the potential to interrogate mechanistic chemistry at the enzyme active site of biocathodes under fuel cell reaction conditions. When benchmarked against the 1100 EW Nafion ionomer in glucose/air enzymatic fuel cells (EFCs), EFCs with laccase air-breathing cathodes prepared from TBA modified Aquivion ionomers were able to reach maximum power densities (P) up to 1.5 times higher than EFCs constructed with cathodes prepared from TBA modified Nafion. The improved performance of EFCs containing the short side chain Aquivion ionomers relative to Nafion is traced to effects of ionomer ion-exchange capacity (IEC, where IEC = EW), where the greater density of SO moieties in the Aquivion materials produces an environment more favorable to mass transport and higher TBA concentrations.
需要将活性酶固定，同时确保与电极的高底物转化率和电子电荷转移率，这是生物电化学领域的一个重要挑战。在这项工作中，我们展示了使用共聚焦拉曼显微镜作为工具，对生物催化膜中的离聚物和蛋白质进行定量和分子尺度结构表征，以帮助开发高效节能的生物燃料电池。研究了一组最近可用的短侧链 Aquivion 离聚物，涵盖了适合酶固定的一系列等效重量 (EW)。Aquivion 离聚物 (790EW、830EW 和 980EW) 以质子交换 (SOH) 形式接收，并用四丁基溴化铵 (TBAB) 处理以中和离聚物并扩大离子域大小以纳入酶。通过使用共聚焦拉曼显微镜，在整个实用的 TBAB:SO 比范围内（0.1 至 1.7），膜 TBA 离子含量的预测值与传统滴定法相比误差在百分之几以内。在生物燃料电池电极中预期的水平上定量了蛋白质掺入膜中。此外，在漆酶催化膜的光谱中，在 400 到 500cm 之间可以看到与催化活性、酶协调的铜中心相关的特征，这表明在燃料电池反应条件下，有潜力在生物阴极的酶活性位点处检测到机制化学。当与 1100EW Nafion 离聚物在葡萄糖/空气酶燃料电池 (EFC) 中进行基准测试时，用 TBA 改性 Aquivion 离聚物制备的漆酶空气呼吸阴极的 EFC 能够达到高达 1.5 倍的最大功率密度 (P)，而用 TBA 改性 Nafion 制备的阴极的 EFC。与 Nafion 相比，含有短侧链 Aquivion 离聚物的 EFC 性能的提高可归因于离聚物离子交换容量 (IEC)的影响，其中 Aquivion 材料中 SO 基团的密度更高，产生了更有利于传质和更高 TBA 浓度的环境。
