@article{YanFrokjarEngelbrektetal.2021,
  author    = {Yan, Jiawei and Fr{\o}kj{\ae}r, Emil Egede and Engelbrekt, Christian and Leimk{\"u}hler, Silke and Ulstrup, Jens and Wollenberger, Ulla and Xiao, Xinxin and Zhang, Jingdong},
  title     = {Voltammetry and single-molecule in situ scanning tunnelling microscopy of the redox metalloenzyme human sulfite oxidase},
  series = {ChemElectroChem},
  volume    = {8},
  journal   = {ChemElectroChem},
  number    = {1},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {2196-0216},
  doi       = {10.1002/celc.202001258},
  pages     = {164 -- 171},
  year      = {2021},
  abstract  = {Human sulfite oxidase (hSO) is a homodimeric two-domain enzyme central in the biological sulfur cycle. A pyranopterin molybdenum cofactor (Moco) is the catalytic site and a heme b(5) group located in the N-terminal domain. The two domains are connected by a flexible linker region. Electrons produced at the Moco in sulfite oxidation, are relayed via heme b(5) to electron acceptors or an electrode surface. Inter-domain conformational changes between an open and a closed enzyme conformation, allowing "gated" electron transfer has been suggested. We first recorded cyclic voltammetry (CV) of hSO on single-crystal Au(111)-electrode surfaces modified by self-assembled monolayers (SAMs) both of a short rigid thiol, cysteamine and of a longer structurally flexible thiol, omega-amino-octanethiol (AOT). hSO on cysteamine SAMs displays a well-defined pair of voltammetric peaks around -0.207 V vs. SCE in the absence of sulfite substrate, but no electrocatalysis. hSO on AOT SAMs displays well-defined electrocatalysis, but only "fair" quality voltammetry in the absence of sulfite. We recorded next in situ scanning tunnelling spectroscopy (STS) of hSO on AOT modified Au(111)-electrodes, disclosing, a 2-5 \% surface coverage of strong molecular scale contrasts, assigned to single hSO molecules, notably with no contrast difference in the absence and presence of sulfite. In situ STS corroborated this observation with a sigmoidal tunnelling current/overpotential correlation.},
  language  = {en}
}
@article{TangWerchmeisterPredaetal.2019,
  author    = {Tang, Jing and Werchmeister, Rebecka Maria Larsen and Preda, Loredana and Huang, Wei and Zheng, Zhiyong and Leimk{\"u}hler, Silke and Wollenberger, Ulla and Xiao, Xinxin and Engelbrekt, Christian and Ulstrup, Jens and Zhang, Jingdong},
  title     = {Three-dimensional sulfite oxidase bioanodes based on graphene functionalized carbon paper for sulfite/O-2 biofuel cells},
  series = {ACS catalysis},
  volume    = {9},
  journal   = {ACS catalysis},
  number    = {7},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {2155-5435},
  doi       = {10.1021/acscatal.9b01715},
  pages     = {6543 -- 6554},
  year      = {2019},
  abstract  = {We have developed a three-dimensional (3D) graphene electrode suitable for the immobilization of human sulfite oxidase (hSO), which catalyzes the electrochemical oxidation of sulfite via direct electron transfer (DET). The electrode is fabricated by drop-casting graphene-polyethylenimine (G-P) composites on carbon papers (CPs) precoated with graphene oxide (GO). The negatively charged hSO can be adsorbed electrostatically on the positively charged matrix (G-P) on CP electrodes coated with GO (CPG), with a proper orientation for accelerated DET. Notably, further electrochemical reduction of G-P on CPG electrodes leads to a 9-fold increase of the saturation catalytic current density (j(m)) for sulfite oxidation reaching 24.4 +/- 0.3 mu A to cm(-2), the highest value among reported DET-based hSO bioelectrodes. The increased electron transfer rate plays a dominating role in the enhancement of direct enzymatic current because of the improved electric contact of hSO with the electrode, The optimized hSO bioelectrode shows a significant catalytic rate (k(cat): 25.6 +/- 0.3 s(-1)) and efficiency (k(cat)/K-m: 0.231 +/- 0.003 s(-1) mu M-1) compared to the reported hSO bioelectrodes. The assembly of the hSO bioanode and a commercial platinum biocathode allows the construction of sulfite/O-2 enzymatic biofuel cells (EBFCs) with flowing fuels. The optimized EBFC displays an open-circuit voltage (OCV) of 0.64 +/- 0.01 V and a maximum power density of 61 +/- 6 mu W cm(-2) (122 +/- 12 mW m(-3)) at 30 degrees C, which exceeds the best reported value by more than 6 times.},
  language  = {en}
}