Fig. 3
Mechanism of the spontaneous reaction between the enzyme–SNO device and glucose. a Synchrotron X-ray diffraction scans of glucose-reacted SmNiO3 (SNO) devices with and without glucose oxidase (GOx) enzyme modification. The scans are along Qz direction around the 002 peak of LaAlO3 substrate (pseudocubic notation). b Angle-dependent X-ray absorption near edge spectroscopy (XANES) spectra on glucose-reacted SNO devices with and without GOx enzyme modification (Ni K-edge). At a surface sensitive incident angle of 0.05o, XANES spectra acquired on the GOx-modified electrode on GSNO show pronounced reduction in the white line peak amplitude and the effective pre-edge humps, as compared to the electrode without any GOx, suggesting orbital filling at the SNO surface, due to the hydrogen transfer. The blue dashed curve in the figure inset is shifted upward for clarity of data presentation. At incidence angle of 5.05o, XANES spectra acquired on GOx-modified device shows negligible difference with respect to that without enzyme modification, which indicates the majority of the film is still pristine SNO. The insets show zoomed-in pre-edge feature in XANES spectra. c Classical MD trajectory of a representative FADH2 molecule. Snapshots show the conformational changes that the FADH2 molecule undergoes over timescales of ~10 ns before approaching the SNO (001) surface (pseudocubic notation). d Several tens of FADH2 near-surface conformations from ~500 ns of classical MD trajectories are sampled and used as starting configurations for AIMD simulations. Two representative samples are illustrated to demonstrate the spontaneous hydrogen transfer from an H site in FADH2 to surface oxygen of SNO (001). In both the depicted cases, one of the hydrogens from FADH2 gets extracted and gets adsorbed into the SNO (001) (zoomed-in view); the extraction process is spontaneous, with an energetic gain as large as 1.8 eV. Classical MD simulations suggest that the steric effects are important and can hinder the hydrogen transfer from FADH2 to SNO (001) as shown by detailed first principles calculations of representative trajectories (see Supplementary Fig. 21)
