# Artificial Photosynthesis: Is Computation Ready for the Challenge Ahead?
## 4 Protein/Surface Interactions
### Adsorption on Low Dimensional Materials
Following recent studies showing that the ET of immobilized cyt is controlled by the interplay between tunneling probability and protein dynamics [201], the authors defined key parameters for the ET process: Redox center location, orientation of the protein on the surface and ET distance. From this study, the authors obtained that in order to favor ET tunneling (which exponentially decays with the distance) the minimal distance between the heme iron atom and the surface should be not higher than 1.3 nm. They obtain a similar distance for the protein adsorbed on GO, which should show efficient ET (Figure 14), while should be less pronounced when adsorbed on graphene, as the distance is now increased up to 1.8 nm. They rationalize these results by considering the different orientation of the heme group relative to the surface. Another study on the adsorption of cyt c\({}_{553}\) on graphene has been performed combining MD and QM approaches to assess both the orientation and the ET ability of the surface [208]. The authors performed docking to obtain the most favorable orientations of the protein over SLG, and considered the three most stable ones as input for MD simulations. The results show that the three structures are thermodynamically stable, and the heme is oriented with different tilt angles and distances with respect to SLG for all of them, which should strongly affect the ET ability of the interfaces. In this work, the authors considered a different approach to assess the ET flow, namely to compute the transfer integral (which is proportional to the electronic coupling) and obtained net ET flow from SLG to the heme group independently form the orientation or distance of the two fragments, but with magnitude strongly dependent on the distance, as previously reported for the tunneling ET mechanism, as well as the tilting, showing highest ET efficiency when heme is (almost) parallel to the SLG surface. Apart from carbon based low dimensional materials, other structures of interest to form bio-interfaces are hexagonal boron-nitride (h-BN) and MoS\({}_{2}\). The first material can be considered as insulator, while the second is a semimetal. These materials are relatively novel, and little is present in literature on their possible protein adsorption abilities and relative ET mechanism. Thus, a substantial increase in the knowledge of biomolecular adsorption at these interfaces is required to control the formation of these hybrid systems. Several works on a simple water/h-BN interface in which novel force field are developed and validated have been reported in literature [209; 210], but only a few MD simulations are present up to date for ternary protein/water/h-BN structures. The main reason behind this is the lack of experimental data to validate the force fields for biomolecular adsorbates. One of these study reports the adsorption of short peptides on h-BN nanotubes and nanosheets [211]. The authors performed MD simulations using a combination of Lennard-Jones parameters for the water/surface interface, and reported the structural deformations of these peptides once adsorbed. Due to the lack of experimental data, this force field combination still needs to be validated, but it is a first attempt to push the field towards novel horizons. Literature on MoS\({}_{2}\) based hybrid bio-interfaces are even scarcer, both experimentally and computationally. A recent report present MD simulations in which combining rules are used to generate the interfacial terms for the force field for bio-MoS\({}_{2}\) interfaces, leading to some inconsistency compared to experimental findings [212]. The lack of tuned force field for these interfaces is the main cause for this mismatch, and fundamental studies are thus needed for these interfaces, especially to verify the force field terms. Yet, despite the need  
Figure 14: The electron transfer pathway of Cyt c on the graphene oxide (GO) surface. Reprinted with permission from [207]. Copyright (2018) Elsevier. of such data, even QM reports are scarce.