Enzymes and Heterogeneous Catalysis

The term heterogeneous catalyst refers to a catalyst which is not present in bulk solution but present in a solid phase such as a surface (1).  An example is the use of metal oxide nanoparticles (Fe3O4) for supporting Fenton reaction for the treatment of waste water (2) instead of soluble metal salts (3).   Heterogenous catalysts have been used for reactions of biochemical interest including the synthesis of a fluorescent probe inside of a cell (4).  Insoluble enzymes (5) can be considered heterogeneous catalysts (6).   Since heterogeneous catalysis is defined by catalyst and reactants/substrates in different phases, heterogeneous catalysis also includes a soluble catalyst (enzyme) and an insoluble substrate (7,8).  It has occurred to me that a soluble enzyme, acting as a surface, could be considered to be a heterogeneous catalyst.


References


1. Bligaard, T. and Nørskov, J.K., Heterogeneous catalysis, in Chemical Bonding at Surfaces and Interfaces, ed. A.NIlsson, L.G.M. Pettersson, and J.K. Nørskov, Chapter 4, pps. 255-321, Elsevier, Amsterdam, Netherlands, 2008. 
2. Dhakshinamoorthy, A., Navalon, S., Alvaro, M., and Garcia, H., Metal nanoparticles as heterogenous Fenton catalysts, ChemSusChem. 5, 46-64, 2012.
3. Neyens, E. and Baeyens, J., A review of classic Fenton’s peroxidation as an advanced oxidation technique, J.Hazard.Mater. 98, 33-59, 2003.
4.  Wang, F., Zhang, Y., Du, Z., Ren, J., and Qu, X., Designed heterogeneous palladium catalysts for reversible light-controlled biorthogonal catalysis in living cells, Nat.Commun. 9:1209, 2018.
5.  Silman, I. and Katchalski, E., Water-insoluble derivatives of enzymes, antigens, and antibodies, Annu.Rev.Biochem. 35, 873-908, 1966.
6.  Xu, F. and Ding, H., A new kinetic model for heterogeneous (or spatially confined) enzymatic catalysis: Contributions from the fractal and jamming (overcrowding) effects, Applied Catalysis A General 317, 70-81, 2007.
7.  Carvalho, A.L., Dias, F.M.V., Nagy, T., et al., Evidence for a dual binding mode of dockerin modules to cohesion, Proc.Natl.Acad.Sci. USA 104, 3089-3094, 2007.
8. Andersen, M., Kari, J., Burch, K., and Westh, P., Michaelis-Menten equation for degradation of insoluble substrate, Math.Biosci. 296, 93-97, 2018.