Multi-step reaction can be carried out efficiently using integrated catalytic system for the manufacture of advanced materials, energy conversion and harvesting, and human-machine interfaces. Nature has shown effective way to carry out multi-step reaction through substrate channeling.¹ Molecular tunneling² and electrostatic guidance³ mechanisms of substrate channeling has been studied extensively in literature and has proven their potential for efficient substrate channeling with minimum intermediate diffusional loss.

Molecular tunneling restricts intermediate diffusion through tunnel wall between active sites, whereas, electrostatic guidance restricts intermediate through surface interaction. Incorporating these two mechanisms into multi-step reaction system can lead to innovative integrated catalytic system.

In this work, continuum modeling has been performed on geometry consist of tunnel and two active sites confined within. Tunnel surface is oppositely charged as of intermediate to introduce electrostatic interaction. System is governed by diffusion and migration as well as reaction kinetics. Effect of reaction kinetics and transport has been studied and defined as Damköhler number. Channeling efficiency is defined by product yield at second active site relative to intermediate production at first active site. Effect of geometrical parameter such as distance between active site (d), distance between active site and bulk (l_e), tunnel diameter(h) as well as ionic strength (I) of the system has been studied. Minimizing intermediate access to the bulk and increasing driving force for the intermediate to transport to active site is required for efficient channeling.

References:

1. I. Wheeldon, S. D. Minteer, S. Banta, S. C. Barton, P. Atanassov and M. Sigman, "Substrate channelling as an approach to cascade reactions", Nat. Chem., 8, 299–309 (2016). doi:10.1038/nchem.2459.
2. E. W. Miles, S. Rhee and D. R. Davies, "The molecular basis of substrate channeling", J. Biol. Chem., 274, 12193–12196 (1999). doi:10.1074/jbc.274.18.12193.
3. A. H. Elcock, G. A. Huber and J. Andrew McCammon, "Electrostatic channeling of substrates between enzyme active sites: Comparison of simulation and experiment", Biochemistry, 36, 16049–16058 (1997). doi:10.1021/bi971709u.