Spatiotemporal Organization of Catalysts Driven by Enhanced Diffusion

Abstract

Recently, both microfluidic and fluorescence correlation spectroscopy experiments have revealed that diffusion coefficients of active biological catalysts (enzymes) rise proportionately to their catalytic rate. Similar effects have also been observed for active material catalysts, such as platinum nanocatalysts in hydrogen peroxide solution. While differences in diffusion coefficients have recently been cleverly exploited to spatially separate active from inactive catalysts, here we investigate the consequences of these novel findings on the spatiotemporal organization of catalysts. In particular, we show that chemical reactions-such as coupled catalytic reactions-may drive effective attraction or repulsion between catalysts which in turn drives their spatiotemporal organization. This, we argue, may have implications for internal cell signaling.

Catalytic enzymes are active matter

“…The enhanced diffusion grows with the reaction rate as the saturation curve of the MM kinetics, , as noted previously by several authors ( 3 , 4 , 21 , 41 , 42 ), although a square root law of Fickian diffusion was sometimes stated, for urease ( 3 ). To explain the data, Riedel et al ( 4 ) suggested the intriguing scenario that the boost originates from sudden release of reaction enthalpy, inducing an asymmetric pressure pulse that displaces the enzyme.…”

“…For this reason, our experiment starts with a uniform enzyme profile and this was observed to evolve an opposing gradient owing to the antichemotactic tendency. A similar effect was recently modeled in spherical geometries by Weistuch and Pressé ( 41 ), who termed the separation of enzyme and substrate “repulsion.”…”

Enhanced Diffusion of Molecular Catalysts is Due to Convection

“…These results have been subject to recent questions regarding the possible dissociation of enzymes at the low substrate concentrations needed for FCS, and some experiments using dynamic light scattering (DLS) or diffusion NMR have been unable to replicate the microscopy results. The theoretical framework surrounding the observed enhanced diffusion remains an open question with multiple proposed models drawing links between enhanced diffusion and reaction rates, binding‐unbinding rates, and reaction thermodynamics, and conclusions ranging from new possibilities in targeted molecular transport to skepticism of enhanced diffusion in sub‐nanometer objects . While proposed models focus on enhanced diffusion in enzymes, their findings should in principle also be applicable to small molecules.…”

Molecular simulation of hydrodesulfurization of coal tar using Pd/ZSM‐5/γ‐Al2O3 catalyst

“…The adsorption and diffusivity on the catalyst have an important impact on the activity of the catalyst . Molecular simulation can effectively predict the adsorption and diffusion properties of different catalysts, providing theoretical explanation of experimental observations …”