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The authors investigate passive tracer transport in chemically reactive mixtures by combining a thermodynamically consistent theoretical framework with particle-based simulations. Understanding this dynamic is crucial for microrheology and modeling transport in crowded biological media, where actively driven chemical reactions dominate over thermal equilibrium. The study reveals that chemical turnover opens a novel relaxation channel that suppresses interaction-induced memory drag, allowing nonequilibrium fluctuations to accelerate tracer diffusion beyond the bare solvent limit.
Active chemical reactions can propel passive tracers faster than their diffusion limit in pure solvent by actively destroying memory-dependent drag forces.
Diffusivity of passive tracers in complex mixtures is widely relevant for industrial applications and for probing biological systems. Interactions with the surrounding medium typically generate a drag force that suppresses tracer diffusion, although self-propulsion can accelerate tracers via active fluctuations. Similar effects are not understood in mixtures with particle conversion and exchange, although these are particularly relevant in biological contexts, where actively driven reactions prevail. By studying a thermodynamically consistent model of chemical reactions in mixtures, we show that reactions provide an additional relaxation pathway that suppresses interaction-induced memory, reducing the drag on tracers and restoring their diffusivity toward the value expected in the absence of solutes. Moreover, active reactions generate nonequilibrium fluctuations that can push tracer diffusivity beyond this limit, an effect we confirm with particle-based simulations. Our results identify chemical activity as a distinct route to controlling mass transport and offer a framework for interpreting microrheology experiments in chemically active mixtures.