Kinetic gating of linear hydrocarbons by a dynamic synthetic pore

Abstract

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  Longer linear hydrocarbons are taken up faster despite their size
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  Size-rate correlation is inverted in a dynamic synthetic pore
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  Pre-complex stabilization accelerates guest uptake kinetics
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  Dynamic pore gating governs kinetic selectivity beyond thermodynamics

One of the central challenges in molecular science is understanding how molecular transport differs from macroscopic intuition. In everyday experience, larger objects move more slowly through confined spaces. However, at the molecular scale, such intuition can break down. Here, we show that longer linear hydrocarbons pass through a dynamic synthetic pore faster than shorter ones, revealing an unexpected inversion of size-rate relationships. This counterintuitive behavior arises from the interplay of pre-complex stabilization and dynamic pore gating. Stronger interactions between the guest and the pore increase the lifetime of encounter complexes, which in turn accelerates passage rather than hindering it. These results demonstrate that molecular transport can be governed by kinetic factors that are fundamentally distinct from thermodynamic stability. More broadly, this work highlights how dynamic host structures can control molecular motion in confined environments. By exploiting kinetic rather than thermodynamic principles, these findings open new strategies for designing selective transport, rapid delivery, and functional molecular systems where dynamics, rather than size or binding strength, determine function.

Passing through a pore is an elementary binding and transport process that is important for the kinetic selection of target molecules. Although the binding of molecules has been extensively discussed in thermodynamics, the effect of the pore and its dynamism on the binding kinetics is not fully understood. Three types of synthetic pores with different dynamic properties were designed and used to reveal the controlling factors of kinetic gating. The pore sizes were almost the same in the three types, but one type of pore exhibited a high gating preference toward linear alkanes. Contrary to the intuition in the macroscopic world, longer alkanes passed through the pores faster than shorter alkanes, and the introduction of an unsaturated carbon-carbon bond in linear hydrocarbons greatly enhanced the passage speed.

Passing through a pore is an elementary binding and transport process that is important for the kinetic selection of target molecules. Although the binding of molecules has been extensively discussed in thermodynamics, the effect of the pore and its dynamism on the binding kinetics is not fully understood. Three types of synthetic pores with different dynamic properties were designed and used to reveal the controlling factors of kinetic gating. The pore sizes were almost the same in the three types, but one type of pore exhibited a high gating preference toward linear alkanes. Contrary to the intuition in the macroscopic world, longer alkanes passed through the pores faster than shorter alkanes, and the introduction of an unsaturated carbon-carbon bond in linear hydrocarbons greatly enhanced the passage speed.

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