Abstract
In biological systems, there are many signal transduction cascades in which a chemical signal is transferred as a series of chemical events. Such successive reaction systems are advantageous because the efficiency of the functions can be finely controlled by regulatory enzymes at an earlier stage. However, most of artificial responsive molecules developed so far rely on single-step conversion, whose response speeds have been difficult to be controlled by external stimuli. In this context, developing artificial conversion systems that have a regulation step similar to the regulatory enzymes has been anticipated. Here we report a novel artificial two-step structural conversion system in which the response speed can be controlled based on a regulatory enzyme-like strategy. In this system, addition of fluoride ion caused desilylation of the siloxycarboxylate ion attached to a helical complex, resulting in the subsequent helicity inversion. The response speeds of the helicity inversion depended on the reactivity of the siloxycarboxylate ions; when a less-reactive siloxycarboxylate ion was used, the helicity inversion rate was governed by the desilylation rate. This is the first artificial responsive molecule in which the overall response speed can be controlled at the regulation step separated from the function step.
Highlights
In responsive molecules using a chemical stimulus, binding with a chemical species causes a structural change that leads to responsive functions (Fig. 1a)
There are cascade systems in which a chemical signal is transferred as a series of chemical events prior to the structural changes leading to their functions (Fig. 1b
We report this new type of two-step structural conversion in which the response speed of the helicity inversion at the final function step was effectively controlled at the regulation step using siloxycarboxylate ions with different reactivities
Summary
In the present LZn3La system, the helicity is sensitively affected by structural differences in the chiral carboxylate ions[40,41], whereas the helicity inversion rate is not significantly affected ( called the intrinsic helix inversion rate, hereafter) These facts inspired us to design a system in which helicity inversion is driven by a slow chemical transformation in the coordinating carboxylate ions. The time-programming in these systems needs to change the intrinsic helix inversion rates, whereas the helix inversion rates of the present system can be controlled at the regulation step without changing the intrinsic helix inversion rates We report this new type of two-step structural conversion in which the response speed of the helicity inversion at the final function step was effectively controlled at the regulation step using siloxycarboxylate ions with different reactivities
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