Abstract
The template effect is a key feature to control the arrangement of building blocks in assemblies, but its kinetic nature remains elusive compared to the thermodynamic aspects, with the exception of very simple reactions. Here we report a kinetic template effect in a self-assembled cage composed of flexible ditopic ligands and Pd(II) ions. Without template anion, a micrometer-sized sheet is kinetically trapped (off-pathway), which is converted into the thermodynamically most stable cage by the template anion. When the template anion is present from the start, the cage is selectively produced by the preferential cyclization of a dinuclear intermediate (on-pathway). Quantitative and numerical analyses of the self-assembly of the cage on the on-pathway revealed that the accelerating effect of the template is stronger for the early stage reactions of the self-assembly than for the final cage formation step itself, indicating the kinetic template effect.
Highlights
Quantitative and numerical analyses of the selfassembly of the cage in the presence of the template anion revealed that the production of the intermediates for the cage is significantly accelerated by the template anion, which is confirmed by the acceleration of the formation of a cyclic model structure in the presence of NO3− and the strong binding of the cyclic structure with NO3−
Due to the high flexibility of the ditopic ligand 1, the resulting cage can bind a variety of anionic species (PF6−, BF4−, ClO4−, ReO4−, and I−) in its cavity, whose size can be changed by twisting the helix in an induced-fit manner
In our previous research on the self-assembly process of this cage from 1 and [PdPy*4](BF4)[2], a 200-nm-sized sheet structure was transiently produced during the self-assembly and this sheet structure was converted to the (BF4−)@ [Pd214]4+ cage[40]
Summary
As seen in DNA-replication, the template effect[1,2] is a powerful strategy for efficient synthesis of assemblies whose building blocks are well arranged, such as macrocycles[3,4,5,6,7,8,9], cages[10,11], interlocked and knotted molecules[12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27], and submicrometer-sized materials[28,29,30,31,32,33,34]. Besides the stabilization of the final cage by the encapsulation of NO3−, a kinetic template effect accelerates the formation of primitive intermediates for the cage by the template anion and contributes strongly to the bifurcation of the self-assembly pathways
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