Coupled Nanomechanical Motions: Metal-Ion-Effected, pH-Modulated, Simultaneous Extension/Contraction Motions of Double-Domain Helical/Linear Molecular Strands

A new class of shape-enforced synthetic polyheterocyclic molecular strands, containing both a helical and a linear domain, has been designed and synthesized. On reaction with Pb­(II), under the effect of cation binding to the coordination subunits, the helical section unfolds into a linear shape in the complex and the linear domain folds into a helical ligand wrapped around the bound cations. Such double-domain ligand strands are thus able to undergo a combined unfolding–folding interconversion on binding and release of metal cations. These changes can be modulated through coupling to a competing ligand that reversibly binds and releases metal cations, when respectively unprotonated and protonated, on effecting alternate pH changes. The resulting process thus performs nanomechanical extension/contraction molecular motions of a linear motor type, which is fueled by acid–base neutralization.一类新型形状约束型合成多杂环分子链已被设计并合成，该类分子链同时包含螺旋域与线性域。当与铅(II)（Pb(II)）发生反应时，在阳离子与配位亚基结合的作用下，其螺旋区段会在配合物中舒展为线性结构，而原线性域则会折叠为包裹配位阳离子的螺旋配体。这类双域配体链因此能够在结合与释放金属阳离子的过程中，发生协同的舒展-折叠互变。该过程可通过与竞争性配体耦合进行调控：当竞争性配体分别处于去质子化与质子化状态时，可可逆地结合与释放金属阳离子，从而引发pH的交替变化。由此产生的过程可实现线性马达型的纳米机械伸展/收缩分子运动，其能量来源为酸碱中和反应。