Conformational selection in artificial catalysts and molecular machines

酶作为一种自发相互转化的构象状态集合存在，这可能使它们具有极高的催化活性。构象选择提出，最快的反应途径沿着反应坐标采样不同的构象状态，提供了较低能量的途径，否则孤立地无法获得任何一个构象。这种机械速率依赖是信息棘轮机制的同义词，这是驱动每一个生物分子机器的过程。尽管酶令人印象深刻的催化活性为化学家提供了灵感，但大多数人工催化剂被设计为静态的，这一特征可能会限制它们的催化潜力。将动力学引入催化剂可以促进棘轮机制，从而允许优化相反的元素步骤，从而超越静态萨巴蒂尔极限。除了利用棘轮机制提高催化效率外，生物学还利用棘轮机制通过合成代谢来构建复杂性合成代谢将低能量的积木转化为高能量的产品，这是一个自耗过程。这种自能转化是可能的，因为它是耦合到一个正交的自能过程，通常使用ATP作为化学燃料。与此相反，大多数合成变换都是能量下降到局部或全局能量最小值的过程。光驱动反应提供了这条规则的一个例外，它允许试剂穿过一个更高的能量平面，并明确地通过棘轮型机制进行。然而，这种转化仅限于那些可以直接或通过催化剂与光相互作用的转化。同样，通过化学燃料也实现了去中心化，但这仅限于熵功。从生物学中获得灵感，将这些燃料自能反应扩展到其他难以实现的成键反应，将极大地扩展化学家的工具箱。生物学广泛使用棘轮机制，这对其效率有重要贡献。将这些原理应用到合成催化和更广泛的合成中，有可能降低成本和能量需求，同时扩大化学家可用的化学转化。

Enzymes exist as a spontaneously interconverting ensemble of conformational states which likely enables their extremely high catalytic activity. Conformational selection proposes that the fastest reaction pathway samples different conformational states along the reaction coordinate, providing access to lower energy pathways otherwise inaccessible to any one conformation in isolation. This mechanical rate dependence is synonymous with information ratchet mechanisms, a process that drives every biological molecular machine. Although the impressive catalytic activities of enzymes have provided inspiration to chemists, the majority of artificial catalysts are designed to be static, a feature that may limit their catalytic potential. The introduction of dynamics to a catalyst can facilitate a ratchet mechanism allowing optimisation for opposing elemental steps thereby surpassing the static Sabatier limit.In addition to using ratchet mechanisms to improve catalytic efficiency, biology utilises ratcheting to build complexity through anabolism.2 Anabolism transforms low energy building blocks into higher energy products, an endergonic process. This endergonic transformation is possible as it is coupled it to an orthogonal exergonic process, generally using ATP as the chemical fuel. In contrast, the majority of synthetic transformations are exergonic proceeding energetically downhill to either a local or global energy minimum. Light driven reactions provide an exception to this rule allowing a higher energy plane to be traversed by the reagents and proceeding explicitly through a ratchet type mechanism. However, such transformations are limited to those which can interact with light either directly or via a catalyst. Similarly, deracemizations have been achieved through chemical fuelling but this is limited exclusively to entropic work. Taking inspiration from biology, to expand these fuelled endergonic reactions to otherwise inaccessible bond forming reactions would greatly expand the chemists' toolbox. Biology makes extensive use of ratchet mechanisms which contribute significantly to its efficiency. The implementation of these principles to synthetic catalysis, and synthesis more generally, has the potential to decrease both the cost and energy requirements whilst simultaneously expanding the chemical transformations available to the chemist.