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Abstract：
Two limiting cases of molecular recognition, induced fit (IF) and conformational selection (CS), play a central role in allosteric regulation of natural systems. The IF paradigm states that a substrate \"instructs\" the host to change its shape after complexation, while CS asserts that a guest \"selects\" the optimal fit from an ensemble of preexisting host conformations. With no studies that quantitatively address the interplay of two limiting pathways in abiotic systems, we herein and for the first time describe the way by which twisted capsule M-1, encompassing two conformers M-1(+) and M-1(-), trap CX4 (X=Cl, Br) to give CX4 ⊂M-1(+) and CX4 ⊂M-1(-), with all four states being in thermal equilibrium. With the assistance of 2D EXSY, we found that CBr4 would, at its lower concentrations, bind M-1 via a M-1(+)→M-1(-)→CBr4 ⊂M-1(-) pathway corresponding to conformational selection. For M-1 complexing CCl4 though, data from 2D EXSY measurements and 1D NMR line-shape analysis suggested that lower CCl4 concentrations would favor CS while the IF pathway prevailed at higher proportions of the guest. Since CS and IF are not mutually exclusive, we reason that our work sets the stage for characterizing the dynamics of a wide range of already existing hosts to broaden our fundamental understanding of their action. The objective is to master the way in which encapsulation takes place for designing novel and allosteric sequestering agents, catalysts and chemosensors akin to those found in nature.
摘要：
分子识别的两种极限情况，诱导拟合(IF)和构象选择(CS)，在自然系统的变构调节中起着核心作用。IF范式指出，底物“指示”主体在络合后改变其形状，而CS断言来宾从预先存在的主机构象的集合中“选择”最佳匹配。由于没有定量解决非生物系统中两种限制途径相互作用的研究，我们在这里和第一次描述了扭曲的胶囊M-1的方式，包括两个构象的M-1（+）和M-1（-），陷阱CX4(X=Cl,Br）给予CX4♪M-1（+）和CX4♪M-1（-），所有四种状态都处于热平衡状态。在2DEXSY的帮助下，我们发现CBr4会,在较低的浓度下，通过对应于构象选择的M-1（）→M-1（-）→CBr4lotM-1（-）途径结合M-1。对于M-1络合CCl4，来自2DEXSY测量和1DNMR线形分析的数据表明，较低的CCl4浓度将有利于CS，而IF途径在较高比例的客体中占优势。由于CS和IF不是互斥的，我们认为，我们的工作为表征各种现有东道主的动态奠定了基础，以扩大我们对它们行动的基本理解。目标是掌握封装发生的方式，以设计新型和变构螯合剂，类似于自然界中发现的催化剂和化学传感器。
