Vital Significance of Addition of "Shape Similarity" between Solutes to Shape Complementarity for More Precise Molecular Recognition in Aqueous Binary Solvents

Precise and specific molecular recognition is vital to living systems. Discrimination has mainly been studied by using particular host molecules (e.g., crown ethers, cyclodextrin and urea derivatives). Several studies in various fields have pointed out that the famous "lock-and-key theory" (the concept of shape complementarity) is, at present, insufficient for understanding precise discrimination. This seems to come from the fact that various types of intermolecular interactions are decisive in such discrimination. This Review intends to describe the novel concept that "shape similarity" between interacting solutes should be added to "shape complementarity" for more precise discrimination to be achieved. Further, the role of shape similarity between solvent and solute molecules is also described. In relation to precise molecular recognition, weak interactions, which depend on the three-dimensional shape of substituents (shape-specific weak interactions), are described. Possibility of alterations in solvent structures is discussed in aqueous binary solvents. DOI 10.1002/tcr.201100001