ABSTRACT
I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 711 II. General Principle of Molecular Imprinting Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 712 III. Covalent Imprinting and Noncovalent Imprinting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 713 IV. Recent Challenges and Progresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 714 V. Molecular Imprinting of Host Molecules Leading to Their Ordered Assembly . . . . . . . . . 715
A. Preparation of Ordered Assemblies of CyD as Receptors for Nanometer-Scaled Guests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 715
B. Structure of Guest-Binding Sites and Analysis of the Molecular Imprinting Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 716
C. Imprinting of CyD on the Surface of Silica-Gel Support . . . . . . . . . . . . . . . . . . . . . . . 718 VI. Use of Metal Complexes as Guest-Binding Site in Water . . . . . . . . . . . . . . . . . . . . . . . . . . . 719 VII. Artificial Enzymes by Molecular Imprinting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 720
A. Use of Monomers Bearing Catalytically Active Groups . . . . . . . . . . . . . . . . . . . . . . . . 720 B. Molecular Imprinting by Using Transition-State Analog as Template . . . . . . . . . . . . 722
VIII. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 722 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 722 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 722
I. INTRODUCTION
A number of elegant host molecules have already been synthesized and showed both high selectivity and binding activity toward the target guest compound. Through these studies, detailed and fundamental knowledge for molecular design of sophisticated receptors has been accumulated. Host-guest chemistry has been so fruitful and mature. From the viewpoint of the practical applications to industry and our daily lives, however, these synthetic receptors have several drawbacks. First, their synthesis usually requires many complicated reaction steps, and thus they are usually too expensive for common industrial use. Second, the design of receptors for large guest molecules is quite difficult, since the scaffolds available (e.g., cyclodextrin [CyD], crown ether, calixarene, and others) are in most cases not much greater than several angstroms. Under these conditions, it is hard to place
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two or more functional groups at notably remote sites (e.g., >10 Å) in the receptors. Third, precise guest recognition in water is difficult, since hydrogen bonding is easily broken due to the competition with the water.
