Single-molecular Anatomy of Solvophobic Effects in Host-guest Interaction

Satoshi Yasuda, Osamu Takeuchi and Hidemi Shigekawa

Institute of Applied Physics, CREST, University of Tsukuba, Tsukuba 305-8573 Japan

Host-guest chemistry is one of the keys for future nanotechnology and biotechnology applications, and its recent progress has been remarkable. However, the detailed design of host-guest systems which exhibit desired functions in predetermined structures has not yet been successful. The most critical drawback is the fact that although the processes include complicated many body effects arising from solvent related factors, the data available through conventional techniques are macroscopic averages of many different species in solutions. By using the techniques of chemical force microscopy and self assembling of monolayer molecules, solvophobic effect on the formation of the b-cyclodextrin (b-CyD) and ferrocene inclusion complex, a typical host-guest system, was successfully measured in a single molecular level. From the analysis of the solvophobic force in various liquid environments, strength of the intrinsic vdW interaction between b-CyD and ferrocene was clearly discriminated. Furthermore, the characteristic excess force appearing in the case of water was also directly confirmed and measured for the first time. (http://dora.ims.tsukuba.ac.jp)