Molecular design of hard-soft ditopic metal-binding sites on a calix[4]arene platform

✍ Scribed by Kwang Nak Koh; Tomoyuki Imada; Takeshi Nagasaki; Seiji Shinkai

• Publisher: Elsevier Science
• Year: 1994
• Tongue: French
• Weight: 327 KB
• Volume: 35
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)73138-8

✦ Synopsis

Ditopic "hard"-"soft" metal binding-sites composed of four EtS(CH&NHCOCH20groups were designed for the iirst time on a calixl4larene pkform. N = 2 is too short to form a bimetallic complex whereas n = 6 is long enough to accept two metal ions. 1H NMR spectral studies established that although Cdz+ bound to the "soft" binding-site excludes Na+ out of the "hard" binding-site, Ag+ can be co-existent with Na+ in the ionophoric cavity. Molecular design of hard-soft ditopic metal binding-sites has heen of much concern as an attractive catalytic site in both enzymatic and artificial systems: a hard metal ion can interact with anionic guests through electrostatic interactions or polarize Lewis-basic functional groups whereas a soft metal ion can mediate electron-transfers or bond -rearrangements which lead to net catalytic rea&mr~.~~ We have been interested in designing various recognition sites using calix[n]arenes as a platform. We noticed that calix[4]amnes would be useful as a potential platform for the &sign of hard-soft ditopic metal binding-sites because the lower rim of calix[4]arenes can be modified into the first binding-site for hard metal ions