作者:Kyu-Sung Jeong、Young Lag Cho、Sung-Youn Chang、Tae-Yoon Park、Jung Uk Song
DOI:10.1021/jo9910841
日期:1999.12.1
Osmium (VI)-bridged macrocycles 1a-c, 2, and 3 assemble spontaneously when osmium tetraoxide, olefins, and L-shaped bispyridyl ligands are mixed in CHCl3. The macrocycles possess well-defined square or rectangular cavities enclosed by aryl walls and act as host molecules. Hydrogen-bond donors on the inner surface of the hosts offer binding sites to accepters of guests with complementary dimensions. The host la binds adipamide G2 (K-a = 3.6 x 10(4) M-1) and terephthalamide G6 (K-a = 2.0 x 10(4) M-1), while it binds negligibly (K-a < 10 M-1) benzamide G5, isophthalamide G9, or 1,4-naphthalenedicarboxamide G10. The larger hosts 2 and 3 bind the longer guests biphenyldicarboxamide G12 and terphenyldicarboxamide G17, respectively, but shorter guests such as adipamide G2 and terephthalamide G6 are not well-bound (K-a < 10 M-1). Hosts 1a-e with different remote substituents (H, OMe, NO2) but identical cavity size were prepared and their binding affinities were measured. The relative binding affinities of the hosts 1a-c to the keto amide G19, ester amide G20, and diester G21 are in the order of 1c (NO2) much greater than 1a (H) > 1b (OCH3). The substituent effects on the binding strength are interpreted in terms of the electron density at the pyridine nitrogen of the hosts and its effect on bifurcated hydrogen bonding.