Haino T, Rudkevich DM, Shivanyuk A, Rissanen K, Rebek J
The Skaggs Institute for Chemical Biology and The Department of Chemistry, The Scripps Research Institute, La Jolla, CA 92037, USA.
Chemistry. 2000 Oct 16;6(20):3797-805. doi: 10.1002/1521-3765(20001016)6:20<3797::aid-chem3797>3.0.co;2-1.
Synthesis of novel water-soluble cavitands 1 and 2 and their complexes--the caviplexes--is described. The solubility in water derives from four primary ammonium groups on the lower rim and eight secondary amide groups on the upper rim. Cavitands 1 and 2 exist as D2d velcraplex dimers in aqueous solution but the addition of lipophilic guests 15-24 induces conformational changes to the vase-like structures. The internal cavity dimensions are 8 x 10 A, and the exchange rates of guests in the caviplexes are slow on the NMR time-scale (room temperature and 600 MHz). The direct observation of bound species and the stoichiometry of the complexes is reported. The association constants (Ka) between 0.4 x 10(-1) (-deltaG295= 0.7 kcalmol(-1)) and 1.4 x 10(2)M(-1) (-deltaG295=2.9 kcalmol(-1)) in D2O and 1.4 x 10(1)(-deltaG295= 1.7 kcalmol(-1)) and 2.8 x 10(4)M(-1)(-deltaG295=6.0 kcalmol(-1)) in [D4]methanol for aliphatic guests 16-24 were determined. Guest exchange rates of the new hosts 1 and 2 are considerably slower than rates observed for typical open-ended cavities in aqueous solution.
