Selective Binding of Trivalent Metals by Hexahomotrioxacalix[3]arene Macrocycles: Determination of Metal-Binding Constants and Metal Transport Studies.
The hexahomotrioxacalix[3]arene macrocycles 1a,b are observed to bind Sc(3+), Lu(3+), Y(3+), and La(3+) more strongly than alkali or alkaline earth metal ions. Binding constants have been determined for the trivalent metal ions using an NMR titration method and are observed to increase with increasing charge-to-radius ratio for the metal ion (Na(+), Li(+), Ca(2+) < Mg(2+) < La(3+) << Y(3+) < Lu(3+) << Sc(3+)) and increasing macrocycle acidity [p-tert-butyloxacalix[3]arene (1a) < p-chlorooxacalix[3]arene (1b)]. Macrocycle 1b is observed to transport Sc(3+) across a liquid membrane without any detectable transport of Li(+) or Mg(2+).
Hampton
Philip D.
PD
Department of Chemistry, University of New Mexico, Albuquerque, New Mexico 87131.
Daitch
Charles E.
CE
Shachter
Amy M.
AM