Sulfate-binding proteins hold their ligands by means of a large number of neutral hydrogen-bonding interactions, but designers of small synthetic receptors generally have had to resort to electrostatic interactions to capture the sulfate ion. Bondy et al. have modified a system for binding sulfate that relies on Pt2+ centers (which provide an electrostatic interaction) that sport four nicotinamide arms (which form hydrogen bonds). Now, by using iso-quinoline ligands derivatized with urea groups, they can stabilize sulfate binding in deuterated dimethyl sulfoxide (DMSO-d6) enough so that they can follow anion binding on the nuclear magnetic resonance time scale. Halides formed 2:1 complexes with these receptors, but the four urea moieties converged on a single sulfate ion in a 1:1 complex featuring eight hydrogen bonds, as revealed by x-ray crystallography. The association constant for sulfate in DMSO exceeded 105. — PDS
J. Am. Chem. Soc. 10.1021/ja039712q (2004).