Stabilization of the open-chain structure of d-galacturonic acid in a dimeric complex with oxovanadium(IV).

The formation of a dimeric VOIV-D-galacturonic acid complex in aqueous solution has been studied by spectroscopic methods, namely e.s.r., electron nuclear double resonance, and electronic absorption. The complex exhibits properties consistent with a metal-metal distance of about 5.0 Å, which is very similar to that found in the well known VOIV-tartrate dimers. The only way to accommodate the metal ions at such a distance and to fit the spectroscopic data is to assume that the ligand co-ordinates to the metal ion through the CO2-, O(4)- and O(3)-, O(2)- donor sets and adopts an open-chain structure which is stabilized by the dimer complex formation.