Interactions of Calcium Ions with Carbohydrates: X-Ray Diffraction and NMR Spectroscopic Studies on the Potassium Salt and the Calcium Salt of d -Clucaric Acid

The crystal structure of potassium d-glucarate was determined by X-ray analysis. The conformation of the glucaric anion in the potassium salt differs from that of the dianion in the crystal of the calcium salt. The proton magnetic resonance spectra of the solutions of the potassium salt and the calcium salt show that the glucarate solution is an equilibrium mixture of the two conformers observed in the crystals. Studies on the induced shifts by adding europium nitrate to the acidic solution indicate that the europium ions are selectively bound to the potassium type conformer. Calcium sequestant by the glucaric acid in alkaline solutions should occur when calcium ions bind the calcium type conformers in a dianionic state.