Abstract
Resolved hydroxy-proton resonance features for various forms of D-ribose in dilute aqueous solutions shift markedly on the addition of calcium chloride. Down-field shifts are assigned to OH groups which bind to Ca2+ ions. These shifts level off in the 1.0–1.5 mol dm–3 region when complexing is complete. Resonances for OH groups which are not involved in complex formation shift linearly to high-field, the shift being greater than that expected for the sum of general Ca2+ and Cl– ionic effects. This is because the Ca2+ ions are removed by complex formation, the up-field shift being largely due to the effect of chloride ions. When chloride is replaced by perchlorate, this up-field shift is greatly enhanced. Approximate equilibrium constants for complex formation have been derived, and the influence of conformational changes is discussed.
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