LANTHANIDE ION EMISSION AS A PROBE OF METAL ION/CARBOHYDRATE INTERACTIONS IS SOLUTION

Author Institution: Department of Chemistry, University of VirginiaInteractions of calcium ions with carbohydrates have been implicated in a number of biological processes such as cell-cell adhesion, calcium transport, calcification, and binding of glycoproteins to cell surfaces. It has been demonstrated that calcium ions complex with both uncharged and anionic carbohydrates in aqueous solution, as well as in hydrated solid-state systems. Recently it has been proposed that neutral sugars containing an ax-eq-ax sequence of vicinal hydroxy groups on six-membered rings form complexes with calcium and other mono- and divalent metal ions of similar size. Similarity of ionic radii, preference for charged or uncharged oxygen donor groups, lack of strong directionality in binding donor groups and a variable coordination number make the trivalent lanthanide ions $(Ln^{3+})$ excellent substitutional probes for $Ca^{2+}$, We report here the use of lanthanide ion emission spectra in characterizing the binding of $Ln^{3+}$ ions to some simple mono- and disaccharides, as well as to some $Ca^{2+}$ binding carbohydrates of biological importance (e.g, N-Acetylneuraminic Acid). Preliminary studies using Circularly Polarized Emission (C.P.E.) spectroscopy indicate binding of $Tb^{3+}$ to a number or carbohydrates displaying the ax-eq-ax sequence. Additionally, pH titrations and CPE show a pH dependent binding of one equivalent of $Tb^{3+}$ or $Eu^{3+}$ to several sugar acids with essentially one species being formed as the pH is raised from 1 to 5. Evidence is presented for the formation of dimeric or polymeric species at higher pH values