Metal ion coordination of macromolecular bioligands: formation of zinc(II)complex of hyaluronic acid

The coordination of zinc(II) ion to hyaluronate (Hya), a natural copolymer, in aqueous solution at pH 6 was investigated by potentiometric and circula r dichroism (CD) spectroscopic methods, and by monitoring the changes in ma croscopic properties by high-precision measurements. The zinc(II)-selective electrode, and CD measurements proved the binding of zinc(II) by Hya. A nu mber of Hya fragments (M, similar to 3.3 x 10(3) - 1.4 x 10(6)) were studie d to estimate the contributions of the polyelectrolyte effect, the solvatio n and host-guest interactions to the extra stabilization of the macromolecu lar zinc(II) complexes as compared with the monomeric unit. The zinc(II) io n activity increase reflected a stability decrease for the fragments with M -r < 4 x 10(4). This molecular weight differs from that where cleavage of t he Hya skeleton starts (similar to5 x 10(5), according to the size-exclusio n gel, and anion-exchange chromatographic behavior of the Hya fragments) an d from that where the polyelectrolyte effect stops (- 6 x 103). The excess volumes and Bingham sheer yield values of the solutions revealed the transf ormation of the coherent random coil structure stabilized by intermolecular association in the NaHya to an intramolecular association producing the gl obular structure of the ZnHya molecule, with a smaller but more strongly bo und solvate water sheet. (C) 2001 Elsevier Science Ltd. All rights reserved .