C-13 NMR AND MOLECULAR MODELING STUDIES OF ALGINIC ACID-BINDING WITH ALKALINE-EARTH AND LANTHANIDE METAL-IONS

The binding of the binary polyuronide alginic acid to alkaline earth ( Mg2+, Ca2+, Sr2+, Ba2+) and lanthanide (La3+, Pr3+, Nd3+, Eu3+, Tb3+) ions was studied by C-13 NMR spectroscopy Divalent metal ions showed a preference for GG blocks and an increase in the extent of binding wit h increasing ionic radius. Molecular modeling studies of calcium-algin ate dimers support the assertion that this preference results from the secondary structure of alginic acid. Trivalent metal ions studied sho wed a preference for GG blocks and an increase in the extent of bindin g for both GG and MM blocks with increasing charge density. The contra st in the mode of interaction of the alkaline earth and lanthanide met al ions with alginic acid can be associated with differences in coordi nation number and/or waters of hydration remaining in the inner sphere of the lanthanide ions.