I. Fructose complexes of Cu 2+ and Fe a+ have been studied by ESR, NMR and magnetic susceptibility measurements. In the case of Fe a+, the experimental parameters have been studied in pH-titration experiments. Ultracentrifugation studies have also been performed in order to study the size of colored species in the Fe a+ solutions.
-
With Cu 2+, the ESR spectra at room temperature as well as at 77 °K indicate the presence of a well-defined complex with approximately axial symmetry around the metal ion. The small line width at 77 °K allows resolution of hyperfine structure in the perpendicular direction also. The room temperature ESR spectrum and the NMR line width are consistent with the formation of a complex consisting of I Cu ~+ ion and 2 fructose molecules.
-
With Fe a+, the ESR signal intensity, NMR line width and magnetic susceptibility go through a minimum at pH 7 as increasing amounts of NaOH are added to an acid solution of the metal ion in the presence of excess fructose. The results are consistent with the formation of a dimer (consisting of 2 fructose molecules and 2 Fe a+ ions joined by oxygen bridges), which breaks up at higher pH values. However, the ultracentrifugation experiments indicate the presence of larger particles, which may be aggregates of the dimer.