Magnetic resonance and susceptibility studies of fructose complexes with copper and iron

Abstract

• 1.

  1. Fructose complexes of Cu²⁺ and Fe³⁺ have been studied by ESR, NMR and magnetic susceptibility measurements. In the case of Fe³⁺, 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 Fe³⁺ solutions.

• 2.

  2. With Cu²⁺, 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 1 Cu²⁺ ion and 2 fructose molecules.

• 3.

  3. With Fe³⁺, the ESR signal intensity, NMR line width and magnetic susceptibility go through a minimum at pH7 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 Fe³⁺ ions joined by oxygen bridges), which breaks up at higher pH values. However, the ultracentrifugation experiments indicate the presence of larger particles, be aggregates of the dimer.