As a basis for understanding the molecular mechanism of gallium localization in tumor cells, the aqueous chemistry of gallium citrate in D2O at 31 °C was investigated by 13C FT-NMR spectroscopy (22.63 MHz). Complexes of the form Gan-(citrate)2n were detected at neutral or mildly acidic pDc's when the molar concentration of citrate was equal to or greater than the molar concentration of added gallium. In this complex, chemical exchange of bound citrate with free citrate is slow on the 13C NMR time scale. Line broadening of the citrate resonances as well as decreases in their apparent 13C spin-lattice relaxation times (T1) indicated formation of gallium citrate polymers in moderately acidic solutions at equal concentrations of gallium and citrate and in neutral solutions when the gallium/citrate concentration ratio was larger than 0.50. The “average diameter” of the polymer, estimated from the line width of the broad citrate CH2 resonance of gallium/citrate 1 M/1 M, was 50 Å at pDc 7.40 and 40 Å at pDc 2.75. The properties of gallium citrate complexes have been compared with those of ferric citrate.
ASJC Scopus subject areas
- Colloid and Surface Chemistry