Effectiveness and toxicity of several DTPA broadening agents for biological ESR spectroscopy

The effectiveness of a standard ESR broadening agent, potassium trioxalatochromiate (CrOx), for use with the spin-label tempone, was compared to that of diethylenetriaminepentaacetic acid (DTPA) containing an ion (Gd, Cr, Mn, Fe) with a large magnetic moment. Signal attenuation, line broadening, toxicity, and cell membrane permeability were compared. As a broadening agent, CrOx was most effective, followed by Fe-DTPA. CrOx proved mildly toxic while Gd-DTPA and Fe-DTPA were virtually non-toxic. The human red blood cell membrane was tested for permeability to Fe- and Gd-DTPA and found to be impermeable to both. In situations where toxicity to cells is critical, the DTPA chelates, particularly Fe-DTPA, may prove an acceptable substitute for CrOx.