Labeling of human IgG with rhodium-105 using a new pentadentate bifunctional ligand

We report the labeling of human gamma globulin with the 105Rh complex of a new pentadentate bifunctional ligand, 1,7-bis(2-hydroxybenzyl)-4-(p-aminobenzyl)diethylenetriamine. Complexes of this ligand with 105Rh were prepared by refluxing rhodium carrier spiked with 105Rh at pH9 in bicarbonate buffer. The complex was treated with an excess concentration of thiophosgene to prepare the isothiocyanate derivative which was extracted into CHCl3. The CHCl3 extract was dried and dissolved in DMF and reacted with a borate solution of human gamma globulin. Labeling yields were generally high and varied from 73% to 93%, depending upon the concentration of human gamma globulin and the isothiocyanate derivative of the complex used. The overall recovery of rhodium activity varied from 59% to 75% without taking into account activity lost due to decay. The conjugation reaction was complete by 4 h. From 0.4 to 8.5 atoms of Rh could be incorporated per molecule of protein by this method. The activated isothiocyanate complex did not show any degradation when stored at room temperature for up to 4 days and then used for conjugation.