Influence of linker unit on performance of palladium(II) coproporphyrin labelling reagent and its bioconjugates

In this paper we describe the preparation of a series of new phosphorescent labelling reagents, based on monosubstituted palladium(II) coproporphyrin-I and the isothiocyanato reactive group. The labelling reagents differ with respect to the chemical composition of the linker unit that combines the reactive group and the porphyrin chromophore. Altogether, seven different labelling reagents are prepared. The new labelling reagents are conjugated with monoclonal mouse IgG to yield label conjugates with variable degrees of conjugation. The effect is studied of linker unit on: (a) the conjugation reaction kinetics; (b) the biological activity of the resulting IgG conjugates; and (c) the efficiency of phosphorescence emission. The results show that an increase in the length of the linker unit has a positive effect on both the reactivity of the label and the biological activity of the resulting conjugates. In addition, the results indicate that the labels with the most hydrophilic linker units exhibit the highest phosphorescence emission efficiencies.