Nakajima and Ikada (1995) investiga

Nakajima and Ikada (1995) investigated the reactions of EDC amide bond formation in aqueous solution using hydrogels of acrylic acid- or maleic acid-containing polymers or other carboxylate molecules to contribute the activatable groups and ethylenediamine or benzylamine as the amine functional groups to be conjugated. Their results indicate that carboxylate activation occurs most effectively with EDC at pH 3.5 to 4.5, while amide bond formation occurs with highest yield in the range of pH 4 to 6. However, EDC hydrolysis occurs maximally at acidic pH values with increasing stability of the carbodiimide in solution at or above pH 6.5. When working with proteins and peptides, experience indicates that EDC-mediated amide bond formation effectively occurs between pH 4.5 and 7.5. Beyond this pH range, however, the coupling reaction occurs more slowly with lower yields.