Conjugation of a Dipicolyl Chelate to Polypeptide Conjugates Increases Binding Affinities for Human Serum Albumin and Survival Times in Human Serum

The affinity for human serum albumin (HSA) of a series of 2–5 kDa peptides covalently linked to 3,5‐bis[[bis(2‐pyridylmethyl)amino]methyl]benzoic acid, a dipicolyl chelator with micromolar affinity for Zn 2+ , was found by surface plasmon resonance to increase in the presence of 1 μ m ZnCl 2 at physiological pH. The dependence on polypeptide hydrophobicity was found to be minor, thus suggesting that the conjugates bound to the metal‐binding site and not to the fatty‐acid‐binding site. The affinity of the conjugates increased strongly with the positive charge of the polypeptides, thus implicating the negatively charged protein surface surrounding the metal‐binding site. The survival times of the peptides in human serum were extended as a consequence of stronger binding to HSA, thus suggesting that Zn 2+ ‐chelating agents might provide a general route to increased survival time of peptides in serum in therapeutic and diagnostic applications without significantly increasing their molecular weights.