BAPTA Alkyne is an excellent building block to introduce BAPTA calcium chelator into a biological molecule that contains an azido group such as azido-modified antibodies, proteins, peptides and oligos via the well-known click chemistry. BAPTA (1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid) is a common calcium-specific chelator. The presence of four carboxylic acid functional groups makes BAPTA possibly binding two calcium ions. The extensive flexibility of the carboxylate ligands is critical to the coordination of calcium and other metal ions. BAPTA is commonly used to chelate Ca2+, similarly to EGTA.