BAPTA (1,2-<u>b</u>is(o-<u>a</u>mino<u>p</u>henoxy)ethane-N,N,Nâ²,Nâ²-<u>t</u>etra<u>a</u>cetic acid) is an aminopolycarboxylic acid with a high affinity for calcium. It is a white solid. It is used in research to chelate Ca<sup>2+</sup>, as it behaves similarly to EGTA and EDTA.
BAPTA, as its conjugate base, binds calcium ions as a decadentate ligand:
According to X-ray crystallography. the four carboxylates, two amines, and two ether oxygens bind to Ca<sup>2+</sup>.
There is a range of reported values for the dissociation constant of BAPTA, though 0.2 üM appears consistently. The rate constant for calcium binding is 500 üM<sup>âÂÂ1</sup> s<sup>âÂÂ1</sup>. The complexation process of calcium ion to BAPTA can be deconvoluted into three main processes: conformational changes of the glicol linker, nitrogen conjugation and electronic effects changes of the benzene rings.
BAPTA is a component of some fluorescent calcium ion indicators such as Calcium Green and Oregon Green 488 BAPTA-1 and -2 (OGB-1, OGB2). These indicators change their fluorescence intensity and fluorescence lifetime depending on the calcium ion concentration.