BAPTA

BAPTA is an aminopolycarboxylic acid with a high affinity for calcium. It is a white solid. It is used in research to chelate Ca²⁺, as it behaves similarly to EGTA and EDTA.

Complexation

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 Ca²⁺.
There is a range of reported values for the dissociation constant of BAPTA, though 0.2 μM appears consistently. The rate constant for calcium binding is 500 μM⁻¹ s⁻¹. 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. These indicators change their fluorescence intensity and fluorescence lifetime depending on the calcium ion concentration.