3. Many proteins are sensitive to divalent cations and often chelating agents are included in protein isolation solutions to bind divalent cations, lowering their concentration, and removing them from proteins. Two common agents used for this purpose are EDTA (Ethylenediaminetetraacetic acid) and EGTA (Ethyleneglycol-bis-(b- aminoethyl ether)-N,N,N',N'-tetraacetic acid). (a) Draw the structures of EDTA and EGTA (b) These agents function by binding divalent cations. EDTA binds both Mg2+ and Ca2+ tightly while EGTA has a greater specificity for Ca2+. (Both will bind a number of other divalent cations as well.) However, cation binding is pH-dependent. In making a solution of EDTA, it is often suggested that the pH of the solution be adjusted to around 8. The pKas of the four acetic acid groups on EDTA are 2.0, 2.67, 6.16 and 10.26. At pH = 8.0, what is the predominant ionic species of EDTA?

(c) To make up 1 L of a 0.5 M solution of EDTA starting with the free acid, approximately how much 10 M NaOH will have to be added to adjust the pH to 7.0? Do you expect this solution to have a pH-buffering capacity? Explain.