Citraconic Anhydride (Methylmaleic anhydride) is used to block primary amine (-NH2) groups at pH 7 to 9. Citraconic anhydride reacts with primary amines to create a reversible amide linkage, which can be reversed under acidic conditions or in the presence of hydroxylamine.
Ethylene glycol bis(succininic acid) N-hydroxysuccinimide ester) is a cleavable, homobifuntional crosslinker that contains two NHS functional groups. The NHS functional groups of EGS are selectively reactive towards primary amines at pH 7 to 9. EGS is cleavable with hydroxylamine at pH 8.5. EGS is often used as a cleavable option when disulfide containing crosslinkers, such as DSP (CovaChem 13304) and DTSSP (CovaChem 13303) are not an option due to the desire to retain disulfide networks of a protein intact.