Thermo Scientific AminoLink Reductant (sodium cyanoborohydride) promotes the formation of stable bonds between aldehyde- and amine-containing molecules, enabling efficient labeling, conjugation, and immobilization of proteins and other molecules. Carbonyl groups such as aldehydes, ketones, and glyoxals react spontaneously with amino groups to form Schiff base intermediates that are in equilibrium with their free forms. The interaction is pH-dependent, being somewhat more efficient in acidic conditions, and especially strong at high pH. Addition of AminoLink Reductant to a reaction in which Schiff base formation has occurred results in complete reduction of the labile Schiff base intermediate to a chemically stable bond. Unlike sodium borohydride, sodium cyanoborohydride is sufficiently mild to avoid adversely reducing aldehydes to nonreactive hydroxyls.
The overall reaction of carbonyl groups to primary amino groups using sodium cyanoborohydride is called reductive amination. Immobilization by reductive amination of amine-containing biological molecules onto aldehyde-containing solid supports is used to create matrices for affinity purification of antibodies and other molecules. To conjugate glycoproteins by reductive amination, sugars in the polysaccharide groups must be oxidized using sodium meta-periodate to create reactive aldehyde groups. Treatment of glycoproteins with sodium meta-periodate generally creates sufficient aldehyde groups to be used as targets for efficient conjugation with amine- or hydrazide-containing molecules, including other proteins, biotin reagents and fluorescent labels. Because glycoproteins contain their own primary amino groups, polymerization of an oxidized protein may occur unless a sufficient molar excess of the intended amine-containing target molecule is added to the reaction.