The pH dependence of borohydride as an aldehyde reductant

Abstract
The aldehyde-reducing capacity of borohydride has been investigated in the sequence periodic acid-borohydride-periodic acid-Schiff and variants. Densitometric studies on rat colonic mucins show that borohydride incompletely blocks periodateengendered aldehydes unless the pH is above 8.2 Below this value, some aldehydes are not reduced and continue to be Schiff-stainable, while others are subsequently generated by the second exposure to periodic acid. The effect is more pronounced in paraffin than in cryostat sections, but does not apply to human colonic mucins.