Question

Illustrate the titration curve of lysine showing the cation, zwitterion and anion on the curve

Answer 1

Lysine, like all the other amino acids are described as amphoteric substances and hence react with both acids and bases as follows

H₃N⁺-RCH-COO^- + H3O⁺ $\iff$ H₃N⁺-RCH-COOH + H₂O

zwitterion acid cation

H₃N⁺ - RCH - COO^- + OH^- $\iff$ H₂N - RCH - COO^- + H₂O

zwitterion base anion

The curve will therefore show pH against Equivalents of OH^- added and the amino acid will be changing from left to right as;

Lys²⁺ $\iff$ Lys⁺ $\iff$ Lys^o $\iff$ Lys^-