Question #44969

An aqueous solution of L-Lysine ($pK_{a1} = 2.20$ for $-\ce{COOH}$, $pK_{a2} = 8.90$ for $\alpha-\ce{NH3+}$, $pK_{a3} = 10.50$ for $\epsilon-\ce{NH3+}$) is reacted with an excess of D-glucose at 298 K. A selective Maillard reaction occurs, forming a Schiff base at the less sterically hindered and intrinsically more basic amino group of L-Lysine. The $pK_a$ of the conjugate acid of the newly formed imine nitrogen is 3.50. Assuming the $pK_a$ values of the unreacted groups remain unchanged and no other side reactions occur, what is the isoelectric point (pI) of the isolated Schiff base conjugate?