The mixture was stirred at 70 °C for 2 h.
Excessive sodium hydroxide was neutralized with 6 mol l−1 hydrochloric acid solution
and the salts were removed by dialysis for 72 h against deionized water.
The dialysis tube was purchased from Sigma-Aldrich Co. LLC (D2272) with pore size 2000 MWCO (molecular weight cut off).
The non-dialyzable portion was lyophilized and stored in 4 °C until use.