Preparation of a recyclable novel thermoresponsive affinity copolymer and its application towards ε-polylysine purification

Thermo-responsive polymers have great potential for industrial applications of bio-separation and purification. However, the poor affinity and low recovery of thermoresponsive copolymers are the main factors limiting their large-scale application. In this paper, a recyclable thermoresponsive affinity copolymer (P-NHM-IDA-Ni2+) was prepared by immobilizing nickel ions (Ni2+) on copolymer P-NHM, and P-NHM -IDA-Ni(2+ )was applied to the purification of epsilon-polylysine. The lower critical solution temperature (LCST) of P-NHM and P-NHM-IDA-Ni2+ were 31.0 degrees C and 34.0 degrees C, respectively. Additionally, the recoveries of both copolymers were over 95.0%. The main parameters, such as pH were investigated to optimize the adsorption conditions. In addition, the Langmuir and Freundlich adsorption models were used to predict the maximum adsorption capacity of epsilon-polylysine. The results of the affinity precipitation demonstrated that the maximum adsorption capacity was 42.9 mg/g, and the adsorption was considered to follow the mono-layer model. The thermodynamic parameters (Delta G(0), Delta H-0 and Delta S-0) of the e-polylysine adsorption indicated that the adsorption was spontaneous and exothermic. The maximum elution recovery (93.5%) was achieved at pH 5.0 with 0.2 M imidazole. The results of tricine-SDS-PAGE and HPLC (Purity: increased from 84% to 99%) showed that the e-polylysine was well separated from the crude extract by using the affinity copolymer P-NHM -IDA-Ni2+.