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

Abstract

Abstract 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 (PNHM-IDA-Ni2+) was prepared by immobilizing nickel ions (Ni2+) on copolymer PNHM, and PNHM-IDA-Ni2+ was applied to the purification of e-polylysine. The lower critical solution temperature (LCST) of PNHM and PNHM-IDA-Ni2+ were 31.0 °C and 34.0 °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 e-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 (ΔG0, ΔH0 and ΔS0) 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 PNHM-IDA-Ni2+.