Effects Of Polymer Charge Structure On The Performance Of Grafted Ion Exchange Chromatography Media

Polymer grafted ion exchange chromatography(IEC)resins generally exhibited significantly higher adsorption capacity(q_m)and uptake rate(D_e/D₀)than traditional chromatography resins,which is attributed to the three-dimensional adsorption space and protein transfer through the flexible chain swings formed by its dense flexible polymer chain.The charge structure of grafted polymer is an important factor affecting its chromatographic behaviors,therefore,referring to recent researches and existing problems about charge structure,poly(ethyleneimine)(PEI)and(3-acrylamido propyl)trimethyl ammonium chloride(DMAPAA-Q)were grafted on Sepharose gel by“grafting to”and“grafting from”methods in this work,respectively,and systematic researches summarized as follows were carried out to improve the IEC performance of the resins by optimizing the charge structure of the grafted polymer.First,a new charge modification route was developed to prepare PEI-derived cation exchange resins(route B,PEI-Rm-Cn),the adsorption and chromatographic behaviors of lysozyme(Lys)were compared with the resins prepared through the previous modification route(route A,PEI-L700-CRn)in detail.The results showed that,the resins from route B obtained a more favorable polymer charge structure via adjusting the modification route.On the one hand,this new route avoids the formation of long-chain electroneutral groups that hinder protein adsorption and reduce equilibrium capacity,on the other hand,the lack of diamide formation makes PEI-R390-C590 exhibited higher flexibility of grafted polymer chain.Therefore,the route B resins show superior IEC performance over the route A resins.For instance,the DBC of PEI-R590-C680(192 mg/m L)is 33%higher than that of PEI-L700-CR680(144mg/m L),and the former behaves 14%higher yield of purified Lys from chicken egg white solution.Then,the resins from route B with better IEC performance were appointed as the research object to study the influence of ionic strength(IS)on adsorption and chromatography behaviors.It is found that PEI-derived cation exchangers with different charge densities exhibit distinct salt tolerance properties,which provides a wide and economical choices for chromatography operations under different IS conditions.Among them,the DBC of PEI-R590-C680 is more than 170 mg/m L under the low salt concentration conditions,which is twice the commercial resin CM Sepharose FF at the same conditions.Finally,the electroneutral monomer acrylamide(AM)and DMAPAA-Q co-grafted anion exchangers were prepared,and through that,the strategy of reducing charge density to optimize the polymer charge structure for improving mass transfer performance developed in the series study on PEI was extended to the“grafting from”method.The study found that,the D_e/D₀ of the resins increased gradually with decreasing ion exchange capacity(IC).When the IC decreases to 127 mmol/L,the D_e/D₀ of FF-p AM-DMAPAA-Q127 increases nearly 2.5 times that of the initial anion exchanger FF-p DMAPAA-Q336,and the DBC of the former is 19%higher than that of the latter.These results showed that reducing the charge density of polymer chain is an effective method to improve the mass transfer performance of DMAPAA-Q grafted resins.In this work,the research achievements on the charge structure of grafted polymer are of great significance for developing high-performance grafted ion exchangers and establishing chromatography operation space.