Effect of cationic polymer adsorbent pK a on the selective removal of endotoxin from an albumin solution
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To obtain fundamental information about the surface-environment effect of adsorbent on the selective adsorption of endotoxin (lipopolysaccharide; LPS) from a protein solution, cross-linked poly(ε-lysine)(PL) and aminated poly(γ-methyll-glutamate) (PMLG-NH2) spherical adsorbents were prepared. The apparent pK a (pK a,app) of the PL and PMLG-NH2 adsorbents was adjusted by controlling the ratio of poly(ε-lysine), in cross-linking, and the amination conditions (time and ratio of diaminoethane in the particles), respectively. When adsorption of LPS and acidic protein, e.g. bovine serum albumin (BSA), by the particles was determined by a batchwise method at pH 7.0 and an ionic strength, μ, of 0.05, they were found to depend strongly on pK a,app but not necessarily on the amino-group content. When pK a,app was increased from 6.8 to 8.2, the LPS-adsorbing capacity was increased from 1.0 to 2.7 mg mL−1 wet adsorbent and the apparent dissociation constant for adsorbent and LPS decreased from 3.7×10−10 to 1.0×10−10 m. Although PMLG-NH2 with the highest pK a,app, 8.2, had the highest LPS-adsorbing activity, it also adsorbed BSA. The BSA-adsorbing activity was sharply reduced when pK a,app was reduced to 6.8 or lower. As a result, the cross-linked PL adsorbent of pK a,app 6.8 had the highest LPS selectivity. The adsorbent could reduce levels of natural LPS associated with acidic protein (ovalbumin or BSA) at pH 7.0 and μ=0.05. The residual LPS concentration in each sample was >100 pg mL−1, and recovery of the protein was >96%.
Key WordsColumn liquid chromatography Lipopolysaccharide Poly(ε-lysine) Poly(γ-methyll-glutamate) Bovine serum albumin
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