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BACKGROUND: Anion exchange resins are used extensively for the purification of acidic proteins. Grafting charged polymers to a rigid porous structure has been shown to improve performance under varying conditions. Understanding the underlying mechanisms is important for the optimum design and selection of material properties and operating conditions. RESULTS: Positively charged grafted polymers incorporated into a rigid, porous polymeric backbone structure are found to significantly enhance adsorption capacity and kinetics of the proteins bovine serum albumin (BSA, M r ∼ 65 kDa) and thyroglobulin (Tg, M r ∼ 660 kDa) but under different conditions. For the smaller BSA, binding increases with grafted polymer length and content and decreases with salt concentration. For the much larger Tg, binding increases with the addition of some salt for the polymer-grafted resins but can be lower than that observed for ungrafted resins without added salt. This behavior is caused by diffusional hindrance due to the bound protein. Increasing the length of the grafted polymer or the pore size of the backbone improves the Tg adsorption kinetics. CONCLUSION: Protein adsorption is controlled by different mechanisms dependent on polymer grafting, backbone structure, and size of the adsorbed protein. Optimum selection of resin properties and conditions is needed to maximize adsorption capacity and mass transfer kinetics.

a b s t r a c tMagnetic exchange bias and coercivity of nanogranular NiFe 2 O 4 /NiO thin films, prepared using flowstabilized microplasmas and post-deposition annealing, have been investigated as a function of ferrimagnet/antiferromagnet phase fraction, grain size, and temperature. Exchange bias (EB) and vertical shifts in hysteresis loops observed in the as-deposited and low-T annealed ( r 600°C) films were attributed to exchange coupling between nanocrystalline NiFe 2 O 4 ( $ 8-10 nm) and a structurally-disordered spin glass (SG)-like phase. At higher annealing temperature (850°C), the observed EB was found to arise from exchange coupling between NiFe 2 O 4 and NiO, rather than a SG phase, most likely due to reduction of structurally-disordered interfaces and a substantial increase in NiFe 2 O 4 grain size ( $ 26 nm).

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