Protein adsorption onto diethylaminoethyl dextran modified anion exchanger:Effect of ionic strength and column behavior

Our previous studies on bovine serum albumin （BSA） adsorption to diethylaminoethyl dextran （DEAE dextran, DexD, grafting-ligand） and DEAE （D, surface-ligand） modified Sepharose FF resins found that all the grafted resins （FF-DexD and FF-D-DexD） exhibited extremely fast uptake rate （effective diffusivity, De, De/Do 〉 1.4）, which was six times greater than the ungrafted resins （De/Do 〈 0.3）. In this work, the influence of ionic strength （IS） on 6 typical DEAE dextran-grafted resins was investigated. Bath adsorption equilibria and kinetics, breakthrough, and linear gradient elution experiments were conducted. Commercial DEAE Sepharose FF was used for comparison. It is found that protein adsorption capacities on DEAE dextran-FF resins and the commercial resin decreased with increasing IS, but DEAE dextran-FF resins exhibited much higher capacity sensitivity to salt concentration. Besides, steeper decrease of adsorption capacities could be obtained at higher graftingligand or surface-ligand density. It is worth noting that the facilitating role of surface-ligand to the ＂chain delivery＂ effect was weakened after adding salt, leading to the less improvement in uptake rate by increasing surface-ligand density at higher IS. Although the uptake rates of the DEAE dextran-FF resins increased first and then decreased with increasing fS, they kept the extremely high level of De values （De/Do 〉 1.1 ） at the their working/binding IS range. Moreover, the DEAE dextran-FF resin displayed much higher adsorption capacities and De values than commercial ungrafted resin in their working condition. Furthermore, the column results of DEAE dextran-FF resins presented higher dynamic binding capacities than and similar elution ISs with DEAE Sepharose FF to achieve similar （or even higher） recoveries suggest the excellent chromatographic column performance of the DEAE dextran-FF resins. Finally, both high recovery and purity of BSA and γ-globulin could be easily achieved using the typical DEAE dextran-FF column, FF-D60-DexD160, to separate their binary mixtures, by step gradient elution. The research has provided new insights into the practical application of the series of DEAE-dextran grafted resins in protein chromatography and proved their superiority.

Catalytic hosts with strong adsorption strength for long shelf-life lithium-sulfur batteries under lean electrolyte

Low electrolyte/sulfur ratio(E/S)is an important factor in increasing the energy density of lithium-sulfur batteries(LSBs).Recently,the E/S has been widely lowered using catalytic hosts that can suppress“shuttle effect”during cycling by relying on a limited adsorption area.However,the shelf-lives of these cathodes have not yet received attention.Herein,we show that the selfdischarge of sulfur cathodes based on frequently-used catalytic hosts is serious under low E/S because the“shuttle effect”during storage process caused by polysulfides(PSs)disproportionation cannot be suppressed using a limited adsorption area.We further prove that the adsorption strength toward PSs,which is unfortunately weak in commonly-used catalytic hosts,is critical for effectively hindering the disproportionation of the PSs.Subsequently,to verify this conclusion,we prepare a sulfur-doped titanium nitride(S-TiN)catalytic array host.As the adsorption strength and catalytic activity of TiN can be improved by S doping simultaneously,the constructed S/S-TiN cathodes under a low E/S(6.5μL·mg−1)exhibit better shelf-life and cycle-stability than those of S/TiN cathodes.Our work suggests that enhancing the adsorption strength of catalytic hosts,while maintaining their function to reduce E/S,is crucial for practical LSBs.

Mass transfer mechanisms in fixed-bed adsorption of erythromycin

The equilibrium and kinetic characteristics of the adsorption of erythromycin to Sepabeads SP825 were determined.The equilibrium data in a batch system was well described by a Langmuir isotherm.The separation performance was investigated in a fixed-bed system with respect to the adsorption superficial velocity,ionic strength and pH.A mathematical model was used to simulate the mass transfer mechanism,taking film mass transfer,pore diffusion and axial dispersion into account.The model predictions were consistent with the experi-mental data and were consequently used to determine the mass transfer coefficients.