Our previous studies on protein adsorption to the anion-exchangers of poly(ethylenimine) (PEI)-grafted Sepharose FF found that both adsorption capacity and uptake rate of bovine serum albumin (BSA) increased greatly when the PEI grafting density reached over a critical ionic capacity (cIC) due to the 3D protein binding and occurrence of “chain delivery” of bound proteins. Moreover, by the investigation on the anion-exchangers of diethylaminoethyl (DEAE)-modified and DEAE-dextran-grafted Sepharose FF, we found the unique role of surface ligand in facilitating protein uptake kinetics on dextran-functionalized anion exchangers as the “transfer station” for the “chain delivery” of bound proteins. However, what would be the contribution of surface ligands on the transport of bound proteins on PEI chains at a wide range across cIC, particularly at the lower IC range where no “chain delivery” was present? We have thus designed this research to answer the question. To this purpose, we fabricated three series of PEI-Sepharose FF resins, one without surface ligand (i.e., FF-PEI) and two with surface DEAE modifications at DEAE coupling densities of 60 and 90 mmol/L (i.e., FF-D60-PEI and FF-D90-PEI), and focused on the role of surface DEAE at different PEI densities in BSA adsorption equilibrium and uptake kinetics in a wide IC range of PEI across cIC (∼600 mmol/L for BSA). It was found that, at low grafting-ligand densities (IC cIC, however, both adsorption capacity and uptake rate changed only slightly (<5% and <10%, respectively) by the addition of surface DEAE groups. The results revealed that at IC < cIC, the surface DEAE groups provided the supplement of available binding sites and facilitated the happenings of the “chain delivery” of bound proteins as the “transfer station”, both of which were limited at the low IC range. However, at IC > cIC, the extended flexible PEI chains have already afforded 3D binding space with high accessibility and easy happening of “chain delivery” of bound proteins, so the surface DEAE groups between neighboring PEI chains did not work in assisting the transport of bound proteins. Moreover, when the IC was lower but close to the cIC, the FF-D-PEI resins exhibited higher uptake rates than FF-PEI resins at a similar or even lower IC values. These findings indicate that surface modification of charged groups in PEI-based anion exchangers of low grafting density would be an efficient strategy to fabricate high performance protein ion exchangers.
Chunli Lei,Zicong Ding,Mengna Tao,Yubo Lu,Lanqing Xu,Bingxu Cheng,Chuanxi Wang,Zhenyu Wang
The enormous potential of carbon dots (CDs) in agriculture has been widely reported, whereas their accurate distribution, transformation, and metabolic fate and potential soil health effects are not clearly understood. Herein, 13C-labeled CDs (13C-CDs) were sprayed on maize leaf, accumulated in all tissues, and promoted photosynthesis. Specifically, 13C-CDs were internalized to participate in the synthesis of glucose, sucrose, citric acid, glyoxylate, and chlorogenic acid, promoting tricarboxylic acid cycle (TCA) and phenylalanine metabolism. Additionally, the catabolism of 13C-CDs in vivo was mainly mediated by O2•– produced by oxidative stress. 13C-CDs did not have an obvious impact on the soil environment at the overall level. The detection of 13C signals in soil fauna suggested 13C-CDs in soil food chain transmission. This study systematically described the exact fate of CDs in plants and potential soil ecological risks and provided a more comprehensive analysis and support for the potential advantages of CDs in agricultural application.
危险品化学品经营许可证（带存储）