A temperature stimuli-responsive polymer, dextran-grafted-PNIPAAm (DGP), was prepared by radical polymerization using cerium nitrate as the initiator. The structure and the grafting ratio of DGP were determined by FT-IR and elemental analysis. The temperature-stimuli responsive behavior of DGP and the size of the DGP self-assemblies at different temperatures were determined by transmittance and dynamic light scattering, respectively. The use of DGP as an artificial chaperone to assist protein refolding in vitro was demonstrated using hen egg white lysozyme (lysozyme) and carbonic anhydrase bovine (CAB) as model proteins. It was shown that the hydrophobic interaction between DGP and the protein being refolded gave a significant reduction in the rate of protein aggregation and a slight reduction in the refolding rate, and consequently gave an improved refolding yield. Moreover, the refolding of lysozyme and CAB at a temperature gradient starting above the LCST of DGP and ending at a lower temperature, which make DGP change from hydrophobic to hydrophilic, gave a significant increase in the refolding yield compared to that carried out at a constant temperature. The process mechanism of DGP assisted protein refolding was presented and the importance of controlling the hydrophobicity of the solution environment for protein refolding was discussed.

Anewmethod for determining the amount of adsorbed protein on membrane surface is developed on the basis of immunoassay using alkaline phosphotase as enzyme label and 4-nitrophenyl phosphate as substrate. Adsorption of human serum albumin (HSA) on HT Tuffryn, a kind of polysulfone microfiltration membrane, in the absence and presence of an electric field is investigated experimentally. It is shown that the adsorption of HSA on HT membrane surface is finished within 5 min and the amount of the adsorbed HSA decreases with the increase in pH but is not sensitive to salt concentration. Desorption of the adsorbed HSA from HT membrane surface can only be achieved with NaOH. Adding surfactants in HSA solution to prevent the adsorption is attempted and Tween 20 shows the best shielding function compared to polyethylene glycol 6000 and pluronic-F108. A critical concentration exists for Tween 20, below which the increase in the concentration of Tween 20 results in a corresponding reduction of adsorbed HSA. Introducing electric field into the adsorption leads to an enhanced adsorption of HSA, which appears to be a function of pH and the electric field strength.

A computational approach to screening monomer for preparing molecularly imprinted polymer (MIP) was proposed, using the binding energy, E, of a template molecule and a monomer as a measure of their interaction. For a specified template molecule, a monomer of higher E is suitable for preparing the MIP. To examine the validity of this approach, theophylline (THO) was chosen as the template molecule and methacrylic acid (MAA), acrylamide (AA) and 2-(trifluoromethyl)acrylic acid (TFMAA) were as the functional monomers, respectively. Density functional theory (DFT) at B3LYP/6-31+G**//B3LYP/3-21G level was used to calculate E. It was shown that TFMAA gave the largest E whileAAgave the smallest. The details of the interaction between the THO with these monomers were also given by this computing approach. The adsorption of THO on the MIP synthesized using different monomers was studied. The MIP synthesized using TFMAA as monomer showed the highest selectivity to THO while the MIP from AA gave the lowest, as predicted from the E calculation. 1H NMR spectroscopy showed that, compared to MAA and AA, a stronger H-bond interaction is formed between TFMAA and THO. FT-IR analysis of the MIPs prepared using these three monomers confirmed the existence of C O and O H groups, which forms H-bond with THO. The results described above have given an insight into the interaction between THO and the monomers, and shown the use of E to facilitate the selection of monomers for the synthesis of MIP.