Sorption of proteins such as cytochrome c, lysozyme or protamine by slightly cross-linked poly(acrylic acid) and bovine serum albumin by slightly cross-linked poly(N,N-dimethyl-N-ethylaminoethyl methacrylate bromide) hydrogels in salt-free and saline aqueous solutions was studied. The polyanionic hydrogel uptakes the proteins at pH below their isoelectric points while polycationic one at pH above them. As a result highly swollen original hydrogel transforms into relatively compact cross-linked polyelectrolyte-protein complex. Sorption of proteins by slightly cross-linked polyelectrolyte hydrogels is a chemically drawn diffusion process. The driving force of the process comes from the gain in the free energy of the interpolyelectrolyte coupling reaction between the protein and oppositely charged segments of the polyelectrolyte network. Apparently the mechanism of protein uptake is similar to that earlier proposed for linear polyelectrolytes. It involves a "relay-race" transfer of protein molecules from one fragment of polyelectrolyte network to the other without radial mixing via interpolyelectrolyte exchange reaction. As a result "core-shell" constructs consisting of an outer weakly swollen complex shell and a highly swollen hydrogel core are formed at intermediate stages of the process. The rate of sorption is determined by the rate of the interpolyelectrolyte exchange reaction, that is the rate of the formation of free fragments of polyelectrolyte network (vacancies) on the inner complex-hydrogel boundary. The amount of vacancies depends on the area of this boundary. Kinetic curves of protein sorption by hydrogels in neutral salt-free solutions could not be fitted under the terms of Fickian diffusion but can be expressed in terms of the kinetic equation derived for a frontal heterogeneous reaction. At the same time kinetics of protein sorption obeys to Fick's diffusion law when the salt concentration increased.

The equilibrium and kinetics of proteins sorption and desorption by oppositely charged lightly crosslinked polyelectrolytes (#PE) were studied. The driving force of the sorption is provided by interpolyelectrolyte addition reaction (IPAR) between oppositely charged ionic groups of protein and #PE resulting in protein–#PE complex (#PPEC) formation. The capacity of different #PEs with respect to the proteins in neutral salt‐free aqueous solutions is rather high, exceeding that of the known heterogeneous crosslinked polyelectrolyte sorbents commonly used for protein sorption in practice. The dependence of the capacity of #PE on pH and the salt concentration in the environmental solution has been revealed and investigated. The equilibrium of IPAR is shifted to the original components under the corresponding pH shift or adding a simple salt. As a result the protein releases into the surrounding solution. The rate of protein uptake and release is also controlled by the pH or/and the ionic strength of the solution. The data obtained show that #PE can be used to design the crosslinked polyelectrolyte constructs for controlled uptake and release of proteins. Copyright © 2003 John Wiley & Sons, Ltd.

We report a single-molecule fluorescence study on the diffusion of star-branched polymer dendrimer-like DNA (DL-DNA). The DL-DNA molecules were synthesized from ligating Y-shaped DNA to the fourth generation. It was found through single particle tracking that the diffusion coefficient of DL-DNA changes in a nonmonotonic fashion with its increased concentration possibly due to arm arrest and arm retraction. The diffusion of DL-DNA in linear lambda DNA solution displayed a monotonic concentration dependence 1 order of magnitude greater than the diffusion of DL-DNA in DL-DNA solution. This difference is attributed to the different conformation of DL-DNA and lambda DNA and the entanglement of lambda DNA with a large radius of gyration. Our diffusion study facilitates DL-DNA transportation for drug delivery.