| In this work, a new family of water-soluble block copolymers of acrylamide and N-alkylacrylamides was designed, synthesized, characterized, and applied for the selective removal of hydrophobic proteins from DNA by microchannel electrophoresis, as well as for the high-resolution separation of DNA molecules. We hypothesized that the inclusion of the hydrophobic N-alkyl subunits in the copolymers could provide protein adsorption by hydrophobic interactions. A series of alkyl acrylamide co-monomers with varying alkyl chain lengths was synthesized and characterized. Copolymers were then synthesized by aqueous micellar polymerization; hydrophobic alkylacrylamide monomers were solubilized in SDS micelles. Octylacrylamide- and dihexylacrylamide-containing copolymers were most effective for protein adsorption, while butyl acrylamides were found to be insufficiently hydrophobic to adsorb even serum albumin proteins.; These "physically crosslinked" (hydrophobically crosslinked) copolymer networks comprising low percentages of dihexylacrylamide (DHA) were also applied for electrophoretic DNA separations, and were discovered to provide remarkably enhanced DNA resolution in a size range critical for genotyping, as compared with linear polyacrylamide (LPA) networks with matched molar masses. Single-molecule videomicroscopic images of DNA electrophoresis reveal novel chain dynamics in the LPA-co-DHA matrices, resembling inch-worm movement, which we believe accounts for the increased DNA resolution. Substantial improvements in DNA peak separation are obtained, in particular, in LPA-co-DHA solutions at polymer/copolymer concentrations near the interchain entanglement threshold.; The electrophoretic migration mechanisms of individual DNA molecules in LPA, HEC, and PEO networks were studied via single-molecule videomicroscopy, as a function of polymer molar mass and concentration. At concentrations near the overlap threshold (C*), transient entanglement coupling is the dominant observed separation mechanism. As polymer concentration is increased, the prevalence of U-shaped transient entanglement coupling-type DNA conformations decreases to zero while DNA reptation sharply increases, until it is the only mechanism observed. The data reduces to form universal curves with a sharp increase in DNA reptation occurring at ∼6.5C* for LPA, while this ratio was 5 in HEC, and 3.5 in PEO. This increase correlates with the polymer entanglement concentration, Ce. This work shows that the observation of electrophoretic DNA dynamics is a useful way to characterize the physical structure of entangled polymer networks. |
