Supports coated with PEI as a new tool in chromatography

PEI coated supports are proposed in this manuscript as a matrix that may permit a new concept in chromatography. Standard supports have their active groups on a “plane” surface, and permit the interaction with an area accounting for not more than 15–20% of the protein surface. The PEI coated supports permitted the interaction of the protein and a polymeric bead, where the protein may penetrate, permitting the interaction with a larger percentage of the protein surface. Here, we present that PEI coated supports are able to more strongly adsorb proteins that are adsorbed on conventional supports and to adsorb proteins that are not adsorbed on these supports. Moreover, more interestingly, the relative adsorption strength was found to be quite different when using PEI coated supports or conventional supports, because the distribution of charged groups in the protein surface may affect very distinctly to the adsorption when using each of these supports. Thus, some proteins that are very strongly adsorbed on conventional supports (having a small area with many anionic groups) were not among the most strongly adsorbed proteins on PEI coated supports, while some proteins that could not be adsorbed on conventional supports (that is, not having a very rich area in anionic groups) become very strongly adsorbed on PEI supports (very likely because they have dispersed around the surface many anionic groups). That is, the desorption pattern from both kind of supports is very different. We presented the results obtained in the fractioning of crude proteins extract from E. coli and whey protein concentrate. The sequential use of DEAE–agarose and PEI permit to improve the purity of the proteins adsorbed on PEI coated supports by more than a 10-fold factor and their further desorption may give only two to three bands in many instances.