Effects of Polyethyleneimine Derivatives on 2-Hydroxy-5-Nitrobenzyl Ionization

Abstract

Abstract A chromophoric reporter on polyethyleneimine (PEI) derivatives was shown to ionize at pHs below its intrinsic pK by varying degrees depending upon its attachment site, other modifications to the polymer, and, in some instances, the buffer. 2-Hydroxy-5-nitrobenzyl bromide (HNB-Br) was reacted with four branched PEI derivatives. In two of these, the parent polymer was substituted with HNB at either primary or tertiary amines. These polymers were not modified further. The other two derivatives contained dodecylbenzyl groups on the same amine type as the reporter group. The tertiary HNB, dodecylbenzyl polymer was further modified by quaternization of all amines with methyl iodide. Tertiary amines of PEI having no alkyl groups perturbed most effectively the pKs of the reporter groups, with 50% ionization occurring two pH units below the previously reported pK of 5.9 in solution. Quaternized, tertiary dodecylbenzyl PEI perturbed the pK of the reporter groups the least, with a 0.4 unit average pK reduction. The primary HNB PEI having no dodecylbenzyl groups induced 50% ionization at pH 4.5 compared to pH 4.75 upon introduction of 10% total amine of dodecylbenzyl groups to some of the remaining primary amines. These results suggest that the core of the parent polymer effects greater perturbation of HNB ionization than does a matrix of quaternary alkyl ammonium ions.