NMR Characterization of Polyethylene Glycol Conjugates for Nanoparticle Functionalization.

The molecular weight, purity, and functionalization of polyethylene glycols are often characterized by 1 H NMR spectroscopy. Oft-forgotten, the typical 1 H NMR pulse sequence is not 13 C decoupled. Hence, for large polymers, the 13 C coupled 1 H peaks arising from the repeating units have integrations comparable to that of the 1 H of the terminal groups. Ignoring this coupling leads to erroneous assignments. Once correctly assigned, these 13 C coupled 1 H peaks can be used to determine both the molecular weight of the polymer and the efficacy of conjugation of a terminal moiety more accurately than the uncoupled 1 H of the repeating unit.