NMR Characterization of Polyethylene Glycol Conjugates for Nanoparticle Functionalization

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

Automated summary

The molecular weight, purity, and functionalization of polyethylene glycols are often determined using 1H NMR spectroscopy. However, the commonly used H-1 NMR pulse sequence does not decouple the C-13 nuclei. This leads to erroneous assignments as the C-13 coupled H-1 peaks from the repeating units have similar integrations to those of the H-1 peaks from the terminal groups. Taking into account this coupling allows for more accurate determination of both the molecular weight of the polymer and the efficacy of conjugation of a terminal moiety compared to using the uncoupled H-1 peaks from the repeating unit.