Figure 1.

Partial structures of methoxyPEG, hydroxyPEG, and t-butoxyPEG and structures of Tween 20 and Tween 80. In the structures of the PEGs, R designates the rest of the polymer, including the proximal terminal group that reacts with the protein to form PEG conjugates; the domains that may serve as epitopes for the formation of anti-PEG antibodies, namely, the distal terminal groups (in shaded ovals) and the PEG backbone, are indicated. In the structures of Tween 20 and Tween 80, R designates the alkyl groups of the fatty acids that distinguish these two detergents from each other (lauric and oleic acids, respectively); 8Z designates the configuration around the double bond in the heptadecenyl chain.