Phosphoric acid-PEG-Phosphoric acid
NTA-PEG-NTA
ASP-PEG-ASP
Cysteine-PEG-Cysteine
L-Lysine-PEG-L-Lysine
Glutathione-PEG-Glutathione
Glutamic acid-PEG-Glutamic acid
MAA-PEG-MAA
CDI-PEG-CDI
DF-PEG-DF
PBA-PEG-PBA