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Release date:2019/11/7 17:15:16
PEGylation is a chemical process that forms a covalent bond between a PEG polymer and a substrate molecule including molecules, macromolecules, particles, and surfaces. PEGylation of different functional groups requires different PEG reagents due to differences in the active sites of the different substrates. Listed below are some commonly used examples of PEGylation reported in the literature.
pegylation reagents

1. PEGylation of amine and grafting of N-terminal PEG: PEG reagent for reaction with amino groups of biomacromolecules
 
PEG Reagents PEGylation Grafting
PEG-NHS The N-hydroxysuccinimide (NHS) active ester of polyethylene glycol carboxylic acid can react with the amine group of lysine. The coupling reaction only requires a short reaction time under mild reaction conditions, pH 7-9, low temperature (5-25°C). A physiologically stable amide bond is formed.
PEG-Aldehyde The primary amine is converted to a secondary amine by reductive amination in the presence of a reducing agent such as sodium borohydride or sodium cyanoborohydride. The pH is important for reductive amination. PEG-Aldehyde is a very good reagent for N-terminal PEGylation grafting.
PEG Epoxide Nucleophilic addition
PEG-Isothiocyanate It reacts with amine to form stable thiourea.
PEG-COOH Usually the acid needs to be activated, such as an NHS ester.
PEG-NPC Under suitable conditions, the amine can be reacted with NPC functionalized PEG.
PEG-Acrylate The Michael addition reaction of amines and acrylates is a relatively slow reaction.
 
2. PEGylation of carboxyl groups

PEG reagent reacts with carboxylic acid in the presence of coupling agents such as DCC(N,N'-Dicyclohexylcarbodiimide) and EDIC (1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide, hydrochloride).
 
PEG Reagents PEGylation Grafting
PEG-Amine Form an amide under DCC or EDC coupling conditions.
PEG-Hydrazide Upon activation by EDIC under weak acidity, the carboxyl group of the protein can readily react with the PEG-hydrazide, while under this particular condition, the amino groups of all reagents remain inactive.
PEG-Halide/sulfonate PEG-halides (chlorides, bromides, iodides, p-toluenesulfonates and mesylate) are reacted with deprotonated carboxyl groups, i.e., -COO-salts.
 
3. PEGylation of thiol groups: thiol-based PEGylation is a free thiol for biomolecules, such as cysteine
 
PEG Reagents PEGylation Grafting
PEG-Maleimide The thiol and C=C double bonds form a physiologically stable bond by Michael addition in the presence of a maleimide ring. The optimum reaction conditions are pH 8.
PEG-OPSS Generate disulfide S-S bonds. The reaction can also be reversed by a reducing agent such as sodium borohydride or thioethanolamine.
PEG-Vinylsulfone A thiol and a C=C double bond form a physiologically stable chemical bond by Michael addition in the presence of a maleimide ring.
PEG-Thiol Generate an oxide of disulfide S-S bonds.
PEG-Halide PEG-halides (chlorides, bromides, iodides, p-toluenesulfonates and mesylate) and free mercaptans. Iodoacetate or iodoacetamide is extremely active against free mercaptans.
 
4. PEGylation of Hydroxyl groups 
 
PEG Reagents PEGylation Grafting
PEG-Isocyanate The hydroxyl group reacts with PEG-NCO, but requires special reaction conditions.
PEG-NPC The hydroxyl group reacts with the NPC to form a carbonate.
PEG-Silane Silanes are particularly suitable for reaction with hydroxylated surfaces.
PEG-Epoxide The best conditions for the reaction of PEG-Epoxide with a hydroxyl group are pH 8.5-9.5.
 
5. PEGylation of Click Chemistry
 
PEG Reagents PEGylation Grafting
PEG-Azide
PEG-Alkyne
The azide and alkyne form a stable 1,2,3-triazole ring in the presence of a copper catalyst. It is called Huisgen azide-alkyne cycloaddition.
PEG-BCN BCN reagents (bicyclo[6.1.0]nonyne) can react with azide-tagged molecules or biomolecules via copper-free Click Chemistry.
PEG-DBCO DBCO (Dibenzocyclooctyne) reagents are one of the most reactive cycloalkynes for strain promoted alkyne azide cycloaddition (SPAAC), which enables Cu-free Click Chemistry.
PEG-TCO TCO reagents (Trans-Cyclooctene Reagents) can be used to label antibodies, proteins and other macromolecules via copper-free Click Chemistry.
PEG-Tetrazine Tetrazine was found the fastest kinetics for bioorthogonal reaction with trans-cyclooctene (TCO) as the dienophile. The chemical stability of tetrazines is lower compared to methyltetrazines.
 
6. Surface PEGylation
 
PEG Reagents PEGylation Grafting
PEG-Thiol PEG-Thiol reacts with most precious metal surfaces such as gold, silver, etc.
PEG-Silane PEG-Silane can react with hydroxylated surfaces such as silica gel, glass, hydroxylated or acid-activated noble metal surfaces (eg, platinum, palladium, etc.).
 
7. PEGylation of polymerization
 
PEG Reagents PEGylation Grafting
PEG-Thiol Multi-arm PEG-thiols can self-crosslink to form disulfide bonds, which can be reversed under appropriate reducing conditions.
PEG-Acrylate 2-arm or 4-arm PEG-acrylate, PEG-methacrylate or PEG-acrylamide can crosslink to form stable C-C bonds
 
8. Reversible PEGylation
PEG Reagents PEGylation Grafting
PEG-Hydrazide PEG-hydrazide can react with a carbonyl group (ketone or aldehyde) to form a hydrazide, which is easily hydrolyzed under acidic conditions.
PEG-Thiol The PEG-S-S-PEG disulfide bond can be cleaved by a suitable reducing agent.
 
Disclaimer: The above information is for general guidance only on the selection of PEGylation reagents. For specific PEGylation grafting processes, please refer to the literature and rely on your own judgment.
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