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.