Polyethylene Glycol (PEG) Modifier Selection Guide

Polyethylene glycol (PEG), also known as polyoxyethylene or polyethylene oxide (PEO), is a synthetic hydrophilic biocompatible polymer. Molecular weights <100,000 are commonly referred to as PEG, while PEG polymers with molecular weights >100,000 are classified as PEOs. Polyethylene glycol is synthesized through the ring-opening polymerization of ethylene oxide. PEG can be polymerized into linear, branched, y-shaped or multi-arm geometric shapes. PEG polymers are amphiphilic and soluble in water and many organic solvents (such as methylene chloride, ethanol, toluene, acetone and chloroform). Low molecular weight (Mw <1,000) PEG is a viscous, colorless liquid, while high molecular weight PEG is a waxy, white solid. The melting point is proportional to the molecular weight, and the upper limit of the melting point is about 67 °C.

Polyethylene Glycol Uses

Polyethylene glycol is non-toxic and usually non-immunogenic, and is approved by the FDA for use as an excipient or carrier in drug formulations, food and cosmetics. Most PEG with molecular weight < 1000 can be quickly removed from the body, and the clearance rate is inversely proportional to the molecular weight of the polymer. In addition, the PEG polymer end can be connected to a variety of functional groups, so that the polymer has more functions. Therefore, PEG has a wide range of applications in biomedical research, such as biological conjugation, drug delivery, surface functionalization, tissue engineering and many other applications.

PEG coupling is the covalent biological coupling of drug targets such as peptides, proteins or oligonucleotides with PEG to optimize the pharmacokinetic characteristics. In drug delivery, PEG can be used as a linker for antibody-drug conjugates (ADCs) or as a surface coating of nanoparticles to improve systemic drug delivery. PEG hydrogel is a water-expanded three-dimensional polymer network that resists protein adhesion and biodegradation. PEG hydrogels are cross-linked by the reaction of PEG end groups, which are commonly used in tissue engineering and drug delivery.

Polyethylene Glycol Selection Guide

Function	Selection Guide
Functionality	Monofunctional polyethylene glycol, containing a chemical reaction end, which can be used for PEGylation, surface bonding and nanoparticle coating.
Functionality	Bifunctional polyethylene glycol, PEG containing two active ends, including the homobifunctional PEG and the heterobifunctional PEG. It is beneficial to the bonding and crosslinking of hydrogels.
Reactivity	Covalent coupling: PEG with active terminal groups, such as n-hydroxysuccinimide ester, sulfhydryl group or carboxyl group, can be covalently coupled to the corresponding functional groups. The chemical reaction properties determine the number of binding sites and PEG for each molecule.
	Linking chemistry requires PEG with azide or alkyne reactive groups. Linking chemistry is a fast, selective, bioorthogonal conjugate or hydrogel formation method.
	Under mild reaction conditions, polyethylene glycol end-capped with acrylate can be rapidly polymerized and photopolymerized.
Polymer Structure	Linear PEG is usually used for PEGylation, bio-coupling and cross-linking.
	Multi-arm PEG (4-, 6-, 8-arm) can be used to crosslink into hydrogels and scaffolds in drug delivery or tissue engineering.
	Y-type PEG is usually used for PEGylation because its branching structure can improve in vivo stability.
Molecular Weight	Bioconjugation: PEG with a molecular weight of ≥ 5 kDa is commonly used to conjugate small molecules, siRNA and peptides. Low molecular weight PEG (≤ 5 kDa) is commonly used for PEGylation of proteins.
	Surface bonding and cross-linking usually use PEG with a molecular weight of < 40 kDa.
	Hydrogel formation: PEG molecular weight affects the grid size and mechanical properties of hydrogels. Typically, PEG with a molecular weight ≥ 5 kDa is used.

What are Uniform PEG Modifiers?

PEG modification is a chemical process that forms covalent bonds between PEG polymers and substrate molecules including molecules, macromolecules, particles, and surfaces. Due to the different active sites of different substrates, PEG modification of different functional groups requires different PEG reagents. The following lists some commonly used PEG modification chemical cases reported in the literature.

PEG Modification of Amines and N-terminal Polyethylene Glycol Grafting

PEG reagents that react with amino groups of biological macromolecules.

PEG Reagents	PEG Modified 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 requires only a short reaction time at mild reaction conditions, pH 7-9, and low temperature (5-25 °C) to form physiologically stable amide bonds.
PEG-Aldehyde	In the presence of reducing agents such as sodium borohydride and sodium cyanoborohydride, primary amines are reduced to secondary amines by reductive amination. The pH value is very important for reductive amination. PEG-aldehyde is a good reagent for N-terminal polyethylene glycol modification.
PEG Epoxide	Nucleophilic addition.
PEG-Isothiocyanate	It reacts with amine to form stable thiourea.
PEG-COOH	Often the acid needs to be activated, such as NHS ester.
PEG-NPC	Under appropriate conditions, amines can react with NPC functional group-modified PEG.
PEG-Acrylate	The Michael addition reaction of amines and acrylates is a relatively slow reaction.

PEG Modification of Carboxyl

PEG reagents react with carboxylic acids in the presence of coupling agents such as DCC (N,N'-dicyclohexylcarbodiimide) and EDIC (N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride).

PEG Reagents	PEG Modified Grafting
PEG-Amine	Under the coupling conditions of DCC or EDC, the reaction produces amides.
PEG-Hydrazide	After EDIC activation under weak acidity, the carboxyl group of the protein can easily react with PEG-hydrazide, and under this special condition, the amino group of all reagents remains inactive.
PEG-Halide/Sulfonate	Reaction of PEG-halides (chloride, bromide, iodide, p-toluenesulfonate and methanesulfonate) with deprotonated carboxyl groups, i.e. -COO- salts.

PEG Modification of Sulfhydryl Groups

PEG modification of sulfhydryl groups is targeted at free thiols of biomolecules, such as cysteine.

PEG Reagents	PEG Modified Grafting
PEG-Maleimide	When thiols and C=C double bonds exist in the maleimide ring, physiologically stable bonding is formed by Michael addition. The optimum reaction condition is pH 8.
PEG-OPSS	The disulfide S-S bond is formed, and the reaction can also be reversed by reducing agents such as sodium borohydride and thioethanolamine.
PEG-Vinylsulfone	When thiols and C=C double bonds exist in the maleimide ring, physiologically stable chemical bonds are formed by Michael addition.
PEG-Thiol	Formation of oxidative disulfide S-S bonds.
PEG-Halide	PEG-halides (chlorides, bromides, iodides, p-toluenesulfonates and methanesulfonates) and free thiols. Iodoacetate or iodoacetamide is highly active for free thiols.

PEG Modification of Hydroxyl

PEG Reagents	PEG Modified Grafting
PEG-Isocyanate	The hydroxyl group reacts with PEG-NCO, but special reaction conditions are required.
PEG-NPC	The hydroxyl group reacts with NPC to form carbonate.
PEG-Silane	Silane is particularly suitable for surface reaction with hydroxylation.
PEG-Epoxide	The best condition for the reaction of PEG-Epoxide with hydroxyl groups is pH 8.5-9.5.

PEG Modification of Click Chemistry

PEG Reagents	PEG Modified Grafting
PEG-Azide PEG-Alkyne	Azide and alkyne form a stable 1,2,3-triazole ring in the presence of a copper catalyst, which is called Huisgen azide-alkyne cycloaddition

Surface PEG Modification

PEG Reagents	PEG Modified Grafting
PEG-Thiol	PEG-Thiol can react with most precious metal surfaces, such as gold, silver, etc.
PEG-Silane	PEG-Silane can react with hydroxylated surfaces, silica, glass, hydroxylated or acid-activated precious metal surfaces, such as platinum, palladium, etc.

PEG Modification of Polymerization Reaction

Under free radical initiators, UV irradiation or high temperature, PEG cross-linkers can polymerize to form gels, particles or cross-linked network structures for drug release and tissue engineering.

PEG Reagents	PEG Modified Grafting
PEG-Thiol	Multi-arm PEG-thiols can self-crosslink to form disulfide bonds and can react reversely under appropriate reduction conditions.
PEG-Acrylate	2-arm PEG or 4-arm PEG-acrylate, PEG-methacrylate or PEG-acrylamide can cross-link to form stable C-C bonds.

Reversible PEG Modification

Reversible PEG modification occurs using specific PEG reagents that can cleave bonds.

PEG Reagents	PEG Modified Grafting
PEG-Hydrazide	PEG-acyl hydrazide can react with carbonyl (ketone or aldehyde) to form acylhydrazone, which is easily hydrolyzed under acidic conditions.
PEG-Thiol	PEG-S-S-PEG disulfide bonds can be cleaved with appropriate reducing agents.

Featured Products from BOC Sciences

Homobifunctional PEG

Polyethylene glycol (PEG) containing two functional groups of the same type is called homodifunctional polyethylene glycol (PEG). BOC Sciences offers a range of homobifunctional PEGs in a range of molecular weights and various functionalities, such as amines, azides, maleimides, NHS esters and thiols. Homobifunctional PEG derivatives can be used in many applications, including surface functionalization and nanomaterials, and as cross-linkers for proteins, peptides, and other biomolecules.

Catalog	Name	Molecular Weight
BPG-0442	Amine-PEG-Amine	MW 400-35k
BPG-0451	Azide-PEG-Azide	MW 600-20k
BPG-0473	DBCO-PEG-DBCO	MW 1k-20k
BPG-0534	MAL-PEG-MAL	MW 600-20k
BPG-0591	SC-PEG-SC	MW 600-40k
BPG-0607	Silane-PEG-Silane	MW 600-20k
BPG-0628	VS-PEG-VS	MW 1k-20k
BPG-1282	Biotin-PEG-Biotin	MW 600-35k
BPG-2848	NHS-PEG-NHS	MW 1k-4k
BPG-2858	SCM-PEG-SCM	MW 2k-7.5k

Heterobifunctional PEG

Heterobifunctional polyethylene glycol (PEG) is a polymer with two different functional groups on each end. This unique structure allows precise and controlled conjugation of a variety of molecules such as proteins, peptides, antibodies, and drugs. BOC Sciences offers a variety of heterobifunctional PEGs with varying molecular weights, spacer lengths, and functional groups to meet the diverse needs of researchers in the biotechnology and pharmaceutical industries.

Catalog	Name	Molecular Weight
BPG-0634	ACA-PEG-SCM	MW 1k-10k
BPG-0639	Acetal-PEG-NHS	MW 1k-10k
BPG-0644	AC-PEG-COOH	MW 1k-10k
BPG-0649	AC-PEG-NH2	MW 1k-10k
BPG-0842	HO-PEG-NH2	MW 1k-10k
BPG-0902	MAL-PEG-Silane	MW 1k-10k
BPG-1226	DSPE-PEG-FITC	MW 1k-5k
BPG-1305	Biotin-PEG-NH2	MW 1k-10k
BPG-2793	Azido-PEG-NHS	MW 1k-4K
BPG-2813	Acrylate-PEG-SCM	MW 2k-7.5k

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