Q: What are the differences among your PEG NHS ester & PEG Acid products?
A: We offer a variety of PEG Acid and PEG NHS ester. These NHS esters react with primary and secondary amine to form a stable amide linkage. This reaction may be carried out in an organic solution with an organic base or may be carried out in an aqueous solution at or around neutral pH or slightly acidic or basic. To PEGylate proteins or nanoparticles, it often requires a large excess of PEG NHS esters due to the competitive hydrolysis reaction in an aqueous solution. Stability of NHS esters is compared by their hydrolysis half-life (T1/2). To mitigate the competitive hydrolysis reaction, organic solvents such as amine-free, anhydrous DMF and DMSO may be used in combination with an aqueous buffer solution.
PEG NHS
esters
Structural characteristics
Amine
reactivity
Stability
Type A: SCM
Methylene (CH2) linkage between PEG and NHS ester
Highly reactive
Hydrolysis half-life: less than five minutes. It often requires the use of a large excess of PEG reagents.
Type B: SG
C4 aliphatic ester linkage between PEG and NHS ester
Very reactive
Hydrolysis half-life: around 20 minutes.
Type C: SS
C3 aliphatic ester linkage between PEG and NHS ester
Very reactive
Hydrolysis half-life: around 10 minutes.
Type D: GAS
C4 aliphatic amide linkage between PEG and NHS ester
Very reactive
Hydrolysis half-life: around 20 minutes.
Type E: SAS
C3 aliphatic amide linkage between PEG and NHS ester
Very reactive
Hydrolysis half-life: around 10 minutes.
SCM: Succinimidyl Carboxyl Methyl ester; SG: Succinimidyl Glutarate ester; SS: Succinimidyl Succinate ester; GAS: GlutarAmide Succinimidyl ester; SAS: SuccinAmide Succinimidyl ester. Note: hydrolysis half-life depends on pH, temperature and other factors of the testing conditions.
PEG acids
Structural characteristics
Type A: AA
Methylene (CH2) linkage between PEG and acid (COOH)
Type B: GA
C4 aliphatic ester linkage between PEG and acid (COOH)
Type C: SA
C3 aliphatic ester linkage between PEG and acid (COOH)
Type D: GAA
C4 aliphatic amide linkage between PEG and acid (COOH)
Type E: SAA
C3 aliphatic amide linkage between PEG and acid (COOH)
AA: Acetic Acid, also called CM - Carboxyl Methyl; GA: Glutaric Acid; SA: Succinic Acid; GAA: GlutarAmide Acid; SAS: SuccinAmide Acid.
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