DBCO-NH-(CH2)4-COOH contains an NHS carbonate group and a DBCO group. The spacer contains a photocleavable nitrobenzyloxyl group, which can be efficiently cleaved under UV to release the conjugated molecules. DBCO on the other hand readily react with azide bearing biomolecule through a copper-free click reaction instantly and in high yield.
Axispharm offers 3000+ PEG Linkers with high purity. Different kinds of PEG Reagents may be available by custom synthesis.