Cross linkers are used for the identification of near-neighbour protein relationships and ligand-receptor interactions. Homobifunctional, amine-reactive NHS esters or imidates, and heterobifunctional, amine-reactive, photoactivatable phenyl azides are the most commonly used crosslinkers for these applications.

• Efficient amine conjugation—NHS ester provides effective conjugation to lysines, N-termini of peptides and other primary amines
• Reversible sulfhydryl conjugation—pyridyldithiol group enables disulfide linkage with reduced cysteines and other sulfhydryl groups, providing a stable but cleavable bond
• Polyethylene glycol—PEG groups are flexible, non-immunogenic, hydrophilic, and often enhance the solubility of attached molecules
• Spacer arm—connects primary amines and sulfhydryl targets
• Upon receipt store at −20 °C protected from moisture

Thermo Scientific Pierce SM(PEG)n is a series of amine-to-sulfhydryl crosslinkers that differ in length from 17,6 to 95,2 angstroms as a result of polyethylene glycol spacer arms containing n equals 2 to 24 ethylene glycol units.

SPDP-type reagents have an amine-reactive N-hydroxysuccinimide (NHS) ester at one end and a suflhydryl-reactive 2-pyridyldithiol group at the opposite end. PEGn-SPDP has a n-unit polyethylene glycol spacer arm, which confers greater solubility to the crosslinker and linked proteins compared to crosslinkers having only hydrocarbon spacers. Pyridyldithiol reagents produce disulfide-containing linkages that can be cleaved with reducing agents such as dithiothreitol (DTT). Crosslinking experiments with SPDP reagents are not limited to those involving proteins. Any of a variety of molecules with primary amines and sulfhydryl groups can be modified or crosslinked using an SPDP reagent.