Maleimide-activated compounds readily react with thiol groups to form thioester-conjugated products. The reaction can take place at pH 7.0 in the presence of amines. Under neutral pH conditions, the maleimide group does not react with histidine or methionine.
The optimum pH for modifying thiols with maleimides is pH 7.0 to 7.5. Generally, the conjugation reaction is carried out in phosphate-buffered saline (PBS) at pH 7.4.
Figure 1: The general reaction scheme of maleimides with thiol group used for bioconjugation and labeling of biomolecules.
Shipping and Storing
Shipping chemical products activated with maleimide is done as a dry lyophilized powder.
Please note: BSI recommends storing dry aliquots as a freeze-dried powder at -20 or (better) -80°C in the presence of a desiccant. The compounds should remain active for up to 6 months when stored as directed.
Reconstitution
We recommend reconstituting molecules activated with maleimide just before conjugation.
For reconstitution: Dissolve maleimide-modified oligos in a neutral or slightly acidic buffer (pH 5.5 to 7.0). DO NOT use basic buffers, and DO NOT use buffers that contain chemicals with amino or thiol groups (e.g., Tris, DTT).
The presence of water will slowly deactivate the maleimide group. Hence, we recommend not storing maleimide-activated molecules such as maleimide-siRNA in buffers or water.
However, siRNA not conjugated to maleimide is stable in buffers and water and can be stored as solution aliquots, preferably at -20 or -80 °C.
Reference
Hermanson, G.T., Bioconjugate Techniques. 2nd Edition, Elsevier 2008
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