MAL-dPEG®2-NHS ester, product number 10266, is a crosslinking reagent that joins a sulfhydryl to a free amine. The sulfhydryl groups react with a maleimide group via a Michael addition reaction. The amines form amide bonds with the crosslinker by nucleophilic substitution of the N-hydroxysuccinimidyl (NHS) ester of a carboxylic acid group. The maleimide and NHS functional groups on the crosslinking compound sit at either end of a short, discrete-length polyethylene glycol chain (dPEG®). The single molecular weight dPEG® spacer is 16 atoms and 17.7 Å long.
One of the most popular, most useful crosslinking reactions in bioconjugate chemistry is the reaction that joins a sulfhydryl group to a free amine. These reactions require heterobifunctional reagents that bridge the two different reactive groups. Initially, such reagents were initially hydrophobic. Now, Quanta BioDesign’s dPEG® products are single molecular weight PEG compounds with discrete chain lengths. Our amphiphilic dPEG® products impart water solubility to conjugates containing them.
Consequently, the problems that accompany hydrophobic crosslinking reagents, such as aggregation and precipitation of biomolecular conjugates, do not exist with dPEG® crosslinkers. For more information about our dPEG® products, please see our “What is dPEG®?” page. Also, click here for answers to our most frequently asked questions.
The NHS ester hydrolyzes readily in water or aqueous buffer. Therefore, conjugation of this end of the molecule should occur before conjugation of the maleimide end of the crosslinker. At pH 7.0 – 7.5, NHS esters react optimally with free amines. However, NHS esters can react with free amines with pH as low as 6.0. As the pH increases, the hydrolysis rate of the ester increases. Thus, we strongly discourage storing MAL-dPEG®2-NHS ester, product number 10266, in water or aqueous buffer. Instead, we recommend that customers make new solutions of the product as needed, use them immediately, and discard unused solutions after use.
The reaction of the maleimide end of MAL-dPEG®2-NHS ester, product number 10266, proceeds optimally at pH 6.5 – 7.5. Use the lowest reasonable pH within this range. Above pH 7.5, free amines compete with free thiols at the maleimide reaction site, which can cause confusing results. Moreover, at higher pH values, the maleimide ring may open to form unreactive maleamic acid. For details about maleimide-thiol reaction chemistry, please click here.
The use of MAL-dPEG®2-NHS ester, product number 10266, has been published in many different scientific paper and patents. The following list highlights some of the more notable uses of this product:
Crosslinking peptides to passivated nanoparticle surfaces;
What can you do with this product? Please click the “Add to Cart” button now to order MAL-dPEG®2-NHS ester, product number 10266.
 Hermanson, G. T. Chapter 6, Heterobifunctional Crosslinkers. In Bioconjugate Techniques, 3rd ed.; Academic Press: New York, NY, 2013; pp 299–340, specifically p. 300. Many scientists engaged in bioconjugation work consider Greg Hermanson’s book to be the definitive reference on the subject. Click here now to read a review of Greg’s book and to purchase it.
 Hermanson, G. T. Chapter 18, PEGylation and Synthetic Polymer Modification. In Bioconjugate Techniques, 3rd ed.; Academic Press: New York, NY, 2013; pp 787–838, specifically p. 794.
 Hermanson, G. T. Chapter 6, op. cit., page 304.
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