NHS-PEGg-maleimide

Dissolve NHS-PEGg-maleimide (MW 601.6) into DMSO at a concentration of 20mM. Short, PEG-type crosslinkers often exist as a thick oily mass, and preparing the solution typically involves dissolving an entire vial of the compound into DMSO to determine accurately the required concentration. Use only dry DMSO to avoid hydrolysis of the NHS ester. 

Add 50 pi of the NHS-PEGg-maleimide solution to the 1ml dendrimer solution and mix thoroughly to dissolve. This represents approximately a 14-fold molar excess of crosslinker over the quantity of dendrimer present, if a G-3 PAMAM dendrimer is used with an ethylenediamine core. The optimum molar ratio of crosslinker-to-dendrimer should be determined experimentally for best performance of the resultant conjugate in its intended application. If enough material is available, doing a series of experiments at different mole ratios of crosslinker-to-dendrimer will help to optimize the resultant conjugate. 

Add 50 pi of the NHS-PEGg-maleimide solution to the 1 ml particle suspension and mix thoroughly to dissolve. 

In a fume hood, dissolve the NHS-PEG -maleimide compound of choice in a dry, water-miscible organic solvent to make a concentrated stock solution. For instance, to prepare a lOOmM solution of the NHS-PEGg-maleimide reagent (MW 601.6), dissolve an entire 100 mg vial of the crosslinker in 1.66 ml of DMAC (dry DMSO or DMF work well, too). 

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