Sulfhydryls with N- p-Iodoethyl trifluoroacetamide Aminoethyl

Aminoethyl-8 has an advantage over ethylenimine modification (next section), due to the potential polymerization of ethylenimine in aqueous solutions. Such polymers are highly cationic and may nonspecifically block protein. The specificity of Aminoethyl-8 for sulfhydryls makes it an optimum choice for modification. 

Add dithiothreitol (DTT) to obtain a 20-fold molar excess over the amount of disulfides present. 

React for 4 h at room temperature, maintaining a blanket of nitrogen over the solution. 

Hgure 82 Aminoethyl-8 can be used to transform a sulfhydryl group into an amine. The intermediate spontaneously undergoes deblocking to release the primary amine group. 

Add a quantity of Aminoethyl-8 in methanol to equal a 25-fold molar excess over the amount of sulfhydryl present (including the amount of DTT added). The solution in methanol should be made concentrated enough so only a small amount of methanol must be added to the reaction solution (i.e., no more than 10% of the final volume). A second addition of modifying agent may be made after 1 h to drive the reaction more completely toward total— SH aminoalkyla-tion. 

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