Nucleophilic ability

If the H2N—C=NH system is considered as a bident nucleophile, internal conjugation strongly increases the nucleophilic ability of the C=NH nitrogen and depresses the nucleophilic ability of the NH2 group195. 

The ADP-ribosyl transfer reaction has a sulfur nucleophile, as compared with water in the non-enzymatic reaction. Given the very weak dependence on nucleophile ability of this reaction, the non-enzymatic transition state with a sulfur nucleophile would be expected to be similar to that with water. 

A variety of diamines to enrich the combination of monomers were also examined. Polymerization using primary dialkylamines (lld-e) and sterically demanding secondary dialkylamines (lla-c) successfully yielded polyamidines with absolute molecular weight of up to 67,200 g/mol. Surprisingly, diarylamines (llf-h) with much weaker nucleophilic ability than alkylamines also served as excellent monomers for this MCP, and the rigid monomer stmcture suppressed cyclization side-reactions. 

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