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We wished to address these obstacles by using copper - free click chemistry to functionalize the dendrimer scaffolds and to exploring the effects of two dendrimer properties ( the targeting ligand and drug linkage ) on cytotoxicity .
 Chemical: copper
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: copper