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In this article we report calculations of the activation free energy for a chemical reaction between propylene oxide and DNA , in particular with the guanine at the N7 position .
 Chemical: propylene oxide; Chemical: guanine
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: propylene oxide; Chemical: guanine