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The conformational flexibility of the C8 - linked guanine adduct formed from attachment of ochratoxin A ( OTA ) was analyzed using a systematic computational approach and models ranging from the nucleobase to the adducted DNA helix .
 Chemical: guanine; Chemical: ochratoxin A; Chemical: OTA; Chemical: nucleobase
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: guanine; Chemical: ochratoxin A; Chemical: OTA; Chemical: nucleobase