17730
To follow the reaction with the peptides and characterize more easily intermediates and adducts , the molecule was first ( 13 ) C isotopically substituted at the most probable reactive position .
 Chemical: ( 13 ) C
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: ( 13 ) C