13867
Through evaluating the activity of BA and simple derivatives on wild - type and mutant alpha 7 receptors , it was observed that the drug - receptor pairs which were capable of hydrogen bonding at residue 36 exhibited significantly less stable desensitization .
 Chemical: hydrogen
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
 Entities: hydrogen 
Answer:
 Chemical: hydrogen