7526
However , when PT is mediated by one to three water molecules acting as a proton relay , the barrier decreases to 29 . 5 , 20 . 4 , and 18 . 5 kcal / mol , respectively .
 None
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:  
Answer:
 None