15673
Vibrational spectroscopic experiments started to shed light on the structural changes , that occur during the photocycle , especially in the hydrogen - bonded network surrounding the protonated D156 and C128 - the DC gate .
 Chemical: hydrogen
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: hydrogen