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The use of water - soluble O - acyl isopeptides enabled us to investigate the biochemical properties of A beta 11 - 42 species , by preparing highly concentrated stock solutions after a pretreatment .
 Chemical: O - acyl
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: O - acyl