In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Acidification , which slowed the reaction of CAA with thiol donors , could also attenuate effects of CAA on necrosis markers , thiol depletion and cysteine protease inhibition in living cells .
### Output Text:
Acidification , which slowed the reaction of <span class="chemical">CAA</span> with <span class="chemical">thiol</span> donors , could also attenuate effects of <span class="chemical">CAA</span> on necrosis markers , <span class="chemical">thiol</span> depletion and <span class="chemical">cysteine</span> protease inhibition in living cells . 