In this task, you are given a sentence. You are expected to recognize the name of any form of chemical substances. Although there might be several correct answers, you need to write one of them.

[EX Q]: Nicotine-induced contraction in the rat coronary artery: possible involvement of the endothelium, reactive oxygen species and COX-1 metabolites.
[EX A]: oxygen

[EX Q]: Efficient induction of apoptosis in HeLa cells by a novel cationic porphycene photosensitizer.
[EX A]: porphycene

[EX Q]: Influence of triterpenoids present in apple peel on inflammatory gene expression associated with inflammatory bowel disease (IBD).
[EX A]:
triterpenoids