21718
In line with previous observations , ( S ) - nicotine exhibited a negative cotton effect centered on 263 nm with vibronic structure ( pi - pi 1 * transition ) and a broad , positive ECD signal at around 240 nm associated with the n - pi 1 * transition .
 ( S ) - nicotine
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 ( S ) - nicotine