6233
Rigid 5 ' - 6 - locked phenanthroline - derived nucleosides chelated to ruthenium and europium ions .
 phenanthroline, nucleosides, ruthenium, europium
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 phenanthroline, nucleosides, ruthenium, europium