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We characterized the iron - sulfur cluster using inductively coupled plasma - atomic emission spectroscopy , absorbance spectroscopy , and electron paramagnetic resonance spectroscopy and found that it is an oxygen - sensitive [ 4Fe - 4S ] ( 2 + ) cluster .
 Chemical: iron - sulfur; Chemical: oxygen; Chemical: [ 4Fe - 4S ] ( 2 + )
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: iron - sulfur; Chemical: oxygen; Chemical: [ 4Fe - 4S ] ( 2 + )