29639
Some reported literatures have recently shown that the overdosed PEI chains , which are free in the solution mixture , also play a vital role in promoting the gene transfection , but the reason is unclear .
 Chemical: PEI
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: PEI