28619
The observations from SEM and TEM suggest that PGlu22 - b - PAla8 initiates the amorphous precursor phase and heterogeneous nucleation of CaCO3 at the air / water interface , while temporarily stabilizes the gelatinous precursors as a process - directing agent ; nevertheless , the initial concentration of Ca ( 2 + ) controls the procedure of crystallization and the final morphology of CaCO3 particles .
 Chemical: PGlu22 - b - PAla8; Chemical: CaCO3; Chemical: Ca ( 2 + ); Chemical: CaCO3
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: PGlu22 - b - PAla8; Chemical: CaCO3; Chemical: Ca ( 2 + ); Chemical: CaCO3