micromolecule

noun

mi·​cro·​mol·​e·​cule ˌmī-krō-ˈmäl-ə-ˌkyül 

: a molecule (as of an amino acid or a fatty acid) of relatively low molecular weight compare macromolecule

micromolecular

-mə-ˈlek-yə-lər 

adjective