each of Am is independently {HEAD ~ a moiety} based on an amino acid or on an amino acid derivative, or on {TAIL ~ a number} of amino acids or derivatives thereof 
based on
each of Am is independently { HEAD ~ a moiety } based on an amino acid or on an amino acid derivative , or on { TAIL ~ a number } of amino acids or derivatives thereof
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH