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