R16 and R17 are each, independently, hydrogen, {HEAD ~ alkyl} of {TAIL ~ 1 12 carbon atoms}, or n Ar 
of
R16 and R17 are each , independently , hydrogen , { HEAD ~ alkyl } of { TAIL ~ 1 12 carbon atoms } , or n Ar
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH