R3 and R4 are independently selected from hydrogen, or an aliphatic, carbocyclic, or heterocyclic group, or R3 and {TAIL ~ R4}, or {HEAD ~ R3} or R4 and Z3 together may form a 5, 6, or 7 membered carbocylic or heterocyclic ring; and 
R3 and R4 are independently selected from hydrogen , or an aliphatic , carbocyclic , or heterocyclic group , or R3 and { TAIL ~ R4 } , or { HEAD ~ R3 } or R4 and Z3 together may form a 5 , 6 , or 7 membered carbocylic or heterocyclic ring ; and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH