{HEAD ~ each Z} is independently selected from the group consisting of —OH, —COOH, —CNHR, —NHCR and {TAIL ~ —NHR}, wherein each R is independently chosen, and defined as above; and 
{ HEAD ~ each Z } is independently selected from the group consisting of — OH , — COOH , — CNHR , — NHCR and { TAIL ~ — NHR } , wherein each R is independently chosen , and defined as above ; and
HEAD 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 TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH