These compounds comprise {HEAD ~ a moiety} which provides {TAIL ~ a detectable species} when released from the compound in an environment of pH 9 or less  
These compounds comprise { HEAD ~ a moiety } which provides { TAIL ~ a detectable species } when released from the compound in an environment of pH 9 or less
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH