R11 is {TAIL ~ H}, {HEAD ~ CH3}, a carboxylic acid or a biologically compatible salt of a carboxylic acid 
R11 is { TAIL ~ H } , { HEAD ~ CH3 } , a carboxylic acid or a biologically compatible salt of a carboxylic acid
OTH OTH TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH