In {HEAD ~ certain embodiments}, X4 is selected from D proline, {TAIL ~ D arginine} and D phenylalanine 
In { HEAD ~ certain embodiments } , X4 is selected from D proline , { TAIL ~ D arginine } and D phenylalanine
OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH