In other embodiments, X4 is selected from a neutral D amino acid, {TAIL ~ a positively charged D amino acid} and {HEAD ~ an aromatic D amino acid} 
In other embodiments , X4 is selected from a neutral D amino acid , { TAIL ~ a positively charged D amino acid } and { HEAD ~ an aromatic D amino acid }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD