In certain embodiments, X6 is selected from {TAIL ~ D arginine}, D tryptophan, D tyrosine, D proline and {HEAD ~ D valine} 
In certain embodiments , X6 is selected from { TAIL ~ D arginine } , D tryptophan , D tyrosine , D proline and { HEAD ~ D valine }
OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD