Edge-to-face indole/indole clusters in designed hairpins: A) turn flanking W/W units showing examples in which the indole at the N-terminus takes on, alternatively, edge and face conformation in the edge-to-face cluster8,9, B) The W/W cluster of KKLTVW-IpGK-WITVSA in aqueous HFIP medium with a circa 180° flip in chi29,11 of the edge-Trp in the gray cluster of panel A, and C) the β-cap arrangement of hairpins with a C-terminal WTG unit in which this Trp bears the edge indole of the EtF cluster.