Enantioselective Discrimination of Histidine by Means of an Achiral Cubane-Bridged Bis-Porphyrin

A Langmuir film of cubane bridged bisporphyrin (H(2)por-cubane-H(2)por) at the air/water interface was developed and characterized. The floating film was successfully employed for the chiral discrimination between L- and D-histidine. The enantioselective behavior persisted after the deposition of the film on a solid support using the Langmuir-Schaefer method. Distinct absorption and reflection spectra were observed in the presence of L- r or D-histidine, revealing that conformational switching was governed by the interaction between H(2)por-cubane-H(2)por and the histidine enantiomer. The mechanism of chiral selection was investigated using an ad hoc modified nulling ellipsometer, indicating the anti-conformation was dominant in the presence of L-histidine, whereas the presence of D-histidine promoted the formation of tweezer conformation.