Abstract
A Langmuir film of cubane-bridged bisporphyrin (H2por-cubane-H2por) 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- or d-histidine, revealing that conformational switching was governed by the interaction between H2por-cubane-H2por 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.
Highlights
Chiral discrimination is a chemical interaction phenomenon, by which a receptor recognizes a specific enantiomer of substrate molecules.[1]
The chiral discrimination of D- and L-histidine was achieved by tuning the conformational switching of a cubane-bridged bisporphyrin (H2por-cubane-H2por)
Spectroscopic investigations of Langmuir films allowed us to monitor the conformations adopted by the bisporphyrin molecules spread at the air/ultrapure water interface of a Langmuir trough
Summary
Chiral discrimination is a chemical interaction phenomenon, by which a receptor recognizes a specific enantiomer of substrate molecules.[1] Different enantiomers of the same molecule may exhibit different properties under physiological conditions. The human olfactory and gustatory systems use chiral interactions. The toxicity and/or efficacy of a molecule depends upon the ratio of enantiomers or the presence of a specific enantiomer in a sample. In 1979, Blaschke and co-workers discovered that Rthalidomide exhibits a therapeutic effect, whereas S-enantiomer is a teratogen.[3] the birth defects could have been avoided if only the R-enantiomer had been used instead of a racemic mixture. Chemists from all over the world have devoted tremendous efforts to the field of chiral discrimination and enantiomeric excess (ee) analysis.[1,4]
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