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Journal of Undergraduate Research

Keywords

achiral hosts, chiral induction, host exchange experiments

College

Physical and Mathematical Sciences

Department

Chemistry and Biochemistry

Abstract

Host exchange experiments (see Figure 1) compare the fit of left-handed molecules (L-) and right-handed molecules (D-) in a host. Molecules that possess this “handedness” property are said to be chiral. In chiral crown ether host exchange experiments, chiral crown ethers distinguish the fit of D-phenylalanine (Phe), D-tyrosine (Tyr), D-tryptophan (Trp), D-histadine (His), and D-aspartic acid (Asp) apart from L-Phe, L-Tyr, L-Trp , L-His, and L-Asp by forming chemically distinct complexes between the chiral host and the left- and right-handed amino acids1-3. Because the L- and D-handed molecules have different physical properties, the rate constants for exchange reactions differ. The condition when the rate constants for L- and Dhanded molecules do not match is called chiral discrimination4-6. The ability of the host to discriminate between L- and D-handed molecular guests is measured via the rate constants. Identical rate constants for L- and D-molecules in a host-guest reaction indicate a nondiscriminating host, and different rate constants indicate a host with good discriminating ability.

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