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Novel Helical Metallocryptand for Size-Selective Recognition of Amino Acid Derivatives with Aliphatic Side Chains
Firdausiah S.
Chemistry A European Journal
Q1Abstract
The novel tris(salen)-type metallocryptand, LNi<sub>3</sub>, was designed and synthesized. Its crystallographic analysis revealed the presence as a helical enantiomeric pair, right-handed (P) and left-handed (M) forms, rather than the meso form, which was energetically supported by density functional theory (DFT) calculations. This LNi<sub>3</sub> host was capable of recognizing amino acid derivatives by several non-covalent interactions, showing a selectivity to those bearing an aliphatic side chain. Its shape-persistent nature of the cryptand facilitated the size-based discrimination, which was clearly demonstrated by <sup>1</sup>H NMR spectroscopic titration studies. Recognition of some of the guests caused the emergence of CD signals, indicating the biased P/M helix inversion equilibrium of LNi<sub>3</sub>. Three aliphatic side-chain guests, Val, Ile, and Leu, caused an M-favored shifting, while two π-containing side-chain guests, Arg and Trp, showed a preference to the P form. This metallocryptand, LNi<sub>3</sub>, overcomes the limitation in recognition of less polar amino acids having an alkyl side chain and provides future applications in molecular recognition, biochemical sensing, and enantiomeric sensing.