Abstract
The homochirality of amino acids in living organisms is one of the great mysteries in the phenomena of life. To understand the chiral recognition of amino acids, we have used scanning tunnelling microscopy to investigate the self-assembly of molecules of the amino acid tryptophan (Trp) on Au(111). Earlier experiments showed only homochiral configurations in the self-assembly of amino acids, despite using a mixture of the two opposite enantiomers. In our study, we demonstrate that heterochiral configurations can be favored energetically when l- and d-Trp molecules are mixed to form self-assembly on the Au surface. Using density functional theory calculations, we show that the indole side chain strongly interacts with the Au surface, which reduces the system effectively to two-dimension, with chiral recognition disabled. Our study provides important insight into the recognition of the chirality of amino acid molecules in life.
Highlights
The homochirality of amino acids in living organisms is one of the great mysteries in the phenomena of life
Since chiral recognition is based on stereochemical interaction between the chiral molecules, it is most prominent in the self-assembly in 3-dimensional (3D) space
By carefully modeling the self-assembled structures using density functional theory (DFT), we demonstrate that the interactions between the Trp molecules and the surface effectively reduces the system to 2D, inducing a breakdown of chiral recognition in the self-assembly of the mixture of l- and d-Trp molecules
Summary
The homochirality of amino acids in living organisms is one of the great mysteries in the phenomena of life. The two enantiomers exhibit identical physical and chemical properties, living organisms use only amino acids of l-chirality This homochirality of the amino acids is one of the great mysteries that need to be explored in life phenomena. Lingenfelder et al investigated the interaction between l-phenylalanine (Phe)–l-Phe and d-Phe–d-Phe pairs and found that stereoselectivity plays a crucial role in the formation of the homochiral c hains12 These pioneering works highlighted the role of chiral recognition in the self-assembly of amino acids. On a Au(111) substrate, which naturally resulted in homochiral self-assembly When both l- and d-Trp molecules were deposited on the substrate simultaneously, we found that heterochiral structures were predominantly formed, providing evidence of the chiral recognition being broken. By carefully modeling the self-assembled structures using density functional theory (DFT), we demonstrate that the interactions between the Trp molecules and the surface effectively reduces the system to 2D, inducing a breakdown of chiral recognition in the self-assembly of the mixture of l- and d-Trp molecules
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