Abstract
The natural DNA double helix consists of two strands of nucleotides that are held together by multiple hydrogen bonds. Here we propose to build an artificial double helix from fragments of two strands connected by covalent linkages therein, but with halogen bonding as the driving force for self-assembling the fragments to the double helix. We succeed in building such a double helix in both solution and solid state, by using a bilateral N-(p-iodobenzoyl)alanine based amidothiourea which in its folded cis-form allows double and crossed C−I···S halogen bonds that lead to right- or left-handed double helix when the two alanine residues are of the same L,L- or D,D-configuration. The double helix forms in dilute CH3CN solution of the micromolar concentration level, e.g., 5.6 μM from 2D NOESY experiments and exhibits a high thermal stability in solution up to 75 °C, suggesting cooperative and thereby strong intermolecular double crossed halogen bonding that makes the double helix stable. This is supported by the observed homochiral self-sorting in solution.
Highlights
The natural DNA double helix consists of two strands of nucleotides that are held together by multiple hydrogen bonds
The DNA double helix, well-known since its discovery by Watson and Crick in 19531, consists of two complementary polynucleotide strands that are connected by multiple hydrogen bonds, with additional stabilization by π–π stacking, between the nucleobase pairs that are covalently attached to the strands
We find that the crossed double C−I···S halogen bonds between cis-form homochiral bilateral N-amidothioureas (e.g., L,L-IA or D,D-IA), as the intra-strand noncovalent interactions, occur to support the single-handed supramolecular double helix in both the solid state and more significantly in extremely dilute CH3CN solution, while the central p-phenylenediamine moiety acts as the inter-strand covalent linkage
Summary
The natural DNA double helix consists of two strands of nucleotides that are held together by multiple hydrogen bonds. We find that the crossed double C−I···S halogen bonds between cis-form homochiral bilateral N-amidothioureas (e.g., L,L-IA or D,D-IA), as the intra-strand noncovalent interactions, occur to support the single-handed supramolecular double helix in both the solid state and more significantly in extremely dilute CH3CN solution, while the central p-phenylenediamine moiety acts as the inter-strand covalent linkage. To our knowledge, this establishes a unique approach to the supramolecular double helix formed in both solid state and dilute solution from synthetic small molecules via intermolecular noncovalent interactions, i.e., the halogen-bonding
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