Single-handed supramolecular double helix of homochiral bis(N-amidothiourea) supported by double crossed C-I•••S halogen bonds

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 center dot center dot center dot 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 mu M from 2D NOESY experiments and exhibits a high thermal stability in solution up to 75 degrees 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.