Helical Chirality
Broader Concept:
Chirality
Paired Concept:
Planar Chirality
Definition: A form of stereoisomerism arising from the three-dimensional screw-like arrangement of atoms or molecular subunits, producing non-superimposable mirror-image structures distinguished by opposite helical handedness rather than a conventional stereogenic center.
Context: Helical chirality occurs when molecular architecture adopts a stable spiral or helical geometry that cannot be superimposed onto its mirror image. Unlike classical point chirality, which originates from tetrahedral stereogenic centers, helical chirality emerges from overall molecular topology and spatial organization.
Helical chirality is commonly observed in: Helicenes (ortho-fused aromatic systems);
Peptides and proteins (α-helices, collagen helices); DNA and RNA structures; Helical polymers; Supramolecular assemblies; Foldamers; Chiral nanomaterials
Helical chirality is typically designated using: P (plus, right-handed) - clockwise screw sense; M (minus, left-handed) - counterclockwise screw sense; The stereochemical stability depends upon the barrier to helix inversion; sufficiently high inversion barriers permit isolation of distinct enantiomeric helices.
Helical chirality influences: Molecular recognition; Circular dichroism (CD); Circularly polarized luminescence (CPL); Chiral catalysis; Biomolecular folding; Materials optical properties; Protein-ligand interactions
Example: DNA predominantly adopts a right-handed B-form helix, [6]Helicene exists as separable P and M enantiomeric helices, α-Helices in proteins are overwhelmingly constructed from L-amino acids, contributing to biological homochirality.
Related Terms: Helicity (P/M); Axial Chirality; Topological Chirality; Homochirality; Conformational Chirality; Foldamers; Chiral Materials
Reference: IUPAC. Compendium of Chemical Terminology (IUPAC Gold Book). 2nd Edition, 1997 (updated 2019).
Yashima, E.; Maeda, K.; Iida, H.; Furusho, Y.; Nagai, K. Helical Polymers: Synthesis, Structures, and Functions. Chemical Reviews, 109, 6102-6211 (2009).
Eliel, E. L.; Wilen, S. H. Stereochemistry of Organic Compounds. Wiley, New York (1994).
