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Dynamic mirror-symmetry breaking in bicontinuous cubic phases.

ABSTRACT: Chiral segregation of enantiomers or chiral conformers of achiral molecules during self-assembly in well-ordered crystalline superstructures has fascinated chemists since Pasteur. Here we report spontaneous mirror-symmetry breaking in cubic phases formed by achiral multichain-terminated diphenyl-2,2'-bithiophenes. It was found that stochastic symmetry breaking is a general phenomenon observed in bicontinuous cubic liquid crystal phases of achiral rod-like compounds. In all compounds studied the Im3?m cubic phase is always chiral, while the Ia3?d phase is achiral. These intriguing observations are explained by propagation of homochiral helical twist across the entire networks through helix matching at network junctions. In the Ia3?d phase the opposing chiralities of the two networks cancel, but not so in the three-networks Im3?m phase. The high twist in the Im3?m phase explains its previously unrecognized chirality, as well as the origin of this complex structure and the transitions between the different cubic phases.

SUBMITTER: Dressel C

PROVIDER: S-EPMC4501316 | biostudies-literature | 2014 Nov

REPOSITORIES: biostudies-literature

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Dynamic mirror-symmetry breaking in bicontinuous cubic phases.

Dressel Christian C Liu Feng F Prehm Marko M Zeng Xiangbing X Ungar Goran G Tschierske Carsten C

Angewandte Chemie (International ed. in English) 20140926 48

Chiral segregation of enantiomers or chiral conformers of achiral molecules during self-assembly in well-ordered crystalline superstructures has fascinated chemists since Pasteur. Here we report spontaneous mirror-symmetry breaking in cubic phases formed by achiral multichain-terminated diphenyl-2,2'-bithiophenes. It was found that stochastic symmetry breaking is a general phenomenon observed in bicontinuous cubic liquid crystal phases of achiral rod-like compounds. In all compounds studied the ...[more]

PMID: 25257551

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Project description:Nonlamellar lipid membranes are frequently induced by proteins that fuse, bend, and cut membranes. Understanding the mechanism of action of these proteins requires the elucidation of the membrane morphologies that they induce. While hexagonal phases and lamellar phases are readily identified by their characteristic solid-state NMR line shapes, bicontinuous lipid cubic phases are more difficult to discern, since the static NMR spectra of cubic-phase lipids consist of an isotropic (31)P or (2)H peak, indistinguishable from the spectra of isotropic membrane morphologies such as micelles and small vesicles. To date, small-angle X-ray scattering is the only method to identify bicontinuous lipid cubic phases. To explore unique NMR signatures of lipid cubic phases, we first describe the orientation distribution of lipid molecules in cubic phases and simulate the static (31)P chemical shift line shapes of oriented cubic-phase membranes in the limit of slow lateral diffusion. We then show that (31)P T2 relaxation times differ significantly between isotropic micelles and cubic-phase membranes: the latter exhibit 2 orders of magnitude shorter T2 relaxation times. These differences are explained by the different time scales of lipid lateral diffusion on the cubic-phase surface versus the time scales of micelle tumbling. Using this relaxation NMR approach, we investigated a DOPE membrane containing the transmembrane domain (TMD) of a viral fusion protein. The static (31)P spectrum of DOPE shows an isotropic peak, whose T2 relaxation times correspond to that of a cubic phase. Thus, the viral fusion protein TMD induces negative Gaussian curvature, which is an intrinsic characteristic of cubic phases, to the DOPE membrane. This curvature induction has important implications to the mechanism of virus-cell fusion. This study establishes a simple NMR diagnostic probe of lipid cubic phases, which is expected to be useful for studying many protein-induced membrane remodeling phenomena in biology.

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Dynamic mirror-symmetry breaking in bicontinuous cubic phases.

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Dynamic mirror-symmetry breaking in bicontinuous cubic phases.

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