Controlling spontaneous mirror symmetry breaking in cubic liquid crystalline phases by the cycloaliphatic ring size.

Rod-like molecules combining a fork-like triple chain end and a cycloaliphatic apex are introduced as a new design concept for materials with broad ranges of bicontinuous cubic (Cubbi) phases. By ring expansion from n = 4 to 12 a sequence of three Cubbi phases is observed; the achiral double gyroid la3[combining macron]d phase, a chiral "Im3m" phase and an achiral re-entrant la3[combining macron]d phase. The chiral "Im3m" phase is formed if the helical twist between the molecules along the networks is in the range of 8.6°-9.5°, either for the individual compounds or their mixtures.

The Solution of the Puzzle of Smectic-Q: The Phase Structure and the Origin of Spontaneous Chirality.

The so-called smectic-Q (SmQ) liquid crystal phase was discovered in 1983 in rod-like molecules, but its structure remain unclear in spite of numerous attempts to solve it. Herein, we report what we believe to be the solution: A unique bicontinuous phase that is non-cubic and is made up of orthogonal twisted columns with planar 4-way junctions. While SmQ had only been observed in chiral compounds, we show that this chiral phase forms also in achiral materials through spontaneous symmetry breaking. The results strongly support the idea of a helical substructure of bicontinuous phases and long-range homochirality being sustained by helicity-matching at network junctions. The model also explains the triangular shape of double-gyroid domains growing within a SmQ environment. SmQ-forming materials hold potential for applications such as circularly polarized light emitters that require no alignment or asymmetric synthesis.

Spontaneous mirror symmetry breaking in a re-entrant isotropic liquid.

An achiral double-swallow tailed tetracatenar compound forms a re-entrant isotropic liquid between a bicontinuous cubic phase and a nematic liquid crystalline phase. This isotropic liquid was found to represent a conglomerate of two immiscible chiral liquids. The chirality is retained and eventually becomes uniform at the transition to the cubic I432 phase.

Chiral self-sorting and amplification in isotropic liquids of achiral molecules.

According to our present knowledge, the spontaneous resolution of racemic mixtures of chiral molecules or chiral conformers of achiral molecules into macroscopic chiral superstructures requires the confinement of these molecules in a crystal lattice, on surfaces or in other well-ordered assemblies. Herein we provide the first experimental evidence that mirror-symmetry breaking can also take place at a liquid-liquid phase transition in isotropic liquids of achiral molecules, even at relatively high temperatures around 200 °C. It is proposed that cooperative segregation of enantiomorphic molecular conformations gives rise to a conglomerate of two chiral and immiscible liquids. In these liquid conglomerates a strong chiral amplification was observed, which led to degeneracy from a stochastic distribution and eventually provided uniform chirality. We anticipate that this work will contribute to the understanding of symmetry breaking in soft matter and provide a new tool for the identification of chirality traces, and possibly affect the discussion of the emergence of chirality in prebiotic systems.

Dynamic mirror-symmetry breaking in bicontinuous cubic phases.

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 Im3̄m cubic phase is always chiral, while the Ia3̄d 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 Ia3̄d phase the opposing chiralities of the two networks cancel, but not so in the three-networks Im3̄m phase. The high twist in the Im3̄m phase explains its previously unrecognized chirality, as well as the origin of this complex structure and the transitions between the different cubic phases.

Tormentic acid derivatives: synthesis and apoptotic activity.

Several derivatives of tormentic acid have been prepared and tested for their antitumor activity. The dichloroacetate 14 is an excellent antitumor active agent acting by an apoptose inducing pathway as demonstrated by OA/PI staining, DNA laddering experiments as well as by an annexin V binding assay.