Chirality Synchronization of Hydrogen‐Bonded Complexes of Achiral N‐Heterocycles

Abstract

2,4-Diamino-6-phenyl-1,3,5-triazines carrying as ingle oligo(ethylene oxide) (EO) chain form an optically isotropic mesophase composed of ac onglomerate of macroscopic chiral domains with opposite sense of chirality even though the constituent molecules are achiral. This mesophase was proposed to result from the helical packingo fh ydrogenbonded triazine aggregates,p roviding long-range chirality synchronization. The results provide first evidence for macroscopic achiral symmetry breaking upon conglomerate formation in an amorphous isotropic phase formed by hydrogenbonded associates of simple N-heterocycles that are related to prebiotic molecules.Chirality is au nique signature of living matter [1] and an intriguing phenomenon in various biomimetic and artificial systems. [2] Enantioselective synthesis,c atalysis,a nd autocatalysis have successfully been developed in recent decades for the synthesis of enantiopure molecules from achiral (prochiral) precursors. [3] Nowadays,t he focus has shifted to the spontaneous emergence of homogeneous chirality in ordered assemblies formed in supramolecular systems [4][5][6][7] by bulk crystallization (e.g., Viedma ripening) [8] and the self-assembly of achiral molecules at interfaces [9] and in helical aggregates. [10][11][12][13] However,s urprisingly,s pontaneous symmetry breaking was recently also observed in liquid crystalline phases, [14,15] ranging from lamellar phases [16] to cubic, [17,18] columnar, [14,15,19] and nematic phases, [20] and even in isotropic liquids of achiral compounds. [14,21] This dynamic route to macroscopic chirality in fluid systems was discussed as af undamentally new source of chirality in prebiotic fluids. [14,21,22] However,i tm ust also be noted that all previously reported molecules forming these symmetry-broken fluids are lipophilic (hydrophobic) molecules combining extended aromatic units with an umber of long aliphatic chains (bent-core mesogens, [12,[15][16][17] 20] di-and oligomesogens, [13, 20] and polycatenar molecules), [14,18,21] which are quite distinct from the molecules expected to have been involved in the chirogenesis of prebiotic aqueous fluids. [22] Herein, we report the first observation of spontaneous macroscopic symmetry breaking in an isotropic mesophase of simple hydrogen-bonding N-heterocycles functionalized with ap olar chain, which renders them compatible with aqueous self-assembly.T hese molecules are based on a4 -phenyl-2,6diamino-1,3,5-triazine core [23] fitted with as ingle tetra(ethylene glycol) chain, which terminates in either am ethoxy group (3a)o ri nahydroxy (3b;S cheme 1). It is shown that hydrogen bonding leads to chiral aggregates that undergo long-range chirality synchronization in the isotropic bulk state,which is associated with the formation of conglomerates of chiral domains with opposite handedness.Thesynthesis of compounds 3 is outlined in Scheme 1(see the Supporting Information for details). Both compounds 3a and 3b exhibit as ingle-phase transition (Scheme 1, bottom and Figure 1a), associated...

The induction of the Ntb phase in mixtures

“…The Ntb phase, characterized by spontaneous formation of chiral domains with a helical pitch on the 10 nm scale and pseudo-layer structure, formed by chemically non-chiral compounds is one of the recently observed examples of chiral symmetry breaking in liquid crystals [1][2][3][4][5][6][7]. Previously this effect has been more associated with higher ordered liquid crystal (LC) phases, such as lamellar, columnar and cubic arrays [8][9][10][11][12]. Ntb phase formation is most commonly associated with systems containing two mesogens separated by flexible odd-numbered spacers.…”

Unrestricted Chiral Patterning by Laser Writing in Liquid Crystalline and Plasmonic Nanocomposite Thin Films

“…[19] Indeed, achiral building blocks were already shown to form homochiral assemblies [20][21][22] and crystals [23,24] or bi-handed films with randomly distributed domains. The enabling phenomenon is chirality synchronization, [25][26][27][28] in which chirality arises during the assembly, for example, directed by the conformational chirality of organic molecules. In this mechanism, initially, a few achiral molecules assemble into chiral clusters and then direct the state of ad-joining molecules propagating the initially adopted chirality.…”