Self-assembly Of Chiral Molecules Research Articles

Self-assembly variation of glycyrrhetinic acid epimers: Assembly mechanism and antibacterial efficacy between 18 α-GA and 18 β-GA

Studies have confirmed that the spatial arrangement of chiral molecules has a decisive influence on supramolecular assembly. However, the effect of epimerization caused by the change of a single chiral center on the self-assembly of chiral molecules has not been reported. Herein, we explored a pair of epimers 18 α-glycyrrhetinic acid and 18 β-glycyrrhetinic acid from Glycyrrhiza uralensis Fisch, which had completely different medicinal activities. In this study, we found that these epimers of glycyrrhetinic acid showed distinct self-assembly properties under the condition of the deionized water and a small amount of DMSO solution. Interestingly, the cis-configured 18 β-GA could form a 'head-to-tail' interlaced structure and further self-assembled to form nanoparticles, while trans-configured 18 α-GA was connected in a “head-to-head” manner, and due to the excessive steric hindrance that made it difficult to assemble. This work not only clearly demonstrates the impact of epimerization due to changes in a single chiral center on the self-assembly of chiral molecules as well as biological activity, but also provides new insights into the self-assembly of natural organic molecules in the development of nanomedicines and biofunctional materials.

Spontaneous Symmetry Breaking of Nanoscale Spatiotemporal Pattern as the Origin of Helical Nanopore Etching in Silicon.

Nanometric chiral objects such as twisted or helical nanoribbons represent a new class of objects having important potential in a large panel of applications, taking advantage, for example, of electromechanical or optical chirality, local chiral environment for catalysis, and chiral recognition. Supramolecular chemistry has played a central role in the production of such structures through either chiral macromolecules/foldamers or the self-assembly of chiral molecules; the latter can also be used as templates for the sol-gel transcription to silica materials, offering them polymorphisms with further structural stability. Here, we report a totally different and dynamic approach to produce helical mesostructures. This study focuses on helical nanopores that are spontaneously formed in the platinum-assisted chemical etching of silicon by dynamic self-organization under a nonequilibrium state. The symmetry breaking of a helical nanopore formation is achieved by the spatial symmetry breaking of a spatiotemporal pattern at the nanoscale and without incorporation of chiral molecules. Rotational motion of the platinum nanocatalyst, which is regarded as a spatiotemporal pattern at the etching frontier (the platinum/silicon interface), induces precession movement of the nanocatalyst, and movement of the catalyst during etching forms helical nanopores in the silicon. We consider that this study is an important milestone to understand the close relation between spatiotemporal pattern formation and the dynamic emergence of symmetry breaking in chemical reactions.

Chiral effect on the self-assembly of chiral molecules synthesized from cholesterol

Abstract One predesigned chiral steroid base compound cholesteryl 4-(carbonyloxy) 4-(hexyloxyl) benzoate (CCH*) and two achiral compounds with various alkyl chain length oxalyl acid N',N'-di(4-(hexyloxy)benzoyl)-hydrazide (AG6) and oxalyl acid N',N'-di(4-(undecyloxy)benzoyl)-hydrazide (AG11) have been successfully synthesized. Formation of asymmetric self-assembled constructions via self-assembly of achiral molecules in chiral environment was investigated. Due to steric hindrance, CCH* could not form gel in any kind of organic solvents. On the other hand, AG6 and AG11 formed achiral gels in many kinds of solvent. The results suggest that polarity, side branch and intermolecular forces are the key factors for the gelation. Temperature-dependent 1H NMR analysis of the fabricated gels show that van der Waals forces and π-π interactions are key factors leading to self-assembly of molecules result in three-dimensional networks. In addition, CCH* was used as a chiral dopant added into achiral compounds forming asymmetric self-assembled constructions. The results indicate that doping of CCH* into achiral gelators giving a chiral environment leads to the formation of helical constructions. The fabricated asymmetric constructions were confirmed using circular dichroism (CD) spectroscopy and small angle X-ray scattering (SAXS).

‘Sergeants-and-Corporals’ principle in chiral induction at an interface

Self-assembly of an achiral porphyrin at the interface between a chiral solvent and an atomically flat substrate renders the monolayer chiral, and a non-racemic solvent can even overrule the intrinsic expression of chirality in the self-assembly of chiral molecules.

Chirality Transfer from a Single Chiral Molecule to 2D Superstructures in Alaninol on the Cu(100) Surface

The formation of 2D chiral monolayers obtained by self-assembly of chiral molecules on surfaces has been widely reported in the literature. Control of chirality transfer from a single molecule to surface superstructures is a challenging and important aspect for tailoring the properties of 2D nanostructures. However, despite the wealth of investigations performed in recent years, how chiral transfer takes place on a large scale still remains an open question. In this paper we report a coupling of scanning tunneling microscopy and low energy electron diffraction measurements with an original theoretical approach, combining molecular dynamics and essential dynamics with density functional theory, to investigate self-assembled chiral structures formed when alaninol adsorbs on Cu(100). The peculiarity of this system is related to the formation of tetrameric molecular structures which constitute the building blocks of the self-assembled chiral monolayer. Such characteristics make alaninol/Cu(100) a good candidate to reveal chiral expression changes. We find that the deposition of alaninol enantiomers results in the formation of isolated tetramers that are aligned along the directions of the substrate at low coverage or when geometrical confinement prevents long-range order. Conversely, a rotation of 14° with respect to the Cu(100) unit vectors is observed when small clusters of tetramers are formed. An insight to the process leading to a 2D globally chiral surface has been obtained by monitoring molecular assemblies as they grow from the early stages of adsorption, suggesting that the distinctive orientation of the self-assembled monolayer originates from a balance of cooperating forces which start acting only when tetramers pack together to form small clusters.

Odd/Even Effect in Self-Assembly of Chiral Molecules at the Liquid−Solid Interface: An STM Investigation of Coadsorbate Control of Self-Assembly

Manipulation of the self-assembly of chiral 2-bromohexadecanoic acid by templates composed of coadsorbed achiral molecules has been investigated at the liquid−solid interface using scanning tunneling microscopy (STM). The template formed by the odd-numbered saturated fatty acid heptadecanoic acid induces coadsorption of R-2-bromo-hexadecanoic acid and S-2-bromo-hexadecanoic acid within a single domain. Specifically, heptadecanoic acid effects an intra-lamellar alternation of R and S-2-bromo-hexadecanoic acid molecules, which is further confirmed by studies of heptadecanoic acid with pure R-2-bromo-hexadecanoic acid. Templates formed by even-numbered acids such as hexadecanoic acid induce the segregation of R- and S-2-bromo-hexadecanoic acid into separate (R or S) domains.