How dissymmetrical tails (i.e. tails of different lengths) in one lipid molecule exert an impact on the structure and properties of the resulting assembly is an intriguing issue in both biological and material senses. However, the underlying mechanism that engenders such phenomena is still obscure, which prompted us to unmask it by exploring the self-assembly behaviours of artificial building blocks comprising dissymmetrical tails. Here, a series of Fmoc-protected ornithine lipids with dissymmetrical alkyl tails was designed and the dissymmetry of the two tails was found to hierarchically tune the self-assembled nanostructures from nanotubes to bundles and nanotwists. With the Fmoc-headgroup employed as a chromophorous probe, it was revealed that the alkyl chain dissymmetry controlled the interacting modes of van der Waals interactions between alkyl tails, π-π stacking between Fmoc motifs and hydrogen bonding formed by the three amide bonds in lipid bilayers. The counterbalance between those noncovalent interactions was responsible for such remarkable tuning ability towards self-assembly and emissive behaviours of the lipids, including circularly polarized light emission. This work provides insight into dissymmetrical tails-regulated biological structures and functions of natural lipids, and also sets up a novel strategy of rationally modulating chiral and emissive properties of supramolecular materials, i.e., tunable CPL materials, by exploitation of the tail dissymmetry.
The organogel formation and self-assembly of a glycine-based achiral molecule were investigated. It has been found that the compound could gel organic solvents either at a lower temperature with lower concentration or at room temperature with higher concentration, which showed different self-assembled nanostructures. At a low temperature of −15 °C, the compound self-assembled into fibrous structures, whereas it formed distinctive flat microbelts at room temperature. When the organogel with nanofibers formed at −15 °C was brought into an ambient condition, chiral twist nanostructures were immediately evolved, which subsequently transferred to a giant microbelt through a hierarchical dendritic twist with the time. Although the compound is achiral, it formed chiral twist with both left- and right-handed twist structures simultaneously. When a trace analogical chiral trigger, l-alanine or d-alanine derivative, was added, a complete homochiral dendritic twist was obtained. Interestingly, a reverse process, i.e. the transformation of the microbelts into twists, could occur upon dilution of the organogel with microbelt structure. During the dilution, both left- and right-handed chiral twists could be formed again. Interestingly, the same branch from the microbelt formed the twist with the same handedness. A combination of the density functional theory (DFT), molecular mechanics (MM), and molecular dynamics (MD) simulations demonstrates that the temperature-induced twisting of the bilayer is responsible for the morphological transformation and evolution of the dendrite twist. This research sheds new light on the hierarchical transformation of the chiral structures from achiral molecules via controlled self-assembly.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Biodiversity contributes to maintaining ecosystem functions when faced with anthropogenic pressures. However, ecosystems are now exposed to a rapidly growing number of such pressures, and it remains unknown whether biodiversity can still sustain ecosystem functioning under anthropogenic pressures. Here we investigated the effects of soil biodiversity on soil functions and properties when faced with an increasing number of simultaneous global change factors (GCFs). Higher soil biodiversity had a positive effect on soil functions and properties when zero and only a few (e.g., 1 – 4) GCFs were applied, but this positive effect was eliminated by the co-occurrence of numerous GCFs. This was attributable to the reduction of soil fungal abundance and the relative abundance of a bacterial cluster. These results suggest that biodiversity can contribute to ecosystem functions only when a few GCFs are active, but that this will be jeopardized by the presence of multiple GCFs. Our study indicates that reducing the number of anthropogenic pressures should be a goal in ecosystem management, in addition to biodiversity conservation.
Two enantiomeric hydrohelicenes containing a hydroxyl group and a π-conjugated nonplanar structure are assembled at the air/water interface. These molecules are found to form spreading films with well-defined surface pressure–area isotherms. Upon transferring the spreading film onto the mica surface, porous nanostructures are observed. The spreading film can be transferred onto solid substrates by the Langmuir–Schaefer (LS) method and the transferred LS films display optical activity as revealed by the circular dichroism (CD) spectra. The P- and M-hydrohelicene enantiomers showed mirrored CD spectra, suggesting that the chirality of the LS films was controlled by molecular chirality. When these molecules are spread on the aqueous solution containing metal ions such as Ag+, Cu2+, and Zn2+, a clear twisted ring nanostructure, which is similar to the Möbius strip, is observed. It is suggested that the interaction between the hydroxyl groups of helicenes and metal ions induced such a ring nanostructure.
Biomaterials
in nature often exhibit hierarchical chiral structures
with an intriguing mechanism involving hierarchical chirality transfer
from molecular to supramolecular and the nano- or microscale level.
To mimic the cross-level chirality transfer, we present here one kind
of host–guest complex system built of β-cyclodextrin
(β-CD), sodium dodecyl sulfate (SDS), and fluorescent dyes,
which show multilevel chirality, including molecular chirality of
β-CD, induced supramolecular chirality of β-CD/SDS host–guest
complexes, a chiral lattice self-assembled nanosheet, mesoscopic chirality
of an assembled helical tube, induced chirality of a dye-doped chiral
tube. The hierarchical chirality involved a chiral lattice self-assembly
process, which can be identified by small-angle X-ray scattering,
optical studies, circular dichroism, and circularly polarized luminescence
spectral measurements. Benefiting from the chiral lattice self-assembly,
intense circularly polarized luminescence was observed from the achiral
dye-doped complexes with a large dissymmetry factor up to +0.1. This
work thus provides a feasible insight for developing hierarchical
chiroptical materials based on the lattice self-assembly.
The effect of hydroxide ion, impurities and oleic acid on molecular structure at hexadecane/water interface was studied with second harmonic generation.
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