A Multicontrolled Enamine Configurational Switch Undergoing Dynamic Constitutional Exchange.

A multiresponsive enamine-based molecular switch is presented, in which forward/backward configurational rotation around the C=C bond could be precisely controlled by the addition of an acid/base or metal ions. Fluorescence turn-on/off effects and large Stokes shifts were observed while regulating the switching process with CuII . The enamine functionality furthermore enabled double dynamic regimes, in which configurational switching could operate in conjunction with constitutional enamine exchange of the rotor part. This behavior was used to construct a prototypical dynamic covalent switch system through enamine exchange with primary amines. The dynamic exchange process could be readily turned on/off by regulating the switch status with pH.

Light-Responsive Actuator of Azobenzene-Containing Main-Chain Liquid Crystal Elastomers with Allyl Sulfide Dynamic Exchangeable Linkages.

Herein, a light-responsive and light-induced bond-exchange-reaction (BER)-capable actuator of the monodomain liquid crystal elastomer (xMLCEazo), developed using main-chain mesogenic oligomers containing azobenzene and allyl sulfide linkages, is investigated. Large quantities of the azobenzene and allyl dithiol linkages are incorporated into the main-chain mesogenic oligomer prepared via thiol-acrylate Michael addition polymerization (TAMAP). The xMLCEazo film is generated via visible-light-induced BER of the drawn polydomain xLCEazo (xPLCEazo) film prepared via TAMAP of tetrathiol cross-linkers and diacrylate-terminated mesogenic oligomers. The xMLCEazo film exhibits large length actuation (38%) through the photothermal effect, along with excellent self-healing and reprogramming properties, under ultraviolet (UV) light irradiation. UV light induced BER of the xMLCEazo film is used to develop complex-shaped actuators with a bilayer film, containing the xMLCEazo and xPLCEazo films, which are bonded by the UV light induced BER without glue. The individual arm of the complex eight-arm flower is remotely actuated under UV light irradiation, and a circular band is rolled under blue laser light irradiation, demonstrating the local remote-controlled actuation and fuel-free motion of the motile soft robot using light irradiation, respectively. Thus, the xMLCEazo film can be expanded to other interesting applications requiring reprogrammable, self-healing, reprocessable, patternable, and remote-controlled light-triggered elastic, rubber-like actuators.

Competitive Intramolecular Hydrogen Bonding: Offering Molecules a Choice.

The conformational preferences of N-((6-methylpyridin-2-yl)carbamothioyl)benzamide were studied in solution, the gas phase and the solid state via a combination of NMR, density functional theory (DFT) and single crystal X-ray techniques. This acyl thiourea derivative can adopt two classes of low energy conformation, each stabilized by a different 6-membered intramolecular hydrogen bond (IHB) pseudoring. Analysis in different solvents revealed that the conformational preference of this molecule is polarity dependent, with increasingly polar environments yielding a higher proportion of the minor conformer containing an NH⋅⋅⋅N IHB. The calculated barrier to interconversion is consistent with dynamic behaviour at room temperature, despite the propensity of 6-membered IHB pseudorings to be static. This work demonstrates that introducing competitive IHB pathways can render static IHBs more dynamic and that such systems could have potential as chameleons in drug design.

Functional Covalent Organic Frameworks' Microspheres Synthesized by Self-Limited Dynamic Linker Exchange for Stationary Phases.

Synthesizing uniform functional covalent organic framework (COF) microspheres is the prerequisite of applying COFs as novel stationary phases for liquid chromatography. However, the synthesis of functionalized COF microspheres is challenging due to the difficulty in maintaining microspheric morphology when conferring functions. Here, a facile and universal "self-limited dynamic linker exchange" strategy is developed to achieve surface functionalization of uniform COF microspheres. Six different types of COF microspheres are constructed, showing the universality and superiority of the strategy. The library of COF microspheres' stationary phases can be further enriched on demand by varying different functional building blocks. The "self-limited dynamic linker exchange" is attributed to the result of a delicate balance of reaction thermodynamics and molecular diffusion energy barrier. As a demonstration, the chiral functional COF microspheres are used as stationary phases of chiral chromatography and realized effective enantioseparation.

Structural and functional roles of non-bilayer lipid phases of chloroplast thylakoid membranes and mitochondrial inner membranes.

The 'standard' fluid-mosaic membrane model can provide a framework for the operation of the photosynthetic and respiratory electron transport systems, the generation of the proton motive force (pmf) and its utilization for ATP synthesis according to the chemiosmotic theory. However, this model, with the bilayer organization of all lipid molecules, assigns no function to non-bilayer lipids - while in recent years it became clear that the two fundamental energy transducing membranes of the biosphere, chloroplast thylakoid membranes (TMs) and inner mitochondrial membranes (IMMs), contain large amounts of non-bilayer (non-lamellar) lipid phases. In this review, we summarize our understanding on the role of non-lamellar phases in TMs and IMMs: (i) We propose that for these membrane vesicles the dynamic exchange model (DEM) provides a more suitable framework than the 'standard' model; DEM complements the 'standard' model by assuming the co-existence of bilayer and non-bilayer phases and their interactions, which contribute to the structural dynamics of the membrane systems and safe-guard the membranes' high protein:lipid ratios. (ii) Non-bilayer phases play pivotal roles in membrane fusion and intermembrane lipid exchanges - essential processes in the self-assembly of these highly folded intricate membranes. (iii) The photoprotective, lipocalin-like lumenal enzyme, violaxanthin de-epoxidase, in its active state requires the presence of non-bilayer lipid phase. (iv) Cardiotoxins, water-soluble polypeptides, induce non-bilayer phases in mitochondria. (v) ATP synthesis, in mammalian heart IMMs, is positively correlated with the amount of non-bilayer packed lipids with restricted mobility. (vi) The hypothesized sub-compartments, due to non-lamellar phases, are proposed to enhance the utilization of pmf and might contribute to the recently documented functional independence of individual cristae within the same mitochondrion. Further research is needed to identify and characterize the structural entities associated with the observed non-bilayer phases; and albeit fundamental questions remain to be elucidated, non-lamellar lipid phases should be considered on a par with the bilayer phase, with which they co-exist in functional TMs and IMMs.

Dynamic exchange between particulate and dissolved matter following sequential resuspension of particles from an urban watershed under photo-irradiation.

Particulate matter (PM) has long-term effects on water quality compared to dissolved matter (DM) during downstream transfer after inflows into an aquatic environment. In the present study, the characteristics, behavior, and effects of PM from an urban watershed under photo-irradiation were investigated through sequential resuspensions before being compared. Changes in the organic matter content, heavy metals (Mn, Fe, Zn, Pb), spectroscopic indices (SUVA254, slope ratio (SR), humidification index (HIX), fluorescence index (FI), and biological index (BIX)), excitation-emission matrix combined with parallel factor analysis components (EEM-PARAFAC), and disinfection by-product formation potential (DBPFP) were analyzed. According to our results, light enhanced the release of organic matter from PM but reduced dissolved heavy metals. The PMU affected by urban-derived pollutants (i.e., rainfall particles, road-deposited sediment, sewer-pipeline-deposited sediment) exhibited higher quantities of terrestrial humic-like organic matter than PMR, which contains base particles from riverines (i.e., soil, sediments). For the PMU, the humic-like fluorescent components (C1 and C2) enhanced under light conditions with every resuspension, whereas the components decreased in the PMR. Consistent with the PARAFAC results, the trihalomethane formation potential (THMFP) of the PMU was enhanced by approximately 2.8 times more than that of the PMR, and exhibited a high correlation with the fluorescent components (C1, r = 0.81, p < 0.001). The principal component analysis results also confirmed that the characteristics of dynamic exchanges between PM and DM were distinguished by PM sources and light, and the photo-released DM and their spectral characteristics displayed opposite behaviors depending on the PM sources during the sequential resuspensions.

Photonic Cholesteric Liquid-Crystal Elastomers with Reprogrammable Helical Pitch and Handedness.

The unique combination of the rubber-like property and the photonic helicoidal structure of cholesteric liquid-crystal elastomers (CLCEs) results in one-handed circular polarized light reflection, the wavelength of which is dictated by the Bragg relationship. Herein, a highly stretchable mechanochromic photonic CLCE film was fabricated by cross-linking mesogenic oligomers having thiol terminal groups, which further reacted to form disulfide (-S-S-) linkages. The mechanically stretched photonic CLCE film reflected both right- and left-handed circular polarized lights with a blue-shifted color. The helicoidal pitch and handedness controlled by the applied strain were programmed through a dynamic exchange reaction between the -S-S- linkages, thus realizing the patterning at selective regions. The pattern almost vanished under unpolarized daylight but was visible under circularly polarized light when the patterned photonic CLCE film had been heated above its isotropic temperature. The hidden patterns of the heat-treated CLCE film reappeared under unpolarized daylight when stretched, demonstrating a data encryption ability. These patterned photonic elastomers can be uniquely used in sensors, actuators, soft robotics, flexible displays, data encryption, and anticounterfeiting applications with a mechanochromic camouflage response.

Lipid Polymorphism of the Subchloroplast-Granum and Stroma Thylakoid Membrane-Particles. I. 31P-NMR Spectroscopy.

Build-up of the energized state of thylakoid membranes and the synthesis of ATP are warranted by organizing their bulk lipids into a bilayer. However, the major lipid species of these membranes, monogalactosyldiacylglycerol, is a non-bilayer lipid. It has also been documented that fully functional thylakoid membranes, in addition to the bilayer, contain an inverted hexagonal (HII) phase and two isotropic phases. To shed light on the origin of these non-lamellar phases, we performed 31P-NMR spectroscopy experiments on sub-chloroplast particles of spinach: stacked, granum and unstacked, stroma thylakoid membranes. These membranes exhibited similar lipid polymorphism as the whole thylakoids. Saturation transfer experiments, applying saturating pulses at characteristic frequencies at 5 °C, provided evidence for distinct lipid phases-with component spectra very similar to those derived from mathematical deconvolution of the 31P-NMR spectra. Wheat-germ lipase treatment of samples selectively eliminated the phases exhibiting sharp isotropic peaks, suggesting easier accessibility of these lipids compared to the bilayer and the HII phases. Gradually increasing lipid exchanges were observed between the bilayer and the two isotropic phases upon gradually elevating the temperature from 5 to 35 °C, suggesting close connections between these lipid phases. Data concerning the identity and structural and functional roles of different lipid phases will be presented in the accompanying paper.