Understanding the Structure of Reversible Coordination Polymers Based on Europium in Electrostatic Assemblies Using Time-Resolved Luminescence

In situ characterization of the structure of reversible coordination polymers remains a challenge because of their dynamic and concentration-responsive nature. It is especially difficult to determine these structures in their self-assemblies where their degree of polymerization responds to the local concentration. In this paper, we report on the structure of reversible lanthanide coordination polymers in electrostatic assemblies using time-resolved luminescence (TRL) measurement. The reversible coordinating system is composed of the bifunctional ligand 1,11-bis­(2,6-dicarboxypyridin-4-yloxy)-3,6,9-trioxaundecane (L₂EO₄) and europium ion Eu³⁺. Upon mixing with the positively charged diblock copolymer poly­(2-vinylpyridine)-<i>b</i>-poly­(ethylene oxide) (P2VP₄₁-<i>b</i>-PEO₂₀₅), electrostatic polyion micelles are formed and the negatively charged L₂EO₄–Eu coordination complex simultaneously transforms into coordination “polymers” in the micellar core. By virtue of the water-sensitive luminescence of Eu³⁺, we are able to obtain the structural information of the L₂EO₄–Eu coordination polymers before and after the formation of polyion micelles. Upon analyzing the fluorescence decay curves of Eu³⁺ before and after micellization, the fraction of Eu³⁺ fully coordinated with L₂EO₄ is found to increase from 32 to 83%, which verifies the occurrence of chain extension of the L₂EO₄–Eu coordination polymers in the micellar core. Our work provides a qualitative picture for the structure change of reversible coordination polymers, which allows us to look into these “invisible” structures

Smart Nanocarrier: Self-Assembly of Bacteria-like Vesicles with Photoswitchable Cilia

Bioinspired cell deformation aids in the design of smart functional molecular self-assemblies. We report on a system of bacteria-like vesicles which release entrapped drug upon developing hairs triggered by UV irradiation, just like cilia stretching from the surface of bacteria. The formation of cilia leads to a less intact membrane, which allows release of entrapped drug. This bioinspired design created a smart nanocarrier that releases the payload <i>via</i> deformation rather than complete breaking

Effect of the Molecular Weight of Polyelectrolyte and Surfactant Chain Length on the Solid-Phase Molecular Self-Assembly

Solid-phase molecular self-assembly (SPMSA) is emerging as an efficient approach, leading to scale-span self-assembled supramolecular films. With SPMSA, freestanding macroscopic supramolecular films can be formed upon mechanically pressing the precipitates formed with polyelectrolytes and oppositely charged surfactants. Herein, we report that the film formation ability and the mechanical strength of the resultant film depend highly on the surfactant chain lengths and the molecular weight of polyelectrolytes. A coarse-grained molecular dynamics study revealed that the longer surfactant chains are beneficial for the ordered assembly of surfactant bilayers in the film, whereas the larger molecular weight of PE favors the enhanced mechanical strength of the film by promoting the long-range order of the surfactant bilayers. The current results disclosed the physical insight of the surfactant chain length and the molecular weight of polyelectrolytes into the film structure and mechanical strength, which is of practical importance in guiding the creation of SPMSA materials

General Approach To Construct Photoresponsive Self-Assembly in a Light-Inert Amphiphilic System

The ability to modulate amphiphilic aggregation reversibly with external stimuli, especially using light as a trigger, is of great importance. This has greatly contributed to the development of applications using self-assembly. However, most previously described systems are based on a specific molecular design and have shown difficultly in their application to light-inert aggregation. Here, we developed a general and effective approach to control the morphology of amphiphilic aggregates by light, which is suitable for different assemblies such as micelles, vesicles, and helixes. Our strategy is to construct a photoresponsive factor into light-inert self-assemblies. On the basis of the different capabilities to form host–guest inclusions between photoresponsive azobenzene sodium and light-inert molecules with cyclodextrin, the transformation of the corresponding amphiphilic aggregation can be controlled easily and reversibly by light stimuli. Not only the nanostructure of the aggregates but also the phase behavior, such as gel formation, can be modulated upon light irradiation using this method

Effect of the Molecular Weight of Polyelectrolyte and Surfactant Chain Length on the Solid-Phase Molecular Self-Assembly

Solid-phase molecular self-assembly (SPMSA) is emerging as an efficient approach, leading to scale-span self-assembled supramolecular films. With SPMSA, freestanding macroscopic supramolecular films can be formed upon mechanically pressing the precipitates formed with polyelectrolytes and oppositely charged surfactants. Herein, we report that the film formation ability and the mechanical strength of the resultant film depend highly on the surfactant chain lengths and the molecular weight of polyelectrolytes. A coarse-grained molecular dynamics study revealed that the longer surfactant chains are beneficial for the ordered assembly of surfactant bilayers in the film, whereas the larger molecular weight of PE favors the enhanced mechanical strength of the film by promoting the long-range order of the surfactant bilayers. The current results disclosed the physical insight of the surfactant chain length and the molecular weight of polyelectrolytes into the film structure and mechanical strength, which is of practical importance in guiding the creation of SPMSA materials

Effect of the Molecular Weight of Polyelectrolyte and Surfactant Chain Length on the Solid-Phase Molecular Self-Assembly

Solid-phase molecular self-assembly (SPMSA) is emerging as an efficient approach, leading to scale-span self-assembled supramolecular films. With SPMSA, freestanding macroscopic supramolecular films can be formed upon mechanically pressing the precipitates formed with polyelectrolytes and oppositely charged surfactants. Herein, we report that the film formation ability and the mechanical strength of the resultant film depend highly on the surfactant chain lengths and the molecular weight of polyelectrolytes. A coarse-grained molecular dynamics study revealed that the longer surfactant chains are beneficial for the ordered assembly of surfactant bilayers in the film, whereas the larger molecular weight of PE favors the enhanced mechanical strength of the film by promoting the long-range order of the surfactant bilayers. The current results disclosed the physical insight of the surfactant chain length and the molecular weight of polyelectrolytes into the film structure and mechanical strength, which is of practical importance in guiding the creation of SPMSA materials

Reversible Transition between SDS@2β-CD Microtubes and Vesicles Triggered by Temperature

Switching between association and dissociation is the well-known strategy for constructing responsive materials based on the host–guest complexes of cyclodextrins (CDs). In this work, we report that temperature may also trigger self-assembly transition in the supramolecular system composed of sodium dodecyl sulfate (SDS) and β-cyclodextrin (β-CD) at a molar ratio of 1:2. We reported previously that, at this ratio, SDS and β-CD form a channel-type SDS@2β-CD supramolecular unit, which further self-assembles into non-amphiphilic vesicles and microtubes driven by hydrogen bonding. Here, we report that the vesicles and microtubes can be reversibly switched between each other upon decreasing and increasing temperature. Control experiments in heavy water suggest that water molecules play a dominating role in the hydrogen bonding between SDS@2β-CD supramolecular units at lower concentration and higher temperature. Under opposite conditions, the hydrogen bonding between CDs is dominating. Therefore, for the 5% system, we observed a vesicle to microtube transition with a decreasing temperature, whereas for the 10% system, we observed the reverse process. Both processes are reversible. This is not only an example of temperature-triggered responsiveness in non-amphiphilic self-assemblies but also a new mode of responsiveness for the host–guest inclusion systems based on CDs. This temperature-responsive process is anticipated to shed light on the design and development of novel advanced materials

Multifunctional Metallo-Organic Vesicles Displaying Aggregation-Induced Emission: Two-Photon Cell-Imaging, Drug Delivery, and Specific Detection of Zinc Ion

Molecules displaying aggregation-induced emission (AIE) property can hardly self-assemble into vesicles desired in design of theranostics. We report the formation of metallo-organic AIE vesicles with triarylamine carboxylate (TPA-1) and Zn²⁺ ions. TPA-1 shows a great binding affinity to Zn²⁺ as a fluorescence turn-on sensor. The vesicles exhibited high fluorescence-emission property under two-photon mode which endows them very good cell imaging ability. Drug-loading experiments suggest a loading capacity for the model anticancer drug 5-fluorouracil (5-Fu) can reach up to 53.4%, and sustained release of the drug is possible in biological environment. This is the first report of supramolecular coordination fluorescent vesicles based on AIE molecule. Further study reveals the fluorescence enhancement of TPA-1 can only be triggered by Zn²⁺, suggesting the ability of specific detection of Zn²⁺. This study indicates that the formation of metallo-organic vesicles can be a multiplatform for cell-imaging, drug carrier, and metal ions detection

Chronic gastric electrical stimulation leads to weight loss via modulating multiple tissue neuropeptide Y, orexin, α-melanocyte-stimulating hormone and oxytocin in obese rats

<div><p></p><p><b><i>Objectives. </i></b>Gastric electrical stimulation (GES) has great potential for the treatment of obesity. We investigated the impact of chronic GES on the alteration of adipose tissue and the regulation of neuropeptide Y (NPY), orexin (OX), α-melanocyte-stimulating hormone (α-MSH) and oxytocin (OXT), and their receptors in several tissues. <b><i>Material and methods.</i></b> Most of the experiments included three groups of diet-induced obesity rats: (1) sham-GES (SGES); (2) GL-6mA (GES with 6 mA, 4 ms, 40 Hz, 2 s on, 3 s off at lesser curvature); and (3) SGES-PF (SGES rats receiving pair feeding to match the consumption of GL-6mA rats). Chronic GES was applied for 2 h every day for 4 weeks. During treatment with GES, food intake and body weight were monitored weekly. The alteration of epididymal fat weight, gastric emptying, and expression of peptides and their receptors in several tissues were determined. <b><i>Results.</i></b> GL-6mA was more potent than SGES-PF in decreasing body weight gain, epididymal fat tissue weight, adipocyte size and gastric emptying. Chronic GES significantly altered NPY, OX, α-MSH and OXT and their receptors in the hypothalamus, adipose tissue and stomach. <b><i>Conclusions. </i></b>Chronic GES effectively leads to weight loss by reducing food intake, fat tissue weight and gastric emptying. NPY, α-MSH, orexin and OXT, and their receptors in the hypothalamus, adipose tissue and stomach appear to be involved in the anti-obesity effects of chronic GES.</p></div

Self-Assembly of Nonionic Surfactant Tween 20@2β-CD Inclusion Complexes in Dilute Solution

It has long been considered that the addition of cyclodextrins (CDs) disfavors the self-assembly of surfactants in dilute solutions since the hydrophobic effect is destroyed upon the formation of the hydrophiphilic CD/surfactant inclusion complex. However, in this work, we found that β-CD/nonionic surfactant inclusion complexes are able to self-assemble into vesicles in dilute solutions, namely in solutions with concentration lower than the CMC of surfactants. When using Tween 20 as a model surfactant, HNMR and MS measurements indicate that the building block for the vesicles is the channel type Tween 20@2β-CD inclusion complex. Structure and IR analysis suggests that the self-assembly of hydrophilic Tween 20@2β-CD is driven by H-bonds between both the headgroup of Tween 20 and the hydroxyl groups of β-CD. The self-assembly of the inclusion complex between the β-CD and the nonionic surfactant in dilute solution is found to be a general phenomenon. Undoubtedly, surfactant@2β-CD inclusion complex can be a novel building block for nonamphiphilic self-assembly, which provides a new physical insight for the influence of cyclodextrins on the self-assembly of surfactants