Cucurbit[8]uril-Containing Multilayer Films for the Photocontrolled Binding and Release of a Guest Molecule

Controllable and large-scale supramolecular vesicle aggregation: orthogonal light-responsive host–guest and metal–ligand interactions

On the basis of the host–guest molecular recognition interaction between β-cyclodextrin and azobenzene, two kinds of supramolecular self-assemblies (Py-CD⊃Azo-C and Py-CD⊃Azo-C3) were constructed.

Antiadhesive and antibacterial properties of pillar[5]arene-based multilayers

A new type of coating, based on carboxylato-pillar[5]arene/poly(allylamine hydrochloride) multilayer films, for the sustained release of antibiotics with in vitro antiadhesive and antimicrobial activity against Gram-positive and Gram-negative bacteria is described.

Host-guest self-assembly toward reversible visible-light-responsive switching for bacterial adhesion

Here we report a facile method to construct reversible visible-light-responsive switching from antibacterial to bioadhesion by host-guest self-assembly of β-cyclodextrin (β-CD) and azobenzene functionalized polycation/polyanion. The visible-light-responsible azobenzene functionalized polycation, poly{6-[(2,6-dimethoxyphenyl)azo-4-(2',6'-dimethoxy)phenoxy]propyl dimethylaminoethyl methacrylate-random-poly(2-(N,N-dimethylaminoethyl) methacrylate) (Azo-PDMAEMA), was synthesized via quaternization reaction between 2,6,2',6'-tetramethoxy-4-(3-bromopropoxy)azobenzene (AzoOMeBr) and poly(2-(N,N-dimethylaminoethyl) methacrylate) (PDMAEMA), and the polyanion, poly{6-[(2,6-dimethoxyphenyl)azo-4-(2',6'-dimethoxy) phenoxy]hexyl acrylate-random-acrylic acid} (Azo-PAA), was synthesized via esterification reaction between 2,6,2',6'-tetramethoxy-4-(6-hydroxyhexyloxy) azobenzene (AzoOMeOH) and poly(acryloyl chloride) (PAC) and subsequent hydrolysis reactions. The switch surface could be achieved via the alternate host-guest assembly of Azo-PDMAEMA and Azo-PAA onto a β-CD-terminated substratum (Sub-CD) through visible light irradiation. The positively charged Azo-PDMAEMA with quaternary ammonium groups exhibited antimicrobial properties and few bacteria were adhered on the surface, while the negatively charged Azo-PAA with carboxyl acid groups exhibited excellent bioadhesive properties and a large number of bacteria were adhered. Interestingly, the switch between antibacterial and bioadhesive could be realized upon visible light irradiation via alternate assembly of Azo-PDMAEMA and Azo-PAA. The proposed approach to manufacturing visible-light-responsive surface with reversible and alterable biofunctionality switching between antibacterial and bioadhesive is simple and efficient, which is promising for preparation of multifunctional polymeric surfaces to encounter multifarious demands for the biomedical and biotechnological applications.

STATEMENT OF SIGNIFICANCE

Light has attracted great attention in building biointerfaces for its precise spatiotemporal control and convenient operation. However, UV light may damage to biological samples and living tissues, which will limit its applications. This study demonstrates a novel visible-light-responsive surface fabricated through reversible assembly of azobenzene functionalized polycations/polyanions on cyclodextrin (CD)-terminated substrate by host-guest interactions between the visible-light-responsive azobenzene mAzo and CD, which has not been examined previously. It is noted that the azobenzene functionalized polycations show strong antibacterial activities, while the polyanions show excellent bioadhesive properties, as can be switched through the alternate assembly upon visible-light irradiation. This facile and versatile approach to visible-light-responsive surfaces holds great potential for switching of bioadhesion.

Robust multi-responsive supramolecular hydrogel based on a mono-component host-guest gelator

Supramolecular hydrogels have been widely investigated, but the construction of stimuli-responsive mono-component host-guest hydrogels remains a challenge in that it is still hard to balance the solubility and gelation ability of the gelator. In this work, three azobenzene-modified β-cyclodextrin derivatives with different alkyl lengths (β-CD-Azo-Cn) have been synthesized. The length of the alkyl chain dramatically influences the solubility and gelation ability of β-CD derivatives in water. Among these derivatives, β-CD-Azo-C8 possesses the lowest minimum gelation concentration (MGC). Based on the host-guest interaction between β-CD and azobenzene units in aqueous solution, which is confirmed by UV-visible and ROESY NMR spectra, the gelators self-assemble and further interwine into networks through the hydrogen bonds on the surface of β-CD cavities. Hydrogels formed by mono-component gelators can collapse under external stimuli such as heating, competition guests and hosts, and UV irradiation. When the concentration of the gelator is more than 8 wt%, the hydrogel exhibits good self-supporting ability with a storage modulus higher than 104 Pa. The gel-sol transition temperature of the hydrogel is near body temperature, indicating its potential applications in biological materials.

Host-Guest Chemistry in Layer-by-Layer Assemblies Containing Calix[n]arenes and Cucurbit[n]urils: A Review

This review provides an overview of the synthesis of layer-by-layer (LbL) assemblies containing calix[n]arene (CA[n]) and cucurbit[n]uril (CB[n]) and their applications. LbL assemblies, such as thin films and microcapsules, containing selective binding sites have attracted considerable attention because of their potential use in separation and purification, sensors for ions and molecules, and controlled release. CA[n]-containing LbL films have been prepared using sulfonated CA[n] and cationic polymers to construct chemical sensors and molecular containers. CA[n]-containing LbL films deposited on the surface of a porous support are useful as ion-selective membranes that exhibit selective permeability to monovalent ions over multivalent ions. CB[n]s have been used as molecular glues for the construction of LbL films and microcapsules by taking advantage of the strong affinity of CB[n]s to aromatic compounds. CB[n]s form a stable 1:1:1 ternary complex with electron-rich and electron-deficient molecules in LbL films to stabilize the assemblies. CB[n]-containing LbL films can also be deposited on the surfaces of micro templates and nanopore membranes to construct microcapsules for controlled release and nanochannels for selective ion transport, respectively.

pH-Responsive Host⁻Guest Complexation in Pillar[6]arene-Containing Polyelectrolyte Multilayer Films

A water-soluble, anionic pillar[6]arene derivative (WP6) is applied as monomeric building block for the layer-by-layer self-assembly of thin polyelectrolyte multilayer films, and its pH-dependent host–guest properties are employed for the reversible binding and release of a methylviologen guest molecule. The alternating assembly of anionic WP6 and cationic diazo resin (DAR) is monitored in-situ by a dissipative quartz crystal microbalance (QCM-D). In solution, the formation of a stoichiometric inclusion complex of WP6 and cationic methylviologen (MV) as guest molecule is investigated by isothermal titration calorimetry and UV-vis spectroscopy, respectively, and attributed to electrostatic interactions as primary driving force of the host–guest complexation. Exposure of WP6-containing multilayers to MV solution reveals a significant decrease of the resonance frequency, confirming MV binding. Subsequent release is achieved by pH lowering, decreasing the host–guest interactions. The dissociation of the host–guest complex, release of the guest from the film, as well as full reversibility of the binding event are identified by QCM-D. In addition, UV-vis data quantify the surface coverage of the guest molecule in the film after loading and release, respectively. These findings establish the pH-responsiveness of WP6 as a novel external stimulus for the reversible guest molecule recognition in thin films.

Solvent Dielectricity-Modulated Helical Assembly and Morphologic Transformation of Achiral Surfactant-Inorganic Cluster Ionic Complexes

Ionic complexes comprising single/double chain cationic surfactant and Lindqvist-type polyoxomolybdate anionic cluster were used for controlled self-assembly in organic solutions. In the solvent with low dielectric constant the complexes self-assembled into flat ribbon like lamellar aggregations with an inverse bilayer substructure where the cluster located at the middle. Under the condition of increased dielectric constant, the solvent triggered the formation of helical self-assemblies, which finally transformed from helical ribbons to the flower-like assemblies due to the bilayer becoming excessively twisted. The self-assembled morphology and the substructure were characterized by SEM, TEM, and XRD. The solvent dielectricity-controlled morphologic transformations modulated by the variation of electrostatic interactions between organic cations and inorganic polyanions were demonstrated by ¹H NMR and IR spectra. The strategy in this work represents an effective route in targeting the chirality-directed functionalization of inorganic clusters by combining controllable and helical assemblies of achiral polyoxometalate complexes in one system.

Photosensitive Layer-by-Layer Assemblies Containing Azobenzene Groups: Synthesis and Biomedical Applications

This review provides an overview of the syntheses of photosensitive layer-by-layer (LbL) films and microcapsules modified with azobenzene derivatives and their biomedical applications. Photosensitive LbL films and microcapsules can be prepared by alternate deposition of azobenzene-bearing polymers and counter polymers on the surface of flat substrates and microparticles, respectively. Azobenzene residues in the films and microcapsules exhibit trans-to-cis photoisomerization under UV light, which causes changes in the physical or chemical properties of the LbL assemblies. Therefore, azobenzene-functionalized LbL films and microcapsules have been used for the construction of photosensitive biomedical devices. For instance, cell adhesion on the surface of a solid can be controlled by UV light irradiation by coating the surface with azobenzene-containing LbL films. In another example, the ion permeability of porous materials coated with LbL films can be regulated by UV light irradiation. Furthermore, azobenzene-containing LbL films and microcapsules have been used as carriers for drug delivery systems sensitive to light. UV light irradiation triggers permeability changes in the LbL films and/or decomposition of the microcapsules, which results in the release of encapsulated drugs and proteins.

Surface-Assembled Mechanically Interlocked Architectures

Since the advent of supramolecular chemistry, there has been keen interest in the synthesis of interlocked molecules, given their unique potential to act as receptors, molecular machines and even motors. Despite advances in the complexity of molecular machines that can be synthesised and operated in solution, reports of the operation or even attachment of complex supramolecular systems on solid surfaces are less common. Synthetic challenges and a lack of adequate characterisation techniques to monitor the thermodynamic and kinetic influences governing assembly at the solution-surface interface has slowed progress in this area of research. This Review looks at the developments in the field of covalently assembled interlocked architectures on gold, silica and polymer surfaces, highlighting the differences observed between solution and surface assembly of these unique structures.

Visible-light-responsive polymeric multilayers for trapping and release of cargoes via host–guest interactions

Visible-light-responsive layer-by-layer assembled polyelectrolyte multilayers are fabricated for reversible trapping and release of cargoes via azobenzene/cyclodextrin host–guest interactions.

Light-Triggered Release of Biomolecules from Diamond Nanowire Electrodes

The controlled release of biomolecules from a substrate surface is a challenging task. Photocleavable linkers appear as attractive candidates for light-triggered delivery. We show here the possibility of creating photoactivable diamond nanowire interfaces, from which molecules can be photochemically released upon irradiation at 365 nm for several minutes. The approach is based on the covalent modification of boron-doped diamond nanowires (BDD NWs) with o-nitrobenzyl containing ligands, to which different biomolecules can be attached via amide bond formation. The photodecomposition reaction and the subsequent release of small proteins such as lysozyme or enzymes such as horseradish peroxidase (HRP) are investigated using electrochemical impedance spectroscopy. Using a colorimetric assay, we demonstrate that, while complete cleavage of HRP was achieved upon irradiation for 10 min at 1 W cm(-2), this exposure time resulted in a partial loss of enzymatic activity.