Synthesis, Photoresponsive Behavior, and Self-Assembly of Poly(acrylic acid)-Based Azo Polyelectrolytes

Polymeric Micro/Nanocarriers and Motors for Cargo Transport and Phototriggered Delivery

Smart polymer-based micro/nanoassemblies have emerged as a promising alternative for transporting and delivering a myriad of cargo. Cargo encapsulation into (or linked to) polymeric micro/nanocarrier (PC) strategies may help to conserve cargo activity and functionality when interacting with its surroundings in its journey to the target. PCs for cargo phototriggering allow for excellent spatiotemporal control via irradiation as an external stimulus, thus regulating the delivery kinetics of cargo and potentially increasing its therapeutic effect. Micromotors based on PCs offer an accelerated cargo-medium interaction for biomedical, environmental, and many other applications. This review collects the recent achievements in PC development based on nanomicelles, nanospheres, and nanopolymersomes, among others, with enhanced properties to increase cargo protection and cargo release efficiency triggered by ultraviolet (UV) and near-infrared (NIR) irradiation, including light-stimulated polymeric micromotors for propulsion, cargo transport, biosensing, and photo-thermal therapy. We emphasize the challenges of positioning PCs as drug delivery systems, as well as the outstanding opportunities of light-stimulated polymeric micromotors for practical applications.

Photosensitive nanocarriers for specific delivery of cargo into cells

Nanoencapsulation is a rapidly expanding technology to enclose cargo into inert material at the nanoscale size, which protects cargo from degradation, improves bioavailability and allows for controlled release. Encapsulation of drugs into functional nanocarriers enhances their specificity, targeting ability, efficiency, and effectiveness. Functionality may come from cell targeting biomolecules that direct nanocarriers to a specific cell or tissue. Delivery is usually mediated by diffusion and erosion mechanisms, but in some cases, this is not sufficient to reach the expected therapeutic effects. This work reports on the development of a new photoresponsive polymeric nanocarrier (PNc)-based nanobioconjugate (NBc) for specific photo-delivery of cargo into target cells. We readily synthesized the PNcs by modification of chitosan with ultraviolet (UV)-photosensitive azobenzene molecules, with Nile red and dofetilide as cargo models to prove the encapsulation/release concept. The PNcs were further functionalized with the cardiac targeting transmembrane peptide and efficiently internalized into cardiomyocytes, as a cell line model. Intracellular cargo-release was dramatically accelerated upon a very short UV-light irradiation time. Delivering cargo in a time-space controlled fashion by means of NBcs is a promising strategy to increase the intracellular cargo concentration, to decrease dose and cargo side effects, thereby improving the effectiveness of a therapeutic regime.

Azopolymer based nanoparticles for phototriggered drug delivery

Controlled release by stimulus-responsive nanoparticles is oriented to increase the specificity of drug delivery, to improve the therapy effectiveness and minimizing side effects. This work presents the synthesis of photosensitive-polymeric nanoparticles as a potential system for localized drug delivery. First, the photoisomerizable amphiphilic-copolymer poly2-[4-phenylazophenoxy]ethyl acrylate-co-acrylic acid (PPAPE), was synthesized. Then, PPAPE was employed to prepare micellar nanoparticles by the nanoprecipitation method. Characterizations of the polymer were performed by proton nuclear magnetic resonance, X-ray photoelectron spectroscopy and FTIR spectroscopy. The morphology of the nanoparticles was analyzed by dynamic light scattering and transmission electron microscopy. Also, photostimulation response was confirmed by UV-VIS spectroscopy. Results indicate that the obtained photoresponsive nanoparticles have the size and photoisomerization necessary to perform the specific release of drugs.

Azobenzene-based solar thermal fuels: design, properties, and applications

Development of renewable energy technologies has been a significant area of research amongst scientists with the aim of attaining a sustainable world society. Solar thermal fuels that can capture, convert, store, and release solar energy in the form of heat through reversible photoisomerization of molecular photoswitches such as azobenzene derivatives are currently in the limelight of research. Herein, we provide a state-of-the-art account on the recent advancements in solar thermal fuels based on azobenzene photoswitches. We begin with an overview on the importance of azobenzene-based solar thermal fuels and their fundamentals. Then, we highlight the recent advances in diverse azobenzene materials for solar thermal fuels such as pure azobenzene derivatives, nanocarbon-templated azobenzene, and polymer-templated azobenzene. The basic design concepts of these advanced solar energy storage materials are discussed, and their promising applications are highlighted. We then introduce the recent endeavors in the molecular design of azobenzene derivatives toward efficient solar thermal fuels, and conclude with new perspectives on the future scope, opportunities and challenges. It is expected that continuous pioneering research involving scientists and engineers from diverse technological backgrounds could trigger the rapid advancement of this important interdisciplinary field, which embraces chemistry, physics, engineering, nanoscience, nanotechnology, materials science, polymer science, etc.

Facile preparation and dual responsive behaviors of starch-based hydrogel containing azo and carboxylic groups

Starch-based hydrogel containing azo group (SHA) was prepared through radical cross-linking reaction among starch- and PVA-based macromonomers, acrylic acid (AA) and 4-acryloyoxyazobenzene (AHAB). AHAB was prepared through an acylation reaction between acryloyl chloride and 4-hydroxyazobenzene (p-HAB), which was obtained by the diazo coupling reaction between aniline and phenol. The structure of SHA was confirmed with Fourier transform infrared spectrometer, thermogravimetric analysis and UV-Visible spectroscopy. SHA displayed pH-sensitive swelling in buffer saline. SHA film also exhibited a reversible trans-cis-trans photoisomerization behavior when they were subjected to alternative UV and visible light irradiation or dark storage. The dual-responsive characteristic was easily to be tailored via varying the initial amount of AHAB or AA.

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.

Photoswitchable azobenzene-appended iridium(iii) complexes

The use of aliphatic-bridging units to append azobenzene fragments on triscyclometalated Ir(iii) complexes permits the construction of photoswitchable organometallics.

Photoresponsive block copolymer: synthesis, characterization, and surface activity control

Amphiphilic block copolymers bearing chromophores are used to achieve photoresponses upon exposure to suitable light, which alter molecular properties, but the photostimulus surface activity control of amphiphilic block copolymers remains to be elucidated. In this work, a series of novel amphiphilic block copolymers consisting of a carboxymethyl betaine monomer (called GLBT) and 4-ethoxy-4'-methacrylamide (EMAAB) with different block ratios have been synthesized using a reversible addition-fragmentation chain-transfer (RAFT) polymerization process. Copolymers were observed to be self-assembled in the aqueous solution above a critical micelle concentration, which was determined by static light scattering measurements and formed vesicles of 120-170 nm in diameter, at different pH values. Copolymers were found to be surface-active at pH 7 but exhibited non-surface activity at acidic and alkaline pH values. After being irradiated with 360 nm UV light, copolymers showed a significant photoresponse both at the surface and in bulk solution as a result of the photoinduced isomerization of azochromophores. The surface property of copolymers was significantly affected by UV irradiation at pH 7, and block copolymers became non-surface-active. The bulk properties changed considerably upon UV exposure where polymer vesicles transformed to micelles as a result of the polarity difference between two azo isomers (cis and trans isomers). All of these transitions were found to be reversible. A new method to control the surface active/nonactive and vesicle/micelle transitions by light and pH has been established by introducing an azobenzene chromophore and GLBT into amphiphlic diblock copolymers.

RAFT copolymerization of acid chloride-containing monomers

Controlled radical copolymerization of acid chloride-containing monomers via RAFT enabled direct synthesis of well-defined reactive polymers and their block polymers which can be readily functionalized further by postpolymerization modification.

Third-order nonlinear optical properties of self-assembled thin films containing tetracarboxylic copper phthalocyanine

Films with alternating layers containing anionic tetracarboxylic copper phthalocyanine [ CuPc(COONa)4 ] and cationic polydiallydimethylammonium chloride (PDDA) were fabricated by electrostatic self-assembled layer-by-layer (LBL) technique. The delicate structure of the film was characterized by a series of techniques. The third-order nonlinear optical properties of the film were measured by the Z-scan technique with laser duration of 4 ns and 21 ps at the wavelength of 532 nm. The film exhibited excellent nonlinear absorption and self-focusing effect. The second-order molecular hyperpolarizability γ value of the film was much larger than that of CuPc(COONa)4 aqueous solution under the irradiation of whether ns or ps pulses. A series of damage experiments of the film for the intense laser pulses were conducted to prove the reliability of the experimental results under the conditions.

Self-assembled graphene/azo polyelectrolyte multilayer film and its application in electrochemical energy storage device

Graphene/azo polyelectrolyte multilayer films were fabricated through electrostatic layer-by-layer (LbL) self-assembly, and their performance as electrochemical capacitor electrode was investigated. Cationic azo polyelectrolyte (QP4VP-co-PCN) was synthesized through radical polymerization, postpolymerization azo coupling reaction, and quaternization. Negatively charged graphene nanosheets were prepared by a chemically modified method. The LbL films were obtained by alternately dipping a piece of the pretreated substrates in the QP4VP-co-PCN and nanosheet solutions. The processes were repeated until the films with required numbers of bilayers were obtained. The self-assembly and multilayer surface morphology were characterized by UV-vis spectroscopy, AFM, SEM, and TEM. The performance of the LbL films as electrochemical capacitor electrode was estimated using cyclic voltammetry. Results show that the graphene nanosheets are densely packed in the multilayers and form random graphene network. The azo polyelectrolyte cohesively interacts with the nanosheets in the multilayer structure, which prevents agglomeration of graphene nanosheets. The sheet resistance of the LbL films decreases with the increase of the layer numbers and reaches the stationary value of 1.0 × 10(6) Ω/square for the film with 15 bilayers. At a scanning rate of 50 mV/s, the LbL film with 9 bilayers shows a gravimetric specific capacitance of 49 F/g in 1.0 M Na(2)SO(4) solution. The LbL films developed in this work could be a promising type of the electrode materials for electric energy storage devices.

Synthesis and characterization of new optically active poly(azo-ester-imide)s via interfacial polycondensation

N,N'-Pyromelliticdiimido-di-L-amino acids (1a-1d) were prepared from the reaction of pyromellitic dianhydride with the corresponding L-amino acids in a solution of glacial acetic acid/pyridine (3:2) at refluxing temperature. 4,4'-sulfonyl bis(4,1-phenylene) bis(diazene-2,1-diyl) diphenol, 4,4'-oxy bis(4,1-phenylene) bis(diazene-2,1-diyl) diphenol and 4,4'-methylene bis(4,1-phenylene) bis(diazene-2,1-diyl) diphenol, were prepared from 4,4'-diamino diphenyl sulfone, 4,4'-diamino diphenyl ether, 4,4'-diamino diphenyl methane, sodium nitrite and phenol following the general procedure of diazo coupling. Interfacial polycondensation method was used to prepare the corresponding poly(azo-ester-imid)s (PAEI(1-12)) in biphasic solution of water/dichloromethane. The resulting polymers (PAEIs) have been obtained in high yields having good inherent viscosities (0.32-0.57 dl g(-1)), optical activities and thermal stabilities.

Surface organization, light-driven surface changes, and stability of semifluorinated azobenzene polymers

A series of polymers with 4-perfluoroalkyl-modified azobenzene side groups was investigated for its light-induced changes in surface properties. The ultraviolet (UV) light activated trans to cis isomerization of the azobenzene group, and the influence of molecular order and orientation on this process were studied using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and water contact angle measurements. Light-induced molecular reorganization in the near-surface region was studied by NEXAFS using in situ UV irradiation of polymer thin films. Differential scanning calorimetry and wide-angle X-ray scattering studies showed that sufficiently long fluoroalkyl groups formed well-ordered smectic mesophases in the bulk, as well as on the surface, which was evidenced by NEXAFS. The disruption of mesogen packing by photoisomerization was found to be influenced by the fluoroalkyl segment length. Surfaces with perfluorohexyl and perfluorooctyl groups that showed high orientational order were also highly resistant to light-induced changes. In such cases, the trans-cis isomerization resulted in greater lowering of the azobenzene phenyl ring order parameters than the perfluoroalkyl order parameters. UV exposure caused reorientation of the phenyl rings of the azobenzene group, but the terminal perfluoroalkyl segments remained more or less ordered.

Analysis of the Formation Mechanism for Thermoresponsive-Type Coacervate with Functional Copolymers Consisting of N-Isopropylacrylamide and 2-Hydroxyisopropylacrylamide

We now report the formation mechanism of the thermoresponsive-type coacervate with the novel functional temperature-sensitive polymer, poly(N-isopropylacrylamide-co-2-hydroxyisopropylacrylamide) (poly(NIPAAm-co-HIPAAm)), synthesized in our laboratory. The effects of introducing the hydrophilic comonomer (HIPAAm) into the copolymer chains and adding salts on the behaviors of the coacervate droplets induced in the poly(NIPAAm-co-HIPAAm) aqueous solutions were investigated. Not only the particle sizes of the coacervate droplets but also the cloud points of the copolymer solutions could be modulated by the HIPAAm content incorporated in the copolymers. Moreover, the particle sizes of the coacervate droplets were also changed by adding salts. Namely, the particle sizes increased with the decreasing HIPAAm composition and increasing NaCl concentration. In addition, the 1H NMR and differential scanning calorimetric measurements suggested that as the HIPAAm content decreased or NaCl concentration increased, dehydration of the copolymers induced in the phase transition and/or separation became much easier. Therefore, on the basis of the findings obtained from these measurements, we determined that the particle sizes of the coacervate droplets induced in the temperature-sensitive polymers increased as the number of the water molecules, which are dissociated from the polymeric chains during the phase transition and/or separation, increased. Besides, to examine the separation of the model solutes, the aqueous two-phase separation with the coacervate droplets of poly(NIPAAm-co-HIPAAm) was carried out. The partitions of Methyl Orange as a model solute under both acidic (pH 2) and basic (pH 12) conditions were performed. The amount of Methyl Orange partitioned into the coacervate droplets at pH 12 is much greater than that at pH 2, which indicated that the coacervate droplets could recognize a slight difference in the polarity or structure between the model solutes.