Conjugated polymers based on metalla-aromatic building blocks.

Conjugated polymers usually require strategies to expand the range of wavelengths absorbed and increase solubility. Developing effective strategies to enhance both properties remains challenging. Herein, we report syntheses of conjugated polymers based on a family of metalla-aromatic building blocks via a polymerization method involving consecutive carbyne shuttling processes. The involvement of metal d orbitals in aromatic systems efficiently reduces band gaps and enriches the electron transition pathways of the chromogenic repeat unit. These enable metalla-aromatic conjugated polymers to exhibit broad and strong ultraviolet-visible (UV-Vis) absorption bands. Bulky ligands on the metal suppress π-π stacking of polymer chains and thus increase solubility. These conjugated polymers show robust stability toward light, heat, water, and air. Kinetic studies using NMR experiments and UV-Vis spectroscopy, coupled with the isolation of well-defined model oligomers, revealed the polymerization mechanism.

Engineering of responsive polymer based nano-reactors for facile mass transport and enhanced catalytic degradation of 4-nitrophenol.

Silver nanoparticles with average diameter of 10±3nm were synthesized within the sieves of poly(N-isopropylacrylamide-2-hydroxyethylmethacrylate-acrylic acid) (p(NIPAAm-HEMA-AAc)) polymer microgels. Free radial emulsion polymerization was employed for synthesis of p(NIPAAm-HEMA-AAc) polymer microgels. Silver nanoparticles were introduced within the microgels sphere by in situ reduction method. Microgels and hybrid microgels were characterized by Fourier transform infrared spectroscopy, ultra violet-visible spectroscopy, transmission electron microscopy and dynamic light scattering measurements. Catalytic activity of Ag-p(NIPAAm-HEMA-AAc) hybrid microgels was studied using catalytic reduction of 4-nitrophenol (4-NP) as a model reaction in aqueous media. The influence of sodium borohydride (NaBH4) concentration, catalyst dose and 4-NP concentration on catalytic reduction of 4-NP was investigated. A linear relationship was found between catalyst dose and apparent rate constant (kapp). The mechanism of catalysis by hybrid microgels was explored for further development in this area. The deep analysis of catalytic process reveals that the unique combination of NIPAAm, HEMA and AAc does not only stabilize silver nanoparticles in polymer network but it also enhances the mass transport of hydrophilic substrate like 4-NP from outside to inside the polymer network.

[Functional analysis on sucrose transporters in sweet potato].

Sweet potato is an important food crop that can also be used as an industrial raw material. Sucrose is the main form of long-distance carbohydrate transport in plants, and sucrose transporter (SUT) regulates the transmembrane transport and distribution of sucrose during plant growth and metabolism. Moreover, SUT plays a key role in phloem mediated source-to-sink sucrose transport and physiological activities, supplying sucrose for the sink tissues. In this study, the full-length cDNA sequences of IbSUT62788 and IbSUT81616 were obtained by rapid amplification of cDNA ends (RACE) cloning according to the transcripts of the two SUT coding genes which were differentially expressed in sweet potato storage roots with different starch properties. Phylogenetic analysis was performed to clarify the classification of IbSUT62788 and IbSUT81616. The subcellular localization of IbSUT62788 and IbSUT81616 was determined by transient expression in Nicotiana benthamiana. The function of IbSUT62788 and IbSUT81616 in sucrose and hexose absorption and transport was identified using yeast functional complementarity system. The expression pattern of IbSUT62788 and IbSUT81616 in sweet potato organs were analyzed by real-time fluorescence quantitative PCR (RT-qPCR). Arabidopsis plants heterologous expressing IbSUT62788 and IbSUT81616 genes were obtained using floral dip method. The differences in starch and sugar contents between transgenic and wild-type Arabidopsis were compared. The results showed IbSUT62788 and IbSUT81616 encoded SUT proteins with a length of 505 and 521 amino acids, respectively, and both proteins belonged to the SUT1 subfamily. IbSUT62788 and IbSUT81616 were located in the cell membrane and were able to transport sucrose, glucose and fructose in the yeast system. In addition, IbSUT62788 was also able to transport mannose. The expression of IbSUT62788 was higher in leaves, lateral branches and main stems, and the expression of IbSUT81616 was higher in lateral branches, stems and storage roots. After IbSUT62788 and IbSUT81616 were heterologously expressed in Arabidopsis, the plants grew normally, but the biomass increased. The heterologous expression of IbSUT62788 increased the soluble sugar content, leaf size and 1 000-seed weight of Arabidopsis plants. Heterologous expression of IbSUT81616 increased starch accumulation in leaves and root tips and 1 000-seed weight of seeds, but decreased soluble sugar content. The results obtained in this study showed that IbSUT62788 and IbSUT81616 might be important genes regulating sucrose and sugar content traits in sweet potato. They might carry out physiological functions on cell membrane, such as transmembrane transport of sucrose, sucrose into and out of sink tissue, as well as transport and unloading of sucrose into phloem. The changes in traits result from their heterologous expression in Arabidopsis indicates their potential in improving the yield of other plants or crops. The results obtained in this study provide important information for revealing the functions of IbSUT62788 and IbSUT81616 in starch and glucose metabolism and formation mechanism of important quality traits in sweet potato.

Biocompatible Anisole-Nonlinear PEG Core-Shell Nanogels for High Loading Capacity, Excellent Stability, and Controlled Release of Curcumin.

Curcumin, a nontoxic and cheap natural medicine, has high therapeutic efficacy for many diseases, including diabetes and cancers. Unfortunately, its exceedingly low water-solubility and rapid degradation in the body severely limit its bioavailability. In this work, we prepare a series of biocompatible poly(vinyl anisole)@nonlinear poly(ethylene glycol) (PVAS@PEG) core-shell nanogels with different PEG gel shell thickness to provide high water solubility, good stability, and controllable sustained release of curcumin. The PVAS nanogel core is designed to attract and store curcumin molecules for high drug loading capacity and the hydrophilic nonlinear PEG gel shell is designed to offer water dispersibility and thermo-responsive drug release. The nanogels prepared are monodispersed in a spherical shape with clear core-shell morphology. The size and shell thickness of the nanogels can be easily controlled by changing the core-shell precursor feeding ratios. The optimized PVAS@PEG nanogels display a high curcumin loading capacity of 38.0 wt%. The nanogels can stabilize curcumin from degradation at pH = 7.4 and release it in response to heat within the physiological temperature range. The nanogels can enter cells effectively and exhibit negligible cytotoxicity to both the B16F10 and HL-7702 cells at a concentration up to 2.3 mg/mL. Such designed PVAS@PEG nanogels have great potential to be used for efficient drug delivery.

Insect-Inspired Strategy for Conferring Reversible, High Responsivity on Microgels to Dilute-Source CO2.

We described an insect-inspired strategy for conferring reversible, high responsivity on polymer microgels to dilute-source CO2 (≤5000 ppm in gas mixtures). This is demonstrated on oligo(ethylene oxide)-based microgels that contain tertiary amines on the polymer chains with proper organic small molecular carbonates in the polymer-solvent system. Similar to the synergistic contribution of the CO2 receptor subunits in mosquitoes for CO2 response, laser light scattering and related studies indicated that the CO2-response of the microgels in terms of the volume changes works through the coordination of different functional moieties in the system, making it different from the conventional CO2-response mechanism. While this pushes the lower response threshold of CO2 concentration down to ca. 1000 ppm, this unique strategy can also satisfy the urge to achieve both effective CO2 capture and facile CO2 release, making it possible to couple the detection with the capture and utilization of indoor excess CO2.

Polymer microgels for the stabilization of gold nanoparticles and their application in the catalytic reduction of nitroarenes in aqueous media.

Polymer microgels containing a polystyrene core and poly(N-isopropylmethacrylamide) shell were synthesized in aqueous media following a free radical precipitation polymerization. Au nanoparticles were fabricated into the shell region of the core-shell microgels denoted as P(STY@NIPM) by the in situ reduction of chloroauric acid with sodium borohydride. Various characterization techniques such as transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-visible) and Fourier transform infrared spectroscopy (FTIR) were used for the characterization of Au-P(STY@NIPM). The catalytic potential of Au-P(STY@NIPM) toward the reductive reaction of 4-nitrophenol (4NP) under various reaction conditions was evaluated. The Arrhenius and Eyring parameters for the catalytic reduction of 4NP were determined to explore the process of catalysis. A variety of nitroarenes were converted successfully into their corresponding aminoarenes with good to excellent yields in the presence of the Au-P(STY@NIPM) system using NaBH4 as a reductant. The Au-P(STY@NIPM) system was found to be an efficient and recyclable catalyst with no significant loss in its catalytic efficiency.

Reversible Regulating the Substrate Specificity of Enzymes in Microgels by a Phase Transition in Polymer Networks.

Here, we report a distinct approach for regulating the substrate specificity of enzymes immobilized in microgels by a phase transition in polymer networks. The finding is demonstrated on glucose oxidase that is immobilized in thermoresponsive poly(N-isopropylacrylamide)-based microgels. Laser light scattering and enzymatic oxidation tests indicate that the broadened specificity appears at low temperatures, at which the gel matrix is in the relatively swollen state relative to its state at microgel synthesis temperature; upon heating to the relative higher temperatures, the gel matrix is not able to shrink further that offers a tight space in which the enzyme resides to retain high glucose specificity. It is proposed that polymer phase transition in the gel matrix mainly alter protein gates that control passage of substrates into active sites, making them open or close to a certain extent that enable reversible regulating the substrate specificity. The finding is also observed on bulk gels under a rational design, making it of potential interest in enzymatic biofuel cell applications.

Inorganic nanoparticles for reduction of hexavalent chromium: Physicochemical aspects.

Hexavalent Chromium [Cr(VI)] is a highly carcinogenic and toxic material. It is one of the major environmental contaminants in aquatic system. Its removal from aqueous medium is a subject of current research. Various technologies like adsorption, membrane filtration, solvent extraction, coagulation, biological treatment, ion exchange and chemical reduction for removal of Cr(VI) from waste water have been developed. But chemical reduction of Cr(VI) to Cr(III) has attracted a lot of interest in the past few years because, the reduction product [Cr(III)] is one of the essential nutrients for organisms. Various nanoparticles based systems have been designed for conversion of Cr(VI) into Cr(III) which have not been critically reviewed in literature. This review present recent research progress of classification, designing and characterization of various inorganic nanoparticles reported as catalysts/reductants for rapid conversion of Cr(VI) into Cr(III) in aqueous medium. Kinetics and mechanism of nanoparticles enhanced/catalyzed reduction of Cr(VI) and factors affecting the reduction process have been discussed critically. Personal future insights have been also predicted for further development in this area.

Hybrid Microgels for Catalytic and Photocatalytic Removal of Nitroarenes and Organic Dyes From Aqueous Medium: A Review.

Polymer microgels loaded with inorganic nanoparticles have gained much attention as catalytic systems for reduction of toxic chemicals. Enhanced catalytic properties of hybrid microgels are related to the stimuli responsive nature of microgels and extraordinary stability of nanoparticles within network of polymer microgels. Catalytic properties of hybrid microgels can be tuned very easily by slight variation in environmental conditions. Herein we have reviewed catalytic reduction of toxic chemicals such as nitroarenes and organic dyes in the presence of appropriate hybrid microgel catalytic systems under different operating conditions of reaction. Recent advancements in catalytic behavior of hybrid microgels with special emphasis on their ability to catalytically degrade various toxic chemicals has been presented in this review.

Physicochemical aspects of inorganic nanoparticles stabilized in N-vinyl caprolactam based microgels for various applications.

The vinyl caprolactam (VCL) based microgel system has become the center of great attention due to its versatile properties. Copolymerization of VCL with an ionic monomer imparts pH responsive properties into the microgel system in addition to thermo-sensitivity. Stimuli responsive behavior of VCL-based microgels makes them prospective and appealing candidates for practical applications covering the fields of drug delivery, catalysis and optical devices. In the last few years, VCL-based microgels have been used as microreactors and stabilizers for the synthesis and stabilization of inorganic nanoparticles to obtain hybrid microgels. The present review article provides a summary of the present-day progress of fabrication, stabilization, categorization and analysis of VCL-based microgels and their hybrids with different morphologies. The stimuli responsive properties and applications of VCL-based hybrid microgels have been reviewed critically. The remaining problems which need to be addressed have been pointed out for further advancement in this field.

One-pot HTST synthesis of responsive fluorescent ZnO@apo-enzyme composite microgels for intracellular glucometry.

Responsive fluorescent microgels, that can selectively, reversibly, and rapidly convert the fluctuation in intracellular glucose level into fluorescence signal, have the potential use for intracellular glucometry to promote the understanding of physiology. Herein, we report one-pot synthesis of such a responsive fluorescent composite microgels, which is made of a representative apo-enzyme, apo-glucose oxidase (apo-GOx), interpenetrated in a composite gel network that is comprised of ZnO quantum dots covalently bonded onto crosslinked poly(ethylene glycol) dimethacrylate. The key of this one-pot synthesis is applying a high-temperature short-time heating (HTST) method, so that the naturally dynamic profile of apo-GOx can be maintained and harnessed on the composite microgels to allow the highly selective response to glucose over a glucose concentration range of 0-20 mM. While the composite microgels can undergo volume phase transitions and convert both an increase and a decrease in glucose concentration into fluorescence signal shortly (<1 s), the changes in average hydrodynamic diameter and fluorescence of the composite microgels can be fully reversible even after twenty cycles of adding/removing glucose, indicating a reversible and rapid time response to the glucose concentration variations. With the composite microgels as biosensors, the fluorescence of the composite microgels embedded in the model cancer cells B16F10 can be modulated in response to intracellular glucose level variations, which are derived from a change in glucose concentration in the culture medium by an external supply, or that can be triggered by biochemical reactions (with the ß-galactosidase catalysed hydrolysis of lactose as a model reaction for achieving increased glucose levels, and the GOx catalysed oxidation of glucose for achieving decreased glucose levels).

Salt-Enhanced CO2-Responsiveness of Microgels.

Here, we report a distinct mechanism for harnessing CO2-responsiveness through enhancing CO2 capture ability. The finding is demonstrated on the microgels that are composed of oligo(ethylene glycol) and sulfonate moieties. Laser light scattering studies on dilute aqueous dispersion of these microgels indicated a low CO2-responsivity, which can be significantly enhanced by adding NaCl and other salts. This salt-enhanced CO2-responsiveness of microgels can be elucidated by the antipolyelectrolyte behavior and its superposition of forming cross-links physically with CO2 as an intermediate. Further results of the filtration experiments on microgel translocation through pores suggest the feasibility of the explanation. The finding is also supported by the CO2 capture-release experiments on the dispersion, which can reversibly absorb and desorb CO2.

Observation of Unusual Thermoresponsive Volume Phase Transition Behavior of Cubic Poly(N-isopropylacrylamide) Microgels.

Here, we report the observation of an unusual thermoresponsive volume phase transition behavior of cubic poly(N-isopropylacrylamide) (PNIPAM) microgels. Cubic PNIPAM microgels with a mean edge size of 125 ± 41 nm were synthesized via electrochemical-initiated radical polymerization with a photovoltaic cell as power supply. In turbidity and laser light scattering studies on dilute aqueous dispersions of these cubic microgels, both the light attenuation and hydrodynamic radius variations with temperature reveal an additional transition at about 25.0 °C, besides the widely reported volume phase transition at the PNIPAM LCST that is typically found for (quasi-)spherical microgels. This unusual thermoresponsive volume phase transition behavior of the cubic microgels can be elucidated by using a core-corona model, with the contribution from each part varying at different temperatures. The finding is also checked by thermal analysis.

Tuning catalysis of boronic acids in microgels by in situ reversible structural variations.

The catalysis of boronic acids immobilized in polymer microgels can be modulated by bubbling with N2/CO2 gas, and in some cases by adding glucose, making their catalytic activity comparable or even superior to that of the corresponding free boronic acid monomers homogeneously dispersed in solutions and, more importantly, making these boronic-acid-containing polymer microgels able to catalyze alternate reactions that may extend the usefulness. This enhanced catalytic function of these boronic-acid-containing microgels as organoboron acid catalysts is plausibly achieved via in situ reversibly structural variations. Kinetic studies have been carried out on the model boronic-acid-catalyzed aza-Michael addition, aldol, amidation, and [4 + 2] cycloaddition reactions in order to better understand the catalytic process.

Synthesis and characterization of poly(N-isopropylmethacrylamide-acrylic acid) smart polymer microgels for adsorptive extraction of copper(II) and cobalt(II) from aqueous medium: kinetic and thermodynamic aspects.

Extraction of toxic heavy metal ions from aqueous medium using poly(N-isopropylmethacrylamide-acrylic acid) (P(NiPmA-Ac)) microgels as adsorbent has been investigated in present study. P(NiPmA-Ac) microgel particles were prepared by free radical precipitation polymerization in aqueous medium. Morphology and size of the prepared microgel particles was investigated by transmission electron microscopy (TEM). The Fourier transform infrared (FT-IR) analysis of pure and metal ion-loaded microgel particles was performed to confirm the presence of various functionalities of microgel particles and their interaction with metal ions extracted from aqueous medium. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to investigate the thermal stability and thermal behavior of pure and metal ion-loaded microgel particles. Contents of metal ions loaded into microgel particles were determined by TGA analysis. It was observed that P(NiPmA-Ac) particles have a potential to extract Cu2+ and Co2+ ions from aqueous medium. The Freundlich adsorption isotherm model best interprets the adsorption process as compared with the Langmuir model. Value of R2 according to the Freundlich adsorption isotherm was found to be 0.994 and 0.993 for Cu2+ and Co2+ ions, respectively. Adsorption process was followed by pseudo second order kinetics for Cu2+ and Co2+ ions with R2 values of 0.999 for both metal ions. Thermodynamic study showed that adsorption process was spontaneous, feasible, and endothermic in nature. Entropy was decreased at adsorbate-adsorbent interface during adsorption process. Adsorbent was recycled and reused for removal of Cu2+ ions, and adsorption efficiency was found to be maintained up to three cycles. Microgel particles also have ability to extract Cu2+ ions efficiently from electroplating wastewater. Graphical abstract.

Fundamentals and applications of acrylamide based microgels and their hybrids: a review.

Acrylamide based microgels have gained a lot of attention in the last three decades due to their potential applications in various fields based on their responsive behavior and chemical stability. In this article, the synthesis, properties, and applications of poly(N-isopropylacrylamide-co-acrylamide) [P(NIPAM-Am)] microgels and P(NIPAM-Am) microgels having an additional ionic moiety in their network [P(NIPAM-Am-IM)] are reviewed. These microgels may swell/deswell reversibly with slight changes in environmental conditions such as change in temperature/pH/ionic strength etc. of the medium. This responsive behavior makes the microgels a potential candidate for use in the field of nanotechnology, drug delivery, sensing and catalysis. A critical overview of the recent research progress in this area along with future perspectives is presented. The discussion is concluded with suggested possible future studies for further development in this area.

Facile synthesis of silver nanoparticles in a crosslinked polymeric system by in situ reduction method for catalytic reduction of 4-nitroaniline.

In this study, poly(N-isopropylmethacrylamide-co-methacrylic acid) microgels prepared by free radical precipitation polymerization were used as micro-reactors for the synthesis and stabilization of silver nanoparticles. UV-Visible spectroscopy, Transmission Electron Microscopy and Fourier-transform infrared spectroscopy were used to characterize both pure and hybrid microgels. The catalytic reduction of 4-nitroaniline was carried out in the presence of hybrid microgels to test their catalytic activity, and the catalysis mechanism was explored by varying the concentrations of reacting species like 4-nitroaniline and NaBH4, as well as the dose of the catalyst. The kinetic data indicates that this reaction follows pseudo-first order. The variation in apparent rate constant (kapp) with respect to NaBH4 concentration also discloses it to be the following Langmuir-Hinshelwood mechanism. The relationship between catalyst concentration and apparent rate constant was found to be increasing in a linear manner. The data obtained also confirmed that silver nanoparticles loaded microgels have the potential to be used as an excellent micro-reactor for selective reduction of 4-nitroaniline to p-phenylenediamine.

Cylindrical NIR-Responsive Metallopolymer Containing Möbius Metalla-aromatics.

Metalla-aromatic complexes are very stable and excellent light-absorbing compounds, owing to their highly conjugated frameworks. The metallopolymers containing metalla-aromatic substructures consist of a new type of functional polymer, because they exhibit characteristics of both metalla-aromatic and polymeric units. Herein, we reported a corn-like cylindrical metallopolymer, prepared from the controlled polymerization of N-isopropylacrylamide (NIPAM) by a polyrotaxane-based macroinitiator, followed by postpolymerization modification with a photothermal metalla-aromatic complex. The corn-like shape of this metallopolymer was confirmed by transmission electron microscopy (TEM). Combining the photothermal effect of the metalla-aromatic unit and the thermosensitive property of PNIPAM, the corn-like metallopolymer exhibits a NIR-responsive behavior and represents a new smart material.

Propeller-like multicomponent microstructures: Self-assemblies of nanoparticles of poly(vinyl alcohol)-coated Ag and/or Cu2O.

Novel propeller-like multicomponent microstructures, which are actually self-assemblies of nanoparticles of poly(vinyl alcohol) (PVA)-coated Ag and/or Cu2O, were synthesized in aqueous solution of amphiphilic polyvinylacetone (PVKA) (ketalization degree D(H) = 0.549), via one-step in situ reduction of Ag+ and Cu2+ under gamma-ray irradiation, utilizing the low hydrolysis rate of PVKA in the dilute acidic solution. Herein, PVA chains are obtained from hydrolyzed PVKA. The reaction mechanism and the formation mechanism are proposed. The room temperature photoluminescence spectrum has also been applied to explore the optical property.

Immobilization of sulfur in microgels for lithium-sulfur battery.

Immobilization of sulfur in microgels is achieved via free radical polymerization of commercial poly(ethylene glycol) dimethacrylate in the solution of sulfur-terminated poly(3-oligo(ethylene oxide)4-thiophene), a copolymer prepared by the inverse vulcanization of S8 with allyl-terminated poly(3-oligo(ethylene oxide)4-thiophene). This microgelation leads to enhanced Li-S battery performance over the sulfur-terminated polymer.