Dopamine-Initiated Photopolymerization for a Versatile Catechol-Functionalized Hydrogel.

Semi-convertible Hydrogel Enabled Photoresponsive Lubrication

Photo-sensitive polyoxometalate-based hybrid materials have attracted much attention in recent years due to their unique photo-responsive properties. Here we represent a new type of photo-sensitive polyoxometalate-based hybrid by covalently tethering chalcone moieties onto Anderson cluster. Various techniques including nuclear magnetic resonance (NMR), Fourier transform infrared spectoscopy (FT-IR), electrospray ionization-mass spectrometry (ESI-MS) and single-crystal X-ray diffraction have been utilized to characterize the structure and composition of the resultant hybrid. The 1H and 13C NMR spectra show well resolved peaks that can be unambiguously assigned and are in good accordance with the molecular structure. Characteristic stretching vibrations of MO and Mo–O–Mo bonds can be found at 940 and 668 cm - 1 in the FT-IR spectrum respectively, whilst the chalcone moieties give stretching bands at 1665/1593 cm–1 (C=O–C=C) and 1568/1511 cm - 1 (C=C). The ESI-MS spectrum of the hybrid provides us more convincing structural in- formations. For instance, the isotopic peaks observed at m / z =2167.81 can be clearly ascribed to the anionic fragment of {[( n -C4H9)4N]2[(MnMo6O24){(CH2)3CNHCOCH2OC6H4C2H2COC6H5}2]} - , suggesting the successful modification of Anderson cluster with chalcone molecules. Single-crystal X-ray diffraction analysis reveals that the hybrid crystallizes in a mono-clinic system with a C2 / c space group, where organic chalcone moieties are covalently bonded to the Anderson cluster via μ 3-oxo bridging ligands. The photo-polymerization properties of the hybrid have been investigated in detail using UV-Vis spectroscopy, 1H NMR, and gel permeation chromatography. For example, when irradiated at UV light of 365 nm the hybrid undergoes a [2 π +2 π ] cycloaddition reaction, leading to an absorbance decrease at wavelength of 332 nm in the UV-Vis spectrum. Meanwhile, a new absorbance peak attributed to the generated cyclobutane structure is observed at 245 nm. This process gives a total photo-polymerization conversion of 37.45%, and is found able to restore when exposed to UV light of 254 nm. After five cycles of alternative irradiation at 365 and 254 nm, the amount of the hybrid monomer can still maintain at 85% of the original ones. The 1H NMR spectrum of the hybrid also shows significant changes when irradiated at UV light of 365 nm. Signals of the unsaturated carbonyl groups of the chalcone moieties at δ 7.83 and 7.73 shift to high field after irradiation, and give corresponding cyclobutane signal at δ 4.80. These results are in accordance with the results of UV-Vis spectroscopy. Weight-average molecular weight of the resulting hybrid polymer is 9.78×105 g/mol as demonstrated by the gel permeation chromatography analysis. This work may provide a new pathway for the fabrication and functional application of novel photo-sensitive polyoxometalate-based hybrids.

Nonplatinum metal complexes of [Pd(L1)Cl2] (C1), [Rh(L1)Cl3(DMSO)] (C2), [Pd(L2)Cl2] (C3), and [Rh(L3)Cl3(DMSO)] (C4) with isoquinoline derivatives have been prepared and characterized. C1–C4 exhib...

Semiquinone (SQ) radicals play a critical role in the long-lasting UV-blocking application of lignin, while their origin and stable structure are unclear. Here, the organosolv lignin extracted from poplar (OL-P) is self-assembled into normal micelles (LNM) with more phenolic hydroxyl groups on the surface, and reverse micelles (LRM) with more methoxyl groups on the surface. After 12h UV irradiation, the SQ radical contents in LNM and LRM increase 33% and 78% respectively. The performance of LNM based sunscreen keeps upswinging due to radical stabilization of phenolic hydroxyl groups. LRM based sunscreen experiences a gradual decrease after reaching maximum UV absorbance due to the quick generation and over oxidation of SQ radicals. Density functional theory (DFT) simulations reveal that methoxyl groups in OL-P has bigger bond length and smaller bond dissociation enthalpy than phenolic hydroxyl groups, and are easy to form SQ radicals. The Gibbs free energy (ΔG) needed for SQ-quinone transformation is above 26.10kcalmol.-1, while that for SQ-hydroquinone transformation is below -66.78kcalmol.-1. Hydroquinone is the stable structure of SQ radicals. This work discloses the origin and stable structure of SQ radicals in lignin under UV irradiation, and provides an important guidance for its long-lasting UV-blocking application.

Degradation of polylactide composites under UV irradiation at 254 nm

Insights of the controlled release effect of functional group on permeation enhancers' enhancement capacity: A study on interaction mechanism and skin barrier function.

In this paper, the bio-based raw material erythritol was used to introduce an acetal structure into the benzoxazine resins. The benzoxazine-based resins containing an erythritol acetal structure could be degraded in an acidic solution and were environmentally friendly thermosetting resins. Compounds and resins were characterized by 1H nuclear magnetic resonance (1H NMR) and Fourier-transform infrared (FT-IR) analyses, and melting points were studied by a differential scanning calorimeter (DSC); the molecular weight was analyzed by gel permeation chromatography (GPC). The dynamic mechanical properties and thermal stability of polybenzoxazine resins were studied by dynamic mechanical thermal analysis (DMTA) and a thermogravimetric analyzer (TGA), respectively. The thermal aging, wet-heat resistance, and degradation properties of polybenzoxazine resins were tested. The results showed that the polybenzoxazine resins synthesized in this paper had good thermal-oxidative aging, and wet-heat resistance and could be completely degraded in an acidic solution (55 °C DMF: water: 1 mol/L hydrochloric acid solution = 5:2:4 (v/v/v)).

Coumarin-containing styrene monomer (CS) was designed and synthesized, which could be used together with styrene (St) and maleic anhydride (MA) to synthesize the photosensitive amphiphilic alternating SMA terpolymer poly(styrene/coumarin-containing styrene-alt-maleic anhydride) (P(St/CS-alt-MA)) via free radical copolymerization. Then a new photosensitive amphiphilic comblike terpolymer (P(St/CS-alt-MAA8)) with long alkyl side chains was obtained by the functional amidolysis reaction between succinic anhydride unit and octylamine, and its structure was characterized by gel permeation in chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), and 1H nuclear magnetic resonance (1H NMR). It was found that the comblike polymer could aggregate by the photo-dimerization of the coumarin pendants under UV irradiation (300 nm), and form nanoscale micelles by self-assembly in selective solvent. The micelles could be modified by the ionization of carboxylic acid groups with NaOH. Pyrene loading experiment and dynamic laser scattering (DLS) showed that the micelle diameter and the loading capacity of precrosslinked polymer were bigger than those of non-crosslinked polymer. Micelles reformed after ionization, which made the hydrophobic area denser and the micelle diameter smaller, while the loading capacity also increased.

A series of azo-based diblock copolymers (DBCs) with various compositions were successfully synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization in anisole with PCAEMA-CTA (macro-CTA), DOPAM (new acrylamide monomer) and AIBN (initiator). Kinetic studies on diblock copolymerization manifested a controlled/living manner with good molecular weight control. Structures and properties of monomers and DBCs were determined by 1 H nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). Liquid crystalline (LC) phases and morphological properties were investigated using optical polarizing microscope (OPM), atomic force microscopy (AFM), scanning electron microscopy (SEM) and small-angle X-ray scattering (SAXS). Experimental results demonstrated that the prepared PCAEMA-CTA and DBCs possessed low polydispersity index (≤1.37). All DBCs revealed sharp endothermic transition peaks corresponding to the smectic-to-nematic phase. DBCs with high azo contents showed batonnet textures of the smectic phase whereas DBCs of low azo segments displayed threaded textures of the nematic phase. DBC with 49 wt% of azo side-chains generated a lamellar compared to DBCs with low azo block (≤41 wt%) or non-azo block (≤38 wt%) which produced hexagonal-type nanostructures. In addition, all DBCs exhibited reversible trans-cis photoisomerization behavior under UV irradiation and dark storage at different intervals of time.

Because of its electricallyconducting properties combined withexcellent thermal stability and transparency throughout the visiblespectrum, tin oxide (SnO2) is extremely attractive as atransparent conducting material for applications in low-emission windowcoatings and solar cells, as well as in lithium-ion batteries andgas sensors. It is also an important catalyst and catalyst supportfor oxidation reactions. Here, we describe a novel nonaqueous sol–gelsynthesis approach to produce tin oxide nanoparticles (NPs) with alow NP size dispersion. The success of this method lies in the nonhydrolyticpathway that involves the reaction between tin chloride and an oxygendonor, 1-hexanol, without the need for a surfactant or subsequentthermal treatment. This one-pot procedure is carried out at relativelylow temperatures in the 160–260 °C range, compatible withcoating processes on flexible plastic supports. The NP size distribution,shape, and dislocation density were studied by powder X-ray powderdiffraction analyzed using the method of whole powder pattern modeling,as well as high-resolution transmission electron microscopy. The SnO2 NPs were determined to have particle sizes between 3.4 and7.7 nm. The reaction products were characterized using liquid-state 13C and 1H nuclear magnetic resonance (NMR) thatconfirmed the formation of dihexyl ether and 1-chlorohexane. The NPswere studied by a combination of 13C, 1H, and 119Sn solid-state NMR as well as Fourier transform infrared(FTIR) and Raman spectroscopy. The 13C SSNMR, FTIR, andRaman data showed the presence of organic species derived from the1-hexanol reactant remaining within the samples. The optical absorption,studied using UV–visible spectroscopy, indicated that the bandgap (Eg) shifted systematically to lowerenergy with decreasing NP sizes. This unusual result could be dueto mechanical strains present within the smallest NPs perhaps associatedwith the organic ligands decorating the NP surface. As the size increased,we observed a correlation with an increased density of screw dislocationspresent within the NPs that could indicate relaxation of the stress.We suggest that this could provide a useful method for band gap controlwithin SnO2 NPs in the absence of chemical dopants.

Carotenoids are a class of biobased conjugated molecules that bear a resemblance to the substructure of polyacetylene, a well-known conductive but insoluble polymer. Solubility is an important physical attribute for processing materials using different techniques. To impart solubility in polymers, alkyl side chains are often included in the molecular design. While these design strategies are well explored in conjugated systems, they have not been implemented with carotenoids as a building block in polymers. Here, we show a series of carotenoid-based polymers with varying side chain lengths to tune solubility. Using carotenoid and p-phenylenediamine-based monomers, degradable and biobased poly(azomethine)s were synthesized via imine polycondensation. Maximum solubilities corresponding to the varying alkyl chain lengths were quantitatively determined by ultraviolet-visible (UV-vis) absorption spectroscopy. Since carotenoids are biobased with known degradation products, the effect of acidic and artificial sunlight-promoted degradation was systematically investigated using UV-vis spectroscopy, 1H nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, gel permeation chromatography (GPC), and high-resolution mass spectroscopy (HRMS). Our polymer system was found to have two modes of on-demand degradation, with acid hydrolysis accelerating the rate of polymer degradation and artificial sunlight generating additional degradation products. This work highlights carotenoid monomers as viable candidates in the design of biobased, degradable, and conjugated polymers.

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Preparation, characterization and drug release behavior of polyion complex micelles

It was previously reported that low doses, but not high doses, of UV trigger the Skp2-mediated proteasomal degradation of the cyclin-dependent kinase inhibitor p21 in mammalian cells. Here we show that both UV-C and UV-B lead to decrease of p21 protein, but not mRNA, level in a dose-dependent fashion in all of six human cell lines and five mouse cell lines tested. Also, high doses of UV reduce the half-life of p21. High doses, but not low doses, of UV induced p21 degradation in both skp2-proficient and -deficient murine embryonic fibroblast cells. UV-induced p21 reduction was rescued by proteasome inhibitors in all human and mouse cell lines tested. Neither a caspase inhibitor nor small interfering RNA against skp2 had an effect on the UV-induced p21 decrease, suggesting that this p21 degradation pathway may not involve caspases, or Skp2. Finally, UV did not induce p21 ubiquitination but still induced its degradation when the E1-activating enzyme was inactivated in an E1 temperature-sensitive mouse embryonic fibroblast cell line. Altogether, these results demonstrate that UV induces p21 degradation through an Skp2 and ubiquitin-independent pathway.

c-Jun is a component of the transcription factor AP-1, which is activated by a wide variety of extracellular stimuli. The regulation of c-Jun is complex and involves both increases in the levels of c-Jun protein as well as phosphorylation of specific serines (63 and 73) by Jun N-terminal kinase (JNK). We have used fibroblasts derived from c-Jun null embryos to define the role of c-Jun in two separate processes: cell growth and apoptosis. We show that in fibroblasts, c-Jun is required for progression through the G1 phase of the cell cycle; c-Jun-mediated G1 progression occurs by a mechanism that involves direct transcriptional control of the cyclin D1 gene, establishing a molecular link between growth factor signaling and cell cycle regulators. In addition, c-Jun protects cells from UV-induced cell death and cooperates with NF-kappaB to prevent apoptosis induced by tumor necrosis factor alpha (TNFalpha). c-Jun mediated G1 progression is independent of phosphorylation of serines 63/73; however, protection from apoptosis in response to UV, a potent inducer of JNK/SAP kinase activity, requires serines 63/73. The results reveal critical roles for c-Jun in two different cellular processes and show that different extracellular stimuli can target c-Jun by distinct biochemical mechanisms.