Lijian Liu

Wuhan University, Wu-han-shih, Hubei, China

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Publications (40)106.9 Total impact

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    ABSTRACT: Kinetic studies of carbene polymerization of ethyl diazoacetate (EDA) by palladium (Pd) or rhodium (Rh) catalysts were investigated by real-time fourier transform infrared (FTIR) spectroscopy. Both (L-prolinate)RhI(1,5-cyclooctadiene) and (L-prolinate)RhI(2,5-norbornadiene) mediated EDA polymerization were proved as first order reactions, suggesting that the formation of “Rh-carbenoid” is the rate determining step. The activation energy (11.24 kJ•mol−1) of the polymerization of “carbenes” generated from EDA with (L-prolinate)RhI(1,5-cyclooctadiene) as the catalyst was calculated from kinetic data via Arrhenius equation. On the other hand, the polymerizations of EDA catalyzed by three kinds of Pd-catalysts were revealed as zero order reactions, suggesting that the rate determining step involves the formation of EDA-Pd transition state complex through a coordinated step. Refilling more EDA to the (bis(acetonitrile)dichloropalladium)-mediated carbene polymerization system did not change the reaction order. The rate constant increases gradually with the enlargement of the dosage of the catalyst and decreases with the cycle-index, which proves the formation of “EDA-Pd transition state complex” and the propagating species with Pd-C bonds at the end of the polymer chain.
    RSC Advances 08/2014; · 3.71 Impact Factor
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    ABSTRACT: Pseudopeptide oligomers as newly developing fluorescent macromolecules are of significant importance and fairly attractive in bioimaging of living cells. We report that a type of efficient fluorescent pseudopeptide oligo(3,4,5-triethoxycarbonyl-2-pyrazoline) is prepared by the novel cyclo-polycondensation of 3,4,5-triethoxycarbonyl-2-pyrazoline that is a weakly-fluorescent chromophore. The pseudopeptide oligomer exhibits a strong red-shift and remarkable fluorescence enhancement compared with the monomer 2-pyrazoline and images living cells in good quality, even though it only consists of fewer than 70 glycine residues whereas for the famous green fluorescent protein (GFP) the amount of the various natural amino acid residues is 238. Oligo(3,4,5-triethoxycarbonyl-2-pyrazoline) is a GFP-mimetic but structurally-simplified fluorescent pseudopeptide with simple chemistry, generated from the only natural resource of glycine.
    Polym. Chem. 07/2014; 5(16).
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    ABSTRACT: The present contribution describes the innovation in the copolymerization of cyclic monomers, ε-caprolactam (ε-CL) and 2,2-dimethyltrimethylene carbonate (DTC), with ethyl diazoacetate (EDA). The characterizations of the obtained copolymers, poly(EA-ran-EDA-ran-ε-CL), poly(EA-ran-EDA-ran-DTC) (EA refers to ethyl acetate group CH3CH2OCOCH= from EDA by nitrogen-releasing), were performed by hydrogen nuclear magnetic resonance spectroscopy (1H NMR), carbon nuclear magnetic resonance spectroscopy (13C NMR) and size exclusion chromatography (SEC). In optimized conditions, the copolymer of ε-CL with EDA possessing Mn (number-average molar mass) of 1300 g/mol and PDI of 2.12 as well as that of DTC with EDA presenting Mn of 8000 g/mol and PDI of 1.47 were obtained. The incorporation of the azo group in the obtained copolymers was determined by the results of elemental analysis (in the range of 3.30-10.22%) and fourier transformed infrared (FT-IR) spectroscopy. Furthermore, the thermal properties of the obtained copolymers were examined by differential scanning calorimeter (DSC). X-ray diffraction (XRD) results showed that the synthesized copolymers were amorphous.
    Polymer International 03/2014; · 2.13 Impact Factor
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    ABSTRACT: Polypyrazoles with molecular weights in the range of 6500–9300 g mol−1 and yields in the range of 71.4–82.5% were synthesized successfully by catalyst-free 1,3-dipolar cycloaddition of bisdiazo compounds to bisalkynes under thermal conditions and lost merely 5% of their weights at temperatures higher than 298 °C. The porous polypyrazole–copper complex with pore diameters in the range of 1–2 μm was prepared by the coordination of polypyrazole and copper sulfate (CuSO4), which is a reusable catalyst for the Huisgen 1,3-diploar cycloaddition of alkynes and organic azides to give the corresponding triazoles with yields over 90%.
    Polym. Chem. 12/2013; 5(2).
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    Macromolecular Chemistry and Physics 11/2013; 214(21). · 2.39 Impact Factor
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    ABSTRACT: Supramolecular polymer micelles were prepared on basis of the inclusion complexation between cyclodextrin carbamates and cellulose derivatives in aqueous media. Cyclodextrin carbamates were synthesized by microwave-assisted method from cyclodextrin and urea. The urea modified cyclodextrin shows the higher yield than the physical mixture of urea/cyclodextrin in the micellization with cellulose derivatives. The supramolecular structure of the core-shell micelles was demonstrated by (1)H NMR spectra, TEM images, and fluorescence spectra. The drug release behavior of the supramolecular polymer micelles was evaluated using prednisone acetate as a model drug. The drug loaded micelles showed steady and long time drug release behavior. With these properties, the supramolecular polymer micelles are attractive as drug carriers for pharmaceutical applications.
    Carbohydrate polymers. 10/2013; 98(1):982-7.
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    ABSTRACT: Nanocomposite hydrogels with tunable mechanical properties and drug release behavior were prepared by halloysite nanotube (HNT), oligo(trimethylene carbonate)-poly(ethylene glycol)-oligo(trimethylene carbonate) diacrylate (TPT), and alginate sodium (AG). The mechanical properties of the hydrogel were greatly enhanced by the addition of small amount of HNT (2 wt%). The drug release behavior of the hydrogels was examined using bovine serum albumin (BSA) as model drug, and TPT hydrogel showed a fickcian diffusion controlled release mechanism, while the BSA transport mechanism in TPT-HNT, TPT-AG, and TPT-AG-HNT hydrogels were anomalous transport. The cytocompatibility of the hydrogel were verified by the MTT assay, and the hydrogel showed comparable cytocompatibility with the widely recognized poly(ethylene glycol) hydrogel.
    Composites Science and Technology 08/2013; 85:126-130. · 3.33 Impact Factor
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    ABSTRACT: Lipophilic 6-O-poly (ϵ-caprolactone)-L-ascorbic acid (AA-6-PCL) is synthesized through ROP of ϵ-caprolactone (CL). The number of repeating CL units in the polymer chain varies from 6 to 19. AA-6-PCL loaded supramolecular polymer micelles (SMPMs) are constructed with β-cyclodextrin (β-CD) and PCL as blocks. Transmission electron microscopy images show a nanospheric morphology of the micelles with a size range of 43.3 ± 5.0 nm. The drug loading contents are 22.53-39.23% for AA-6-PCL. AA-6-PCL exhibits high radical scavenging capacity (93.96-96.73%) and efficient scavenging potency, and a cytotoxicity study proves the excellent cytocompatibility of AA-6-PCL loaded β-CD/PCL SMPMs, which altogether herald their potential application in the study of the induced pluripotent stem cells.
    Macromolecular Bioscience 08/2013; · 3.74 Impact Factor
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    ABSTRACT: To develop hydrogels with high mechanical strength for cell encapsulation and three-dimensional culture is a critical challenge for cartilage tissue engineering. In this study, novel double network (DN) hydrogels were fabricated and phosphate buffer solution (PBS) was used as the solvent to facilitate cell encapsulation. The tough DN hydrogels were prepared through a two-step photopolymerization using neutral oligo(2,2-dimethyltrimethylene carbonate)–poly(ethylene glycol)–oligo(2,2-dimethyltrimethylene carbonate)–diacrylate (DPD–DA) chains for the first network and methacrylated hyaluronic acid (HA–GMA) chains for the second network. The fracture stress values of the optimized and cell-laden DN hydrogels were 8.38 ± 0.67 MPa and 6.28 ± 1.26 MPa, respectively, which showed comparable mechanical strength with natural articular cartilage tissue. The live/dead cell viability assay of cell-laden DN hydrogels demonstrated the tough DN hydrogels have comparable cytocompatibility with PEG hydrogels. After long-term culture, cartilage-specific extra cellular matrix accumulated in these DN hydrogels. The results indicated the potential of the novel DN hydrogels as cartilage tissue engineering scaffolds.
    J. Mater. Chem. B. 08/2013; 1(34).
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    ABSTRACT: Bisdiazo compounds were synthesized and underwent denitrogen alkene polymerization (DNAP) via the formation of an sp2 carbon bond in the presence of copper(II) catalysts, affording unsaturated polymers with molecular weights in the range of 2900 to 35400 Da. The copper-catalyzed denitrogen alkene polymerization of bisdiazo compounds allows the efficient synthesis of unsaturated polyesters.
    New Journal of Chemistry 06/2013; 37(7):1874-1877. · 2.97 Impact Factor
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    ABSTRACT: The structure of graphene oxide (GO) enables it to act as the olefin in cyclopropanation reaction with ethyl diazoacetate (EDA) under microwave irradiation. This versatile synthetic method offers a powerful method for the rapid chemical modification of GO. The attachment of carbethoxycarbene (CEC) to GO was confirmed by the results of FTIR, XPS, Raman, and UV–vis analysis.
    Chemical Physics Letters 01/2013; 556:376–379. · 2.15 Impact Factor
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    ABSTRACT: A series of biodegradable hydrogels based on oligo(2,2-dimethyltrimethylene carbonate)-block-poly(ethylene glycol)-block-oligo(2,2-dimethyltrimethylene carbonate) diacrylate (DPD-DA) precursor with varied length of hydrophilic poly(ethylene glycol) (PEG) segment and hydrophobic oligo(2,2-dimethyltrimethylene carbonate) (ODTC) segment were prepared by photopolymerization. Hydrophobic interaction was found to affect the properties of the hydrogel. The elastic modulus and toughness of the hydrogel could be tuned by altering the lengths of the hydrophobic ODTC segment as well as the hydrophilic PEG segment. In a monolayer culture, the number of swine cartilage chondrocytes (SCCs) attached to the hydrogel surface increased along with an increase in the length of ODTC segment in the precursor. SCCs cultured on the surface of hydrogel and photo-encapsulated in the hydrogel demonstrated comparable cytocompatibility with the widely recognized PEG hydrogel.
    RSC Advances 11/2012; 3(1):157-165. · 3.71 Impact Factor
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    ABSTRACT: Supramolecular polymer micelles (SMPMs) were constructed from natural and natural-derived polymers: β-cyclodextrin (β-CD)/maleic anhydride modified β-cyclodextrin (MAh-β-CD) and methylcellulose (MC) in aqueous solution by one-pot self-assembly procedure, in which, β-CD and MAh-β-CD inclusion complexes were used as the hydrophilic shell and the free MC as the core. The shapes of the SMPMs were regular spheres with diameters of 25 ± 5 nm. The critical micelle concentrations, calculated from steady-state fluorescence emission spectra, were around 15.13 and 20.89 mg/L for MC/β-CD and MC/MAh-β-CD SMPMs, respectively. The in vitro drug release behaviors of the micelles were studied using prednisone acetate as a model drug, and the results showed that the MC/MAh-β-CD micelle had a drug-enrichment core and excellent drug released behaviors with a sustaining release time of 700 h.
    Carbohydrate Polymers 09/2012; 90(1):569–574. · 3.48 Impact Factor
  • Journal of Controlled Release 11/2011; 152 Suppl 1:e17-8. · 7.63 Impact Factor
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    Journal of Controlled Release 11/2011; 152 Suppl 1:e57-8. · 7.63 Impact Factor
  • Journal of Controlled Release 11/2011; 152 Suppl 1:e52-4. · 7.63 Impact Factor
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    ABSTRACT: An intelligent drug delivery nanosystem has been developed based on biodegradable supramolecular polymer micelles (SMPMs). The drug release can be triggered from SMPMs responsively by a bioactive agent, L-phenylalanine in a controlled fashion. The SMPMs are constructed from ethylcellulose-graft-poly(ε-caprolactone) (EC-g-PCL) and α-cyclodextrin (α-CD) derivate via host-guest and hydrophobic interactions. It has been found that these SMPMs have disassembled rapidly in response to an additional L-phenylalanine, due to great affinity discrepancy to α-CD between L-phenylalanine and PCL. Experiments have been carried out on trigger-controlled in vitro drug release of the SMPMs loaded with a model porphyrin based photosensitizer THPP. The result shows that the SMPMs released over 85% THPP in 6 h, which is two orders magnitudes faster than that of control. Also investigated is the photodynamic therapy (PDT) of THPP-loaded SMPMs with and without L-phenylalanine on MCF-7 carcinoma cell line. An effective trigger-concentration dependent lethal effect has been found showing promise in clinical photodynamic therapy.
    Macromolecular Rapid Communications 03/2011; 32(6):540-5. · 4.93 Impact Factor
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    ABSTRACT: Hyaluronan (HA) and aliphatic oligo-carbonate based biodegradable hydrogels were synthesized via photopolymerization of a methacrylated HA (HA-GMA) with oligo(2,2-dimethyltrimethylene carbonate)-block-poly(ethylene glycol)-block -oligo(2,2-dimethyltrimethylene carbonate) diacrylate (DPD-DA). Hydrogels with tunable physical properties such as swelling behavior, crosslink density, and mesh size were fabricated with different concentrations of HA-GMA or DPD-DA. Hydrogel–bovine serum albumin (BSA) construct was prepared by in situ photopolymerization. BSA release from the construct was evaluated in vitro and the release behavior can be controlled by adjusting the concentration of the precursors. By tailoring the concentration of different precursors in the hydrogels, more sustained release of BSA can be achieved (i.e., 120h). The cytotoxicity of this novel hydrogel was also investigated and the hydrogel proved to be comparably cytocompatible to PEG hydrogels.
    Carbohydrate Polymers - CARBOHYD POLYM. 01/2011; 86(4):1484-1490.
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    ABSTRACT: To probe into the industrialization possibility of microwave-assisted ring-opening polymerization (ROP) of ɛ-caprolactone (ɛ-CL), it was performed with monomer mass from 750 to 2450g using a self-designed industrial microwave oven (6000W) catalyzed by stannous octanoate (Sn(Oct)2) (M/Cat=1000). The large-scale ROP of ɛ-CL proceeded smoothly at various microwave power levels (850, 1700, and 2550W) and produced poly(ɛ-caprolactone) (PCL) with weight-average molar mass (Mw) from 66,000 to 12,2000g/mol within 40min in a yield over 93%. The structure of PCL was characterized by 1H and 13C NMR, FT-IR, DSC and WAXD. We propose that the microwave ROP of ɛ-CL is a potential technology to prepare PCL commercially.
    Journal of Industrial and Engineering Chemistry - J IND ENG CHEM. 01/2010; 16(5):872-875.
  • Xiaogang Yang, Lijian Liu
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    ABSTRACT: Novel pH-responsive polyglycerol (PG)-based hydrogels were successfully synthesized through the reaction of epichlorohydrin with L-lactic acid (LLA) in the presence of sodium hydroxide (NaOH), and cetyltrimethylammonium bromide as a phase transfer catalyst at room temperature, followed by hydrolysis, polymerization, and crosslinking reactions. The resultant gel was characterized by carbon nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared measurement, and it was found that incorporated LLA was bound to PG network as a pendant acidic substituent by the hydroxyl group of LLA (PGL gel). The PGL hydrogels with different LLA contents and equilibrium swelling ratios (ESRs) were prepared by changing the feed ratios of materials. The results determined by chemical titration showed that under the applied conditions the efficiency of introducing the carboxyl group into PG network was about 86% and the amount of LLA in the hydrogel reached to about 17 wt %. The swelling behavior of the hydrogels in different environmental mediums was investigated, and the results showed that the hydrogels are pH-, ionic strength-, and cationic charge-responsive. The hydrogels also have the reversible swelling/deswelling properties. These pH-responsive PG-based hydrogels will have potential applications in biomedical and related areas. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
    Journal of Applied Polymer Science 02/2009; 112(6):3209 - 3216. · 1.40 Impact Factor