Xiangxiang Jia

Biopolymer-based supramolecular micelles from β-cyclodextrin and methylcellulose

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.

Synthesis and characterization of fluorescent oligo(3,4,5-triethoxycarbonyl-2-pyrazoline)

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.

Kinetic study of carbene polymerization of ethyl diazoacetate by palladium and rhodium catalysts

Kinetic studies of the 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 to be 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 the 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 an 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 increase 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.

Host-guest chemistry of cyclodextrin carbamates and cellulose derivatives in aqueous solution.

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.

One-pot catalyst-free synthesis of down- and upconversion fluorescent oligopyrazolines from diazoacetates and maleic anhydride

Conventionally, each fluorophore is only illuminated with the wavelength of incident light shorter (downconversion) or longer (upconversion) than that of emitted light. However, the oligopyrazolines presented in this paper are the down- and upconversion fluorescent molecules with a maximum emission at 445 nm, which are facilely synthesized from diazoacetates and maleic anhydride (MA) without any catalyst by a newly developed one-pot process. The intermediates of oligopyrazolines are formed through 1,3-dipolar cycloaddition and a cascade ring-opening insertion, which transform into oligomers in situ with molecular weight around 2 × 103 g mol−1. The structures of the subunits and resulting oligopyrazolines are clarified clearly by MALDI-TOF-MS and the quantum yield with excitation at 350 nm is in the range of 12–19%. A cell experiment with HeLa cells demonstrates its promising potential for bioimaging applications.

One-step synthesis of polypyrazoles and self-assembled polypyrazole–copper catalysts for click chemistry

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%.

Wavelength-focusing organic molecular materials with diazoacetate or fumarate as a monofluorophore

The wavelength of incident light can be shifted by down-conversion (DC) and up-conversion (UC) photofluorescence. DC and UC molecules are typically independent one-way conversion species, and UC should be stimulated by a laser source. In this paper, we find that diazoacetate- and fumarate-containing fluorescent molecules are wavelength-focusing species of simulated solar radiation. Monochromatic UV and NIR lights (354/696, 457/819 or 346/686 nm) are synchronously focused to 454, 473 or 454 nm, respectively, using (5R)-5-cyano-3-carbmenthoxy-2-pyrazoline, 3-carbethoxy-2-pyrazoline grafted polyvinyl alcohol and a cyclic oligomer of ethyl diazoacetate with carbethoxy carbene and allyl acrylate. With a broadband light source, portions of the 300–500 nm and 580–800 nm wavelength bands of incident light are synchronously converted to 507 nm using a copolymer of PEG and fumarate, which offers a promising way to harvest the UV and NIR portions of sunlight in the visible region.

Copolymerization of alkyl diazoacetates with α,β-unsaturated aldehydes: synthesis and application

Copolymerization between alkyl diazoacetates and α,β-unsaturated aldehydes, which is a one-pot, one-step and catalyst-free reaction, is presented. The product is a ternary copolymer composed of an alkyl diazoacetate, an α,β-unsaturated aldehyde and an α-carbalkoxy carbene, which is derived from the alkyl diazoacetate by the release of N2. Thus, the reaction is named as the C1N2/C2/C1 copolymerization. Various diazoacetates and α,β-unsaturated aldehydes were utilized to establish the methodology. The products are down-/up-conversion fluorescence molecules that can significantly enhance cell imaging through the synchronized excitation of near-ultraviolet and near-infrared light and may be widely used in other optical fields. The up-conversion fluorescence is the result of a two-photon excitation process.

Synthesis of 6-O-poly(ϵ-caprolactone)-L-ascorbic acid and its controlled release from supramolecular polymer micelles.

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.