Lifeng Yan

Amino-grafted graphene as a stable and metal-free solid basic catalyst

Metal-free catalysts are essential for various chemical reactions in industrial chemistry. Amino-functionalized carbon is a cheap and environmentally friendly solid basic catalyst. Here, NEt3-graphene solid basic catalyst has been synthesized through a consecutive deprotonation/carbometalation and electrophilic substituent. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), elemental analyses, thermal analyses, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) studies confirmed the formation of the target structure. Catalytic hydrolysis of ethyl acetate reveals that the amino-grafted graphene has a high catalytic activity.

Disulfide Core Cross-Linked PEGylated Polypeptide Nanogel Prepared by a One-Step Ring Opening Copolymerization of N-Carboxyanhydrides for Drug Delivery

A novel disulfide core cross-linked PEGylated polypeptide nanogel has been synthesized by a one-step ring opening copolymerization of γ-benzyl L-glutamate N-carboxyanhydride and L-cystine N-carboxyanhydride using an amino group-terminated poly(ethylene glycol) methyl ether as initiator. Characterization of products confirms the formation of a core cross-linked PEGylated nanogel with disulfide linkages with a size of about 250u2009nm, and these studies also confirm that this nanogel can easily be broken by glutathione. Cell viability experiments show the good biocompatibility of the as-prepared polymer. Studies relating to loading and controlled release of indomethacin under reduction-sensitive conditions reveal that the nanogel is a good candidate for drug delivery systems.

Efficient Synthesis of Poly(acrylic acid) in Aqueous Solution via a RAFT Process

The direct polymerization of acrylic acid (AA) in aqueous solution for high molecular weight by means of living radical polymerization is still difficult. Here, AA was polymerized homogeneously in water by a reversible addition-fragmentation transfer polymerization (RAFT) in the presence of a water-soluble trithiocarbonate as a RAFT agent. Various ratios [AA]:[RAFT agent] were investigated to aim at different molecular weights. The polymerization exhibited living free-radical polymerization characteristics at different ratios [AA]: [RAFT agent]: controlled molecular weight, low polydispersity and well-suited linear growth of the number-average molecular weight, M n with conversion. The chain transfer to solvent or polymer was suppressed during the polymerization process, thus high linear PAA with high molecular weight and low PDI can be obtained. Moreover, using the generated PAA as a macro RAFT agent, the chain extension polymerization of PAA with fresh AA displayed controlled behavior, demonstrated the ability of PAA to reinitiate sequential polymerization.

Hydrogenated Graphene as Metal-free Catalyst for Fenton-like Reaction

Carbonaceous catalysts are potential alternatives to metal catalysts. Graphene has been paid much attention for its high surface area and light weight. Here, hydrogenated graphene has been prepared by a simple gamma ray irradiation of graphene oxide aqueous suspension at room temperature. Transmission electron microscopic, element analysis, X-ray photoelectron spectroscopy, and UV-Vis spectrophotometer studies verified the hydrogenation of graphene. The as-prepared hydrogenated graphene can be used as a metal-free carbonaceous catalyst for the Fenton-like degradation of organic dye in water.

Near infrared imaging-guided photodynamic therapy under an extremely low energy of light by galactose targeted amphiphilic polypeptide micelle encapsulating BODIPY-Br2

Near infrared (NIR) imaging-guided photodynamic therapy (PDT) is attractive, especially the utilization of one dye as both a photosensitizer and fluorescent probe, and the as-synthesized BODIPY-Br2 molecule is a candidate. Here, a galactose targeted amphiphilic copolymer of a polypeptide was synthesized and its micelles work as nanocarriers for BODIPY for targeting the NIR imaging-guided PDT of hepatoma cancer cells. At the same time, BODIPY could light up the cytoplasm for real-time imaging and kill cancer cells when the light was switched on. In vitro tests performed on both HepG2 and HeLa cells confirmed that the as-prepared PMAGP-POEGMA-PLys-B micelles showed efficient cell suppression of the cells with galactose receptors in the presence of light under an extremely low energy density (6.5 J cm-2). This protocol highlights the potential of polypeptides as biodegradable carriers for NIR image-guided and confined targeting photodynamic therapy.

An amphiphilic block copolymer conjugated with carborane and a NIR fluorescent probe for potential imaging-guided BNCT therapy

A carborane-containing triblock copolymer conjugated with a near infrared (NIR) fluorescence probe has been synthesized via reversible addition fragmentation chain transfer (RAFT), ring open polymerization (ROP), and conjugations of a cyanine NIR dye. Reactions were traced by means of 1H-NMR, GPC and FT-IR. The NIR amphiphilic copolymer with polycaprolactone and polycarborane as hydrophobic segments and poly(ethylene glycol)methyl ether methacrylate as the hydrophilic segment could self-assemble into micelles in aqueous solution, and was characterized by means of DLS and TEM. In the copolymer, carborane works as a boron neutron capture therapy (BNCT) agent while the aminocyanine (Cy) dye works as a NIR bioimaging agent, and the nanoparticles of the copolymers are a potential theranostic BNCT system for cancer therapy, which was supported by MTT experiments and in vitro fluorescence microscopy studies.

Emulsifier-free ultrasonic emulsion copolymerization of styrene with acrylic acid in water

A copolymer of styrene with acrylic acid (Poly(St–co–AA)) was directly synthesized by random emulsion copolymerization under ultrasonic irradiation without any volatile organic solvent (VOC) and emulsifier being used. Only water was used as solvent. The copolymer has been characterized by FT-IR spectra and H-NMR; its characteristic viscosity has been used to measure its average molecular weight. Our results show that high monomer conversion and short induction period were achieved. The effects of ultrasonic power and time on the average molecular weight and monomer conversion are discussed. The self-assembly behavior of the copolymer into regular pattern structures was imaged by atomic force microscopy (AFM).

Thermal Denaturation of Plasmid DNA Observed by Atomic Force Microscopy

(50 ng/ml) Plasmid DNA solutions were heated at different temperatures, and thermal denaturation of plasmid DNA was directly observed by atomic force microscopy (AFM). At room temperature DNA shows some open circular and supercoiled structure on the surface of new cleaved mica. When temperature was increased above 50°C, DNA molecules were partly denatured and the AFM images show globule structure inside the DNA chains. The globule structure resulted from a separation of double-strands into single ones with a subsequently coil-to-globule transition or intrachain recombination of base pairs. Above 80°C DNA appeared as granular structure, which came from complete denaturation and collapse of single strands. At 100°C DNA took place degradation into pieces. AFM studies also show that thermal denaturation of heterogeneous DNA is a multistep process with A–T base pairs separated first and G–C ones latter.

[a]-Phenanthrene-Fused BF2 Azadipyrromethene (AzaBODIPY) Dyes as Bright Near-Infrared Fluorophores

A new substitution pattern of BF2 azadipyrromethene (azaBODIPY) dyes was obtained by phenanthrene fusion through a key palladium-catalyzed intramolecular C-H activation reaction. These [a]-phenanthrene-fused azaBODIPYs have a near planar structure of the phenanthrene-fused azadipyrromethene core in the crystalline state. The chromophore absorbs (log ε > 5) and fluoresces (ϕ = 0.32-0.38) strongly above 700 nm with excellent photostability and may be used as an attractive bright NIR bioimaging agent.

Carborane and cyanine conjugated galactose targeted amphiphilic copolymers for potential near infrared imaging-guided boron neutron capture therapy (BNCT)

ABSTRACT Near infrared fluorescent galactose targeted glycopolymer containing m-carborane has been synthesized through ring open and atom transfer radical polymerization, followed by post-functionalization with a cyanine NIR dye. The copolymer could self-assemble into micelles which work as a potential agent for imaging-guided boron neutron capture therapy. The NIR micelles revealed no cytotoxicity for HepG2 cells. An enhanced and fast endocytosis due to the specific interaction between the HepG2 cells and the glycopolymer could be traced by fluorescence microscopy, and the bioimaging makes it possible to trace the nanoparticles and provides information where and when the neutron irradiation should be triggered. GRAPHICAL ABSTRACT