Yichen Yan

A naked-eye chemosensor for fluoride ions: a selective easy-to-prepare test paper

A new naked-eye chromogenic chemosensor based on 2-thiohydantoin shows high selectivity for fluoride ions and is used to develop a test paper for detection of fluoride ions in the solid state.

A new fluorescent probe based on styrylcyanine dye containing pyridine: dissimilar fluorescent response to Cu2+ and Pb2+

A highly sensitive fluorescent probe (1) based on styrylcyanine dye for Cu2+ and Pb2+ has been developed. Probe 1 exhibited fluorescent turn-off sensing ability to Cu2+. On the other hand, 1 displayed ratiometric fluorescent response towards Pb2+ with a distinct fluorescent color change from blue to orange. The 1H NMR titrations revealed that the fluorescent response of 1 to Cu2+ and Pb2+ is triggered by the interaction of the pyridine unit and the metal ion. Detection limits of 1 to Cu2+ or Pb2+ were calculated as 1.24 and 3.41 × 10−6 M, respectively, by standard deviation and linear fitting. Furthermore, 1 can also be used as a sensor for detection of Cu2+ and Pb2+ in a test strip.

Thiourea-functionalized poly(phenyleneethynylene): fluorescent chemosensors for anions and cations

A novel poly(phenyleneethynylene) containing thiourea groups [poly(1)] was synthesized. The anion sensing ability of poly(1) was assessed using tetra-n-butylammonium (TBA) salts of a series of anions in DMF. The addition of F− changed the color of the polymer solution in DMF from yellow to orange and quenched the fluorescence, whereas the visible color and fluorescence of the solution only varied slightly upon the addition of Cl−, HSO4−, Br−, CH3COO−, C6H5COO−, and NO3−; this indicates that poly(1) exhibits an F− sensing ability. 1H NMR titrations of poly(1) revealed that the colorimetric and fluorescent response of poly(1) is triggered by thiourea/F− hydrogen bonding. Poly(1) also exhibited a turn-off fluorescence Ag+ sensing ability. The addition of Ag+ quenched the fluorescence of the polymer, while the addition of Pb2+, Zn2+, Cu2+, Mn2+, K+, Na+, and Co2+ resulted in only slight changes to the fluorescence. The sensor containing poly(1) and Ag+ shows a turn-on fluorescence adenosine diphosphate (ADP) sensing ability.

Organic Radical Contrast Agents Based on Polyacetylenes Containing 2,2,6,6‐Tetramethylpiperidine 1‐Oxyl (TEMPO): Targeted Magnetic Resonance (MR)/Optical Bimodal Imaging of Folate Receptor Expressing HeLa Tumors in Vitro and in Vivoa

Nitroxides have great potential as magnetic resonance imaging (MRI) contrast agents for tumor detection. Polyacetylenes(PAs) containing 2,2,6,6-tetramethyl-piperidine oxyl (TEMPO) and poly(ethylene glycol) were synthesized via metathesis polymerization of the corresponding substituted acetylenes to be used for targeted bimodal MRI /optical imaging of tumors. The poly(ethylene glycol) in the polyacetylenes enables covalent conjugation of carboxyl fluorescein and folic acid (FA) with hydroxyl groups to develop targeted multifunctional organic radical contrast agents (ORCAs). In vitro studies confirm the excellent binding specificity and subsequent enhanced cellular internalization of the targeted ORCAs (PA-TEMPO-FI-FA) without cytotoxicity. In vivo T1-weighted MRI demonstrates the active tumor targeting ability of PA-TEMPO-FI-FA to generate specific contrast enhancement in mice bearing HeLa tumors. Moreover, longitudinal optical imaging displays high tumor accumulation after 1 h post-injection of PA-TEMPO-FI-FA. These results indicate that multifunctional ORCAs may provide a tumor-targeted delivery platform for further molecular imaging guided cancer therapy.

Poly(phenyleneethynylene) nanoparticles: preparation, living cell imaging and potential application as drug carriers

Conjugated polymer nanoparticles (PPE nanoparticles) are fabricated by the self-assembly of novel amphiphilic poly(phenyleneethynylenes). The morphology and cytotoxicity of PPE nanoparticles were investigated. Moreover, confocal fluorescence microscopy and flow cytometry assay revealed the effective internalization of PPE nanoparticles. PPE nanoparticles were also used as a carrier for drug delivery systems. Upon encapsulating an anticancer drug, DOX, PPE nanoparticles exhibited high drug loading efficiency (26.6 wt%) and good release properties. Subsequently, DOX loaded PPE nanoparticles were investigated by employing dynamic light scattering and transmission electron microscopy. Finally, cell uptake, cytotoxicity and Western blotting analysis were carried out, which revealed that PPE nanoparticles successfully deliver the drug into cancer cells and retain the anticancer bioactivity of DOX. All these results indicated that this new type of PPE nanoparticles would be a promising drug delivery system for therapeutic delivery and/or bioimaging applications.

Efficient gene and siRNA delivery with cationic polyphosphoramide with amino moieties in the main chain

Although a series of cationic polymers has been designed and synthesized by various kinds of strategies, the lower transfection efficiency and higher cytotoxicity are still a major problem for successful gene therapy. In this study, a novel cation polyphosphoramide (denoted as PPA) with amino moieties in the main chain was synthesized by polycondensation of ethyl dichlorophosphate with N1-(2-aminoethyl)-N1-(1-methyl)-1, 2-ethanediamine and investigated as non-viral vectors for gene transfection in target cells. Gel retardation analysis showed that PPA could efficiently retard the mobility of DNA at a lower N/P ratio. The size and zeta potential measurements found that these PPA/pDNA polycomplexes exhibited a decreased size and increased zeta potential. The cytotoxicity assay further revealed that PPA was non-toxic to different cells even at higher concentrations. It was also observed that polyionic complexes at a lower ratio of PPA/DNA (3 : 1) exhibited higher transfection efficiency. Interestingly, protein phosphorylation and a luciferase reporter assay showed that overexpression of the target gene (GFP-PKD2) transfected with PPA could enhance phosphorylation of PKD2, downstream IκB degradation and luciferase reporter activity of NF-κB signalling pathway in response to PMA, the agonist for PKD2 and NF-κB activation, indicating that the synthesized PPA could effectively deliver more than one exogenous genes into target cells and their proteins showed a functional role in target cells. More importantly, Western blotting and immunofluoescence staining of NF-κB p65 nuclear translocation showed that siRNA could be also delivered by PPA effectively, and exhibited silencing of the target gene as well as the signaling pathway in A549 cancer cells and HeLa cells. These results suggested that this novel cation polyphosphoramide could be used as an efficient carrier for plasmid and siRNA in future gene therapy applications.

Fluorescent probe based on heteroatom containing styrylcyanine: pH-sensitive properties and bioimaging in vivo.

A novel fluorescent probe based on heteroatom containing styrylcyanine is synthesized. The fluorescence of probe is bright green in basic and neutral media but dark orange in strong acidic environments, which could be reversibly switched. Such behavior enables it to work as a fluorescent pH sensor in the solution state and a chemosensor for detecting acidic and basic volatile organic compounds. Analyses by NMR spectroscopy confirm that the protonation or deprotonation of pyridinyl moiety is responsible for the sensing process. In addition, the fluorescent microscopic images of probe in live cells and zebrafish are achieved successfully, suggesting that the probe has good cell membrane permeability and low cytotoxicity.

Synthesis, Chiroptical Properties of a Helical Polyacetylene Derivative Carrying Urea Moieties

A novel phenylacetylene derivative containing urea groups was synthesized and polymerized with a Rh catalyst to give the corresponding polymer, poly(1) with moderate number-average molecular weights. The poly(1) was soluble in toluene, CHCl3, CH2Cl2, THF, DMF, and DMSO, but insoluble in hexane, diethyl ether and MeOH. The specific rotation and circular dichroism (CD) spectroscopic studies revealed that poly(1) took predominantly one-handed helical structures. The presence of intramolecular hydrogen bonding was confirmed by liquid-state IR spectroscopy. The helicity of poly(1) could be tuned by temperature and anion. The helical conformation of the polymer was stable against Br- but susceptible to F−.