Poly(L-histidine)-tagged 5-aminolevulinic acid prodrugs: new photosensitizing precursors of protoporphyrin IX for photodynamic colon cancer therapy

Renjith P Johnson,1* Chung-Wook Chung,2* Young-Il Jeong,2 Dae Hwan Kang,2 Hongsuk Suh,3 Il Kim,11WCU Centre for Synthetic Polymer Bioconjugate Hybrid Materials, Department of Polymer Science and Engineering, Pusan National University, Pusan, 2National Research and Development Center for Hepatobiliary Cancer, Pusan National University, Yangsan Hospital, Yangsan, Gyeongnam, 3Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Pusan, Korea*These authors contributed equally to this workBackground: 5-Aminolevulinic acid (ALA) and its derivatives have been widely used in photodynamic therapy. The main drawback associated with ALA-based photodynamic therapy (ALA-PDT) and ALA fluorescence diagnosis results from the hydrophilic nature of ALA and lack of selectivity for tumor versus nontumor cells. The application of certain triggers, such as pH, into conventional sensitizers for controllable 1O2 release is a promising strategy for tumor-targeted treatment.Methods: A series of pH-sensitive ALA-poly(L-histidine) [p(L-His)n] prodrugs were synthesized via ring opening polymerization of 1-benzyl-N-carboxy-L-histidine anhydride initiated by the amine hydrochloride group of ALA itself. As an alternative to ALA for PDT, the synthesized prodrugs were used to treat a cultured human colon cancer HCT116 cell line under different pH conditions. The effect of ALA-p(L-His)n derivatives was evaluated by monitoring the fluorescence intensity of protoporphyrin IX, and measuring the cell survival rate after suitable light irradiation.Results: The cytotoxicity and dark toxicity of ALA and synthesized ALA-p(L-His) derivatives in HEK293T and HCT116 cells in the absence of light at pH 7.4 and 6.8 shows that the cell viability was relatively higher than 100%. ALA-p(L-His)n showed high phototoxicity and selectivity in different pH conditions compared with ALA alone. Because the length of the histidine chain increases in the ALA-p(L-His)n prodrugs, the PDT effect was found to be more powerful. In particular, high phototoxicity was observed when the cells were treated with ALA-p(L-His)15, compared with treatment using ALA alone.Conclusion: The newly synthesized ALA-p(L-His)n derivatives are an effective alternative to ALA for enhancing protoporphyrin IX production and the selectivity of the phototoxic effect in tumor cells.Keywords: 5-aminolevulinic acid, photodynamic therapy, poly(L-histidine), bioconjugate, cancer cell

Electroluminescence in polymer-fullerene photovoltaic cells

We report electroluminescence (EL) in photovoltaic (PV) cells based on semiconducting polymer-fullerene composites. By applying a forward bias to the PV cells, the devices exhibited a clear EL action with a peak around 1.5 eV. We ascribe this peak to an "electric field-assisted exciplex" formed between the electrons in the fullerenes and the holes in the polymers, thereby resulting in radiative recombination in the composites. This finding is totally unexpected because of a strong photoluminescence quenching in the same materials. Since the same devices also showed typical photovoltaic effects under illumination, our results demonstrate a dual functionality in one device; polymer photovoltaic cells and polymer light-emitting diodes.open464

Fabrication of Water Soluble Conjugated Polymers for WOLED

Recently, the novel organic materials for white OLEDs have been researched, but it is not easy to apply polymers to WPLEDs. However, because water soluble conjugated polymers can be spin-coated on organic soluble conjugated polymers, when organic soluble blue and red emission polymers, and water soluble green emission polymer were used as multi-layer device, WPLEDs can be produce by the total color of self emission at multi-layer. Water soluble anionic poly(9,9-bis(4'-sulfonatobutyl)fluorene-co-alt-1,4-phenylene) (anion-PF(Na+)) was synthesized, and we investigated the white color emission by multi-layer of this class of anionic conjugated polyelectrolytes and organic conjugated polymers (MEH-PPV) using the following device structure: ITO/PEDOT: PSS/anion-PF(Na+)/MEH-PPV/Al, because anionic PFP can get the self-blue emission and green emission by aggregation effect in film condition. Finally, the color of devices made using different device structure of ITO/PEDOT: PSS/MEHPPV/anion-PF(Na+)/Al was compared, and this device can get the blue and red emission because the green emission of anionic PFP was absorbed in MEH-PPV.close

Organic photovoltaic cells based on conjugated polymer/fullerene composites

We fabricated organic photovoltaic cells using poly[2-methoxy,5-(2'-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH-PPV) and fullerene derivative, [6,6]-phenylen C-61-butyric acid methyl ester (PCBM), composites with various concentrations of the PCBM. The devices exhibit photoluminescence quenching and enhancement in photovoltaic response with increasing PCBM concentrations, both of which are associated with the photoinduced charge transfer characteristics of these materials. We also investigate the PCBM concentration dependence on the device performance near the percolation threshold for fullerene derivative charge transport channel, and discuss the role of fullerene interpenetrating networks in these organic photo voltaic cells.close343

Enhanced open circuit voltage by hydrophilic ionic liquids as buffer layer in conjugated polymer-nanoporous titania hybrid solar cells

We demonstrate the fabrication of a nanoporous titania (NP-TiO(2)) network structure by using a polystylene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymer template and modifying the surface of NP-TiO(2) with ionic liquids (ILs), bmim-BF(4) and benmim-Cl. The effect of the molecular weight of PS-b-P4VP on the morphology of the NP-TiO(2) and IL-modified NP-TiO(2) are characterized by scanning electron microscopy and contact angle measurements. Subsequently, hybrid solar cells are fabricated using MEH-PPV and NP-TiO(2), and the effect of IL layers and IL concentrations on device performances are evaluated under AM 1.5 G illumination. The devices containing bmim-BF(4) and benmim-Cl show drastically enhanced open circuit voltages (V(oc)) of 1.05 V and 0.91 V, respectively, while the reference device without an IL layer exhibits a V(oc) of 0.60 V. Significantly improved V(oc) can be attributed to the change in interfacial energy levels by formation of ionic double layers at the TiO(2)/IL and at the IL/MEH-PPV interfaces. We also observed the trend that short circuit current decreased and V(oc) increased with increasing IL concentration, which is ascribed to interruption of charge transfer from MEH-PPV to TiO(2) and the change in interfacial energy level by shifting the vacuum level, respectively.close121

Synthesis and properties of polyfluorene, containing oxadiazole and carbazole units as pendants for white light-emitting diodes

Polyfluorene-based conjugated polymer, containing oxadiazole and carbazole units as pendants, was prepared as the emitting layer in light-emitting diodes (LEDs) to show that it has higher maximum brightness and electroluminescence (EL) efficiency as compared to poly(9,9-bis(2-ethylhexyl)fluorene-2,7-diyl). The prepared polymer, poly[9-(6-(N-carbazolyl)-hexyl)-9-(6-(4-(5-phenyl-1,3,4-oxadiazolyl)-phenoxy)-hexyl)-fluorene-2,7-diyl] was used as the emitting layer in LEDs. Oxadiazole and carbazole units as pendants caused aggregation to generate broad peak around 547 nm. The Commission internationale de l'eclairage coordinate of the LEDs was (0.28, 0.30) which is quite close to that of the standard white of National Television Systems Committee (0.31, 0.33). The maximum brightness and EL efficiency of the device with aluminum cathode were 6400 cd/m2 at 10V and 0.50 cd/A at 290mA/cm2, respectively.close10