Hybrid Structure White Organic Light Emitting Diode for Enhanced Efficiency by Varied Doping Rate.

Novel materials based on Zn(HPB)2 and Ir-complexes were synthesized as blue or red emitters, respectively. White organic light emitting diodes were fabricated using the Zn(HPB)2 as a blue emitting layer, Ir-complexes as a red emitting layer and Alq3 as a green emitting layer. The obtained experimental results, were based on white OLEDs fabricated using double emission layers of Zn(HPB)2 and Alq3:Ir-complexes. The doping rate of the Ir-complexes was varied at 0.4%, 0.6%, 0.8% and 1.0%. When the doping rate of the Alq3:Ir-complexes was 0.6%, a white emission was achieved. The Commission Internationale de l'Eclairage coordinates of the device's white emission were (0.316, 0.331) at an applied voltage of 10.75 V.

White organic light-emitting diodes with Zn-complexes.

This paper reviews OLEDs fabricated using Zn-complexes. Zn(HPB)2, Zn(HPB)q, and Zn(phen)q were synthesized as new electroluminescence materials. The electron affinity (EA) and ionization potential (IP) of Zn complexes were also determined and devices were characterized. Zn complexes such as Zn(HPB)2, Zn(HPB)q, and Zn(phen)q were found to exhibit blue and yellow emissions with wavelengths of 455, 532, and 535 nm, respectively. On the other hand, Zn(HPB)2 and Zn(HPB)q were applied as hole-blocking materials. As a result, the OLED efficiency by using Zn(HPB)2 as a hole-blocking material was improved. In particular, the OLED property of Zn(HPB)2 was found to be better than that of Zn(HPB)q. Moreover, Zn(phen)q was used as an electron-transporting material and compared with Alq3. The performance of the device with Zn(phen)q as an electron-transporting material was improved compared with Alq3-based devices. The Zn complexes can possibly be used as hole-blocking and electron-transporting materials in OLED devices. A white emission was ultimately realized from the OLED devices using Zn-complexes as inter-layer components.

Synthesis and electroluminescent properties of a novel electroluminescence material of bis-2-(4-(diphenylphosphino)phenyl)benzo[d]oxazole (DPB).

A new light-emissive material, bis-2-(4-(diphenylphosphino)phenyl)benzo[d]oxazole (DPB), has been synthesized and characterized by FT-NMR, FT-IR, UV-Vis and elemental analysis. DPB has the band gap of 4.3 eV between HOMO and LUMO levels. The photoluminescence (PL) of DPB was measured at 410 nm from the chloroform solution. The electroluminescent (EL) devices with structures of ITO/NPB/DPB/LiF/Al and ITO/NPB/DPB/Alq3/LiF/Al were constructed and showed maximum emission at 540 nm. The device using DPB as emitting material showed the luminance of 1000 cd/m2 at 11 V. The CIE chromaticity of the device showed near the region of white color emission.

Influence of diquat on growth and death of HepG2 cells using quartz crystal and micro CCD camera.

Diquat is widely used agent which produces toxicity in human and implicated as an environmental toxicity. HepG2 cell was cultured onto an indium tin oxide (ITO) surface of quartz crystal modified a collagen film. In this paper, we investigated the physical properties and the morphological change of the HepG2 cells cultured onto the ITO electrode of the quartz crystal sensor with micro CCD camera. The resonance responses of the quartz crystal and the morphological change were directly monitored. After seeding the cells and diquat injection into the chamber, the resonance frequency and the resonance resistance were obtained with real time morphologies. From the resonance characteristics and the series of morphologies, we could know the diquat to be death and weakening of the cells.

Optical and electrical properties of merocyanine dye LB films by various time of UV irradiation and heat treatment.

The Langmuir-Blodgett (LB) technique provides many possibilities for the control of film thickness, dimensions, and molecular structures on the nanometer scale. Various kinds of dye molecules have been found to form the J-aggregation which has been used as sensitizers of silver halide photography for long time. In recent years, they attract attention as model systems for investigating the ultra-fast exciton dynamics, materials for ultra-fast nonlinear optical devices, fluorescence probes for mitochondrial membranes. We fabricated the merocyanine dye LB films with arachidic acid (AA). In order to observe the J-aggregation of the merocyanine dye LB films, CdCl2 and KHCO3 solutions were added in subphase. From the optical absorption spectra of the mixed dye LB films (6Me-Ds:AA = 1:2) at different layers, the optical absorption peak was about 520 nm. However, the optical absorption peak of the LB films was shifted to 600 nm, when CdCl2 and KHCO3 solutions were added. This is the consequence result to the J-aggregation of the merocyanine dye. We also investigated the optical absorption peak of the LB films according to various time at 60 degrees C and 275 nm UV. We measured the STM morphology of the merocyanine dye LB film (1 layer) before UV irradiation and heat treatment. The morphology size of the LB film on HOPG was 5 nm. The roughness and molecular size were about 66.163 pm and 0.176 nm, respectively. The J-aggregation of this type was also accompanied by large morphological changes. We analyze the morphology and electrical properties of the LB films by the scanning tunneling microscopy (STM).

Temperature dependent electrical properties of organic light-emitting diodes using a Zn complex.

We synthesized a new electroluminescent material [(1,10-phenanthroline)(8-hydroxyqu inoline)] Zn(phen)q. The temperature dependence of the electrical properties of OLED using Zn(phen)q are studied to understand the electrical conduction mechanism. The current density-voltage characteristics are measured in the temperature range of 60 approximately 240 K and analyzed using a hopping model with an exponential trap distribution. At temperatures above 150 K, hopping conduction with an exponential trap distribution is dominant. We have obtained a characteristic trap depth of E(t) = 0.13 eV.

A Deep Blue Organic Light Emitting Diodes Characteristic of Isomerically-Featured Phosphine Oxides Containing N-Phenyl Benzimidazole.

An isomeric series of phosphine oxides with N-phenyl benzimidazole such as 2-DPPI, 3-DPPI and 4-DPPI were synthesized for organic light emitting diodes (OLED). The thermal properties of DPPI isomers were determined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). OLED devices using DPPI isomers as the emitting material were fabricated, which configuration was ITO/MoOx [30 nm]/NPB [500 nm]/DPPI [300 nm]/Alq3 [200 nm]/Liq[10 nm]/Al [120 nm]. The emitting colors of the devices were respectively a deep-blue (430 nm, 4-DPPI) and greenish-yellows (510-580 nm, 3-DPPI and 530 nm, 2-DPPI). In particular, the emitting color of 4-DPPI device was not changed during the alteration of applied voltages (6.5-11.5 V), and the CIE coordinate was a satisfactory deep-blue (0.161, 0.101).

QSAR analysis of pyrazolidine-3,5-diones derivatives as Dyrk1A inhibitors.

Individuals with Down syndrome (DS) suffer from mental retardation. Overexpression and the resulting increased specific activity of Dyrk1A kinase located on chromosome 21 cause a learning and memory deficit in Dyrk1A transgenic mice. To search for therapeutic agents with Dyrk1A inhibition activity, previously we obtained HCD160 as a new hit compound for Dyrk1A inhibition. In the present study, we synthesized 34 HCD160 derivatives to investigate the quantitative structure-activity relationship (QSAR). This analysis could provide important information for novel drug discovery for treatment of DS related learning and memory deficits.

Cytotoxicity of p-tyrosol and its derivatives may correlate with the inhibition of DNA replication initiation.

p-Tyrosol is a phenolic compound present in different dietary sources that can exert mild antioxidant properties based on in vitro and in vivo studies. In our study, two p-tyrosol derivatives (p-tyrosyl gallate and p-tyrosyl acetate) were synthesized and compared together with p-tyrosol and gallic acid for their cytotoxic activities on human cancer cells. p-Tyrosyl gallate had the most potent cytotoxicity and the major cytotoxic mechanism of its action was studied. We found that in HeLa cells, p-tyrosyl gallate can effectively induce cell cycle arrest during S phase and inhibited in vitro simian virus (SV40 DNA) replication. In addition, p-tyrosyl gallate can inhibit three important functional replication proteins (topoisomerase I, RPA and pol alpha-primase), especially pol alpha-primase. These results suggest that p-tyrosyl gallate-induced cell cycle arrest during S phase correlates with the inhibition of DNA replication. Pol alpha-primase may be the main target molecule. Taken together, we suggest that p-tyrosyl gallate is a strong anticancer drug candidate that warrants further investigation.

Flavonoid glycosides isolated from Salicornia herbacea inhibit matrix metalloproteinase in HT1080 cells.

Flavonoid glycosides, isorhamnetin 3-capital O, Cyrillic-beta-d-glucoside, and quercetin 3-O-beta-d-glucoside were isolated from Salicornia herbacea and their inhibitory effects on matrix metalloproteinase-9 and -2 (MMP-9 and -2) were evaluated in human fibrosarcoma cell line (HT1080). In zymography experiments, these flavonoid glycosides led to the reduction of the expression levels and activities of MMP-9 and -2 without any significant difference between these flavonoid glycosides. Protein expression levels of both MMP-9 and MMP-2 were inhibited and TIMP-1 (tissue inhibitor of metalloproteinase-1) protein level was enhanced by these flavonoid glycosides. Moreover, a transfection study carried out with AP-1 reporter construct revealed that the reporter activity was suppressed by treatment with isorhamnetin 3-capital O, Cyrillic-beta-d-glucoside. Therefore, these results suggested that these flavonoid glycosides have a potential as valuable natural chemopreventive agents for cancer.

Zinc complex based on 2-(5-methyl-2-hydroxyphenyl)benzotriazole: synthesis and electroluminescence characteristics.

Zinc (II) [2-(5-methyl-2-hydroxyphenyl)benzotriazole] (Zn(MHB)2) was synthesized and characterized by FT-NMR, FT-IR, UV-Vis, XPS and elemental analysis. The photoluminescence of Zn(MHB)2 was measured at 516 nm from the DMF solution. The HOMO (6.6 eV) and LUMO (3.1 eV) energy levels of Zn(MHB)2 were estimated from the measurement of cyclic voltammetry. The devices with structure of ITO/NPB/Zn(MHB)2/Alq3/LiF/Al were constructed to investigate their electroluminescent (EL) performance. Zn(MHB)2 was found to be a good hole-blocking material in the EL devices.

Fabrication and characterization of organic light-emitting diodes using zinc complexes as hole-blocking layer.

2-(2-Hydroxyphenyl)benzoxazole (HPB) was employed as organic ligand and the corresponding zinc complexes (Zn(HPB)2 and Zn(HPB)q) were synthesized. And their EL properties were characterized. The structures of zinc complexes were determined with FT-NMR, FT-IR, UV-Vis, and XPS. The thermal stability showed up to about 300 degrees C under nitrogen flow, which was measured by TGA. The photoluminescence (PL) of zinc complexes were measured from the DMF solution. The PL emitted in blue and yellow region, respectively. The EL devices were fabricated by the vacuum deposition. Two kinds of OLEDs devices were fabricated; ITO/NPB (40 nm)/Zn complexes (60 nm)/LiF/Al and ITO/NPB (40 nm)/Alq3 (60 nm)/Zn complexes (5 nm)/LiF/Al. Both of the EL properties as the emitting and the hole-blocking layer were investigated. The EL emission of Zn(HPB)q exhibited green light centered at 532 nm. The device showed a turn-on voltage at 5 V and a luminance of 6073 cd/m2 at 10 V. Meanwhile, the maximum EL the emission of the Zn(HPB)2 device was found to be at 447 nm. And the device showed a luminance of 2813 cd/m2 at 10 V. The ITO/NPB (40 nm)/Alq3 (60 nm)/Zn(HPB)2 (5 nm)/LiF/Al device showed increased luminance of L=17000 cd/m2 compared to L=12000 cd/m2 for similar device fabricated without the hole-blocking layer. And the turn-on voltage was significantly affected by the existence of the hole-blocking layer.

White OLED in Hybrid Structure for Enhancing Color Purity.

We synthesized the red emission material, bis(1,4-bis(5-phenyloxazol-2-yl)phenyl) iridium(picolate) [Ir-complexes] and the blue emission material, bis (2-(2-hydroxyphenyl) benzoxazolate)zinc [Zn(HPB)2]. White Organic Light Emitting Diodes were fabricated by using Zn(HPB)2 for a blue emitting layer, Ir-complexes for a red emitting layer and a tris (8-hydroxy quinoline)aluminum [Alq3] for a green emitting layer. The important experimental results obtained, white OLED was fabricated by using double emitting layers of Zn(HPB)2 and Alq3:Ir-complexes, and hole blocking layer of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline[BCP]. We also varied the thickness of BCP. When the thickness of BCP layer was 5 nm, white emission was achieved. We obtained a maximum luminance of 5400 cd/m2 at a current density of 650 mA/cm2. The CIE coordinates was (0.339, 0.323) at voltage of 10 V.

Mechanism of cell cycle arrest by (8E,13Z,20Z)-strobilinin/(7E,13Z,20Z)-felixinin from a marine sponge Psammocinia sp.

Furanosesterterpenes, isolated from a marine sponge Psammocinia sp. have been reported to display significant cytotoxicity to some cancer cell lines. In this study, EZZ, an inseparable 1:1 mixture of (8E,3Z,20Z)-strobilinin and (7E,3Z,20Z)-felixinin, showed significant antiproliferative effect on human cervix carcinoma cell line (HeLa). Cell cycle analysis revealed that EZZ could arrest HeLa cells in S phase with a concomitant decrease in the cell population of G1 phase. By using simian virus (SV40) DNA in vitro replication system, we found that EZZ could inhibit DNA replication, which suggests that EZZ-induced S phase arrest might be the direct result of blocked DNA synthesis. Furthermore, low concentration of EZZ was found to be capable of significantly inhibiting the DNA cleavage by topoisomerase I (topo I) and reducing the polymerase alpha-primase (pol alpha-primase) activity, while the ssDNA binding activity of replication protein A (RPA) was less affected. Taken together, these results suggest that EZZ-induced cell cycle arrest in S phase correlate with the inhibition of DNA replication, and topo I and pol alpha-primase might be the two main target molecules.

Polyacetylenes from a marine sponge Petrosia sp. inhibit DNA replication at the level of initiation.

In the course of our search for bioactive metabolites from the marine sponges collected from Korean water, we found that the polyacetylenes of marine sponge, genus Petrosia, deliver significant selective cytotoxicity against several human tumor cell lines. The effects of polyacetylene on DNA replication were examined using simian virus 40 DNA replication system in vitro. We found that polyacetylenes inhibited DNA replication, and predominantly inhibited the initiation stage of DNA replication. Polyacetylenes inhibited the DNA cleavage by topoisomerase I, and also significantly reduced polymerase alpha-primase activity. The ssDNA binding activity of replication protein A was little affected by polyacetylenes. We suggest that polyacetylenes might inhibit proteins required to establish replication forks during the initiation reaction, and their cytotoxicities might be related to the inhibitory effect they have on this fundamental cellular process.

Cytotoxicity of psammaplin A from a two-sponge association may correlate with the inhibition of DNA replication.

BACKGROUND: SV40 DNA replication system is a very useful tool to understand the mechanism of replication, which is a tightly regulated process. Many environmental and cellular factors can induce cell cycle arrest or apoptosis by inhibiting DNA replication. In the course of our search for bioactive metabolites from the marine sponges, psammaplin A was found to have some anticancer properties, the possible mechanism of which was studied. METHODS: Cell viability was determined by Cell Counting Kit-8 (CCK-8) to count living RAW264.7 cells by combining 2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium (WST-8) and 1-methoxy-phenazine methosulfate (1-methoxy-PMS). The effect of psammaplin A on DNA replication was carried out in SV40 DNA replication system in vitro. The activities of topoisomerase I and polymerase alpha-primase were measured by the relaxation of superhelical plasmid DNA and the incorporation of [3H]dTTP to the template respectively. The ssDNA binding activity of RPA was assessed by Gel Mobility Shift Assay (GMSA). RESULTS: We have found that psammaplin A delivers significant cytotoxic activity against the RAW264.7 cell line. It was also found that psammaplin A could substantially inhibit SV40 DNA replication in vitro, in which polymerase alpha-primase is one of its main targets. CONCLUSION: Taken together, we suggest that psammaplin A-induced cytotoxicity may correlate with its inhibition on DNA replication. Psammaplin A has the potential to be developed as an anticancer drug.

Antiproliferation of HeLa cells by 3,4,5-trihydroxy-N-[2-p-tolylethyl]-benzamide is associated with induction of DNA damage and inhibition of DNA replication.

The compound 3,4,5-trihydroxy-N-[2-p-tolylethyl]-benzamide (THTEB) is one of the derivatives of tyrosol, which is p-tyrosol combined with gallic acid by an amide bond. In this study, THTEB displayed a significant antiproliferative effect on human cervical carcinoma (HeLa) cells. Cell cycle analysis revealed that THTEB could arrest HeLa cells in the S phase with a concomitant decrease in the cells' G0/G1 and G2/M phases. According to the [3H]thymidine incorporation assay results, we found that THTEB could inhibit DNA replication, which suggests that THTEB-induced S phase arrest might be the direct result of blocked DNA synthesis. However, THTEB had very weak effect on replication protein A (RPA)'s ssDNA binding activity and the topoisomerase I (topo I)-mediated DNA relaxation activity, signifying that RPA and topo I were not the main target molecules in the inhibition of DNA replication. Furthermore, by using alkaline single-cell gel electrophoresis (comet assay), we found severe DNA damage caused by THTEB. In conclusion, these results suggest that THTEB could induce tumor cell antiproliferation correlated with DNA damage and DNA replication inhibition, but the target molecule of THTEB remains elusive.

Monitoring of anticancer effect of cisplatin and 5-fluorouracil on HepG2 cells by quartz crystal microbalance and micro CCD camera.

We have developed a monitoring system for evaluating the effect of anticancer agents, such as cisplatin and 5-fluorouracil (5-FU). The system mainly consisted of a quartz crystal microbalance (QCM) with indium tin oxide (ITO) electrodes and a micro CCD camera that can function in a humid CO(2) incubator. Human hepatoma cell line HepG2 cells were cultured and treated with the anticancer agents. As the behavior on the resonance frequency (F)-resonance resistance (R) diagram shows the viscoelastic change on the surface of the QCM, the effect of the anticancer agent was evaluated with the F-R diagram and the micro CCD camera, in comparison with the results in the case of general culturing (no anticancer agent injection). During general culturing, the resonance frequency decreased and the resonance resistance increased. This means that the mass loading of a viscous material occurred on the QCM. Observing with the micro CCD camera, the cancer cells were spread, divided, and the number of the cells increased. On the other hand, when the anticancer agent was injected to the culturing cancer cells, the resonance frequency and the resonance resistance increased continuously. This means a decrement of the mass effect and an increment of the viscosity on the QCM. From the observation with the micro CCD camera, the number of the cells did not change. The cells shrinked and changed the shape flat to round by loosing the cell activity in the case of 5-FU treatment. These results indicate the anticancer agents were effective to the culturing cancer cells.

Characterization of the electrical and optical properties of viologen devices using chlorophyll a as an electron excimer.

This paper uses self-assembled monolayers (SAMs) on an Au(111) substrate to detect the unique characteristics of viologen molecules using scanning tunneling microscopy (STM), and reports the orientation and surface changes of molecules at the nano level in real-time. In particular, the rectification characteristics of the viologen molecule were observed at the molecular level using scanning tunneling spectroscopy (STS). After verifying the rectification characteristics of viologen molecules, an experiment was carried out to demonstrate the possibility of applying viologen to photodiodes and switching devices by forming a thin film of chlorophyll a on the viologen SAMs using the Langmuir-Blodgett (LB) method. This material mimics the photoinduced electron transport phenomenon in the early stage of photosynthesis in living plants. This study demonstrates the applicability of viologen to bioelectronic photodiodes and switching devices based on photo effects by observing the topography, current sensing, and current-voltage (I-V) characteristics using current-sensing atomic force microscopy (CS-AFM) by introducing light to the AFM-tip/chlorophyll a/viologen/Au(111) substrate structure.

Synthetic tyrosyl gallate derivatives as potent melanin formation inhibitors.

Three tyrosyl gallate derivatives (1-3) with variable hydroxyl substituent at the aromatic ring of tyrosol were synthesized and evaluated as potent inhibitors on tyrosinase activity and melanin formation in melan-a cells. Among three tyrosyl gallate derivatives, 4-hydroxyphenethyl 3,4,5-trihydroxybenote (1) (IC(50)=4.93 microM), 3-hydroxyphenethyl 3,4,5-trihydroxybenote (2) (IC(50)=15.21 microM), and 2-hydroxyphenethyl 3,4,5-trihydroxybenote (3) (IC(50)=14.50 microM) exhibited significant inhibitory effect on tyrosinase activity. Compound 1 was the most active compound, though it did not show the inhibitory effect on melanin formation in melan-a cells. However, compounds 2 (IC(50)=8.94 microM) and 3 (IC(50)=13.67 microM) significantly suppressed the cellular melanin formation without cytotoxicity. This study shows that the position of hydroxyl substituent at the aromatic ring of tyrosol plays an important role in the intracellular regulation of melanin formation in cell-based assay system.