Total syntheses of macleanine and lycoposerramine-S.

Total syntheses of fawcettimine-class Lycopodium alkaloids having an imino bridge between C5 and C13 were accomplished. Fawcettimine was first prepared in 10 steps from a known compound, and the characteristic structures, including the imino bridge, were constructed via the formation of a bridgehead imine.

Unlocking the Full Potential of Electron-Acceptor Molecules for Efficient and Stable Hole Injection.

Understanding the hole-injection mechanism and improving the hole-injection property are of pivotal importance in the future development of organic optoelectronic devices. Electron-acceptor molecules with high electron affinity (EA) are widely used in electronic applications, such as hole injection and p-doping. Although p-doping has generally been studied in terms of matching the ionization energy (IE) of organic semiconductors with the EA of acceptor molecules, little is known about the effect of the EA of acceptor molecules on the hole-injection property. In this work, the hole-injection mechanism in devices is completely clarified, and a strategy to optimize the hole-injection property of the acceptor molecule is developed. Efficient and stable hole injection is found to be possible even into materials with IEs as high as 5.8 eV by controlling the charged state of an acceptor molecule with an EA of about 5.0 eV. This excellent hole-injection property enables direct hole injection into an emitting layer, realizing a pure blue organic light-emitting diode with an extraordinarily low turn-on voltage of 2.67 V, a power efficiency of 29 lm W-1 , an external quantum efficiency of 28% and a Commission Internationale de l'Eclairage y coordinate of less than 0.10.

Unravelling the electron injection/transport mechanism in organic light-emitting diodes.

Although significant progress has been made in the development of light-emitting materials for organic light-emitting diodes along with the elucidation of emission mechanisms, the electron injection/transport mechanism remains unclear, and the materials used for electron injection/transport have been basically unchanged for more than 20 years. Here, we unravelled the electron injection/transport mechanism by tuning the work function near the cathode to about 2.0 eV using a superbase. This extremely low-work function cathode allows direct electron injection into various materials, and it was found that organic materials can transport electrons independently of their molecular structure. On the basis of these findings, we have realised a simply structured blue organic light-emitting diode with an operational lifetime of more than 1,000,000 hours. Unravelling the electron injection/transport mechanism, as reported in this paper, not only greatly increases the choice of materials to be used for devices, but also allows simple device structures.

Understanding coordination reaction for producing stable electrode with various low work functions.

The realisation of a cathode with various work functions (WFs) is required to maximise the potential of organic semiconductors that have various electron affinities. However, the barrier-free contact for electrons could only be achieved by using reactive materials, which significantly reduce the environmental stability of organic devices. We show that a stable electrode with various WFs can be produced by utilising the coordination reaction between several phenanthroline derivatives and the electrode. Although the low WF of the electrode realised by using reactive materials is specific to the material, the WF of the phenanthroline-modified electrode is tunable depending on the amount of electron transfer associated with the coordination reaction. A phenanthroline-modified electrode that has a higher electron injection efficiency than lithium fluoride has been demonstrated. The observation of various WFs induced by the coordination reaction affords strategic perspectives on the development of stable cathodes unique to organic electronics.

Universal Strategy for Efficient Electron Injection into Organic Semiconductors Utilizing Hydrogen Bonds.

Molecular n-dopants that can lower the electron injection barrier between organic semiconductors and electrodes are essential in present-day organic electronics. However, the development of stable molecular n-dopants remains difficult owing to their low ionization potential, which generally renders them unstable. It is shown that the stable bases widely used in organic synthesis as catalysts can lower the electron injection barrier similar to that in conventional n-doping in organic optoelectronic devices. In contrast to conventional n-doping, which is based on the electron transfer from dopants with low ionization potential, the reduction of the injection barrier caused by adding bases is determined by the formation of hydrogen bonds between the hosts and the bases, providing energy-level-independent electron injection. The observation of the efficient electron injection induced by hydrogen bonding affords new perspectives on the method for controlling the behavior of electrons unique to organic semiconductors.

Effects of Energy-Level Alignment on Characteristics of Inverted Organic Light-Emitting Diodes.

Inverted organic light-emitting diodes (iOLEDs) without the use of alkali metals have attracted extensive attention owing to the demand for the realization of flexible OLEDs that do not require stringent encapsulation. In this paper, we discuss the correlation between the characteristics of iOLEDs and the energy-level alignment at cathode/organic layer interfaces examined by ultraviolet photoelectron spectroscopy. Two similar electron-transporting materials having different orbital energies, 2,8-bis(diphenylphosphoryl)dibenzo[ b, d]thiophene (PPT) and 2,8-bis(diphenylphosphoryl)dibenzo[ b, d]thiophene sulfone (PPT-S), are inserted between the cathode/polyethyleneimine and the emitting layer in the iOLED. The iOLED employing PPT-S exhibits a lower driving voltage and a higher efficiency than that employing PPT, which is consistent with the orbital energies of the two molecules. Although the stabilities of these two molecules are expected to be similar, the iOLED employing PPT-S exhibits an operational lifetime that is more than 100 times longer than that of the iOLED employing PPT. It was found that the difference in operational lifetime is caused by the difference in the energy-level alignment at the cathode/organic layer interfaces. Our results are expected to promote the development of promising materials and device configurations for fabricating efficient and operationally stable iOLEDs.

Effect of Host Moieties on the Phosphorescent Spectrum of Green Platinum Complex.

Highly efficient, operationally stable, and pure-color organic light-emitting diodes (OLEDs) are of considerable significance for developing practical wide-color-gamut displays. Further, we have demonstrated the feasibility of an efficient pure green phosphorescent OLED (PHOLED) by employing a narrow-band platinum complex and a top-emitting structure. The utilization of the thermally activated delayed fluorescence (TADF) material as the phosphorescent host is expected to serve as a promising solution for obtaining operationally stable PHOLEDs with high color purity. However, the emission spectrum of the platinum complex in the TADF host exhibits a considerably broad emission spectrum. This study investigates the cause of the spectral change by evaluating the photoluminescence spectra of the platinum complex in various hosts exhibiting different molecular structures. The triazine unit in the host material was observed to result in exciplex formation between the lowest unoccupied molecular orbital (LUMO) of the host and the highest occupied molecular orbital (HOMO) of the platinum complex. Therefore, the TADF material that sterically hinders the triazine unit is considered to be suitable to prevent both exciplex formation and spectral broadening.

Long-Lived Flexible Displays Employing Efficient and Stable Inverted Organic Light-Emitting Diodes.

Although organic light-emitting diodes (OLEDs) are promising for use in applications such as in flexible displays, reports of long-lived flexible OLED-based devices are limited due to the poor environmental stability of OLEDs. Flexible substrates such as plastic allow ambient oxygen and moisture to permeate into devices, which degrades the alkali metals used for the electron-injection layer in conventional OLEDs (cOLEDs). Here, the fabrication of a long-lived flexible display is reported using efficient and stable inverted OLEDs (iOLEDs), in which electrons can be effectively injected without the use of alkali metals. The flexible display employing iOLEDs can emit light for over 1 year with simplified encapsulation, whereas a flexible display employing cOLEDs exhibits almost no luminescence after only 21 d with the same encapsulation. These results demonstrate the great potential of iOLEDs to replace cOLEDs employing alkali metals for use in a wide variety of flexible organic optoelectronic devices.

Operational lifetimes of organic light-emitting diodes dominated by Förster resonance energy transfer.

Organic light-emitting diodes are a key technology for next-generation information displays because of their low power consumption and potentially long operational lifetimes. Although devices with internal quantum efficiencies of approximately 100% have been achieved using phosphorescent or thermally activated delayed fluorescent emitters, a systematic understanding of materials suitable for operationally stable devices is lacking. Here we demonstrate that the operational stability of phosphorescent devices is nearly proportional to the Förster resonance energy transfer rate from the host to the emitter when thermally activated delayed fluorescence molecules are used as the hosts. We find that a small molecular size is a requirement for thermally activated delayed fluorescence molecules employed as phosphorescent hosts; in contrast, an extremely small energy gap between the singlet and triplet excited states, which is essential for an efficient thermally activated delayed fluorescent emitter, is unnecessary in the phosphorescent host.

Highly efficient and stable organic light-emitting diodes with a greatly reduced amount of phosphorescent emitter.

Organic light-emitting diodes (OLEDs) have been intensively studied as a key technology for next-generation displays and lighting. The efficiency of OLEDs has improved markedly in the last 15 years by employing phosphorescent emitters. However, there are two main issues in the practical application of phosphorescent OLEDs (PHOLEDs): the relatively short operational lifetime and the relatively high cost owing to the costly emitter with a concentration of about 10% in the emitting layer. Here, we report on our success in resolving these issues by the utilization of thermally activated delayed fluorescent materials, which have been developed in the past few years, as the host material for the phosphorescent emitter. Our newly developed PHOLED employing only 1 wt% phosphorescent emitter exhibits an external quantum efficiency of over 20% and a long operational lifetime of about 20 times that of an OLED consisting of a conventional host material and 1 wt% phosphorescent emitter.

Selective antibacterial and apoptosis-modulating activities of mastic.

Mastic is a resinous exudate obtained from the stem and the main leaves of Pistacia lentiscus. We have reported the antiplaque effect of mastic-containing chewing gum on the oral cavity. We hypothesize that mastic may be a multifunctional food which has some beneficial pharmaceutical properties. The aim of this study was to assess the biological activity of solid and liquid types of mastic by cytotoxicity against fibroblasts, radical-scavenging activities and inhibitory effect on cell death of oral polymorphonuclear leukocytes (OPMNs). Mastic showed selective antibacterial action against Porphyromonas gingivalis and Prevotella melaninogenica, but no anti-HIV activity. Among a total of thirteen human cell types, promyelocytic leukemia HL-60 was the most sensitive to the cytotoxicity of mastic, followed by myeloblastic leukemia (ML-1, KG-1), erythroleukemia (K-562), oral squamous cell carcinoma (HSC-2, HSC-3, HSC-4), hepatocellular carcinoma (HepG2), glioblastoma (T98G, U87MG) and normal oral cells (gingival fibroblast, pulp cell, periodontal ligament fibroblast, most resistant). Mastic did not induce the differentiation of myelogenous leukemic cells into maturing cells with higher nitroblue tetrazolium-reducing activity, but induced apoptotic cell death, characterized by internucleosomal DNA fragmentation, caspase-3 activation and a decline in the intracellular concentration of putrescine. The cytotoxicity of mastic against leukemic cells did not diminish during its storage. On the other hand, mastic inhibited the spontaneous apoptosis of OPMNs. Mastic showed hydroxyl radical-scavenging activity. The selective antibacterial and apoptosis-modulating activity of mastic suggests its possible beneficial effects on oral health.

Synergistic induction of gene expression during the differentiation into mature macrophage in human myeloblastic leukemia cells treated with TPA and KH1060.

Treatment of human myeloblastic leukemia ML-1 cells with the phorbol ester TPA in combination with the vitamin D(3) analogue KH1060 will induce a synergistic differentiation to mature macrophage with multinuclei. To investigate the mechanism underlying this differentiation and the synergistic effect, a cDNA microarray and Northern blot analysis were used to examine gene expression profiles of ML-1 cells treated with TPA and/or KH1060. Results show that KH1060 enhanced several TPA-induced gene expressions and that TPA enhanced several KH1060-induced gene expressions. Studies with inhibitors of signaling molecules suggested that PKC and MAPK pathways play an important role in the differentiation induced by TPA and KH1060, and that they are associated with the synergistic induction of genes. The results of this study indicate the possibility that the expression of various genes are induced synergistically by cross-talk between TPA and KH1060 signals. It is likely that the synergistic effect on gene expression leads to the synergistic induction of differentiation by both reagents.

The effects of nanoparticles on mouse testis Leydig cells in vitro.

We have indicated the possibility that nanoparticles such as diesel exhaust particles (DEP) and titanium dioxide (TiO(2)) may impair the male mouse reproductive system. In this study, to evaluate the direct effect of nanoparticles on testis-constituent cells, we examined the effect of DEP, TiO(2) and carbon black (CB) on mouse Leydig TM3 cells, the testosterone-producing cells of the testis. The uptake of three nanoparticles into Leydig cells was detected using transmission electron microscopy (TEM) or field emission type scanning electron microscopy/energy-dispersive X-ray spectroscopy (FE-SEM/EDS). We examined the cytotoxicity and the effect on gene expression by treatment with nanoparticles. TiO(2) was more cytotoxic to Leydig cells than other nanoparticles. The proliferation of Leydig cells was suppressed transiently by treatment with TiO(2) or DEP. The expression of heme oxygenase-1 (HO-1), a sensitive marker for oxidative stress, was induced remarkably by treatment with DEP. Furthermore, CB and DEP slightly increased the gene expression of the steroidogenic acute regulatory (StAR) protein, the factor that controls mitochondrial cholesterol transfer. In this study, we found that DEPs, TiO(2) and CB nanoparticles were taken up by Leydig cells, and affected the viability, proliferation and gene expression. The patterns were unique for each nanoparticle.

Granulocyte macrophage colony-stimulating factor enhances retinoic acid-induced gene expression.

We reported previously that treatment of human myeloblastic leukemia ML-1 cells with all-trans retinoic acid (ATRA) in combination with GM-CSF enhances the granulocytic differentiation, which is induced only slightly by ATRA alone. To investigate the mechanism underlying this differentiation and the synergistic effect of ATRA and GM-CSF, we used cDNA microarray to examine gene expression profiles of ML-1 cells treated with ATRA and/or GM-CSF. We identified 22 up-regulated genes in ML-1 cells treated with both reagents and examined the expression of these genes in cells treated with ATRA and/or GM-CSF by Northern blot analysis. Comparison of cells treated with both reagents and cells treated with ATRA or GM-CSF alone revealed that expression of nine of the 19 genes was induced synergistically by combined treatment with ATRA and GM-CSF. Expression of most of these genes was increased only slightly by ATRA alone, and this induction was enhanced by the addition of GM-CSF. These results indicate that GM-CSF enhances ATRA-induced gene expression. Moreover, studies with inhibitors of signaling molecules suggested that activation of JAK2 is associated with the synergistic induction of several genes by ATRA and GM-CSF. JAK2 inhibitor suppressed induction of NBT-reducing activity in ML-1 cells treated with both reagents. It is likely that the enhancer effect of GM-CSF on ATRA-induced gene expression leads to the differentiation induced synergistically by ATRA combined with GM-CSF. Further studies of the mechanism underlying this effect may identify better approaches for the treatment of RA-insensitive leukemia.

Bone morphogenetic protein-2 suppresses invasiveness of TSU-Pr1 cells with the inhibition of MMP-9 secretion.

Bone morphogenetic protein (BMP), which is a member of the transforming growth factor beta (TGF-beta) superfamily, has powerful osteoinductive effects and various biological activities in a variety of cells. The effect of BMP-2 on the human carcinoma cell line TSU-Pr1 was examined. BMP-2 was found to inhibit the migration and invasiveness, but not the proliferation, of TSU-Pr1 cells. Gel zymography for matrix metalloproteinases (MMPs) and urokinase-type plasminogen activator (uPA) detection revealed that BMP-2 down-regulated the activity of MMP-9, but not of MMP-2 or uPA. BMP-2 also reduced the secretion of MMP-9 into the culture media, but did not affect the secretion of MMP-2, Timp-1, Timp-2 or Timp-3. These results suggest that BMP-2 inhibits migration and decreases MMP-9 secretion to suppress the invasiveness of TSU-Pr1 cells. This is the first report of a role for BMP signaling in reducing the invasiveness of cancer cells.

Alteration of gene expression in response to bone morphogenetic protein-2 in androgen-dependent human prostate cancer LNCaP cells.

Bone morphogenetic protein (BMP)-2, a multifunctional member of the transforming growth factor (TGF)-beta superfamily with powerful osteoinductive effects, has various biological activities in a variety of cells. We observed that BMP-2 inhibits cell proliferation in the androgen-dependent human prostate cancer cell line, LNCaP. To investigate the mechanism of inhibition of androgen-dependent growth by BMP-2, we compared the gene expression in LNCaP cells treated with dihydrotestosterone (DHT) to that of LNCaP cells treated with DHT and BMP-2, using DNA microarray analysis. Of 8,400 human genes on the gene chip, 38 genes were up-regulated by >2.0-fold and 48 genes were down-regulated by <0.5-fold by treatment with BMP-2. These genes were involved in a variety of cellular functions, including signal transduction, transcription regulation, enzymes, transporters, structural molecules and translation. RT-PCR analysis showed that CH1CL and BMX were up-regulated and DACH1 and WNT5A were down-regulated by treatment with BMP-2. Furthermore, we detected an increase of WNT5A protein in the medium by DHT and inhibition of the increase by BMP-2. In the present study, we identified several BMP-2-responsive genes in LNCaP cells. Further studies of the roles of these genes may clarify the mechanisms underlying the inhibition of cell proliferation by BMP-2 and identify better approaches for the prevention and treatment of prostate cancer.

Analysis of gene expression during staurosporine-induced neuronal differentiation of human prostate cancer cells.

Staurosporine induces neuronal differentiation and suppresses malignancy of human prostate cancer TSU-Pr1 cells. To investigate the mechanism underlying neuronal differentiation and suppression of malignancy, we used cDNA microarrays to examine gene expression profiles in TSU-Pr1 cells treated with staurosporine. mRNAs isolated from untreated and staurosporine-treated TSU-Pr1 cells were hybridised to microarrays consisting of approximately 9100 genes. Changes in gene expression were verified by Northern blot analysis. Staurosporine-responsive genes were involved in a variety of cellular functions including growth regulation, differentiation, replication, DNA repair, G2/M transition and inhibition of apoptosis. Interestingly, expression of genes associated with cell proliferation and malignancy, such as Cyr61 and CTGF, was reduced. Expression of CD73/NT5E, which is involved in neuronal differentiation, was increased. In the present study, we identified various staurosporine-responsive genes in TSU-Pr1 cells. Further studies of the roles of these genes may clarify the mechanisms underlying neuronal differentiation and inhibition of malignancy by staurosporine and identify better approaches for the prevention and treatment of prostate cancer.

Bone morphogenetic protein-2 induces hypophosphorylation of Rb protein and repression of E2F in androgen-treated LNCaP human prostate cancer cells.

Bone morphogenetic protein-2 (BMP-2), a multifunctional member of the transforming growth factor (TGF)-beta, superfamily, has powerful osteoinductive effects and causes cell cycle arrest in a variety of transformed cell lines. We have observed BMP-2-induced inhibition of cell proliferation in an androgen-dependent human prostate cancer cell line (LNCaP). To investigate the mechanism of inhibition of androgen-dependent growth by BMP-2, we examined the effect of dihydrotestosterone (DHT) and/or BMP-2 on cell cycle-related proteins in LNCaP cells. BMP-2 decreased the phosphorylation of retinoblastoma (Rb) protein induced by treatment with DHT. DHT-induced expression of cyclin A and cyclin-dependent kinase 2 (CDK2) protein was also inhibited by co-treatment with BMP-2. Furthermore, BMP-2 induced expression of p21(WAF1/CIP1), a CDK inhibitor. These results indicate that changes in expression of these proteins lead to modulation of the phosphorylation state of Rb. DHT-induced E2F-1 protein and mRNA expressions was also inhibited by BMP-2, suggesting that BMP-2 inhibits DHT-induced growth of LNCaP cells through a decrease in E2F protein expression and suppression of E2F activity by hypophosphorylation of Rb.

Induction of plasminogen activator inhibitor-2 is associated with suppression of invasive activity in TPA-mediated differentiation of human prostate cancer cells.

We previously reported that 12-O-tetra-decanoylphorbol-13-acetate (TPA) induces microglia-like differentiation and decreases malignancy in human prostate cancer TSU-Pr1 cells. To investigate the mechanism underlying differentiation and decrease of malignancy in TSU-Pr1 cells treated with TPA, we attempted to identify genes expressed differentially during the differentiation using differential display. We successfully detected plasminogen activator inhibitor type-2 (PAI-2) as one gene up-regulated by TPA treatment. The change in expression of PAI-2 by TPA was blocked by treatment with protein kinase C or mitogen-activated protein kinase inhibitors. We also found that secretion of PAI-2 protein was increased by TPA treatment. Moreover, we demonstrated that suppression of invasive activity of TSU-Pr1 cells by TPA treatment was blocked by co-treatment with anti-PAI-2 antibody. These results suggest that induction of PAI-2 is associated with suppression of invasive activity in TSU-Pr1 cells treated with TPA.