Youngjin Kang

Blue Phosphorescent Ir(III) Complex with High Color Purity: fac-Tris(2′,6′-difluoro-2,3′-bipyridinato-N,C4′)iridium(III)

A blue phosphorescent iridium(III) complex (1) bearing fluorine-substituted bipyridine (dfpypy) has been synthesized and characterized to investigate the effect of the substitution and replacement of the phenyl ring in ppy (phenylpyridine) with pyridine on the solid state structure and its photoluminescence. The optical properties and electrochemical behaviors of 1 have also been systematically evaluated. The structure of 1 has also been determined by a single-crystal X-ray diffraction analysis. There are varied intermolecular interactions caused by the pyridine and fluorine substituents, such as C-H...N, C-H...F, and pi...pi interactions of either face-to-face type or edge-to-face C-H...pi and halogen...pi in crystal packing. In electrochemistry, the remarkably higher oxidation potential than that of FIrpic was observed. The emission lambda(max) of 1 at room temperature is at 438 nm with a higher PL quantum efficiency. Complex 1 exhibits intense blue emission with high color purity (CIE x = 0.14, y = 0.12), which has been attributed to metal-to-ligand charge-transfer triplet emission based on DFT calculations.

Effects of 13-alkyl-substituted berberine alkaloids on the expression of COX-II, TNF-α, iNOS, and IL-12 production in LPS-stimulated macrophages

Berberine, a major alkaloidal component of Coptidis Rhizoma, has antibacterial activity, anti-inflammatory effect, antitumor and antimotility actions. We suggested that one of possible mechanisms of anti-bacterial activity of berberine may be based on the production of interleukin (IL)-12. Recently 13-alkyl-substituted berberines were shown to be better activity than berberine against certain bacteria species and human cancer cell lines. In the present study, therefore, the effects of 13-methylberberine (13-MB) and 13-ethylberberine (13-EB) on the production of IL-12 and expression of iNOS, TNF-alpha and COX-II were investigated using macrophages in culture. In LPS-stimulated RAW 264.7 cells, these alkaloids decreased the nitrites, concentration-dependently. The concentration of 50% inhibition of NO production (IC50) by 13-MB and 13-EB was 11.64 and 9.32 microM, respectively. The suppressed expression of iNOS protein was responsible for the reduction of NO production. Neither the expression of mRNA of iNOS, COX-II and TNF- alpha nor protein of COX-II and TNF-alpha was affected by both 13-MB and 13-EB, but production of PGE2 in LPS-stimulated RAW 264.7 cells was significantly reduced. Another striking finding of the present study is that 13-MB and 13-EB increased production of IL-12 in LPS-treated splenic macrophages. These results indicate that posttranscriptional regulatory mechanism of iNOS gene expression by 13-MB and 13-EB is involved, and COX-II activity is inhibited by 13-MB and 13-EB, respectively. In conclusion, the present study demonstrates that 13-methyl- and 13-ethylberberine alkaloids can be useful as an immunotherapeutic compound for induction of IL-12, which is potentially applicable for tumors, infectious disease, and airway inflammation.

Silole-spaced triarylamine derivatives as highly efficient organic sensitizers in dye-sensitized solar cells (DSSCs)

Three new organic dyes that contain the dithienosilole (DTS) moiety as spacer have been synthesized and their photophysical/electrochemical properties, theoretical calculation and dye-sensitized solar cell (DSSC) performance have been investigated. The overall conversion efficiencies for DSSCs based on these dyes range from 6.73 to 7.50%, comparable to a (3–5′-[N,N-bis(9,9-dimethylfluorene-2-yl)phenyl]2,2′-bithiophene-5-yl}-2-cyanoacrylic acid (JK-2)-sensitized device (7.63%), fabricated and measured under the same experimental conditions. The DSSC constructed from one of the three compounds shows a higher open-circuit voltage (VOC) compared to those of the other two dye sensitized solar cells due to an increased electron lifetime (τe) in the conduction band of TiO2.

Formation of Azaborines by Photoelimination of B,N‐Heterocyclic Compounds

Highly fluorescent π-conjugated polycyclic azaborines can be prepared from B,N-heterocyclic compounds with a BR2 -CH2 unit through the elimination of an R-H molecule (see scheme). These clean photoelimination reactions occur both in solution and in polymers doped with the precursors.

Highly efficient blue phosphorescent and electroluminescent Ir(III) compounds

Three new Ir(III) compounds with deep-blue phosphorescence have been synthesized. These molecules have the general formula of Ir(C∧N)2(L∧X), where C∧N = 2′,6′-difluoro-2,3′-bipyridine (dfpypy) and L∧X = ancillary ligand such as 2-picolinate, pic (1), acetylacetonate, acac (2), or dipivaloylmethanoate, dpm (3). The ancillary ligands have been found to significantly destabilize both HOMO and LUMO levels of the Ir(III) complexes, compared to Ir(dfpypy)3, without significantly changing the phosphorescence energy. Compounds 1–3 emit bright blue phosphorescence with λmax = 440–460 nm and quantum efficiencies of 0.60–0.95 in solution and the solid state. Double-layer electroluminescent devices using compounds 1–3 as the dopant, CDBP (4,4′-bis(9-carbazolyl)-2,2′-dimethylbiphenyl) as the host/hole transporting layer, and TPBi (1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene) as the electron transport layer have been fabricated. These EL devices show pure blue colour with high efficiency. The EL device of compound 3 at the doping level of 20 wt% shows the best performance with EQE of 10–15% at the brightness of 10–1000 cd m−2 and the maximum current efficiency of 22 cd A−1.

Regulation of Lipopolysaccharide-Induced Inducible Nitric-Oxide Synthase Expression through the Nuclear Factor-κB Pathway and Interferon-β/Tyrosine Kinase 2/Janus Tyrosine Kinase 2-Signal Transducer and Activator of Transcription-1 Signaling Cascades by 2-Naphthylethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (THI 53), a New Synthetic Isoquinoline Alkaloid

The effects of 2-naphthylethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (THI 53), on nitric oxide (NO) production and inducible nitric-oxide synthase (iNOS) protein induction by lipopolysaccharide (LPS) were investigated in RAW 264.7 cells and mice. In cells, THI 53 concentration dependently reduced NO production and iNOS protein induction by LPS. In addition, THI 53 inhibited NO production and iNOS protein induction in LPS-treated mice. LPS-mediated iNOS protein induction was inhibited significantly by the specific tyrosine kinase inhibitor α-cyano-(3-hydroxy-4-nitro)cinnamonitrile (AG126) as well as by THI 53. In addition, a c-Jun NH2-terminal kinase (JNK) inhibitor anthra[1,9-cd]pyrazole-6 (2H)-one) (SP600125) but not an extracellular regulated kinase inhibitor [2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one (PD98029)] or a p38 inhibitor [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB230580)] reduced the iNOS protein level induced by LPS. Moreover, a Janus kinase 2 (JAK2) inhibitor α-cyano-(3,4-dihydroxy)-N-benzylcinnamide (AG490) dose-dependently prevented LPS-mediated iNOS protein induction. LPS activated phosphorylations of tyrosine kinases, especially tyrosine kinase 2 (Tyk2) and signal transducer and activator of transcription-1 (STAT-1); these were reduced by THI 53. LPS also phosphorylated the JNK pathway; however, this phosphorylation was unaffected by THI 53. Interestingly, a JNK inhibitor (SP600125) and another tyrosine kinase inhibitor (genistein) significantly inhibited STAT-1 phosphorylation, suggesting that the LPS-activated JNK pathway and a tyrosine kinase pathway (especially Tyk2) may link to the STAT-1 pathway, which is involved in iNOS induction. However, THI 53 regulates LPS-mediated iNOS protein induction by affecting the Tyk2/JAK2-STAT-1 pathway, not the JNK pathway. The inhibition by THI 53 of LPS-induced NO production was recovered by a tyrosine phosphatase inhibitor (Na3VO4), which supports the possibility that THI 53 inhibits the LPS-induced inflammatory response through regulation of tyrosine kinase pathways. THI 53 also inhibited LPS-mediated interferon (IFN)-β production and nuclear factor-κB (NF-κB) activation. Thus, THI 53 may regulate LPS-mediated inflammatory response through both the NF-κB and IFN-β/Tyk2/JAK2-STAT-1 pathways.

Prevention of the expression of inducible nitric oxide synthase by a novel positive inotropic agent, YS 49, in rat vascular smooth muscle and RAW 264.7 macrophages

The effects of a novel positive inotropic isoquinoline compound, YS 49, on NO production and iNOS protein expression were investigated in cultured rat aortic vascular smooth muscle cells (RAVSMC) and RAW 264.7 cells exposed to lipopolysaccharide (LPS) plus interferon‐γ (IFN‐γ). In addition, the effects of YS 49 on vascular hyporeactivity in vitro and ex vivo, and on survival rate (mice) and serum NOx (rat) levels, were also investigated in LPS‐treated animals. Pre‐ or co‐treatment of YS 49 with LPS plus IFN‐γ, concentration‐dependently reduced NO production in RAVSMC and RAW 264.7 cells (IC50 values, 22 and 30 μM, respectively). Although the inhibitory effect on NO production was reduced when YS 49 was applied 2 and 4 h after cytokine in RAW 264.7 cells, it was still statistically significant (P<0.05). YS 49 reduced iNOS mRNA expression in LPS‐treated rat aorta in vitro, an effect which was associated with restoration of contractility to the vasoconstrictor, phenylephrine (PE), and reduction in L‐arginine‐induced relaxation. Serum NOx levels were significantly (P<0.01) reduced by YS 49 (5 mg kg−1, i.p.) in LPS‐treated rats (10 mg kg−1, i.p.). Administration of YS 49 (10 and 20 mg kg−1) 30 min prior to LPS (10 mg kg−1) also significantly (P<0.01) increased the subsequent survival rates in mice. Finally, expression of iNOS protein induced by LPS plus IFN‐γ in RAVSMC and RAW 264.7 cells was suppressed by YS 49, in a concentration‐dependent manner. These data strongly suggest that YS 49 suppresses iNOS gene expression induced by LPS and/or cytokines in RAVSMC and RAW 264.7 cells at the transcriptional level. YS 49 could therefore be beneficial in septic shock and other diseases associated with iNOS over‐expression.

Synthesis and characterization of polyaromatic compounds using tri(naphthyl)indium.

A variety of polyaromatic compounds bearing 1- and 2-naphthyl groups were prepared from the reactions of corresponding halides with tri(1- and 2-naphthyl)indium in good to excellent yields. Thermal, photophysical and electrochemical behaviors of carbazoles having naphthyl groups were studied. They have shown to be promising host and hole transporting materials in organic electroluminescence due to their high thermal stability, electrochemical reversibility and wide band gap.

Fluorine-free blue phosphorescent emitters for efficient phosphorescent organic light emitting diodes

Two blue phosphorescent Ir(III) compounds with a main fluorine-free bipyridine ligand have been synthesized. These molecules have the general formula of Ir(C⁁N)2(L⁁X), where C⁁N = 2′,6′-dimethoxy-4-methyl-2,3′-bipyridine [(MeO)2pypy] and L⁁X = ancillary ligand, such as acetylacetonate (acac) (1) or 2-picolinate (pic) (2). Thermal, photophysical, and electrochemical properties of 1 and 2 have also been investigated systematically. The two compounds show high thermal stability with a decomposition temperature of ∼350 °C due to strong and varied intermolecular interactions. A sky-blue emission with moderate phosphorescence quantum efficiency (ΦPL = 0.49–0.54) is observed in the spectral region of 460–470 nm for all compounds, which is attributed to both metal-to-ligand charge transfer (MLCT) and ligand-centered (LC) transition. Compounds 1 and 2 show only ∼10 nm red-shifted emission in the fluid state, compared to similar fluorinated iridium counterparts. Multi-layered electroluminescent devices using compounds 1 and 2 as the dopant and 9-(3-(9H-carbazol-9-yl)phenyl)-9H-carbazol-3-yl)diphenylphosphine oxide as a host material have been fabricated. The electroluminescent device of 2 at a doping level of 5 wt% shows the best performance with an external quantum efficiency of 15.3% and the color coordinate of (0.16, 0.28) at a brightness of 100 cd m−2.

Distribution and accumulation of storage protein-1 in ovary of Hyphantria cunea Drury

Storage protein-1 (SP-1) is a major storage protein found in the hemolymph and fat body of Hyphantria cunea. In this study, the uptake and accumulation of SP-1 into the ovary of H. cunea was investigated using biochemical and immunocytochemical methods. SP-1 in H. cunea has a high methionine content (4.6%) but is not female-specific, like other high methionine storage proteins. In the 6-day-old pupal ovary, SP-1 was detectable in trace amounts but accumulated to significant levels toward the end of the pupal stage. After adult emergence, SP-1 rapidly decreased in the ovarian follicles and remained low in the egg. This suggest that SP-1 is either extensively modified or degraded, causing a loss of its antigenic property in the ovary after adult emergence. During vitellogenesis, SP-1 is present in the hemolymph and penetrates through the tunica propria to reach the perioocytic space. From there, SP-1 is incorporated into yolk bodies. These results clearly show that SP-1 is taken up by the developing oocyte. Its disappearance suggests that SP-1 might be an amino acid reservoir for providing precursors for egg formation, in contrast to yolk proteins, which are utilized during postembryonic development.