Youngeup Jin

Novel bile acid derivatives induce apoptosis via a p53-independent pathway in human breast carcinoma cells

We have compared the anti-proliferative effects of ursodeoxycholic acid (UDCA), chenodeoxycholic acid (CDCA) and their derivatives, HS-1183, HS-1199 and HS-1200, on MCF-7 (wild-type p53) and MDA-MB-231 (mutant p53) cells. While UDCA and CDCA exhibited no significant effect, their novel derivatives inhibited the proliferation of both cell lines in a concentration-dependent manner, concomitant with apoptotic nuclear changes and the increase of a sub-G1 population and DNA fragmentation. Furthermore, we also observed an increase in the ratio of pro-apoptotic protein Bax to anti-apoptotic protein Bcl-2 and cleavages of lamin B and poly(ADP-ribose) polymerase (PARP) in MCF-7 and MDA-MB-231 cells. Cell cycle related proteins, cyclin D1 and D3, as well as retinoblastoma protein (pRb) were down-regulated, while the level of cyclin-dependent kinase inhibitor p21(WAF1/CIP1) was increased in both cancer cells after treatment with novel bile acids. These findings suggest that these cytotoxic effects of novel bile acid derivatives on human breast carcinoma cells were mediated via apoptosis through a p53-independent pathway.

Effect of substituted side chain on donor-acceptor conjugated copolymers

The effects of substitute side chain (alkyl or alkoxy) on optical and electrical properties of low-band-gap conjugated copolymers were investigated using poly(2,7-dihydroindeno[2,1-a]indene-co-4,7-di-2-thienyl-2,1,3-benzothiadiazole), poly(2,7-dihydroindeno[2,1-a]indene-co-4,7-bis(4-hexyl-2-thienyl)-2,1,3-benzothiadiazole) (PININE-DHTBT), and poly(2,7-dihydroindeno[2,1-a]indene-co-4,7-bis[3-(hexyloxy)-2-thienyl]-2,1,3-benzothiadiazole) (PININE-DHOTBT). Alkyl introduced PININE-DHTBT exhibits blueshifted absorption spectrum, while alkoxy introduced PININE-DHOTBT exhibits redshifted absorption spectrum. Because of steric hindrance of alkyl or alkoxy side chain, highest occupied molecular orbitals of PININE-DHTBT and PININE-DHOTBT highly localized on donor segments, thereby decreasing hole mobilities of PININE-DHTBT and PININE-DHOTBT. Consequently, despite the spectral advantage of PININE-DHOTBT for photovoltaic cells, the actual solar cell property of PININE-DHOTBT was not enhanced.

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.

Structure-function relationships of conjugated polyelectrolyte electron injection layers in polymer light emitting diodes

The characteristics of conjugated polymer light-emitting diodes containing poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene) as the emissive layer and cationic or anionic conjugated polyelectrolytes (CPEs) as the electron injection layer are reported. Structure variations involving backbone, type of counterion, and charge were used to establish structure-function relationships. More efficient electron injection from Al and better device performance are attained with CPEs bearing negative charges. For cationic CPEs having the same counterion but different conjugated structures, one observes better device efficiency using the material with higher electron mobility. Thus, both charge and backbone are important for optimizing device performance.

A low-bandgap alternating copolymer containing the dimethylbenzimidazole moiety

A new acceptor unit containing dimethyl-2H-benzimidazole was synthesized and utilized for the synthesis of a conjugated polymer containing electron donor–acceptor pairs for OPV devices. The dimethyl-2H-benzimidazole unit was designed to act as a substitute for the BT unit of PCDTBT. This novel dimethyl-2H-benzimidazole unit has two methyl groups which can supply higher solubility than those of the BT series. A thin film of PCDTMBI, containing the dimethyl-2H-benzimidazole unit, shows two broad absorption bands with maxima at 400 and 636 nm and an absorption onset of 756 nm, corresponding to a band gap of 1.64 eV. The oxidation onset of PCDTMBI was estimated to be 0.67 V, which corresponds to a HOMO energy level of −5.47 eV. The LUMO energy level of the polymer was thus determined to be −3.82 eV. A device with a PCDTMBI:PC71BM blend had a VOC value of 0.65 V, a JSC value of 10.0 mA cm−2, and a FF of 0.48, leading to an efficiency of 3.12%. The enhanced efficiency of PCDTMBI was caused by the higher IPCE value between 400 and 700 nm and high mobility (2.2 × 10−3 cm2 V−1 s−1).

Apoptosis and modulation of cell cycle control by synthetic derivatives of ursodeoxycholic acid and chenodeoxycholic acid in human prostate cancer cells

The effects of synthetic derivatives of ursodeoxycholic acid (UDCA), HS-1183, and chenodeoxycholic acid (CDCA), HS-1199 and HS-1200, on the proliferation of human prostate carcinoma PC-3 cells were investigated. Whereas CDCA and UDCA had no effects on the growth of cells in a concentration range we have tested, HS-1199 and HS-1200 completely inhibited the cell proliferation, and HS-1183 showed a weak inhibitory activity. This proliferation-inhibitory effect of the synthetic bile acid derivatives was due to the induction of apoptosis, which was confirmed by observing DNA fragmentation, chromatin condensation and cleavage of PARP. Flow cytometric analysis also revealed that the synthetic bile acid derivatives arrested the cell cycle progression at the G1 phase, which effects were associated with inhibition of phosphorylation of pRB and enhanced binding of pRB and E2F-1. They also suppressed Cdk2 and cyclin E-dependent kinase activities without changes of their expressions. Furthermore, the synthetic bile acids increased the levels of Cdk inhibitor, p21WAF1/CIP1, expression and activated the reporter construct of p21WAF1/CIP1 promoter in p53-independent manner, and p21WAF1/CIP1 proteins induced by the synthetic bile acid derivatives were associated with Cdk2 and proliferating cell nuclear antigen. These distinctive features suggest that it is possible to create the new drugs useful for cancer therapy from the synthetic bile acid derivatives as lead compounds.

Organic photovoltaic cells based on conjugated polymer/fullerene composites

Abstract Recently, upon mixing buckminsterfullerene, C60, into semiconducting conjugated polymers, an interesting photophysical phenomenon has been discovered. The photoinduced electron transfer from semiconducting polymers onto C60 is reversible, ultrafast with a quantum efficiency approaching unity, and metastable. This photoinduced electron transfer leads to a number of potentially interesting applications, including photodetectors and photovoltaic cells. In this work, we briefly present the photophysics and associated device applications of conjugated polymer–fullerene composites.

Highly efficient imide functionalized pyrrolo[3,4-c]pyrrole-1,3-dione-based random copolymer containing thieno[3,4-c]pyrrole-4,6-dione and benzodithiophene for simple structured polymer solar cells

As an effort to improve the photovoltaic properties of a highly efficient large band gap (2.11 eV) alternating copolymer, P(BDT-TDPPDT), comprised of electron rich benzodithiophene (BDT) and novel electron accepting pyrrole-based imide functionalized 4,6-bis(thiophen-2-yl)-2,5-dioctylpyrrolo[3,4-c]pyrrole-1,3-dione (TDPPDT) derivatives, we incorporated a relatively strong electron accepting thiophene-based imide functionalized thieno[3,4-c]pyrrole-4,6-dione (TPD) unit in its main chain via random copolymerization between BDT, TDPPDT and TPD units to give polymer P1. The incorporation of a TPD unit resulted in significant improvement in the optoelectrical and photovoltaic properties. P1 exhibits lower optical band gap (1.91 eV) and a deeper lowest unoccupied molecular orbital (LUMO) energy level compared to those of P(BDT-TDPPDT). The hole mobility of P1 was 3.66 × 10−4 cm2 V−1 s−1 and the PSC made with a simple device structure of ITO/PEDOT:PSS/P1:PC70BM(1 : 2.25 wt%) + 3 vol%/Al gave a maximum power conversion efficiency (PCE) of 7.03% with high photovoltaic parameters, such as an open-circuit voltage (Voc) of 0.87 V, a short-circuit current (Jsc) of 11.52 mA cm−2 and a fill factor (FF) of 70%. Interestingly, P1-based PSCs exhibited a high incident photon to current efficiency (IPCE) of a maximum of 78% at 410 nm and a more than 70% response between 370–590 nm. The PCE achieved in this study is the highest value reported thus far among PSCs made with random copolymers.

Improved electron injection in polymer light-emitting diodes using anionic conjugated polyelectrolyte

We report improved performance in polymer light-emitting diodes incorporating conjugated polyelectrolytes as an electron injection layer (EIL). When we introduce water soluble conjugated polymers, poly[9,9′-bis(4-sulfonatobutyl)fluorene-co-alt-1,4-phenylene] (anionic PFP), between the aluminum (Al) cathode and emissive layer, the devices show an increased electroluminescence efficiency with a lowered turn-on voltage. We believe the mobile Na+ ions in the EIL layer directly influences the device efficiency by forming a low work function layer at the interface between the EIL and Al cathode, thereby facilitating the electron injection into the emissive layer.

Exciton Binding Energies in Conjugated Polyelectrolyte Films

Molecular design: The electronic structure of conjugated polyelectrolytes as a function of ionization potential (IP) and electron affinity (EA) is determined using X-ray absorption and emission spectroscopy (see figure). Different functional groups give rise to dissimilar transport gaps and exciton binding energies.