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Khadka, Daulat Bikram,Park, Seojeong,Jin, Yifeng,Han, Jinhe,Kwon, Youngjoo,Cho, Won-Jea Elsevier 2018 European journal of medicinal chemistry Vol.143 No.-
<P><B>Abstract</B></P> <P>With a goal of identifying potent topoisomerase (topo) inhibitor, the C4-aromatic ring of the anticancer agent, 3,4-diarylisoquinolone, was strategically shifted to design 1,3-diarylisoquinoline. Twenty-two target compounds were synthesized in three simple and efficient steps. The 1,3-diarylisoquinolines exhibited potent anti-proliferative effects on cancer cells but few compounds spared non-cancerous cells. Inhibition of topo I/IIα-mediated DNA relaxation by several derivatives was greater than that by camptothecin (CPT)/etoposide even at low concentration (20 μM). In addition, these compounds had little or no effect on polymerization of tubulin. A series of biological evaluations performed with the most potent derivative <B>4cc</B> revealed that the compound is a non-intercalative topo I catalytic inhibitor interacting with free topo I. Collectively, the potent cytotoxic effect on cancer cells including the drug resistance ones, absence of lethal effect on normal cells, and different mechanism of action than topo I poisons suggest that the 1,3-diarylisoquinolines might be a promising class of anticancer agents worthy of further pursuit.</P> <P><B>Highlights</B></P> <P> <UL> <LI> 1,3-Diarylisoquinoline was designed based on structure of 3,4-diarylisoquinoline. </LI> <LI> 1,3-Diarylisoquinolines were cytotoxic against cancer cells. </LI> <LI> Several derivatives inhibited topo I/IIα activity even at low concentration. </LI> <LI> 1,3-Diarylisoquinolines had weak or no antitubulin activity. </LI> <LI> 1,3-Diarylisoquinoline <B>4 cc</B> is a non-intercalative topo I catalytic inhibitor. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Effects of Ge Alloying on Device Characteristics of Kesterite-Based CZTSSe Thin Film Solar Cells
Khadka, Dhruba B.,Kim, SeongYeon,Kim, JunHo American Chemical Society 2016 The Journal of Physical Chemistry Part C Vol.120 No.8
<P>The impacts of Ge alloying on crystal growth and device properties of kesterite-based CZTSSe thin film solar cells fabricated by chalcogenization of sputtered stacks in S/Se ambient were investigated. It was found that Ge-alloyed CZTSSe material improved the grain growth, compactness of film texture, and crystallinity of absorber layers as, a consequence of the device efficiencies were enhanced from similar to 3 to 6%. The investigations on optoelectronic characteristics of devices illustrated that the improvements in devices were mainly governed by decrease in diode ideality factor, suppression of crossover effect between white and dark J-V curves, and reduction of defect level in Ge-alloyed CZTSSe solar cell device. These results suggest the possibility to achieve a further improvement in the optoelectronic characteristics of the devices that could be accomplished by optimization of the technological processes with a fine-timing of the Ge content in the layers.</P>
Adaptive current tDCS up to 4 mA
Khadka, Niranjan,Borges, Helen,Paneri, Bhaskar,Kaufman, Trynia,Nassis, Electra,Zannou, Adantchede L.,Shin, Yungjae,Choi, Hyeongseob,Kim, Seonghoon,Lee, Kiwon,Bikson, Marom Elsevier 2020 Brain stimulation Vol.13 No.1
<P><B>Abstract</B></P> <P><B>Background</B></P> <P>Higher tDCS current may putatively enhance efficacy, with tolerability the perceived limiting factor.</P> <P><B>Objective</B></P> <P>We designed and validated electrodes and an adaptive controller to provide tDCS up to 4 mA, while managing tolerability. The adaptive 4 mA controller included incremental ramp up, impedance-based current limits, and a Relax-mode where current is transiently decreased. Relax-mode was automatically activated by self-report VAS-pain score >5 and in some conditions by a Relax-button available to participants.</P> <P><B>Methods</B></P> <P>In a parallel-group participant-blind design with 50 healthy subjects, we used specialized electrodes to administer 3 daily session of tDCS for 11 min, with a lexical decision task as a distractor, in 5 study conditions: adaptive 4 mA, adaptive 4 mA with Relax-button, adaptive 4 mA with historical-Relax-button, 2 mA, and sham. A tablet-based stimulator with a participant interface regularly queried VAS pain score and also limited current based on impedance and tolerability. An Abort-button provided in all conditions stopped stimulation. In the adaptive 4 mA with Relax-button and adaptive 4 mA with historical-Relax-button conditions, participants could trigger a Relax-mode ad libitum, in the latter case with incrementally longer current reductions. Primary outcome was the average current delivered during each session, VAS pain score, and adverse event questionnaires. Current delivered was analyzed either excluding or including dropouts who activated Abort (scored as 0 current).</P> <P><B>Results</B></P> <P>There were two dropouts each in the adaptive 4 mA and sham conditions. Resistance based current attenuation was rarely activated, with few automatic VAS pain score triggered relax-modes. In conditions with Relax-button option, there were significant activations often irrespective of VAS pain score. Including dropouts, current across conditions were significantly different from each other with maximum current delivered during adaptive 4 mA with Relax-button. Excluding dropouts, maximum current was delivered with adaptive 4 mA. VAS pain score and adverse events for the sham was only significantly lower than the adaptive 4 mA with Relax-button and adaptive 4 mA with historical-Relax-button. There was no difference in VAS pain score or adverse events between 2 mA and adaptive 4 mA.</P> <P><B>Conclusions</B></P> <P>Provided specific electrodes and controllers, adaptive 4 mA tDCS is tolerated and effectively blinded, with acceptability likely higher in a clinical population and absence of regular querying. Indeed, presenting participants with overt controls increases rumination on sensation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Designed and validated an adaptive controller with electrode to maximize tDCS upto 4 mA while maintaining tolerability. </LI> <LI> Conditions with overt subject controls increase rumination on sensation, decreasing tolerability. </LI> <LI> No difference in VAS or adverse events among 2 mA, adaptive 4 mA, and sham. </LI> <LI> Adaptive 4 mA tDCS is relatively tolerated with specific electrodes and controller. </LI> </UL> </P>
Large-scale Growth of Quasifreestanding Graphene by using a Single-step Process
KHADKA ISHWOR BAHADUR,Park Ji-Hoon,Kim Eun Hye,Kim Hyun-Woo,Lee Do Hee,Kim Jin Wook,Kim Beom Joo,Ahn Joung Real 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.77 No.9
Various methods have been suggested to realize freestanding or suspended graphene, which is expected to exhibit the intrinsic properties of graphene. However, in previously reported methods, multiple-step processes have been applied to produce freestanding graphene on a substrate. Here, we demonstrate that quasifreestanding graphene on a substrate can be realized through a simple single-step process. In this experiment, self-etching of nano-scale SiC steps of 8° off-axis vicinal SiC contributed to the formation of quasifreestanding graphene on an Si-faced SiC wafer, which was confirmed using low-energy electron diffraction, Raman spectroscopy, scanning electron microscopy and two-probe resistance measurements. Such a single-step technique for the growth of quasifreestanding graphene could pave the way towards graphene-based silicon-carbide micro-electronics.
Topoisomerase inhibitors as anticancer agents: a patent update
Khadka, Daulat B,Cho, Won-Jea Informa UK, Ltd. 2013 Expert opinion on therapeutic patents Vol.23 No.8
<P><B><I>Introduction:</I></B> Topoisomerases (topos) are nuclear enzymes that resolve topological problems associated with DNA during various genetic processes. The essential role of topos in vital processes of the cell, their elevated level in solid tumors and cell death due to their inhibition make topos inhibitors as a potent class of antineoplastic agents.</P><P><B><I>Areas covered:</I></B> This review specifically summarizes patents embracing topo I, topo I and II inhibitors. The review covers topos inhibitors which are structurally close to camptothecin (CPT), natural products such as lamellarins and synthetic trisubstituted pyridines. It largely focuses on chemical entities developed by systematic structure-activity relationship (SAR) studies of natural benzo[<I>c</I>]phenanthridine (nitidine) and synthetic protoberberine (coralyne) established as antineoplastic agents targeting topo(s). In addition, indenoisoquinolines and evodiamines initially discovered through COMPARE analysis and receptor-based virtual screening (VS) respectively have been discussed.</P><P><B><I>Expert opinion:</I></B> Along with conventional techniques, computer-aided VS, molecular modeling and docking studies have been applied for drug design, discovery and development. Computer-aided tools provide a rational way to explain pharmacological activities of topos inhibitors under study. Comparative study of crystal structures of topo I/II-DNA-drug ternary complex and use of appropriate pharmacological screening methods will lead to potential anticancer drugs in the coming days.</P>