Toward High-Performance Pt-Based Nanocatalysts for Oxygen Reduction Reaction through Organic–Inorganic Hybrid Concepts

Sharma, Monika,Jung, Namgee,Yoo, Sung Jong American Chemical Society 2018 Chemistry of materials Vol.30 No.1

<P>Pt-based multistructured nanocatalysts such as alloy, core–shell, and surface Pt-rich nanoparticles have been extensively studied for hydrogen fuel cell applications, and their catalytic performances for oxygen reduction reactions have been significantly upgraded for decades. Due to these technical enhancements, Pt-based nanoarchitectures have turned out to be compatible with commercially accessible fuel cell systems. In addition, based on physical and electrochemical backgrounds for the basic catalyst nanoarchitectures, novel catalyst designs with organic–inorganic hybrid concepts have been recently developed to more effectively improve the electrochemical reaction activities and durabilities. In this review, the typical class of Pt-based nanocatalysts are systematically explained according to their compositions and structures, and the emerging class of organic–inorganic hybrid catalyst designs are then thoroughly introduced. It is expected that the most recent improvements of Pt-based nanoarchitectures will have great effects on the future works for the commercialization of fuel cell catalysts.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2018/cmatex.2018.30.issue-1/acs.chemmater.7b03422/production/images/medium/cm-2017-034226_0037.gif'></P>

Suitable reference genes for relative quantification of miRNA expression in prostate cancer

Schaefer, Annika,Jung, Monika,Miller, Kurt,Lein, Michael,Kristiansen, Glen,Erbersdobler, Andreas,Jung, Klaus Korean Society for Biochemistry and Molecular Bion 2010 Experimental and molecular medicine Vol.42 No.11

Real time quantitative PCR (qPCR) is the method of choice for miRNA expression studies. For relative quantification of miRNAs, normalization to proper reference genes is mandatory. Currently, no validated reference genes for miRNA qPCR in prostate cancer are available. In this study, the expression of four putative reference genes (hsa-miR-16, hsa-miR-130b, RNU6-2, SNORD7) was examined with regard to their use as normalizer. After SNORD7 was already shown an inappropriate reference gene in preliminary experiments using total RNA pools, we studied the expression of the putative reference genes in tissue and normal adjacent tissue sample pairs from 76 men with untreated prostate carcinoma collected after radical prostatectomy. hsa-miR-130b and RNU6-2 showed no significantly different expression between the matched malignant and non-malignant tissue samples, whereas hsa-miR-16 was significantly underexpressed in malignant tissue. Softwares geNorm and Normfinder predicted hsamiR-130b and the geometric mean of hsa-miR-130b and RNU6-2 as the most stable reference genes. Normalization of the four miRNAs hsa-miR-96, hsamiR-125b, hsa-miR-205, and hsa-miR-375, which were previously shown to be regulated, shows that normalization to hsa-mir-16 can lead to biased results. We recommend using hsa-miR-130b or the geometric mean of hsa-miR-130b and small RNA RNU6-2 for normalization in miRNA expression studies of prostate cancer.

Suitable reference genes for relative quantification of miRNA expression in prostate cancer

Annika Schaefer,Monika Jung,Kurt Miller,Michael Lein,Glen Kristiansen,Andreas Erbersdobler,Klaus Jung 생화학분자생물학회 2010 Experimental and molecular medicine Vol.42 No.11

Real time quantitative PCR (qPCR) is the method of choice for miRNA expression studies. For relative quantification of miRNAs, normalization to proper reference genes is mandatory. Currently, no validated reference genes for miRNA qPCR in prostate cancer are available. In this study, the expression of four putative reference genes (hsa-miR-16, hsa-miR-130b, RNU6-2,SNORD7) was examined with regard to their use as normalizer. After SNORD7 was already shown an inappropriate reference gene in preliminary experiments using total RNA pools, we studied the expression of the putative reference genes in tissue and normal adjacent tissue sample pairs from 76 men with untreated prostate carcinoma collected after radical prostatectomy. hsa-miR-130b and RNU6-2 showed no significantly different expression between the matched malignant and non-malignant tissue samples, whereas hsa-miR-16was significantly underexpressed in malignant tissue. Softwares geNorm and Normfinder predicted hsamiR-130b and the geometric mean of hsa-miR-130b and RNU6-2 as the most stable reference genes. Normalization of the four miRNAs hsa-miR-96, hsamiR-125b, hsa-miR-205, and hsa-miR-375, which were previously shown to be regulated, shows that normalization to hsa-mir-16 can lead to biased results. We recommend using hsa-miR-130b or the geometric mean of hsa-miR-130b and small RNA RNU6-2 for normalization in miRNA expression studies of prostate cancer.

Boosting the oxygen reduction activity of a nano-graphene catalyst by charge redistribution at the graphene-metal interface

Sung, Hukwang,Sharma, Monika,Jang, Jeonghee,Lee, Sang-Young,Choi, Myoung-gil,Lee, Kyubock,Jung, Namgee The Royal Society of Chemistry 2019 Nanoscale Vol.11 No.11

<P>N-Doped carbon materials have been intensively studied to replace Pt catalysts for the oxygen reduction reaction (ORR) in anion exchange membrane fuel cells (AEMFCs). However, the low doping level in these catalysts results in a limited number of ORR active sites, so high catalyst loading is still required. Hence, the electrode thickness becomes extra thick, causing large mass transfer resistance in AEMFCs. In this study, we propose a unique hybrid catalyst concept utilizing charge redistribution at the graphene-transition metal interface to modify the electronic structure of graphene and simultaneously create multiple carbon active sites. The hybrid catalyst consists of n-type nano-graphene shells (NGS) three-dimensionally coated on the surface of transition metal nanoparticles highly dispersed on carbon supports. The n-type NGS catalysts efficiently facilitate oxygen adsorption owing to facile charge transfer from the metal nanoparticles underneath and provide abundant active carbon sites owing to their structural benefits. As a result, despite the same catalyst loading, the NGS catalyst shows high ORR activity and greater durability than a carbon-supported Pt (Pt/C) catalyst.</P>

Boosting Fuel Cell Durability under Shut-Down/Start-Up Conditions Using a Hydrogen Oxidation-Selective Metal-Carbon Hybrid Core-Shell Catalyst

Jang, Jeonghee,Sharma, Monika,Choi, Daeil,Kang, Yun Sik,Kim, Youngjin,Min, Jiho,Sung, Hukwang,Jung, Namgee,Yoo, Sung Jong American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.31

<P>Performance degradation generated by reverse current flow during fuel cell shut-down/start-up is a big challenge for commercialization of polymer electrolyte membrane fuel cells in automobile applications. Under transient operating conditions, the formation of H<SUB>2</SUB>/O<SUB>2</SUB> boundaries on Pt surfaces and the occurrence of undesired oxygen reduction reaction (ORR) in an anode cause severe degradation of carbon supports and Pt catalysts in a cathode because of an increase of the cathode potential up to ∼1.5 V. Herein, to directly prevent the formation of H<SUB>2</SUB>/O<SUB>2</SUB> boundaries in the anode, we propose a unique metal-carbon hybrid core-shell anode catalyst having Pt nanoparticles encapsulated in nanoporous carbon shells for selective H<SUB>2</SUB> permeation. This hybrid catalyst exhibits high hydrogen oxidation reaction (HOR) selectivity along with fully subdued ORR activity during long-term operation because of the excellent stability of the carbon molecular sieves. Furthermore, the HOR-selective catalyst effectively suppresses the reverse current flow in a single cell under shut-down/start-up conditions.</P> [FIG OMISSION]</BR>

유기 리간드 제어를 통한 고분산 팔라듐 나노 촉매의 합성 및 음이온교환막 연료전지를 위한 산소 환원 반응 특성 분석

성후광,장정희,정남기,Sung, Hukwang,Sharma, Monika,Jang, Jeonghee,Jung, Namgee 한국재료학회 2018 한국재료학회지 Vol.28 No.11

In anion exchange membrane fuel cells, Pd nanoparticles are extensively studied as promising non-Pt catalysts due to their electronic structure similar to Pt. In this study, to fabricate Pd nanoparticles well dispersed on carbon support materials, we propose a synthetic strategy using mixed organic ligands with different chemical structures and functions. Simultaneously to control the Pd particle size and dispersion, a ligand mixture composed of oleylamine(OA) and trioctylphosphine(TOP) is utilized during thermal decomposition of Pd precursors. In the ligand mixture, OA serves mainly as a reducing agent rather than a stabilizer since TOP, which has a bulky structure, more strongly interacts with the Pd metal surface as a stabilizer compared to OA. The specific roles of OA and TOP in the Pd nanoparticle synthesis are studied according to the mixture composition, and the oxygen reduction reaction(ORR) activity and durability of highly-dispersed Pd nanocatalysts with different particles sizes are investigated. The results of this study confirm that the Pd nanocatalyst with large particles has high durability compared to the nanocatalyst with small Pd nanoparticles during the accelerated degradation tests although they initially indicated similar ORR performance.

Change of Multiple-Layered Phospholipid Vesicles Produced by Electrostatic Deposition of Polymers during Storage

Chun, Ji-Yeon,Weiss, Jochen,Gibis, Monika,Choi, Mi-Jung,Hong, Geun-Pyo De Gruyter 2016 International Journal of Food Engineering Vol.12 No.8

<P><B>Abstract</B></P><P>In this study, 1 wt% lecithin (–), chitosan (+), and λ-carrageenan (–) were prepared to manufacture multiple-layered liposomes with optimal formulations developed in a previous study by using layer-by-layer electrostatic deposition. We observed their particle size, ζ-potential, sedimentation behavior, and microstructure for 6 weeks. Multiple-layered liposomes were quenched with calcein to evaluate stability in terms of factors such as encapsulation efficiency and released amount of calcein. The particle size of multi-layered liposomes increased with storage periods and the ζ-potential of multiple-layered liposomes gained a neutral charge. Interestingly, negatively charged layered liposomes were smaller than positively charged layered liposomes and showed a lower polydispersity index. Moreover, the ζ-potential did not apparently change compared to positively charged layered liposomes. For the calcein release study, multiple-layered liposomes significantly sustained quenched calcein more than that observed using non-layered liposomes. This study showed that it was possible to increase the thickness of the liposome surface and to manipulate its charge using chitosan and λ-carrageenan through electrostatic deposition. Results showed that manufacturing negatively charged multiple-layer (over 4-layer) liposomes with charged biopolymer improved the physicochemical stability of liposomes.</P>

Facile backbone structure determination of human membrane proteins by NMR spectroscopy

Klammt, Christian,Maslennikov, Innokentiy,Bayrhuber, Monika,Eichmann, C챕dric,Vajpai, Navratna,Chiu, Ellis Jeremy Chua,Blain, Katherine Y,Esquivies, Luis,Kwon, June Hyun Jung,Balana, Bartosz,Pieper, Ur Nature Publishing Group, a division of Macmillan P 2012 Nature methods Vol.9 No.8

Although nearly half of today's major pharmaceutical drugs target human integral membrane proteins (hIMPs), only 30 hIMP structures are currently available in the Protein Data Bank, largely owing to inefficiencies in protein production. Here we describe a strategy for the rapid structure determination of hIMPs, using solution NMR spectroscopy with systematically labeled proteins produced via cell-free expression. We report new backbone structures of six hIMPs, solved in only 18 months from 15 initial targets. Application of our protocols to an additional 135 hIMPs with molecular weight <30 kDa yielded 38 hIMPs suitable for structural characterization by solution NMR spectroscopy without additional optimization.

다공성 탄소층이 코팅된 하이브리드 표면 구조를 갖는 산소 환원 반응용 PtCo 합금 나노 촉매

장정희,모니카 샤르마,성후광,김순표,정남기,Jang, Jeonghee,Sharma, Monika,Sung, Hukwang,Kim, Sunpyo,Jung, Namgee 한국재료학회 2018 한국재료학회지 Vol.28 No.11

During a long-term operation of polymer electrolyte membrane fuel cells(PEMFCs), the fuel cell performance may degrade due to severe agglomeration and dissolution of metal nanoparticles in the cathode. To enhance the electrochemical durability of metal catalysts and to prevent the particle agglomeration in PEMFC operation, this paper proposes a hybrid catalyst structure composed of PtCo alloy nanoparticles encapsulated by porous carbon layers. In the hybrid catalyst structure, the dissolution and migration of PtCo nanoparticles can be effectively prevented by protective carbon shells. In addition, $O_2$ can properly penetrate the porous carbon layers and react on the active Pt surface, which ensures high catalytic activity for the oxygen reduction reaction. Although the hybrid catalyst has a much smaller active surface area due to the carbon encapsulation compared to a commercial Pt catalyst without a carbon layer, it has a much higher specific activity and significantly improved durability than the Pt catalyst. Therefore, it is expected that the designed hybrid catalyst concept will provide an interesting strategy for development of high-performance fuel cell catalysts.