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Koo, B.,Lee, J.,Lee, Y.,Kim, J.K.,Choi, N.S. Pergamon Press 2015 ELECTROCHIMICA ACTA Vol.173 No.-
The organophosphorus compounds tris(trimethylsilyl) phosphite (TMSP) and vinylene carbonate (VC) have been considered for use as functional additives to improve the electrochemical performance of Li<SUB>1.1</SUB>Mn<SUB>1.86</SUB>Mg<SUB>0.04</SUB>O<SUB>4</SUB> (LMO)/graphite full cells. Our investigation reveals that the combination of VC and TMSP as additives enhances the cycling properties and storage performance of full cells at 60<SUP>o</SUP>C. The unique functions of the TMSP additive in the VC electrolyte are investigated via ex situ X-ray photoelectron spectroscopy (XPS) and <SUP>19</SUP>F nuclear magnetic resonance (NMR) measurements. The TMSP additive effectively eliminates trace water and hydrogen fluoride (HF) and produces a protective film on the LMO cathode that alleviates manganese dissolution at 60<SUP>o</SUP>C.
Photoluminescence study of high energy proton irradiation on Cu(In,Ga)Se<sub>2</sub> thin films
Koo, B.,Lee, J.H.,Shin, D.,Ahn, B.T.,Shin, B. Elsevier Sequoia 2016 THIN SOLID FILMS - Vol.603 No.-
We have studied the effect of proton irradiation on Cu(In,Ga)Se<SUB>2</SUB> (CIGS) thin films using photoluminescence (PL). We used a 10MeV proton beam with varying doses from 10<SUP>9</SUP> to 10<SUP>12</SUP>cm<SUP>-2</SUP>. Intensity-dependent low temperature PL measurements suggest that the proton irradiation does not create a new defect level but instead changes the number of preexisting defects in the detection range of the PL system. By comparing PL spectra after the proton irradiation with those obtained after thermal annealing under inert gas as well as under hydrogen gas ambient, we find that the irradiation-induced change in the defect structure does not originate from the incorporation of hydrogen but from energetics of the irradiating particles. Electrical resistivity of the proton irradiated CIGS thin films is shown to decrease after the proton irradiation, and this is explained by the reduction of the concentration of compensating donor-like defects, specifically selenium vacancies, based on the PL results.
Intramitochondrial transfer and engineering of mammalian mitochondrial genomes in yeast
Yoon, Young Geol,Koob, Michael D. Elsevier 2019 Mitochondrion Vol.46 No.-
<P><B>Abstract</B></P> <P>Mitochondrial genomes (mtDNA) depend on the nuclear genome with which they have evolved to provide essential replication functions and have been known to replicate as xenotransplants only in the cells of closely related species. We now report that complete mouse mitochondrial genomes can be stably transplanted into the mitochondrial network in yeast devoid of their own mtDNA. Our analyses of these xenomitochondrial yeast cells show that they are accurately replicating intact mouse mtDNA genomes without rearrangement and that these mtDNA genomes have the same overall topology as the mtDNA present in the mouse mitochondrial network (<I>i.e.</I>, circular monomers). Moreover, non-mtDNA replication and selection sequences required for maintaining the mitochondrial genomes in bacterial hosts are dispensable in these yeast mitochondria and could be efficiently and seamlessly removed by targeted homologous recombination within the mitochondria. These findings demonstrate that the yeast mtDNA replication system is capable of accurately replicating intact mammalian mtDNA genomes without sequence loss or rearrangement and that yeast mitochondria are a highly versatile host system for engineering complete mammalian mitochondrial genomes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Entire mouse mtDNA can be stably transferred to the mitochondrial network in yeast devoid of their own mtDNA. </LI> <LI> The transferred mtDNA is accurately replicated with the same overall topology as the mtDNA present in the mouse mitochondria. </LI> <LI> The foreign non-mtDNA sequences could be seamlessly eliminated by targeted homologous recombination within the mitochondria. </LI> </UL> </P>
Re-engineering the mitochondrial genomes in mammalian cells
Young Geol Yoon,Michael D Koob,Young Hyun Yoo 대한해부학회 2010 Anatomy & Cell Biology Vol.43 No.2
Mitochondria are subcellular organelles composed of two discrete membranes in the cytoplasm of eukaryotic cells. They have long been recognized as the generators of energy for the cell and also have been known to associate with several metabolic pathways that are crucial for cellular function. Mitochondria have their own genome, mitochondrial DNA (mtDNA), that is completely separated and independent from the much larger nuclear genome, and even have their own system for making proteins from the genes in this mtDNA genome. The human mtDNA is a small (~16.5 kb) circular DNA and defects in this genome can cause a wide range of inherited human diseases. Despite of the significant advances in discovering the mtDNA defects, however, there are currently no effective therapies for these clinically devastating diseases due to the lack of technology for introducing specific modifications into the mitochondrial genomes and for generating accurate mtDNA disease models. The ability to engineer the mitochondrial genomes would provide a powerful tool to create mutants with which many crucial experiments can be performed in the basic mammalian mitochondrial genetic studies as well as in the treatment of human mtDNA diseases. In this review we summarize the current approaches associated with the correction of mtDNA mutations in cells and describe our own efforts for introducing engineered mtDNA constructs into the mitochondria of living cells through bacterial conjugation.
Horizontal Localization in Simulated Unilateral Hearing Loss
Anvarsamarein Parisa,Nazeri Ahmad Reza,Sameni Seyyed Jalal,Kamali Mohammad,Zarrin Koob Homa 대한청각학회 2018 Journal of Audiology & Otology Vol.22 No.1
Background and Objectives: The ability to localize a sound source is one of the binauralhearing benefits in a horizontal plane based on interaural time difference and interaural intensitydifference. Unilateral or bilateral asymmetric hearing loss will affect binaural hearing and leadto sound locating errors. In this cross sectional analytical descriptive study, the localization errorwas investigated when participants turned their heads to the sound source with closedeyes and after simulating unilateral hearing loss by placing earplugs inside the right ear canal. Subjects and Methods: This cross sectional analytical descriptive study was carried out on30 right-handed adults, 22 female and 8 male (average: 25 years, standard deviation: 3.16). They were selected with the available random access method. Horizontal localization wasevaluated with five speakers located at 0, ±30, and ±60 degree azimuths at a 1-meter distancefrom the examinee. Narrow-band noise signals were delivered at 35 dB SL in two “withoutearplug” and “with earplug” situations and the results were compared. The study was performedbetween September and December 2016 in Tehran, Iran. Results: Significantdifferences were observed in localization errors between the “with earplug” and “without earplug”situations. The localization differences were greater for left-side speakers (-30 and -60degrees) compared with right-side speakers (+30 and +60 degrees). The differences weremore apparent at 4,000 and 6,000 Hz, which confirmed the effect of unilateral simulatedhearing loss on interaural latency differences. Conclusions: Simulating hearing loss by usingan earplug in one ear (right) increased localization errors at all frequencies. The errorsincreased at higher frequencies.
윤영걸,Sun-Hee Park,Jee Suk Lee,Chunlan Yan,Chan Bae Park,Michael D Koob,유영현 한국생물공학회 2013 Biotechnology and Bioprocess Engineering Vol.18 No.2
Frataxin, a small nuclear-encoded protein targeted to mitochondria, is known to play an important role in both the mitochondrial respiratory chain and iron homeostasis. The protein is highly conserved in most eukaryotic organisms with no major structural changes, suggesting that it serves a crucial function in all organisms. Recently,purified frataxin was used as a therapeutic treatment of Friedreich’s ataxia, a common degenerative disorder that results from a frataxin protein deficiency, by directly applying the protein to the diseased cells. In this report, we describe a novel and rapid method of synthesizing genes encoding frataxin proteins for the purpose of efficient protein production. The artificial yeast and human frataxin genes were synthesized by direct assembly of serial deoxyoligonucleotide primers designed based on the optimal nucleotide sequences. When we tested the expression of these synthetic genes in two E. coli host strains, the yeast frataxin gene was expressed 20 folds higher in Rosetta (DE3) cells than in BL21 (DE3) cells, whereas the expression levels of human frataxin were similar in both E. coli strains. Attenuation of the Fenton reactions by the purified yeast and human frataxin proteins was observed under the defined conditions, which suggests that the recombinant frataxin proteins are active and functional. The procedure described here could be applied to many known genes or to generate novel synthetic genes that can be redesigned by arranging functional domains from previously identified genes and to study the structure and function of synthetic recombinant proteins and potential usage.