19 results on '"Myeongkee Park"'
Search Results
2. Integrated Micropillar Polydimethylsiloxane Accurate CRISPR Detection System for Viral DNA Sensing
- Author
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Mengdi Bao, Jiacheng He, Qian He, Kenneth Hass, Ke Du, Li Liu, Peiwu Qin, and Myeongkee Park
- Subjects
Trans-activating crRNA ,Microchannel ,Polydimethylsiloxane ,General Chemical Engineering ,Hybridization probe ,General Chemistry ,Fluorescence ,Article ,lcsh:Chemistry ,chemistry.chemical_compound ,lcsh:QD1-999 ,chemistry ,Biophysics ,CRISPR ,Denaturation (biochemistry) ,DNA - Abstract
A fully Integrated Micropillar Polydimethylsiloxane Accurate CRISPR deTection (IMPACT) system is developed for viral DNA detection. This powerful system is patterned with high-aspect-ratio micropillars to enhance reporter probe binding. After surface modification and probe immobilization, the CRISPR-Cas12a/crRNA complex is injected into the fully enclosed microchannel. With the presence of a double-stranded DNA target, the CRISPR enzyme is activated and denatures the single-stranded DNA reporters from the micropillars. This collateral cleavage releases fluorescence reporters into the assay, and the intensity is linearly proportional to the target DNA concentration ranging from 0.1 to 10 nM. Importantly, this system does not rely on the traditional dye-quencher-labeled probe, thus reducing the fluorescence background presented in the assay. Furthermore, our one-step detection protocol is performed on-chip at isothermal conditions (37 °C) without using complicated and time-consuming off-chip probe hybridization and denaturation. This miniaturized and fully packed IMPACT chip demonstrates sensitive and accurate DNA detection within 120 min and paves ways to the next-generation point-of-care diagnostics, responding to emerging and deadly pathogen outbreaks.
- Published
- 2020
3. Single Chlamydomonas reinhardtii cell separation from bacterial cells and auto‐fluorescence tracking with a nanosieve device
- Author
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Abbi Miller, Mengdi Bao, Grant Korensky, Ke Du, Xinye Chen, Blanca H. Lapizco-Encinas, and Myeongkee Park
- Subjects
biology ,Chemistry ,Clinical Biochemistry ,Microfluidics ,Biophysics ,Cell separation ,Chlamydomonas reinhardtii ,Auto fluorescence ,Tracking (particle physics) ,biology.organism_classification ,Biochemistry ,Fluorescence ,Analytical Chemistry - Published
- 2020
4. Selective photocatalytic conversion of benzyl alcohol to benzaldehyde or deoxybenzoin over ion-exchanged CdS
- Author
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Ki-Jeong Kim, Myeongkee Park, Hyun Sung Kim, Myung Jong Kang, Sung Gyu Lee, and Hangil Lee
- Subjects
Ion exchange ,Process Chemistry and Technology ,Nanoparticle ,Photochemistry ,Catalysis ,Benzaldehyde ,chemistry.chemical_compound ,chemistry ,X-ray photoelectron spectroscopy ,Benzyl alcohol ,Photocatalysis ,Selectivity ,General Environmental Science ,Visible spectrum - Abstract
The visible light absorbing CdS nanoparticles were partially modified with Au2S and Ag2S via a simple cation exchange process to prepare heterostructure photocatalysts (denoted as Au2S@CdS and Ag2S@CdS), which were employed for the conversion of aromatic alcohols to valued-added products, such as benzaldehyde and C-C coupling products, including deoxybenzoin and hydrobenzoin. When Au2S@CdS was used as the photocatalyst, benzaldehyde was obtained as the main product with a selectivity of 99%, and when Ag2S@CdS was used as the photocatalyst, deoxybenzoin was obtained as the main product with a selectivity of 95%. The critical photogenerated electron and hole transfer occurring during the photocatalytic reaction was systemically investigated by performing various control experiments and using in-situ high-resolution X-ray photoelectron spectroscopy. In addition, with the photocatalytic system proposed in this study, benzyl alcohol could be photoconverted into benzaldehyde or deoxybenzoin almost completely with high selectivity by altering the cocatalyst component via simple ion exchange.
- Published
- 2022
5. Bioinspired Metal–Organic Framework Catalysts for Selective Methane Oxidation to Methanol
- Author
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Bunyarat Rungtaweevoranit, Sirine C. Fakra, Christopher A. Trickett, Saeed Alshehri, Gabor A. Somorjai, Omar M. Yaghi, Yi-Sheng Liu, Xiaokun Pei, Jayeon Baek, Myeongkee Park, Roc Matheu, and Sultan A. Alshmimri
- Subjects
Methane monooxygenase ,Metalation ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,Methane ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Biomimetic Materials ,Density Functional Theory ,Metal-Organic Frameworks ,Molecular Structure ,biology ,Methanol ,General Chemistry ,021001 nanoscience & nanotechnology ,Combinatorial chemistry ,0104 chemical sciences ,Oxygen ,Models, Chemical ,chemistry ,Anaerobic oxidation of methane ,Oxygenases ,biology.protein ,Metal-organic framework ,0210 nano-technology ,Selectivity ,Oxidation-Reduction ,Copper - Abstract
Particulate methane monooxygenase (pMMO) is an enzyme that oxidizes methane to methanol with high activity and selectivity. Limited success has been achieved in incorporating biologically relevant ligands for the formation of such active site in a synthetic system. Here, we report the design and synthesis of metal-organic framework (MOF) catalysts inspired by pMMO for selective methane oxidation to methanol. By judicious selection of a framework with appropriate topology and chemical functionality, MOF-808 was used to postsynthetically install ligands bearing imidazole units for subsequent metalation with Cu(I) in the presence of dioxygen. The catalysts show high selectivity for methane oxidation to methanol under isothermal conditions at 150 °C. Combined spectroscopies and density functional theory calculations suggest bis(μ-oxo) dicopper species as probable active site of the catalysts.
- Published
- 2018
6. Integrated Micropillar Polydimethylsiloxane Accurate CRISPR Detection (IMPACT) System for Rapid Viral DNA Sensing
- Author
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Mengdi Bao, Qian He, Ke Du, Peiwu Qin, Myeongkee Park, and Kenneth Hass
- Subjects
Trans-activating crRNA ,chemistry.chemical_compound ,Polydimethylsiloxane ,Chemistry ,Hybridization probe ,Biophysics ,CRISPR ,Surface modification ,Denaturation (biochemistry) ,Fluorescence ,DNA - Abstract
A fully Integrated Micropillar Polydimethylsiloxane Accurate CRISPR Detection (IMPACT) system is developed for viral DNA detection. This powerful system is patterned with high-aspect ratio micropillars to enhance reporter probe binding. After surface modification and probe immobilization, CRISPR Cas12a/crRNA complex is injected into the fully enclosed system. With the presence of double-stranded DNA target, the CRISPR enzyme is activated and non-specifically cleaves the ssDNA reporters initially immobilized on the micropillars. This collateral cleavage releases fluorescence dyes into the assay, and the intensity is linearly proportional to the target DNA concentration ranging from 0.1 to 10 nM. Importantly, this system does not rely on traditional dye-quencher labeled probe thus eliminating the fluorescence background presented in the assay. Furthermore, our one-step detection protocol is performed at isothermal conditions (37°C) without using complicated and time-consuming off-chip probe hybridization and denaturation. This miniaturized and fully packed IMPACT chip demonstrates rapid, sensitive, and simple nucleic acid detection and is an ideal candidate for the next generation molecular diagnostic platform for point-of-care (POC) applications, responding to emerging and deadly pathogen outbreaks.
- Published
- 2020
- Full Text
- View/download PDF
7. Single Chlamydomonas reinhardi (C. reinhardtii) cell separation from bacterial cells and auto-fluorescence tracking with a nano-sieve device
- Author
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Xinye Chen, Myeongkee Park, Grant Korensky, Blanca H. Lapizco-Encinas, Abbi Miller, Mengdi Bao, and Ke Du
- Subjects
Materials science ,biology ,Polydimethylsiloxane ,Chlamydomonas ,technology, industry, and agriculture ,biology.organism_classification ,Tracking (particle physics) ,Volumetric flow rate ,law.invention ,Sieve ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,law ,Nano ,Photolithography ,Layer (electronics) - Abstract
A planar, transparent, and adaptable nano-sieve device is developed for efficient microalgae/bacteria separation. In our strategy, a sacrificial layer is applied in the dual photolithography patterning to achieve a one-dimensional channel with a very low aspect ratio (1:10,000). Microalgae/bacteria mixture is then introduced into the deformable polydimethylsiloxane (PDMS) nano-channel. The hydrodynamic deformation of the nano-channel is regulated to allow the bacteria cells to pass through while leaving the microalgae cells trapped in the device. At a flow rate of 4 μl/min, ~100% of the microalgae cells are trapped in the device. Additionally, this device is capable of immobilizing single cells in a transparent channel for auto-fluorescence tracking. These microalgae cells demonstrate minimal photo-bleaching over 250 s laser exposure and can be used to monitor hazardous compounds in the sample with a continuous flow fashion. Our method will be valuable to purify microalgae samples containing contaminations and study single cell heterogeneity.
- Published
- 2020
- Full Text
- View/download PDF
8. High-throughput and all-solution phase African Swine Fever Virus (ASFV) detection using CRISPR-Cas12a and fluorescence based point-of-care system
- Author
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Grant Korensky, Dongmei Yu, Ke Du, Peiwu Qin, Juwon Kim, Mengdi Bao, Myeongkee Park, Juhong Chen, Mingyeong Shin, and Qian He
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Swine ,Point-of-Care Systems ,Biomedical Engineering ,Biophysics ,DNA, Single-Stranded ,02 engineering and technology ,Biosensing Techniques ,01 natural sciences ,African swine fever virus ,Fluorescence ,Viral Proteins ,03 medical and health sciences ,chemistry.chemical_compound ,Cleave ,Electrochemistry ,Animals ,CRISPR ,African Swine Fever ,030304 developmental biology ,Trans-activating crRNA ,Detection limit ,0303 health sciences ,biology ,030306 microbiology ,010401 analytical chemistry ,RNA ,General Medicine ,021001 nanoscience & nanotechnology ,biology.organism_classification ,African Swine Fever Virus ,Virology ,0104 chemical sciences ,chemistry ,Nucleic acid ,CRISPR-Cas Systems ,0210 nano-technology ,DNA ,Biotechnology - Abstract
Here we report the development of a high throughput, all-solution phase, and isothermal detection system to detect African Swine Fever Virus (ASFV). CRISPR-Cas12a programmed with a CRISPR RNA (crRNA) is used to detect ASFV target DNA. Upon ASFV DNA binding, the Cas12a/crRNA/ASFV DNA complex becomes activated and degrades a fluorescent single stranded DNA (ssDNA) reporter present in the assay. We combine this powerful CRISPR-Cas assay with fluorescence-based point-of-care (POC) system we developed for rapid and accurate virus detection. Without nucleic acid amplification, a detection limit of 1 pM is achieved within 2 hrs. In addition, the ternary Cas12a/crRNA/ASFV DNA complex is highly stable at physiological temperature and continues to cleave the ssDNA reporter even after 24 hrs of incubation, resulting in an improvement of the detection limit to 100 fM. We show that this system is very specific and can differentiate nucleic acid targets with closely matched sequences. The high sensitivity and selectivity of our system enables the detection of ASFV in femtomolar range. Importantly, this system features a disposable cartridge and a sensitive custom designed fluorometer, enabling compact, multiplexing, and simple ASFV detection, intended for low resource settings.
- Published
- 2019
9. Difference Bands in Time-Resolved Femtosecond Stimulated Raman Spectra of Photoexcited Intermolecular Electron Transfer from Chloronaphthalene to Tetracyanoethylene
- Author
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David P. Hoffman, Richard A. Mathies, Myeongkee Park, and Scott R. Ellis
- Subjects
Chemistry ,Scattering ,Overtone ,02 engineering and technology ,Tetracyanoethylene ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,Spectral line ,0104 chemical sciences ,chemistry.chemical_compound ,Electron transfer ,Excited state ,Electron affinity ,Femtosecond ,Physical and Theoretical Chemistry ,0210 nano-technology - Abstract
The time-resolved femtosecond stimulated Raman spectra (FSRS) of a charge transfer (CT) excited noncovalent complex tetracyanoethylene:1-chloronaphthalene (TCNE:ClN) in dichloromethane (DCM) is reported with 40 fs time resolution. In the frequency domain, five FSRS peaks are observed with frequencies of 534, 858, 1069, 1392, and 1926 cm–1. The most intense peaks at 534 and 1392 cm–1 correspond to fundamentals while the features at 858, 1069, and 1926 cm–1 are attributed to a difference frequency, an overtone and a combination frequency of the fundamentals, respectively. The frequency of the 1392 cm–1 fundamental corresponding to the central C═C stretch of TCNE•– is red-shifted from the frequency of the steady state radical due to the close proximity and electron affinity of the countercation. The observation of a FSRS band at a difference frequency is analyzed. This analysis lends evidence for alternative nonlinear pathways of inverse Raman gain scattering (IRGS) or vertical-FSRS (VFSRS) which may contrib...
- Published
- 2018
10. Critical Role of Methylammonium Librational Motion in Methylammonium Lead Iodide (CH3NH3PbI3) Perovskite Photochemistry
- Author
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Richard A. Mathies, Minliang Lai, Jeffrey B. Neaton, Myeongkee Park, Nikolay Kornienko, Peidong Yang, and Sebastian E. Reyes-Lillo
- Subjects
chemistry.chemical_classification ,Photoluminescence ,Hydrogen bond ,Chemistry ,Mechanical Engineering ,Iodide ,Bioengineering ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Microstructure ,Photochemistry ,01 natural sciences ,0104 chemical sciences ,symbols.namesake ,Octahedron ,symbols ,General Materials Science ,0210 nano-technology ,Raman spectroscopy ,Spectroscopy ,Perovskite (structure) - Abstract
Raman and photoluminescence (PL) spectroscopy are used to investigate dynamic structure–function relationships in methylammonium lead iodide (MAPbI3) perovskite. The intensity of the 150 cm–1 methylammonium (MA) librational Raman mode is found to be correlated with PL intensities in microstructures of MAPbI3. Because of the strong hydrogen bond between hydrogens in MA and iodine in the PbI6 perovskite octahedra, the Raman activity of MA is very sensitive to structural distortions of the inorganic framework. The structural distortions directly influence PL intensities, which in turn have been correlated with microstructure quality. Our measurements, supported with first-principles calculations, indicate how excited-state MA librational displacements mechanistically control PL efficiency and lifetime in MAPbI3—material parameters that are likely important for efficient photovoltaic devices.
- Published
- 2017
11. Excited-state vibrational dynamics toward the polaron in methylammonium lead iodide perovskite
- Author
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Sergei Tretiak, Richard A. Mathies, Jeffrey B. Neaton, Peidong Yang, Amanda Neukirch, Scott R. Ellis, D. Dietze, Sebastian E. Reyes-Lillo, Minliang Lai, and Myeongkee Park
- Subjects
Materials science ,Science ,Wave packet ,Iodide ,General Physics and Astronomy ,02 engineering and technology ,Perovskite ,010402 general chemistry ,Polaron ,01 natural sciences ,Article ,General Biochemistry, Genetics and Molecular Biology ,symbols.namesake ,Ultrafast laser spectroscopy ,Perovskite (structure) ,chemistry.chemical_classification ,Multidisciplinary ,General Chemistry ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Lead ,chemistry ,Chemical physics ,Excited state ,Methylammonium ,symbols ,Condensed Matter::Strongly Correlated Electrons ,Density functional theory ,0210 nano-technology ,Raman spectroscopy - Abstract
Hybrid organic–inorganic perovskites have attractive optoelectronic properties including exceptional solar cell performance. The improved properties of perovskites have been attributed to polaronic effects involving stabilization of localized charge character by structural deformations and polarizations. Here we examine the Pb–I structural dynamics leading to polaron formation in methylammonium lead iodide perovskite by transient absorption, time-domain Raman spectroscopy, and density functional theory. Methylammonium lead iodide perovskite exhibits excited-state coherent nuclear wave packets oscillating at ~20, ~43, and ~75 cm−1 which involve skeletal bending, in-plane bending, and c-axis stretching of the I–Pb–I bonds, respectively. The amplitudes of these wave packet motions report on the magnitude of the excited-state structural changes, in particular, the formation of a bent and elongated octahedral PbI64− geometry. We have predicted the excited-state geometry and structural changes between the neutral and polaron states using a normal-mode projection method, which supports and rationalizes the experimental results. This study reveals the polaron formation via nuclear dynamics that may be important for efficient charge separation., Elucidating electron-phonon coupling in hybrid organic-inorganic perovskites may help us to understand the high photovoltaic efficiency. Here, the authors observe low-frequency Raman modes and related nuclear displacements of the Pb–I framework, indicating how these vibrational motions lead to polaron formation in perovskites.
- Published
- 2018
12. Microfluidic System for Detection of Viral RNA in Blood Using a Barcode Fluorescence Reporter and a Photocleavable Capture Probe
- Author
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Jean L. Patterson, Anthony Griffiths, Richard A. Mathies, Ricardo Carrion, Holger Schmidt, Ke Du, and Myeongkee Park
- Subjects
0301 basic medicine ,Microfluidics ,02 engineering and technology ,medicine.disease_cause ,Fluorescence ,Article ,Analytical Chemistry ,03 medical and health sciences ,chemistry.chemical_compound ,Fluorometer ,medicine ,DNA Barcoding, Taxonomic ,Humans ,Detection limit ,Ebola virus ,Chromatography ,Hybridization probe ,RNA ,Microfluidic Analytical Techniques ,021001 nanoscience & nanotechnology ,Ebolavirus ,Photochemical Processes ,Molecular biology ,030104 developmental biology ,chemistry ,RNA, Viral ,RNA extraction ,0210 nano-technology ,DNA Probes ,DNA - Abstract
A microfluidic sample preparation multiplexer (SPM) and assay procedure is developed to improve amplification-free detection of Ebola virus RNA from blood. While a previous prototype successfully detected viral RNA following off-chip RNA extraction from infected cells, the new device and protocol can detect Ebola virus in raw blood with clinically relevant sensitivity. The Ebola RNA is hybridized with sequence specific capture and labeling DNA probes in solution and then the complex is pulled down onto capture beads for purification and concentration. After washing, the captured RNA target is released by irradiating the photocleavable DNA capture probe with ultraviolet (UV) light. The released, labeled, and purified RNA is detected by a sensitive and compact fluorometer. Exploiting these capabilities, a detection limit of 800 attomolar (aM) is achieved without target amplification. The new SPM can run up to 80 assays in parallel using a pneumatic multiplexing architecture. Importantly, our new protocol does not require time-consuming and problematic off-chip probe conjugation and washing. This improved SPM and labeling protocol is an important step toward a useful POC device and assay.
- Published
- 2017
13. Coherent Nuclear Wave Packets Generated by Ultrafast Intramolecular Charge-Transfer Reaction
- Author
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Myeongkee Park, Taiha Joo, Kyoung Chul Ko, So Young Kim, Chul Hoon Kim, and Jin Yong Lee
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Chemistry ,Wave packet ,Analytical chemistry ,Fluorescence ,Molecular physics ,Reaction rate ,chemistry.chemical_compound ,Modulation ,Intramolecular force ,parasitic diseases ,General Materials Science ,Physical and Theoretical Chemistry ,Time-resolved spectroscopy ,Laurdan ,Ultrashort pulse - Abstract
Intramolecular charge-transfer (ICT) dynamics, including reaction coordinates, structural changes, and reaction rate, has been noted experimentally and theoretically. Here we report the ICT dynamics of laurdan investigated by time-resolved fluorescence at extreme time resolution of 30 fs. A single high-frequency coherent nuclear wave-packet motion on the product potential surface is observed through the modulation of the fluorescence intensity in time. Theory and experiment show that this vibrational mode involves large displacement of the carbon atoms in the naphthalene backbone, which indicates that the naphthalene backbone coordinates are strongly coupled to the ICT reaction of laurdan, not the twisting or planarization of the dimethylamino group.
- Published
- 2012
14. Sub-10 nm patterning with DNA nanostructures: a short perspective
- Author
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Zheng Zhang, Myeongkee Park, Junjun Ding, Huan Hu, and Ke Du
- Subjects
Novel technique ,Materials science ,Nanophotonics ,Bioengineering ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,chemistry.chemical_compound ,Nanomanufacturing ,Dna nanostructures ,DNA origami ,General Materials Science ,Particle Size ,Electrical and Electronic Engineering ,Mechanical Engineering ,DNA ,General Chemistry ,021001 nanoscience & nanotechnology ,Nanostructures ,0104 chemical sciences ,Nanolithography ,Nanoelectronics ,chemistry ,Mechanics of Materials ,0210 nano-technology - Abstract
DNA is the hereditary material that contains our unique genetic code. Since the first demonstration of two-dimensional (2D) nanopatterns by using designed DNA origami ∼10 years ago, DNA has evolved into a novel technique for 2D and 3D nanopatterning. It is now being used as a template for the creation of sub-10 nm structures via either 'top-down' or 'bottom-up' approaches for various applications spanning from nanoelectronics, plasmonic sensing, and nanophotonics. This perspective starts with an histroric overview and discusses the current state-of-the-art in DNA nanolithography. Emphasis is put on the challenges and prospects of DNA nanolithography as the next generation nanomanufacturing technique.
- Published
- 2017
15. Coherent and homogeneous intramolecular charge-transfer dynamics of 1-tert-butyl-6-cyano-1,2,3,4-tetrahydroquinoline (NTC6), a rigid analogue of DMABN
- Author
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Young Ho Rhee, Taiha Joo, Donghong Im, and Myeongkee Park
- Subjects
education.field_of_study ,Chemistry ,Population ,Relaxation (NMR) ,Solvation ,Conical intersection ,chemistry.chemical_compound ,Benzonitrile ,Crystallography ,Intramolecular force ,Excited state ,Physical and Theoretical Chemistry ,education ,Tetrahydrofuran - Abstract
We report the intramolecular charge-transfer (ICT) dynamics of 1-tert-butyl-6-cyano-1,2,3,4-tetrahydroquinoline (NTC6), a planar analogue of 4-(dimethylamino)benzonitrile (DMABN), by using time-resolved fluorescence (TRF) and TRF spectra (TRFS). TRFS allow accurate determination of the ICT dynamics free from the spectral relaxation caused by the solvation and vibronic relaxation. For NTC6 in tetrahydrofuran (THF), the locally excited (LE) state is populated exclusively presumably via a conical intersection from the initial photoexcited S2 (La) state, and the LE state undergoes ICT single exponentially with a time constant of 1.8 ± 0.2 ps. In acetonitrile, however, both LE (22%) and ICT (78%) states are populated from the S2 state, and the population in the LE state undergoes ICT in 800 ± 100 fs. The ICT state undergoes further relaxation in 1.2 ps along the solvation and the intramolecular nuclear coordinates involving the rotation of the amino group to form a twisted ICT state. Coherent nuclear wave packet motions of 130 cm(-1), which can be assigned to the -C≡N group bending mode, were observed in the TRF of the reactant (LE) and product (ICT) states, indicating that the ICT reaction is partially coherent. Compared with DMABN, the ICT dynamics of NTC6 are quite homogeneous, and we speculated on the narrow conformational distribution of NTC6 in the ground state along the rotation of the amino group due to its rigid structure.
- Published
- 2014
16. Structural diversity induced by pyrene intercalators in homogeneous oligodeoxyguanylates
- Author
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Taiha Joo, Byeang Hyean Kim, Hyun Seok Jeong, Jeong Wu Yi, and Myeongkee Park
- Subjects
Models, Molecular ,Pyrenes ,Base Sequence ,Molecular Structure ,Stereochemistry ,Chemistry ,Dimer ,Intercalation (chemistry) ,Intermolecular force ,Structural diversity ,Trimer ,Intercalating Agents ,chemistry.chemical_compound ,Spectrometry, Fluorescence ,Tetramer ,Oligodeoxyribonucleotides ,Computational chemistry ,Homogeneous ,Sequence Homology, Nucleic Acid ,Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization ,Pyrene ,Nucleic Acid Conformation ,Molecular Biology ,Biotechnology - Abstract
Homogeneous oligodeoxyguanylates incorporating small-molecule intercalator pyrene moieties in a 1,5 relationship form various structures of dimer, trimer, tetramer and internal hairpin form that are yellowish in color because of the intermolecular interactions between the pyrene units.
- Published
- 2010
17. Ultrafast Intramolecular Charge Transfer (ICT) Dynamics of 4- (dimethylamino)benzonitrile (DMABN)
- Author
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Chulhoon Kim, Myeongkee Park, and Taiha Joo
- Subjects
Benzonitrile ,chemistry.chemical_compound ,chemistry ,Intramolecular force ,Charge (physics) ,Acetonitrile ,Photochemistry ,Ultrashort pulse - Abstract
Formation times of intramolecular charge-transfer (ICT) state of 4-(dimethylamnio)benzonitrile (DMABN) in acetonitrile are resolved by time constants of 30 fs, 180 fs, and 2.7 ps, denoting the ICT state can be created through multi ways.
- Published
- 2010
18. Intramolecular Charge Transfer Dynamics of a Planarized Analogue of 4-(dimethylamino)benzonitrile (DMABN) by Time-Resolved Fluorescence
- Author
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Donghong Im, Myeongkee Park, So Young Kim, Taiha Joo, and Young Ho Rhee
- Subjects
Benzonitrile ,chemistry.chemical_compound ,Chemistry ,Stereochemistry ,Physics ,QC1-999 ,Intramolecular force ,Time constant ,Charge (physics) ,Time-resolved spectroscopy ,Photochemistry - Abstract
Intramolecular charge transfer (ICT) of confined 1-tert-butyl-6-cyano-1, 2, 3, 4-tetrahydroquinoline (NTC6) is determined with a single time constant of ∼1 ps regardless of solvents, although ICT of 4-(dimethylamino)benzonitrile (DMABN) shows dispersive dynamics in solvents.
- Published
- 2013
19. Mechanically and structurally robust sulfonated block copolymer membranes for water purification applications
- Author
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Yeo J, Sungjee Kim, Kim Th, Soo Young Kim, Myeongkee Park, and Du Yeol Ryu
- Subjects
Materials science ,Ionic bonding ,Bioengineering ,Portable water purification ,One-Step ,Permeability ,Water Purification ,Divalent ,chemistry.chemical_compound ,X-Ray Diffraction ,Pentanes ,Scattering, Small Angle ,Polymer chemistry ,Butadienes ,Pressure ,Copolymer ,General Materials Science ,Electrical and Electronic Engineering ,Nuclear Magnetic Resonance, Biomolecular ,chemistry.chemical_classification ,Mechanical Engineering ,Temperature ,Membranes, Artificial ,General Chemistry ,Nanostructures ,Molecular Weight ,Membrane ,chemistry ,Chemical engineering ,Mechanics of Materials ,Polystyrenes ,Nanofiltration ,Polystyrene - Abstract
The effective removal of ionic pollutants from contaminated water using negatively charged nanofiltration membranes is demonstrated. Block copolymers comprising polystyrene (PS) and partially hydrogenated polyisoprene (hPI) were synthesized by varying chain architectures. A one step procedure of cross-linking (hPI blocks) and sulfonation reactions (PS chains) was then carried out, which was revealed as an effective method to enhance mechanical integrity of membranes while hydrophilic sulfonated chains remain intact. In particular, the control of chain architecture allows us to create a synergetic effect on optimizing charge densities of the membrane, water permeability, and mechanical integrity under water purification conditions. The best performing membrane can almost completely (>99%) reject various divalent cations and also show NO(3)(-) rejection > 85% and Na(+) rejection > 87%. Well defined nanostructures (tens of nanometers) as well as the periodically arranged water domains (a few nanometers) within hydrophilic phases of the hydrated membranes were confirmed by in situ neutron scattering experiments.
- Published
- 2012
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