Structural Insights for β-Lactam Antibiotics

( Dogyeoung Kim ),( Sumin Kim ),( Yongdae Kwon ),( Yeseul Kim ),( Hyunjae Park ),( Kiwoong Kwak ),( Hyeonmin Lee ),( Jung Hun Lee ),( Kyung-min Jang ),( Donghak Kim ),( Sang Hee Lee ),( Lin-woo Kang ) 한국응용약물학회 2023 Biomolecules & Therapeutics(구 응용약물학회지) Vol.31 No.2

Antibiotic resistance has emerged as a global threat to modern healthcare systems and has nullified many commonly used antibiotics. β-Lactam antibiotics are among the most successful and occupy approximately two-thirds of the prescription antibiotic market. They inhibit the synthesis of the peptidoglycan layer in the bacterial cell wall by mimicking the D-Ala-D-Ala in the pentapeptide crosslinking neighboring glycan chains. To date, various β-lactam antibiotics have been developed to increase the spectrum of activity and evade drug resistance. This review emphasizes the three-dimensional structural characteristics of β-lactam antibiotics regarding the overall scaffold, working mechanism, chemical diversity, and hydrolysis mechanism by β-lactamases. The structural insight into various β-lactams will provide an in-depth understanding of the antibacterial efficacy and susceptibility to drug resistance in multidrug-resistant bacteria and help to develop better β-lactam antibiotics and inhibitors.

Detection of Rapid Atrial Arrhythmias in SQUID Magnetocardiography

김기웅,권혁찬,김기담,이용호,김진목,김인선,임현균,박용기,김두상,임승평,Kim Kiwoong,Kwon Hyukchan,Kim Ki-Dam,Lee Yong-Ho,Kim Jin-Mok,Kim In-Seon,Lim Hyun-Kyoon,Park Yong-Ki,Kim Doo-Sang,Lim Seung-Pyung The Korean Superconductivity Society 2005 Progress in superconductivity Vol.7 No.1

We propose a method to measure atrial arrhythmias (AA) such as atrial fibrillation (Afb) and atrial flutter (Afl) with a SQUID magnetocardiograph (MCG) system. To detect AA is one of challenging topics in MCG. As the AA generally have irregular rhythm and atrio-ventricular conduction, the MCG signal cannot be improved by QRS averaging; therefore a SQUID MCG system having a high SNR is required to measure informative atrial excitation with a single scan. In the case of Afb, diminished f waves are much smaller than normal P waves because the sources are usually located on the posterior wall of the heart. In this study, we utilize an MCG system measuring tangential field components, which is known to be more sensitive to a deeper current source. The average noise spectral density of the whole system in a magnetic shielded room was $10\;fT/{\surd}Hz(a)\;1\;Hz\;and\;5\;fT/{\surd}Hz\;(a)\;100\;Hz$. We measured the MCG signals of patients with chronic Afb and Afl. Before the AA measurement, the comparison between the measurements in supine and prone positions for P waves has been conducted and the experiment gave a result that the supine position is more suitable to measure the atrial excitation. Therefore, the AA was measured in subject's supine position. Clinical potential of AA measurement in MCG is to find an aspect of a reentry circuit and to localize the abnormal stimulation noninvasively. To give useful information about the abnormal excitation, we have developed a method, separative synthetic aperture magnetometry (sSAM). The basic idea of sSAM is to visualize current source distribution corresponding to the atrial excitation, which are separated from the ventricular excitation and the Gaussian sensor noises. By using sSAM, we localized the source of an Afl successfully.

Development of a bio-magnetic measurement system and sensor configuration analysis for rats

Kim, Ji-Eun,Kim, In-Seon,Kim, Kiwoong,Lim, Sanghyun,Kwon, Hyukchan,Kang, Chan Seok,Ahn, San,Yu, Kwon Kyu,Lee, Yong-Ho American Institute of Physics 2017 Review of scientific instruments Vol.88 No.4

Effect of Additional Reference Current in a Reference Junction-Double Relaxation Oscillation SQUID (RJ-DROS)

Kim, Jin-Mok,Lee, Yong-Ho,Kwon, Hyukchan,Kim, Kiwoong,Sasada, Ichiro IEEE 2007 IEEE transactions on applied superconductivity Vol.17 No.1

<P>A double relaxation oscillation SQUID with a reference junction (RJ-DROS) already has a fixed reference current, so that it holds a fixed flux-to-voltage characteristics when fabricated. When an additional current flows through the reference junction but not through the signal junction in the RJ-DROS, we have obtained the variation of its characteristics. The additional reference current has an effect on reducing the fixed reference current, which results in changing averaged relaxation voltage and transfer coefficient. In particular, while the critical current of the signal SQUID exceeds the reference current, the averaged relaxation voltage at the reference junction is enlarged by the added bias current combined with an additional current and an initial bias current. Therefore the additional reference current can provide the RJ-DROS with variable modulation depth and width within the operating range. Although the characteristics of RJ-DROSs are fixed differently each to each when they are fabricated, the additional current can adjust their characteristics to the same one, which is useful for controlling DROSs in a multichannel DROS system. However, an input-bias current in the preamplifier detecting the outputs at the reference junction, acts as an additional current, and then makes the reference current shift from the optimum current or deviate from the operating range, the input-bias current needs to be regulated within the operating range</P>

Substrate temperature-dependent diffusion from CdS/ZnO:Al layer into the absorber layer in Cu(In, Ga)Se2 solar cell during the deposition of ZnO:Al window layer

Kim Kiwoong,Yi Yeonjin,Han Daeyeop,Choi Jinchul 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.79 No.9

The effect of the substrate temperature during the deposition of a ZnO:Al (AZO) window layer on the performance of Cu(In, Ga)Se2 (CIGS) solar cells was studied. Although the structural, electrical and optical properties of separate AZO films are enhanced with higher substrate temperature, the overall performance of final CIGS solar cells is deteriorated. At higher substrate temperature, the diffusion of Cd, Zn and Al into the CIGS absorber layer was observed with secondary ion-mass spectroscopy measurements. This diffusion could form a buried p–n junction, resulting in deteriorated device characteristics.

Hole injection improvement using ultrathin Li-TFSI layer in organic light-emitting diodes

Kim Kiwoong,Yi Yeonjin,Lee Hyunbok 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.79 No.10

A high device performance of organic light-emitting diodes (OLEDs) can be achieved by minimizing the hole injection barrier (HIB) at the anode interface. However, the work function of indium tin oxide (ITO) is not sufficiently high; thus, the use of an appropriate hole injection layer (HIL) is necessary. In this study, we demonstrated that bis(trifluoromethane) sulfonimide lithium salt (Li-TFSI) is an efficient HIL to decrease the HIB in OLEDs. The device performances of hole-only devices (HODs) and OLEDs were significantly enhanced by the insertion of the ultrathin Li-TFSI HIL between the N,N′- di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) hole transport layer and ITO. In situ ultraviolet photoelectron spectroscopy measurements revealed that the work function of ITO was considerably increased by the deposition of the Li-TFSI HIL. Accordingly, the HIB from ITO to NPB was remarkably reduced. This is the origin of the hole injection improvements in the HODs and OLEDs with the Li-TFSI HIL. Thus, Li-TFSI would be an efficient interface modifier to increase the work function of the electrode and decrease the HIB in various electronic devices.

Direct p-doping of Li-TFSI for efficient hole injection: Role of polaronic level in molecular doping

Kim, Kiwoong,Jeong, Junkyeong,Kim, Minju,Kang, Donghee,Cho, Sang Wan,Lee, Hyunbok,Yi, Yeonjin Elsevier 2019 APPLIED SURFACE SCIENCE - Vol.480 No.-

<P><B>Abstract</B></P> <P>Bis(trifluoromethane)sulfonimide lithium salt (Li-TFSI) has been popularly employed as an efficient p-dopant that increases the conductivity of a hole transport layer (HTL) in perovskite solar cells and dye-sensitized solar cells. However, the working mechanism of the Li-TFSI dopant is a long-standing question. The hygroscopicity of Li-TFSI makes it difficult to isolate the exact doping mechanism. In this study, we unveil the role of Li-TFSI in the p-doping to the <I>N</I>,<I>N</I>′-di(1-naphthyl)-<I>N</I>,<I>N</I>′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) HTL. A series of systematic in situ measurements using ultraviolet and inverse photoelectron spectroscopy reveal that electron transfer from NPB to Li-TFSI occurs due to the lower-lying negative polaronic level of Li-TFSI rather than the positive polaronic level of NPB. The hole injection barrier between NPB and indium tin oxide is significantly reduced with Li-TFSI doping, enhancing the device performance of hole-only devices and organic light-emitting diodes dramatically. With excessive dopants, however, the agglomerative property of Li-TFSI became dominant, decreasing the doping efficiency. These results provide robust guidelines for developing an efficient doping method for a molecular system with high conductivity.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Electronic structure of Li-TFSI and NPB was investigated using in situ UPS and IPES. </LI> <LI> Electron transfer occurred from NPB to Li-TFSI through their polaronic levels. </LI> <LI> Hole injection barrier was reduced by 0.70 eV with Li-TFSI doping. </LI> <LI> Device performance of OLEDs was significantly enhanced with Li-TFSI doping. </LI> <LI> With excessive dopants, agglomeration of Li-TFSI decreased doping efficiency. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Energy Exchangeable Fluidized Bed Process for CO₂ Capture

Kiwoong Kim(김기웅),Dae Jin Kim(김대진),Minkee Choi(최민기),Yong Ki Park(박용기) 한국에너지기후변화학회 2022 한국에너지기후변화학회 학술대회 Vol.2022 No.5

Nature-inspired thermo-responsive multifunctional membrane adaptively hybridized with PNIPAm and PPy

Kim, Hyejeong,Kim, Kiwoong,Lee, Sang Joon Nature Publishing Group 2017 NPG Asia Materials Vol.9 No.10

<P>Specialized plant tissues, such as the epidermis of a leaf covered with stomata, consist of soft materials with deformability and electrochemical properties to achieve specific functions in response to various environmental stimuli. Stimulus-responsive hydrogels with electrochemical properties are good candidates for imitating such special functionalities in nature and thus have great potential in a wide range of academic and industrial applications. However, hydrogel-incorporated conductive materials are usually mechanically rigid, which limits their application in other fields. In addition, the fabrication technology of structured functional hydrogels has low reproducibility due to the required multistep processing. Here, inspired by nature, specifically the stimulus-responsive functionalities of plants, a new thermo-responsive multifunctional hybrid membrane (HM) is synthesized through the in situ hybridization of conductive poly(pyrrole) (PPy) on a photopolymerized poly(N-isopropylacrylamide) (PNIPAm) matrix. The morphological and electrical properties of the fabricated HM are investigated to characterize various aspects of its multiple functions. In terms of morphology, the HM can be easily fabricated into various structures by smartly utilizing photopolymerization patterning, and it exhibits thermo-responsive deformability. In terms of functionality, it exhibits various electrical and charge responses to thermal stimuli. This simple and efficient fabrication method can be used as a promising platform for fabricating a variety of functional devices.</P>

Crossly charged microfluidic device for spontaneous filtration without an external power supply

Kim, Kiwoong,Lee, Sang Joon Academic Press 2019 Analytical biochemistry Vol.577 No.-

<P><B>Abstract</B></P> <P>Spontaneous filtration without a power supply was investigated using highly charged precursor mixtures instead of recognized microfluidic desalination techniques. The proposed filtration method consisted of a main channel (depth: 1 mm) and shallow channels (depth: 400 μm) in which the precursor mixture was injected. The filtration performance of the proposed device was evaluated by injecting a fluorescent dye that moved toward the centerline of the main channel. The respective rejection rates of CaCl<SUB>2</SUB>, NaCl, CaSO<SUB>4</SUB>, and Na<SUB>2</SUB>SO<SUB>4</SUB> were 3.16%, 30.13%, 43.74%, and 36.32%, respectively. This trend can be explained by the mechanism of Donnan exclusion theory. The focusing of charged species toward the centerline of the main channel was caused by highly charged surfaces. The proposed filtration method exhibited a migration of charged microparticles toward a certain direction. This particle migration behavior was consistent with the simulation data. These results suggested that the proposed filtration method had strong potential for desalinating brackish water or salty surface water without an external power supply.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A spontaneous filtration of ions and charged particles without an external electrical power supply. </LI> <LI> Crossly charged channel surfaces had the same surface charge between diagonal-directional shallow channels. </LI> <LI> The proposed method exhibited a noticeable filtration performance by focusing charged materials toward a certain direction. </LI> <LI> This work can be considered a promising paradigm of nature-inspired desalination technology. </LI> </UL> </P>