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 Desalination Membrane Bioinspired by Mangrove Roots for Spontaneous Filtration of Sodium Ions

Kim, Kiwoong,Kim, Hyejeong,Lim, Jae Hong,Lee, Sang Joon American Chemical Society 2016 ACS NANO Vol.10 No.12

<P>The shortage of available fresh water is one of the global issues presently faced by humanity. To determine a solution to this problem, the survival strategies of plants have been examined. In this study, a nature-inspired membrane with a highly charged surface is proposed as an effective membrane for the filtration of saline water. To mimic the desalination characteristics of mangrove roots, a macroporous membrane based on polyethylene terephthalate is treated with polyelectrolytes using a layer-by-layer deposition method. The fabricated membrane surface has a highly negative charged zeta-potential value of -97.5 +/- 4.3 mV, similar to that of the first layer of mangrove roots. Desalination of saline water using this membrane shows a high salt retention rate of 96.5%. The highly charged surface of the membrane may induce a relatively thick and stable ion depletion zone in front of the membrane. As a result, most co-ions are repelled from the membrane surface, and counterions are also rejected by virtue of their electroneutrality. The water permeability is found to be 7.60-7.69 L/m(2).h, which is 10 times higher than that of the reverse osmosis desalination method. This nature-inspired filtration membrane exhibits steady desalination performance over 72 h of operation, successfully demonstrating the stable filtration of saline water. This nature-inspired membrane is applicable to the design of a small-scale, portable, and energy-free desalination device for use in third-world countries or small villages.</P>

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.

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

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>

Nocturnal Desaturation in the Stroke Unit Is Associated With Wake-Up Ischemic Stroke

Kim, Tae Jung,Ko, Sang-Bae,Jeong, Han-Gil,Lee, Ji Sung,Kim, Chi Kyung,Kim, Yerim,Nam, Kiwoong,Mo, Heejung,Joon An, Sang,Choi, Huimahn Alex,Yoon, Byung-Woo American Heart Association, Inc. 2016 Stroke Vol.47 No.7

<P>Background and Purpose-Wake-up stroke (WUS) represents a quarter of all ischemic strokes and may be a specific subgroup. Nocturnal desaturation secondary to sleep-disordered breathing is an independent risk factor for stroke, but the association between nocturnal desaturation and WUS remains unclear. We investigated the relationship between nocturnal desaturation using oxygen desaturation index and WUS in patients with acute stroke in the stroke unit. Methods-A total of 298 patients admitted for acute ischemic stroke to the stroke unit between July 2013 and May 2015 were enrolled. The oxygen desaturation index was calculated using pulse oximetry data sampled every 1 minute during 9 hours on the first night (10:00 PM-7:00 AM) of the stroke unit admission, and nocturnal desaturation was defined as an oxygen desaturation index of 5 at least per hour. We compared the clinical characteristics and nocturnal desaturations between patients with and without WUS. Results-Among all patients (age, 67.7 +/- 12.6 years; male, 54.4%), 26.5% patients had WUS. The proportion of nocturnal desaturation was significantly greater in patients admitted with WUS (29.1% versus 12.3%, P=0.001). The age, sex, risk factors except for hyperlipidemia, stroke severity, and stroke mechanisms were similar between the 2 groups. After adjustment for covariates, it was found that nocturnal desaturation was significantly more common in the WUS group (odds ratio, 3.25; 95% confidence interval, 1.63-6.46). Conclusions-Nocturnal desaturation was more frequently observed in patients admitted with WUS during the first night in the stroke unit. This suggests that nocturnal desaturation is a possible modifiable risk factor for the occurrence of WUS.</P>

Promoting alkali and alkaline-earth metals on MgO for enhancing CO₂ capture by first-principles calculations

Kim, Kiwoong,Han, Jeong Woo,Lee, Kwang Soon,Lee, Won Bo The Royal Society of Chemistry 2014 Physical chemistry chemical physics Vol.16 No.45

<P>Developing next-generation solid sorbents to improve the economy of pre- and post-combustion carbon capture processes has been challenging for many researchers. Magnesium oxide (MgO) is a promising sorbent because of its moderate sorption-desorption temperature and low heat of sorption. However, its low sorption capacity and thermal instability need to be improved. Various metal-promoted MgO sorbents have been experimentally developed to enhance the Cc sorption capacities. Nevertheless, rigorous computational studies to screen an optimal metal promoter have been limited to date. We conducted first-principles calculations to select metal promoters of MgO sorbents. Five alkali (Li-, Na-, K-, Rb-, and Cs-) and 4 alkaline earth metals (Be-, Ca-, Sr-, and Ba-) were chosen as a set of promoters. Compared with the CO2 adsorption energy on pure MgO, the adsorption energy on the metal-promoted MgO sorbents is higher, except for the Na-promoter, which indicates that metal promotion on MgO is an efficient approach to enhance the sorption capacities. Based on the stabilized binding of promoters on the MgO surface and the regenerability of sorbents, Li, Ca, and Sr were identified as adequate promoters among the 9 metals on the basis of PW91/GGA augmented with DFT+D2. The adsorption energies of CO2 on metal-promoted MgO sorbents for Li, Ca, and Sr atoms are -1.13, -1.68, and -1.48 eV, respectively.</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.

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>