About

Hyung J. Kim is a professor in the Department of Chemistry at Carnegie Mellon University. His research focuses on the molecular simulation and theoretical study of ionic liquids, including their solvation properties, interfacial behaviors, and applications in various chemical processes. His work involves ab initio calculations, classical molecular dynamics simulations, and development of force fields to understand the interactions and behaviors of ionic liquids and related systems. Additionally, his research extends to studying solvation phenomena, charge transfer, and the structural and dynamic heterogeneities in ionic liquids, contributing to the broader understanding of these complex fluids and their potential applications in energy storage, carbon capture, and other fields.

Research topics

• Chemistry
• Organic chemistry
• Surgery
• Immunology
• Internal medicine
• Biology
• Gastroenterology
• Cell biology
• Combinatorial chemistry
• Pathology
• Nursing
• Medicine
• Biochemistry

Selected publications

• Design of ionic liquids as a desiccant for the liquid desiccant type air conditioning system

  Chemistry Letters · 2024-08-26 · 3 citations

  articleOpen accessSenior authorCorresponding

  Abstract Recently, liquid desiccant air conditioners (LDACs) have gained rapidly growing interest as an important candidate for an energy-efficient air conditioner. By enabling moisture absorption from the air, ionic liquids (ILs) can serve as a novel desiccant source for LDACs. For insights into the design and optimization of ILs to this end, we herein present a survey of studies on dehumidification and other relevant properties of ILs and offer some molecular perspective on their feasibility as a desiccant.

  PublisherOA PDFDOI

• On the Moisture Absorption Capability of Ionic Liquids

  The Journal of Physical Chemistry B · 2024-06-14 · 12 citations

  articleOpen accessSenior authorCorresponding

  Due to their many attractive physicochemical properties, ionic liquids (ILs) have received extensive attention with numerous applications proposed in various fields of science and technology. Despite this, the molecular origins of many of their properties, such as the moisture absorption capability, are still not well understood. For insight into this, we systematically synthesized 24 types of ILs by the combination of the dimethyl phosphate anion with various types of alkyl group-substituted cyclic cations─imidazolium, pyrazolium, 1,2,3-triazolium, and 1,2,4-triazolium cations─and performed a detailed analysis of the dehumidification properties of these ILs and their aqueous solutions. It was found that these IL systems have a high dehumidification capability (DC). Among the monocationic ILs, the best performance was obtained with 1-cyclohexylmethyl-4-methyl-1,2,4-triazolium dimethyl phosphate, whose DC (per mol) value is 14 times higher than that of popular solid desiccants like CaCl2 and silica gel. Dicationic ILs, such as 1,1′-(propane-1,3-diyl)bis(4-methyl-1,2,4-triazolium) bis(dimethyl phosphate), showed an even better moisture absorption, with a DC (per mol) value about 20 times higher than that of CaCl2. Small- and wide-angle X-ray scattering measurements of eight types of 1,2,4-triazolium dimethyl phosphate ILs were performed and revealed that the majority of these ILs form nanostructures. Such nanostructures, which vary with the identity of the IL and the water content, fall into three main categories: bicontinuous microemulsions, hexagonal cylinders, and micelle-like structures. Water in the solutions exists primarily in polar regions in the nanostructures; these spaces function as water pockets at relatively low water concentrations. Since the structure and stability of the aggregated forms of the ILs are mainly governed by the interactions of nonpolar groups, the alkyl side chains of the cations play an important role in the DC and temperature-dependent equilibrium water vapor pressure of the IL solutions. Our experimental findings and molecular dynamics simulation results shed light on the moisture absorption mechanism of the IL aqueous solutions from a molecular perspective.

  PublisherOA PDFDOI

• Spectroscopic and Chemical Properties of Ionic Liquids: Computational Study

  The Chemical Record · 2023-05-11 · 1 citations

  reviewOpen access1st authorCorresponding

  Abstract A brief account is given of highlights of our computational efforts – often in collaboration with experimental groups – to understand spectroscopic and chemical properties of ionic liquids (ILs). Molecular dynamics, including their inhomogeneous character, responsible for key spectral features observed in dielectric absorption, infra‐red (IR) and fluorescence correlation spectroscopy (FCS) measurements are elucidated. Mechanisms of chemical processes involving imidazolium‐based ILs are illustrated for CO 2 capture and related reactions, transesterification of cellulose, and Au nanocluster‐catalyzed Suzuki cross‐coupling reaction with attention paid to differing roles of IL ions. A comparison with experiments is also made.

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• Infrared Spectroscopy of Li⁺ Solvation in Diglyme: Ab Initio Molecular Dynamics and Experiment

  The Journal of Physical Chemistry B · 2023-10-11 · 9 citations

  articleOpen accessSenior authorCorresponding

  Infrared (IR) spectra of solutions of the lithium salt LiBF4 in diglyme, CH3O(CH2CH2O)2CH3, are studied via IR spectroscopy and ab initio molecular dynamics (AIMD) simulations. Experiments show that the major effects of LiBF4, compared to neat diglyme, are the appearance of a new broad band in the 250–500 cm–1 frequency region and a broadening and intensity enhancement of the diglyme band in the 900–1150 cm–1 region accompanied by a red-shift. Computational analysis indicates that hindered translational motions of Li+ in its solvation cage are mainly responsible for the new far-IR band, while the changes in the mid-IR are due to Li+-coordination-dependent B–F stretching vibrations of BF4– anions coupled with diglyme vibrations. Molecular motions in these and lower frequency regions are generally correlated, revealing the collective nature of the vibrational dynamics, which involve multiple ions/molecules. Herein, a detailed analysis of these features via AIMD simulations of the spectrum and its components, combined with analysis of the generalized normal modes of the solution components, is presented. Other minor spectral changes as well as diglyme conformational changes induced by the lithium salt are also discussed.

  PublisherDOI

• Hyperthermia accelerates neuronal loss differently between the hippocampal CA1 and CA2/3 through different HIF‑1α expression after transient ischemia in gerbils

  International Journal of Molecular Medicine · 2022-02-28 · 11 citations

  articleOpen access

  The hippocampus has a different vulnerability to ischemia according to the subfields CA1 to CA3 (initials of cornu ammonis). It has been reported that body temperature changes during ischemia affect the degree of neuronal death following transient ischemia. Hypoxia‑inducible factor 1α (HIF‑1α) plays a key role in regulating cellular adaptation to low oxygen conditions. In the present study, we investigated the pattern of neuronal death (loss) in CA1 and CA2/3 following 5 min transient forebrain ischemia (TFI) under hyperthermia (39.5±0.2˚C) and the relationship between neuronal death and changes in HIF‑1α expression using western blot analysis and immunohistochemistry in gerbils. Normothermia or hyperthermia was induced for 30 min before and during the TFI, and neuronal death and HIF‑1α expression were observed at 0, 3, 6 and 12 h, 1, 2 and 5 days after TFI. Under normothermia, TFI‑induced neuronal death of CA1 pyramidal neurons occurred on day 5 after TFI, but CA2/3 pyramidal neurons did not die. In contrast, under hyperthermia, the death of CA1 and CA2/3 pyramidal neurons was observed on day 2 after TFI. Under normothermia, HIF‑1α expression was significantly elevated in both CA1 and CA2/3 pyramidal neurons at 12 h and 1 day after TFI, and the increased HIF‑1α immunoreactivity in CA1 was dramatically reduced from 2 days after TFI, but not in CA2/3 pyramidal neurons. Under hyperthermia, the basal expression of HIF‑1α in the sham group was significantly higher in both CA1 and CA2/3 pyramidal neurons at 0 h after TFI than in the normothermia group. HIF‑1 expression was continuously higher, peaked at 12 h after TFI, and then significantly decreased from 1 day after TFI. Overall, the present results indicate that resistance to ischemia in CA2/3 pyramidal neurons is closely associated with the persistence of increased expression of HIF‑1α after ischemic insults and that hyperthermia‑induced exacerbation of death of pyramidal neurons is closely related to decreased HIF‑1α expression after ischemic insults.

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• Mass Spectrometry of Au₁₀(4-<i>tert-</i>butylbenzenethiolate)₁₀ Nanoclusters Using Superconducting Tunnel Junction Cryodetection Reveals Distinct Metastable Fragmentation

  Journal of the American Society for Mass Spectrometry · 2022-02-11 · 7 citations

  article

  Cryodetection mass spectrometry (MS) was used to study the Au10(TBBT)10 (TBBT = 4-tert-butylbenzenethiolate) catenane nanocluster. The matrix-assisted laser desorption ionization (MALDI) process generates distinct fragments that can be arranged into two distinct regimes: (i) in-source fragmentation, which occurs rapidly in a relatively short (<170 ns) time frame, and (ii) metastable fragmentation, which occurs postacceleration during a time-of-flight (TOF) mass analysis over a longer time frame (>170 ns–250 μs). Using MALDI-TOF MS with superconducting tunnel junction (STJ) cryodetection, distinct metastable nanocluster fragments were resolved at lower energies deposited into the detector. The results also demonstrated that STJ cryodetection MS can be used to acquire multiple (>10), simultaneous tandem mass spectra in a single experiment. Simulated fragmentation of the Au10 nanocluster using ab initio molecular dynamics (AIMD) revealed the different fragmentation processes and confirmed the MS results. Using both the empirical MS data and AIMD calculations, fragmentation pathways are proposed for Au10(TBBT)10, which terminate with two small, stable ringed species.

  PublisherDOI

• FcγRIIB controls antibody-mediated target cell depletion by ITIM-independent mechanisms

  Cell Reports · 2022 · 23 citations

  • Cell biology
  • Biology
  • Immunology

  Many therapeutic antibodies deplete target cells and elicit immunotherapy by engaging activating Fc gamma receptors (FcγRs) on host effector cells. These antibodies are negatively regulated by the inhibitory FcγRIIB (CD32B). Dogma suggests inhibition is mediated through the FcγRIIB immunoreceptor tyrosine-based inhibition motif (ITIM), negatively regulating immunoreceptor tyrosine-based activation motif (ITAM)-mediated signaling from activating FcγR. To assess this, we generated experimental models expressing human (h)FcγRIIB on targets or effectors, lacking or retaining ITIM signaling capacity. We demonstrate that signaling through the hFcγRIIB ITIM is dispensable for impairing monoclonal antibody (mAb)-mediated depletion of normal and malignant murine target cells through three therapeutically relevant surface receptors (CD20, CD25, and OX40) affecting immunotherapy. We demonstrate that hFcγRIIB competition with activating FcγRs for antibody Fc, rather than ITIM signaling, is sufficient to impair activating FcγR engagement, inhibiting effector function and immunotherapy.

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• Universal Solvent Viscosity Reduction via Hydrogen Bonding Disruptors

  2022-06-27

  reportOpen access

  Liquid Ion Solutions LLC (DBA RoCo Global) in partnership with Carnegie Mellon University and Carbon Capture Scientific LLC, has performed lab-scale development and evaluation of novel additives that lower the viscosity of water-lean amine solvents for post-combustion carbon dioxide capture. This project focuses on developing additives that minimize the formation of long-range electrostatic and hydrogen bonding (HB) networks, decreasing the solvent viscosity, improving diffusion, and improving the process economics. The project objectives included: 1) performing computer simulation to understand the molecular interactions of the additive molecules in water-lean CO₂ capture solvents, 2) design and synthesis of HB disruptors additives, 3) performance testing with additive molecules on model amine solvents, and 4) demonstration of the effectiveness of the optimized additives in the presence of synthetic flue gas. To meet the abovementioned objectives, the project team utilized a holistic approach that combines molecular simulation, experimental testing, and economic analysis studies. The project team developed ab initio molecular model and then perform computer simulation to develop relationship between hydrogen bonding, viscosity, and performed quantitative analysis of additive on the viscosity of the solvent. The team completed computational comparative study on a range of organic functional groups such as ethers, esters, cyclic carbonates, alkanes, and ammonium salts for their effect on viscosity gaining key insights into molecular interactions and the impact of various functional groups and molecular shapes on viscosity. Assisted with molecular simulation insights, the project team conducted additive synthesis and testing, including a proof-of-concept study, additive screening, optimization, and synthetic flue gas testing. The experimental proof-of-concept study proved that the hydrogen bonding acceptors result in significant decrease of viscosities. Detailed additive screening (exploring various functionalities and molecular structures) has been performed. Several promising additives showed excellent reduction in viscosity (30-41%) at 5% additive loading, and over 50% viscosity reduction at 10% additive loading for the model solvents. The team also performed complex screening studies on additive loadings and mixing effect among additives using the design of experiments. Based on multiple screening experiments, one additive-solvent candidate was down-selected for synthetic flue gas testing. A 100-hour continuous absorption/desorption study was conducted under simulated flue gas using a lab-scale continuous capture and separation system. No degradation (for both solvent and additive) was observed based on the GC results of the solvent samples collected from the continuous study. The team conducted preliminary engineering analyses and cost-benefit analyses to quantify the potential economic benefits of the additive approach for solvent viscosity reduction. Based on the experimental data, CO₂ capture cost savings from the capital and operating cost savings are estimated at $\$$4.7/tonne and $\$$0.3/tonne CO₂ captured, respectively. Considering the additive cost, the net benefit is estimated to be between $\$$4.32~$\$$4.86/tonne CO₂ captured.

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• Infrared Spectroscopy of Li⁺ Solvation in EmimBF₄ and in Propylene Carbonate: Ab Initio Molecular Dynamics and Experiment

  The Journal of Physical Chemistry B · 2022-11-03 · 10 citations

  articleOpen accessSenior authorCorresponding

  Infrared (IR) spectra of solutions of the lithium salt LiBF4 in the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EmimBF4) and in the organic solvent propylene carbonate (PC) are studied via infrared spectroscopy and ab initio molecular dynamics (AIMD) simulations. The measurements show that the major effects of LiBF4 in both solutions, compared to their neat counterparts, are the appearance of a new broad band in the 300–450 cm–1 frequency region and a broadening of the IR structure in the 900–1200 cm–1 region with the development of a new peak at 980 cm–1. Computational analysis indicates that hindered translational motions of Li+ in its solvation cage are mainly responsible for the former, while the latter is due to Li+-induced structural changes and accompanying vibrational frequency shifts of constituent ions and molecules of the solutions. In addition, molecular motions in these and lower-frequency regions are generally correlated, disclosing the collective nature of the vibrational dynamics, which involve multiple ions/molecules. Herein, a detailed analysis of these features via AIMD simulations of the spectrum and its components arising from auto- and cross-correlations of motions of constituent molecular species, combined with generalized normal modes of the solutions and normal modes of small Li+-containing clusters, is presented. Other minor spectral changes caused by the lithium salt as well as the interaction-induced effect on IR spectra are also discussed.

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• Non-Gaussianities in the extended EFT of inflation

  Journal of Cosmology and Astroparticle Physics · 2022-01-01

  preprintOpen accessSenior authorCorresponding

  Abstract In earlier works, we studied the validity of Extended Effective Field Theory of Inflation (EEFToI) in the regime where initial conditions are set with dispersion relations ω 2 ∝ k 6 . We had also evaluated and examined the power spectrum for some interesting corners of the parameter space. In this paper, we compute the bispectrum in the EEFToI, take a closer look at the strong coupling constraints and calculate the size of the non-Gaussianities in those regions of parameter space. We also investigate the shape of triangles that contribute to the enhancement of non-Gaussianities in this regime. We find that there are allowed parts of parameter spaces where EEFToI description with initial conditions set with ω 2 ∝ k 6 is sensible and interesting.

  PublisherDOI

Recent grants

• International Collaboration in Chemistry: A Combined Computational and Spectroscopic Study of Structure and Charge Transfer Dynamics of Ionic Liquids in Heterogeneous Environments

  NSF · $398k · 2012–2016

Frequent coauthors

• Youngseon Shim

  Samsung (South Korea)

  91 shared

• M. Y. Choi

  42 shared

• Nilesh R. Dhumal

  Florida Gulf Coast University

  41 shared

• Johannes Kiefer

  University of Bremen

  39 shared

• Hadi Abroshan

  Schrodinger (United States)

  32 shared

• Daun Jeong

  31 shared

• Gao Li

  Dalian Institute of Chemical Physics

  21 shared

• Swati R. Manjari

  University at Albany, State University of New York

  20 shared

Labs

• The Kim GroupPI

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Education

• Ph.D.

  State University of New York at Stony Brook

  1988

Awards & honors

• Invitational Fellowship, JSPS (Japan Society for the Promoti…
• KIAS Scholar, School of Computational Sciences, Korea Instit…
• Adjunct Professor of Physics, Korea University (2007)
• Visiting Associate Professor of Chemistry, University of Col…
• Distinguished Visiting Associate Professor of Physics, BK21,…