https://scholar.dgist.ac.kr/handle/20.500.11750/348 2026-04-04T13:17:53Z 2026-04-04T13:17:53Z Lhee, SangMoon Kim, Sunhee Nam, Hong Gil https://scholar.dgist.ac.kr/handle/20.500.11750/59003 2025-09-01T10:10:10Z 2018-02-19T15:00:00Z

Title: The Localization of Biological Compounds on the Soft Interface of Microdroplet May Answer the Accelerated Reaction Rates Inside Microdroplet Author(s): Lhee, SangMoon; Kim, Sunhee; Nam, Hong Gil Abstract: Many researchers have reported that microdroplet environment is a good reaction bath providing the remarkably accelerated chemical reaction rates and is directing the reaction path differently from the corresponding bulk-phase reactions. Since the related thermodynamic parameters gave the clues to the uneven distribution of molecules inside the small-compartmentalized space, we have visualized the localization of several biological compounds inside the aqueous microdroplet including proteins, nucleic acids, and carbohydrates with the help of some fluorescence microscopy techniques. Now, we present the localization of molecules on the water-oil interface is common under physiological condition and the charge states of molecules and interface contributes to the variation of the distribution. The observation of the molecules on the interface by means of fluorescence anisotropy gives us some suggestions that the molecular movement on the interface is not only spatially restricted, but is also guided with orientation. We suggest that such the guided movements with some degree of order is another contribution factor to accelerating the unfavorable reaction including enzymatic reactions.

2018-02-19T15:00:00Z Lee, Jae Kyoo Nam, Hong Gil Zare, Richard https://scholar.dgist.ac.kr/handle/20.500.11750/59002 2025-09-01T08:40:12Z 2017-04-01T15:00:00Z

Title: Accelerated biomolecular kinetics revealed by microdroplet fusion mass spectrometry Author(s): Lee, Jae Kyoo; Nam, Hong Gil; Zare, Richard Abstract: We have developed a new time-resolved mass spectrometry using fused microdroplets (PNAS, 2016). This technique enables (1) recording fast chemical reactions on the microsecond timescale which is about two orders of magnitude faster than previously developed time-resolved mass spectrometry, (2) capturing early molecular events occurring within a few microseconds, and (3) studying liquid-phase kinetics in confined environment such as in microdroplets which contrasts against the studies carried out in reactions in bulk solution. The power of this technique to monitor fast kinetics and to detect reaction intermediates was demonstrated through the kinetic studies of protein unfolding, the hydrogen-deuterium exchange in peptides, and protein-ligand interactions. We have found a markedly high acceleration of reaction rates in microdroplets by factors of 103 to 106 compared to bulk solutions regardless of reaction mechanisms, including specific covalent and nonspecific noncovalent bonding (Q Rev Biophys, 2015). To address the mechanism of the reaction acceleration, we examined several factors influencing the acceleration of acid-induced chlorophyll demetallation. The investigation of the effect of charge and the different solvent composition on the reaction rate acceleration revealed that the reaction acceleration was mainly attributed to the micro-confinement effect rather than the introduced charges, solvent composition, and solvent evaporation effect in microdroplet. The behavior of accelerated reaction suggests that the biochemical reactions occurring in confined environments such as in cells would significantly differ from what has been conventionally understood.

2017-04-01T15:00:00Z Lee, Jae Kyoo Nam, Hong Gil Zare, Richard https://scholar.dgist.ac.kr/handle/20.500.11750/59000 2025-09-01T08:40:11Z 2017-04-01T15:00:00Z

Title: Laser desorption/ionization droplet delivery mass spectrometry for live single cell analysis and imaging Author(s): Lee, Jae Kyoo; Nam, Hong Gil; Zare, Richard Abstract: We have developed a new high-resolution ambient ionization mass spectrometry techniques named laser desorption/ionization droplet delivery mass spectrometry (LDIDD-MS) (Anal Chem, 2016). A pulsed UV laser beam (266 nm) is focused on a surface covered with target analytes to induce their desorption and ionization (Fig. 1A). A spray of liquid droplets is simultaneously directed onto the laser-focused surface region to capture the ionized analytes and deliver them to a mass spectrometer. This approach of rapid and effective capturing of molecules after laser desorption/ionization allows the limit of detection for the amino acid lysine to be as low as 2 amol under ambient ionization conditions. A high spatial resolution around 3 µm for mass spectrometric imaging of a mouse brain tissue was achieved. The LDIDD-MS was employed for single-cell analysis of cellular apoptosis. A significant differences in the profiles of fatty acids and lipids between normal healthy cells and apoptosis-induced HEK cells was observed (Fig. 1B). We observed upregulation of phosphatidylcholine lipid with a relatively shorter carbon chain length and downregulation of phosphatidylcholine with a relatively longer carbon chain length, suggesting a possible new mechanism for apoptotic morphological changes. This technique also allows for a direct measurement of liquid-phase samples including amino acids, peptides, and proteins. A real-time detection of exocytosed neurotransmitters from live PC12 cells, which has been a significant challenge for mass spectrometric analysis, was achieved without damaging cells.

2017-04-01T15:00:00Z Lee, Jae Kyoo Samanta, Devleena Nam, Inho Nam, Hong Gil Zare, Richard N. https://scholar.dgist.ac.kr/handle/20.500.11750/58999 2025-09-01T08:40:11Z 2018-02-19T15:00:00Z

Title: Spontaneous Reduction of Biomolecules on the Surface of Water Droplets Author(s): Lee, Jae Kyoo; Samanta, Devleena; Nam, Inho; Nam, Hong Gil; Zare, Richard N. Abstract: Reduction and oxidation reactions are a family of reactions that involves the transfer of electrons between species. Redox reactions play a crucial role in living organism as they are involved in photosynthesis, respiration, and metabolism. Chemical reactions in confined environments behave differently than the same ones in bulk solution. We have found that chemical reactions are significantly accelerated in micron-sized aqueous droplets (microdroplets) by the factor over 105 for various reactions including protein unfolding, protein-ligand binding, chlorophyll demetallation, and hydrogen-deuterium exchange (PNAS 2015, Q Rev Biophys 2016 and 2017). We also found that the reactions with a high thermodynamic barrier can spontaneously occur in microdroplets by lowering the entropy change at the water surface (PNAS, in press). Here we present spontaneous reduction of biomolecules including pyruvate, cystine, lipoic acid, and fumarate with up to ∼ 95 % reduction efficiency within hundreds of microseconds at the water-air interface on microdroplets without an added reducing agent. The reduction efficiency decreased as the concentration of pyruvate increased above 10 nM, suggesting the capacity of the reducing power of water microdroplet is limited to around tens of nanomoles per liter. The increase of surface-to-volume ratio of the microdroplets by generating smaller microdroplets led to increased reduction efficiency, indicating the reduction occurs at or very near the surface of microdroplets. The increase of O2 composition in the surrounding gas reduced reduction efficiency, suggesting that the oxidation of OH- due to a strong electric field at the water surface is a probable mechanism of the reduction. This discovery of spontaneous reduction at the water-air interface may provide a new biophysical mechanism of altering metabolomic balance without the participation of charge carriers or reducing agents/enzymes as well as elucidating the reduction of biomolecules in the prebiotic era.

2018-02-19T15:00:00Z