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Fluorescence Modulation in UiO-66-NH2 via Photooxidation and Selective Reduction

2025-08-31T15:00:00Z

Title: Fluorescence Modulation in UiO-66-NH2 via Photooxidation and Selective Reduction Author(s): Ahn, Yongdeok; Park, Minsoo; Son, Younghu; Cho, Juhyeong; Park, Min Jeong; Seo, Daeha; Yoon, Minyoung Abstract: Metal-organic frameworks with emissive ligands offer tunable photophysical properties that are sensitive to their coordination environment and structural configuration. In this study, we demonstrate that the fluorescence of UiO-66-NH2 can be modulated through photo-oxidation-induced quenching and subsequent solvent-mediated recovery. Upon visible-light irradiation, reactive oxygen species induce two distinct oxidation pathways: irreversible oxidation of the ligand and reversible oxidation of the metal-oxo cluster. These redox events lead to partial disruption of the coordination environment and result in fluorescence loss. Reduction using mild alcohols selectively removes adsorbed oxidative species from Zr6O4(OH)4, leading to partial recovery of fluorescence and porosity. The extent of fluorescence restoration correlates with both the reducing strength and molecular size of the alcohol, reflecting its ability to penetrate internal pores and access to redox-active sites. Notably, some alcohol-treated samples exhibited nitrogen uptake beyond that of pristine UiO-66-NH2, suggesting redux-induced structural reorganization and defect-assisted pore expansion. These results establish a structure-function relationship in MOFs governed by localized redox chemistry, providing a platform for designing reconfigurable optical materials with switchable photophysical and porous characteristics.

Real-Time Visualisation of Reaction Kinetics and Dynamics: Single-Molecule Insights into the Iminium-Catalysed Diels-Alder Reaction

2025-10-31T15:00:00Z

Title: Real-Time Visualisation of Reaction Kinetics and Dynamics: Single-Molecule Insights into the Iminium-Catalysed Diels-Alder Reaction Author(s): Park, Minsoo; Ahn, Yongdeok; Cho, Juhyeong; Jang, Juhee; Lee, Wonhee John; Seo, Sangwon; Lee, Sunggi; Seo, Daeha Abstract: Investigation of the fundamental microscopic processes occurring in organic reactions is essential for optimising both organocatalysts and synthetic strategies. In this study, single-molecule fluorescence microscopy was employed to study the Diels-Alder reaction catalysed by a first-generation MacMillan catalyst, providing direct insights into its kinetic dynamics. This reaction proceeds via a series of reversible processes under equilibrium conditions (S -><- IM1 -><- IM2 -> P, IM1 and IM2: N,O-acetal and iminium ion intermediates, respectively). The individual reaction trajectories of single molecules were directly observed in real-time, and the kinetic transitions between the different states were quantitatively analysed using a hidden Markov model, thereby enabling precise determination of the kinetic rate constants and transition probabilities at the single-molecule level. In particular, the unique structural features of the MacMillan catalyst were probed to reveal how specific interactions stabilise the reaction intermediates and influence their kinetic behaviours. These findings highlight the importance of single-molecule fluorescence microscopy in understanding the fundamental mechanisms of organic reactions and guiding the rational design of more effective catalysts.

Reconciling a Kinetic Model for Dimerization of the EGFR Using Single-Molecule Tracking in Living Cells

2025-08-31T15:00:00Z

Title: Reconciling a Kinetic Model for Dimerization of the EGFR Using Single-Molecule Tracking in Living Cells Author(s): Kim, Kiwook; Jang, Juhee; Cho, Juhyeong; Ahn, Yongdeok; Jeong, Seunghyeon; Shin, Jiwon; Yea, Kyungmoo; Lee, Wonhee John; Seo, Daeha Abstract: Epidermal growth factor receptor (EGFR) dimerization plays a pivotal role in cellular signaling, influencing proliferation and disease progression, particularly in cancer. Despite extensive studies, the quantitative relationship between EGFR expression levels and dimerization efficiency remains incompletely understood. In this study, we investigated EGFR dimerization kinetics using ensemble-level biochemical assays and single-molecule tracking (SMT) in living cells. Our findings revealed noncanonical negative cooperative dimerization, where the monomer-to-dimer transition rate decreased as EGFR expression increased, challenging the assumptions of a simplistic reaction model. Furthermore, we identified a dimer-specific degradation pathway highlighting the open-system nature of the plasma membrane environment. These findings establish a quantitative framework for understanding EGFR dimerization dynamics, offering insights into the complex regulatory principles governing membrane protein interactions. This model not only improves our understanding of EGFR-mediated signaling but also suggests broader applicability for the therapeutic targeting of membrane protein systems.

Inflammatory cytokine-primed MSC-derived extracellular vesicles ameliorate acute lung injury via enhanced immunomodulation and alveolar repair

2025-07-31T15:00:00Z

Title: Inflammatory cytokine-primed MSC-derived extracellular vesicles ameliorate acute lung injury via enhanced immunomodulation and alveolar repair Author(s): Jeong, Jongwon; Park, Jun-Kook; Shin, Jiwon; Jung, Inseong; Kim, Hyun-Woo; Park, Anyeseu; Cho, Hanchae; Kang, Sung-Min; Shin, Sanghee; Park, Eunju; Kim, Jisuk; Noh, Soojeong; Ahn, Yongdeok; Kim, Do-Kyun; Lee, Jeong Yoon; Seo, Daeha; Baek, Moon-Chang; Yea, Kyungmoo Abstract: Background: Acute lung injury (ALI) is characterized by excessive inflammation and alveolar damage, arising from pathogens or systemic insults such as sepsis, and can progress to severe acute respiratory distress syndrome (ARDS). Despite its severity, effective pharmacological treatments remain unavailable, and current clinical interventions are limited to supportive care such as mechanical ventilation. Mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) have emerged as promising candidates for lung repair, but insufficient immunosuppressive capacity often limits their efficacy. Methods: Human adipose-derived mesenchymal stem cells (hADMSCs) were primed with IFN-γ and TNF-α to enhance the immunomodulatory properties of their secreted EVs. We characterized unprimed control MSC-EVs (C-MEVs) and primed MSC-EVs (P-MEVs) by transmission electron microscopy, nanoparticle tracking analysis, and western blotting for EV markers. Functional assays in THP-1 and A549 cells examined anti-inflammatory potency and barrier regeneration against lipopolysaccharide (LPS)-induced damage. A preclinical mouse model of LPS-induced ALI was used to evaluate inflammatory cytokine expression, immune cell infiltration, pulmonary edema, and vascular leakage. Finally, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-infected Vero E6 cells were tested whether P-MEVs could mitigate the inflammatory damage characteristic of virus-triggered acute lung injury. Results: Primed hADMSCs exhibited elevated expression of immunosuppressive molecules (e.g., COX-2, IDO, TSG-6), without changing EV morphology or yield. P-MEVs mitigated LPS-induced inflammation more effectively than C-MEVs in THP-1 and A549 cells. In vivo, P-MEVs more robustly attenuated inflammatory cytokines, immune cell recruitment, and lung injury markers in mice challenged with LPS. In SARS-CoV-2-infected Vero E6 cells, P-MEVs suppressed cytopathic effects and inflammatory responses more potently than C-MEVs. Mechanistic analyses revealed that these enhancements were associated with elevated miRNA levels, including miR-221-3p, involved in inhibiting inflammatory pathways. Conclusion: Inflammatory cytokine priming substantially augments the immunomodulatory and tissue-regenerative efficacy of hADMSC-derived EVs, offering superior therapeutic effects in ALI models and promising activity against SARS-CoV-2-induced lung damage. These findings underscore the therapeutic potential of P-MEVs as an innovative, cell-free platform for treating severe pulmonary disorders, including ARDS. © 2025 Elsevier B.V., All rights reserved.