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Bromide oxidation by bromate in a frozen solution and reactive bromine species production

2026-02-09T07:08:50Z

Title: Bromide oxidation by bromate in a frozen solution and reactive bromine species production Authors: Ahn, Yong-Yoon; Quoc Anh Nguyen; Andrea Spolaor; Sefano Frassati; Elena Barbaro; Giulio Cozzi; Clara Turetta; Hoon Oh; Jaesang Lee; Kim, Kitae Abstract: A sudden increase in tropospheric reactive bromine species (such as BrO radical) concentration has been observed in the Arctic springtime (bromine explosion). The reactive bromine radicals originate from the Br2 oxidation; however, the role of ice chemistry in bromine activation, especially freezing-induced Br- oxidation for Br2 production, is not significantly considered yet. Notably, the freezing phenomenon is prevalent in polar region. In this study, we demonstrate that the Br- containing water freezing can provide a potential Br- oxidation pathway. The oxidation of Br- by BrO3- was negligible under aqueous conditions, while it was highly accelerated (time scale of several years to minute) by freezing the solution. We proposed that the accelerated chemical reaction was due to the freezing concentration effect. The chemical transformation mechanism was suggested. The chemical transformation of Br- was considered using the UV-visible absorbance spectrometer and the high-resolution mass spectroscopy (HRMS) measurement. The total Br content was measured using inductive coupled plasma mass spectroscopy (ICP-MS) and the dissolved Br species was monitored using ion chromatography. The spatial distribution of in-situ generated hypobromous acid in ice was analyzed using the Raman microscopy. The Br- oxidation is increased as the decrease of initial pH and increase of reactant dose, but the influence of freezing temperature was not significant. This study provides experimental evidence for the freezing-induced bromide activation in the ice.

Photooxidation of Natural and Waste Cr(III)-Bearing Hydroxides in Water and Ice: Cr(III)-O2 Complex Mediated Oxidation and Effect of Natural Organic Matter

2026-02-10T04:30:21Z

Title: Photooxidation of Natural and Waste Cr(III)-Bearing Hydroxides in Water and Ice: Cr(III)-O2 Complex Mediated Oxidation and Effect of Natural Organic Matter Authors: Yi Hu; Juanshan Du; Chung, Hyun Young; Kim, Kitae; Lee, Giehyeon; Choi, Wonyong Abstract: The photooxidative dissolution of Cr(III)-bearing hydroxides (Cr(OH)3 and FexCr1？x(OH)3) is proposed as a potential abiotic source of Cr(VI) in environments. Compared to the dark oxidation of Cr(OH)3 by O2, photoirradiation enhanced Cr(VI) production in both aqueous and frozen solutions. In the presence of natural organic matter (NOM), the photoproduction of Cr(VI) was significantly promoted in aqueous solution but hindered in frozen solution. Photosensitized NOM induced the production of H2O2 that played the dual roles of enhancing Cr(OH)3 oxidation in aqueous solution and accelerating Cr(VI) reduction in frozen solution. The in situ generated Cr(VI) in the Cr(OH)3/NOM/UV system was gradually accumulated during the repeated cycles of aqueous？frozen phase transitions and light？ dark variations, which confirms that the stable Cr(OH)3 can be a source of natural Cr(VI) under realistic environmental conditions. The photooxidative dissolution of Cr(OH)3 is proposed to involve the complex formation between dissolved Cr(OH)4 ？ and O2, which subsequently undergoes the photoinduced charge transfer, resulting in the oxidation of Cr(III) to Cr(VI) with the concurrent reduction of O2 to H2O2 via ？O2 ？. A similar mechanistic behavior was also observed with FexCr1？x(OH)3 (x = 0.3, 0.5, and 0.7) for the photooxidative production of Cr(VI). This study unveils an underappreciated pathway of Cr(VI) production from natural and waste Cr(III)-bearing hydroxides.

Crystallization Mechanisms of Porous and Compact Amorphous Solid Water Films

2025-08-22T08:30:12Z

Title: Crystallization Mechanisms of Porous and Compact Amorphous Solid Water Films Authors: Lee, Du Hyeong; Kim, Kitae Abstract: Amorphous solid water (ASW), formed by vapor deposition on cryogenic substrates (<130 K), transforms into crystalline ice at high temperatures. However, some aspects of the crystallization mechanism, such as the nucleation process, remain unclear. In this study, the crystallization kinetics of porous ASW (pASW) and compact ASW (cASW) were evaluated to identify their nucleation sites. ASW films were grown under ultrahigh vacuum conditions by background and tube-doser deposition, and their porosities were controlled by adjusting the deposition temperature and angle. In addition, the crystallized fractions were measured using desorption spectrometry. The results reveal that the pASW crystallization is triggered within the film interior, whereas the nucleation of cASW films occurs on their surfaces. Owing to the presence of pores, the pASW films crystallize faster than the cASW ones, and the crystallization activation energy of the former (68.9 kJ mol(-1)) is lower than that of the latter (79.8 kJ mol(-1)). These findings highlight the role of porosity in the crystallization of ASW, providing insights into the behavior of water molecules in cryogenic environments including polar atmospheres and the surfaces of planets and satellites.

Ice affinity purification system for recombinant proteins using a DUF3494 ice-binding protein

2025-08-22T04:47:57Z

Title: Ice affinity purification system for recombinant proteins using a DUF3494 ice-binding protein Authors: Hoang, Trang; Nguyen, Dieu Linh; Kim, Bo-Mi; Choi, Woong; Cho, Sung Mi; Kim, Han-Woo; Han, Se Jong; Kim, Kitae; Lee, Jun Hyuck; Do, Hackwon Abstract: Protein purification is essential for the isolation of specific proteins from mixtures. Conventional affinity tags have advanced recombinant protein purification. However, their reliance on costly resins and complex procedures often limits scalability and affordability. In this study, we identified three ice-binding domains (CoIBD1, CoIBD2, and CoIBD3) in Candidatus Cryosericum odellii SMC5 to evaluate their potential as protein purification tags. These domains exhibited hyperactive ice-binding properties, including high thermal hysteresis and ice recrystallization inhibition activities; additionally, they bound to multiple ice planes, enabling efficient attachment to ice surfaces. Through sequence and structural analyses, we engineered an enhanced variant that retained these ice-binding traits while achieving improved thermal and chemical stability: eCoIBD1. We then used eCoIBD1 as a fusion tag to develop the Ice Affinity Purification (IAP) system and evaluated its performance with GFP as a model protein. The IAP system achieved 87 % purity after two purification rounds, recovering 29 % of the initial protein from the crude extract. Consistent performance was observed in the presence of additives such as dithiothreitol and glycerol. The IAP system provides a cost-effective, environmentally friendly alternative to traditional methods by leveraging ice as a renewable binding medium, thereby eliminating the need for expensive resins or regeneration steps.