pH-Dependent Kinetics of Imidazole Production in Aqueous Glyoxal/Ammonium Sulfate Microdroplets

IF 2.9 3区化学 Q2 CHEMISTRY, MULTIDISCIPLINARY ACS Earth and Space Chemistry Pub Date : 2025-03-30 DOI:10.1021/acsearthspacechem.5c00023

Marcus Marracci, and , Craig Murray*,

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Abstract

The kinetics of imidazole formation in optically levitated glyoxal/ammonium sulfate aqueous microdroplets has been investigated using single-particle Raman spectroscopy. The microdroplet diameters (∼25 μm) were measured using brightfield microscopy. Individual microdroplets were produced from bulk solutions with pH in the range 4.0–9.3 and confined for up to 6 h in the optical levitation apparatus, which was maintained at a constant relative humidity (RH) of ∼70%. Imidazole bands at 920, 1230, and 1470 cm^–1 were observed to grow in as the confined microdroplets aged; the effective formation rate constants increased with initial bulk solution pH, reflecting the increased concentration of nucleophilic NH₃ as the acid–base equilibrium is shifted. However, the imidazole formation rates do not increase to the extent that would be expected based on previous bulk kinetics measurements. Preliminary experiments observing microdroplets dispensed sequentially from the same bulk solution suggest that imidazole formation is accelerated in the microdroplets by a factor of ∼7. The apparent rate acceleration can be explained by preconcentration of the reactants as the initially dispensed microdroplets lose water and equilibrate with the apparatus RH.

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乙二醛/硫酸铵微滴生产咪唑的ph依赖动力学

采用单粒子拉曼光谱研究了光学悬浮乙二醛/硫酸铵水溶液微滴中咪唑的形成动力学。使用明场显微镜测量微滴直径（~ 25 μm）。单个微滴从pH值在4.0-9.3范围内的散装溶液中产生，并在光学悬浮装置中限制长达6小时，该装置保持在恒定的相对湿度（RH）约70%。在920、1230和1470 cm-1处观察到咪唑带随着受限微滴的老化而变长；有效生成速率常数随着初始体积溶液pH值的增加而增加，反映了随着酸碱平衡的转移，亲核NH3浓度的增加。然而，咪唑的形成速率并没有增加到基于先前的体动力学测量所期望的程度。初步实验观察了从相同体积溶液中按顺序分配的微滴，结果表明咪唑在微滴中的形成速度加快了约7倍。当初始分配的微滴失去水分并与仪器RH平衡时，反应物的预浓缩可以解释表观速率加速。

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来源期刊

ACS Earth and Space Chemistry Earth and Planetary Sciences-Geochemistry and Petrology

CiteScore

5.30

自引率

11.80%

发文量

249

期刊介绍： The scope of ACS Earth and Space Chemistry includes the application of analytical, experimental and theoretical chemistry to investigate research questions relevant to the Earth and Space. The journal encompasses the highly interdisciplinary nature of research in this area, while emphasizing chemistry and chemical research tools as the unifying theme. The journal publishes broadly in the domains of high- and low-temperature geochemistry, atmospheric chemistry, marine chemistry, planetary chemistry, astrochemistry, and analytical geochemistry. ACS Earth and Space Chemistry publishes Articles, Letters, Reviews, and Features to provide flexible formats to readily communicate all aspects of research in these fields.

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