Influence of strong iron-binding ligands on cloud water oxidant capacity

Immobilization of Agaricus bisporus Polyphenol Oxidase 4 on mesoporous silica: Towards mimicking key enzymatic processes in peat soils

HYPOTHESIS

The use of immobilized enzyme-type biocatalysts to mimic specific processes in soil can be considered one of the most promising alternatives to overcome the difficulties behind the structural elucidation of riverine humic-derived iron-complexes. Herein, we propose that the immobilization of the functional mushroom tyrosinase, Agaricus bisporus Polyphenol Oxidase 4 (AbPPO4) on mesoporous SBA-15-type silica could contribute to the study of small aquatic humic ligands such as phenols.

EXPERIMENTS

The silica support was functionalized with amino-groups in order to investigate the impact of surface charge on the tyrosinase loading efficiency as well as on the catalytic performance of adsorbed AbPPO4. The oxidation of various phenols was catalyzed by the AbPPO4-loaded bioconjugates, yielding high levels of conversion and confirming the retention of enzyme activity after immobilization. The structures of the oxidized products were elucidated by integrating chromatographic and spectroscopic techniques. We also evaluated the stability of the immobilized enzyme over a wide range of pH values, temperatures, storage-times and sequential catalytic cycles.

FINDINGS

This is the first report where the latent AbPPO4 is confined within silica mesopores. The improved catalytic performance of the adsorbed AbPPO4 shows the potential use of these silica-based mesoporous biocatalysts for the preparation of a column-type bioreactor for in situ identification of soil samples.

Emerging investigator series: aqueous-phase processing of atmospheric aerosol influences dissolution kinetics of metal ions in an urban background site in the Po Valley

Metals are an important atmospheric aerosol component; their impacts on health and the environment depend also on their solubility, dissolution kinetics and chemical form in which they are present in the aerosol (e.g., oxidation state, inorganic salt or oxide/hydroxide, organic complex). In this study, we investigated the impact of fog processing on the solubility and dissolution of metals in PM_2.5 samples collected in an urban background site in Padova (Italy). For each sample, we determined the solubility and dissolution kinetics of 17 elements in a solution simulating fog water in the winter season in the Po Valley (pH 4.7, T 5 °C, and water content ∼0.5 g m^-3). We also determined water-soluble inorganic and organic compounds having ligand properties. We used the model E-AIM IV to calculate the aerosol liquid water (ALW) content and pH, and we used the model Visual MinteQ to determine the speciation picture of the most important elements under conditions of both deliquescent aerosol (ALW and pH calculated using E-AIM IV, ambient temperature) and simulated fog. We found that the dissolution of Al, Cu, and Fe metal ions, predicted to be largely coordinated with organic compounds under fog conditions, was either immediate or considerably faster in samples collected on days with observed fog events compared with those collected on days having drier conditions. For readily soluble elements, such as As, Cd, Cr, Sr, and Zn, such an effect was not observed. Our study highlights the importance of coordination chemistry in atmospheric aerosol and fog in determining the bioavailability of particle-bound metals.