Vertical ozone formation mechanisms resulting from increased oxidation on the mountainside of Mount Tai, China.

The vertical distribution of ozone (O3) within the boundary layer (BL) and its ground-level effects have been extensively studied. However, observational limitations in obtaining high-resolution, real-time data on O3 and its precursors, especially volatile organic compounds (VOCs), have led to a scarcity of research on O3 formation sensitivity and mechanisms. Online measurements for O3, nitrogen oxides (NO x ), and VOCs were made on the mountainside of Mount Tai (∼550 m a.s.l.) in China during the summer of 2022 and were compared with the data from a ground-level site. The Master Chemical Mechanism (V3.3.1) was used to uncover a positive correlation between NO x and photochemical reaction rates on the mountainside, marking it as a NO x -limited regime in contrast to the VOC-limited regime identified at surface. On the mountainside, lower NO levels limited hydroxyl radicals (OH) recycling reactions, resulting in earlier O3 peaks and higher concentrations of hydroperoxy radicals (HO2) and organic peroxy radicals (RO2). The arrival of fresh air masses rich in NO accelerated OH radical cycling, enhanced atmospheric oxidization, and significantly impacted surface O3 concentrations though vertical transport. Moreover, NO x reduction scenario simulations show that when considering vertical transport, the peak O3 production rate at the surface is lower due to differences in O3 formation sensitivity vertically. This study highlights the significant sensitivity of O3 formation to NO within the BL, underscoring the potential impact of vertical in situ O3 formation above the ground on surface-level O3 concentrations through vertical exchange, particularly in cities with mountainous terrain.

Development of a broad-spectrum one-step immunoassay for detection of glucocorticoids in milk using magnetosome-based immunomagnetic beads.

Immunomagnetic beads provide novel tools for high-throughput immunoassay techniques. In this study, protein G (PG) was immobilized onto bacterial magentic particles (BMPs) using an additional cysteine residue at the C-terminus. A broad-spectrum monoclonal antibody against glucocorticoids (GCs) was attached to BMPs through PG-Fc interaction, generating BMP-PG-mIgG immunomagentic beads. A sensitive one-step immunoassay was developed for GCs based on combination of BMP-PG-mIgG and dexamethasone-horseradish peroxidase tracer (DMS-HRP). The developed assay exhibited half inhibitory concentrations (IC50) for dexamethasone (DMS), betamethasone (BMS), prednisolone (PNS), hydrocortisone (HCS), beclomethasone (BCMS), cortisone (CS), 6-α-methylprednisone (6-α-MPNS), fludrocortisone acetate (HFCS) of 0.98, 1.49, 2.42, 9.29, 1.63, 6.13, 7.3, and 4.89 ng/mL, respectively. The method showed recoveries ranging rates from 86.5 % to 117 % with a coefficient of variation less than 12.3 % in milk sample, which showed a good correlation with LC-MS/MS. Thus, the proposed assay offers a rapid and broad-spectrum screening tool for simultaneous detection of GCs in milk.

Enhanced reductive degradation of chloramphenicol by sulfidated microscale zero-valent iron: Sulfur-induced mechanism, competitive kinetics, and new transformation pathway.

Crystalline iron sulfide (FeSx, i.e., FeS or FeS2) minerals as sulfur sources were used to prepare the mechanochemically sulfidated microscale zero-valent iron ((FeSx+ZVI)bm). Metastable FeS and FeS2 precursors were generated via aqueous coprecipitation and applied to fabricate FeSx@ZVI samples. (FeSx+ZVI)bm and FeSx@ZVI exhibited better chloramphenicol (CAP) degradation than ZVI due to the increase in specific surface areas, the decrease of electrochemical impedance, the formation of galvanic cells, and sulfur-induced pitting and local acidity. (FeSx+ZVI)bm had better CAP removal capacity than FeSx@ZVI under different S/Fe molar ratios, initial pH, and oxygen conditions. At the same time, FeSx@ZVI showed better electron utilization under oxic conditions, related to their Fe0 and sulfur spatial distribution. Nitro reduction and dechlorination of CAP by (FeSx+ZVI)bm produced nitroso, azoxy, amine, and monodechlorination products, while dechlorination was not involved in the degradation process of CAP by FeSx@ZVI. A new transformation pathway of nitroso-CAP to amine-CAP mediated by azoxy products is proposed via coupling a chain decay multispecies model and DFT calculations. The larger competitive reaction rates among O2, CAP, and its degradation products was determined by their lower LUMO energy. The contribution of direct electron transfer to nitro reduction was greater than that of atomic hydrogen, but the opposite was true for dechlorination. FeSx@ZVI had a larger DET contribution than (FeSx+ZVI)bm, and FeS2 promoted the DET contribution better than FeS. Toxicity assessment indicated that the rapid transformation of nitroso and azoxy products was crucial for eliminating the biotoxicity of CAP.

Identification and engineering on the nonconserved residues of metallo-ß-lactamase-type thioesterase to improve the enzymatic activity.

The standalone metallo-ß-lactamase-type thioesterase (MßL-TE), belongs to the group V nonreducing polyketide synthase agene cluster, catalyzes the rate-limiting step of product releasing. Our work first investigated on the orthologous MßL-TEs from different origins to determine which nonconserved amino acid residues are important to the hydrolysis efficiency. A series of chimeric MßL-TEs were constructed by fragment swapping and site-directed mutagenesis, in vivo enzymatic assay showed that two nonconserved residues A19 and E75 (numbering in HyTE) were critical to the catalytic performance. Protein structure modeling suggested that these two residues are located in different areas of HyTE. A19 is on the entrance to the active sites, whereas E75 resides in the linker between the two ß strands which hold the metal-binding sites. Combining with computational simulations and comparative enzymatic assay, different screening criteria were set up for selecting the variants on the two noncatalytic and nonconserved key residues to improve the catalytic activity. The rational design on A19 and E75 gave five candidates in total, two (A19F and E75Q) of which were thus found significantly improved the enzymatic performance of HyTE. The double-point mutant was constructed to further improve the activity, which was increased by 28.4-fold on product accumulation comparing to the wild-type HyTE. This study provides a novel approach for engineering on nonconserved residues to optimize enzymatic performance.