Search Results (7)

Isoprene (C₅H₈), the most abundant biogenic volatile organic compound (400–600 Tg C yr⁻¹), exerts complex NO_x-dependent influence on tropospheric ozone, yet its representation remains absent in many climate models. This study aims to quantify isoprene’s impact on tropospheric chemical composition using the Russian Earth system model INM-CM6.0 with newly implemented isoprene oxidation chemistry. Two 12-year experiments (2008–2019) were conducted: a control run without isoprene and an experiment with the Mainz Isoprene Mechanism (MIM1: 44 reactions, 16 species). Results reveal a NO_x-dependent two-layer vertical structure. In the tropical surface layer (0–5 km, 20° S–20° N), ozone decreases by 10–15 ppb through radical termination under low-NO_x (<100 ppt), with 15–30% OH reduction and 30–60% CO increase. In the middle troposphere (8–12 km), ozone increases by 10–15 ppb through thermal decomposition of vertically transported PAN and MPAN. In subtropics (20–35°) with elevated NO_x (>500 ppt), isoprene stimulates ozone formation at all altitudes (+3–12 ppb). Oxidation product distributions establish a spatial hierarchy: local (ISON, NALD: 0–5 km), regional (MPAN: to 8 km), and global (PAN: reaching high latitudes at 8–12 km). Comparison with CAMS, MERRA-2, and ERA5 reanalyses shows substantial improvement: tropical CO discrepancies decrease from 20–30% to 10–15%, OH by factors of 2–3, and ozone overestimation from 30–40% to 10–15%. These findings demonstrate that explicit isoprene chemistry is essential for accurate tropospheric composition simulation, particularly given the projected 21–57% emission increases by 2100 under climate warming. Full article

Ginseng (Panax ginseng C. A. Meyer), a traditional Chinese medicine, and the rare ginsenosides contained in it have various physiological activities. 25-OH-PPT (T19) is a rare natural dammarane-type ginseng sapogenin. Pharmacological studies have shown that T19 has good hypoglycemic, antioxidant, and anti-inflammatory activities. In the research, we optimized the T19 enrichment process and explored the potential mechanism of T19 in myocardial oxidative stress. Firstly, we studied a hydrolysis process on ginseng stems and leaves ginsenosides. Optimization factors include acid types, acid concentrations, ultrasound time, and ultrasound temperature. To develop safer preparation conditions more suitable for production scaleup, we studied the difference in hydrolysis between inorganic acid and food acids. The results show that using hydrochloric acid to hydrolyze ginsenosides in ginseng stems and leaves can increase the content of T19 to 12.16%. When using edible citric acid, the maximum content of T19 is 1.9%. However, using citric acid for hydrolysis has higher safety and non-toxic properties. Meanwhile, the myocardial protective effect of T19 was evaluated, indicating that T19 could effectively reduce isoproterenol (ISO)-induced oxidative stress injury by reducing the levels of LDH and CK-MB and regulating the contents of antioxidant enzymes SOD, lipid peroxidation product MDA, and non-enzymatic antioxidant GSH in cardiomyocytes. Further study demonstrated that regulation of fibrosis markers Collagen I, Collagen III, and α-SMA was involved in the potential mechanism of T19 efficiency. Full article

Volatile organic compounds (VOCs), particularly monoaromatic hydrocarbon compounds (MACHs), pose a potential risk to the atmospheric environment and human health. Therefore, the progressive development of efficient detection methodologies is a pertinent need, which is still a challenge at present. In this study, we present a rapid and sensitive method to detect trace amounts of MACHs using a bifunctional SERS composite substrate. We prepared an Au/SiO₂ enhanced layer and a porous Cu(OH)₂ adsorption layer via microfluidic-assisted gas-liquid interface self-assembly. The composite substrate effectively monitored changes in benzaldehyde using time-varying SERS spectra, and track-specifically identified various VOCs such as benzene, xylene, styrene, and nitrobenzene. In general, the substrate exhibited a rapid response time of 20 s to gaseous benzaldehyde, with a minimum detection concentration of less than 500 ppt. Further experimental assessments revealed an optimum Cu(OH)₂ thickness of the surrounding adsorption layer of 150 nm, which can achieve an efficient SERS response to MACHs. Furthermore, the recoverable and reusable property of the composite substrate highlights its practicality. This study presents a straightforward and efficient approach for detecting trace gaseous VOCs using SERS, with significant implications in the designing of SERS substrates for detecting other VOCs. Full article

It is shown that the potassium polytitanate powder (PPT) synthesized at 500 °C via the treatment of powdered TiO₂ (rutile) in molten mixtures of KOH and KNO₃ is a cheap and effective catalyst of H₂O₂ chemical decomposition in aqueous solutions. At the same time, the PPT catalytic activity strongly depends on the [TiO₂]:[KOH]:[KNO₃] weight ratio in the mixture used for the synthesis, increasing with [KNO₃] in the order of PPT (30:30:40) < PPT (30:50:20) < PPT (30:70:0). The obtained results are explained by increased [Ti³⁺] in the PPT structure (XPS data), which is grown in this order from 0 to 4.0 and 21.9 at.%, respectively, due to the reduced oxidation activity of the melt used for PPT synthesis. The mechanism of the autocatalytic process taking place in the PPT-H₂O₂-H₂O system is analyzed. Taking into account the data of FT-IR spectroscopy, it is assumed that the increased catalytic activity of the investigated materials is related to the increased surface concentration of the Ti⁴⁺-O(H)-Ti⁴⁺ groups, formed from the Ti³⁺-O(H₃O⁺)-Ti⁴⁺ clusters and further transformed into Ti-O-O-H catalytic centers. Some possible applications of the PPT-H₂O₂-H₂O catalytic system, including the oxidation processes of green chemistry and photo-catalysis, are discussed. Full article

A non-thermal plasma, air purification device (PlasmaShield^®, MD250, Keswick, SA, Australia), was investigated using spatially resolved optical emission spectroscopy. The emission spectra were measured with two spatial dimensions to analyze and identify the transition lines of excited NO–γ (A²Σ–X²Π), N₂ (C³Π–B³Π), and N₂⁺ (B²Σ–X²Σ) systems. The N₂ emission band at 337 and 316 nm were used to determine the spatially resolved vibrational temperature of N₂ molecules, $T_{vib}^{N_2}$. It was found that the average N₂ vibrational temperatures in the x and y directions are almost the same. Two key operating parameters, supplied power and air flow, influence the N₂ vibrational temperature. The results demonstrate that applying higher supplied power increases the vibrational temperature, while changes in air flow velocity do not affect the vibrational temperature values. The phenomenological plasma temperature (PPT) was also estimated from the N₂ vibrational temperature. It was observed that PlasmaShield^® generates excited N₂ and NO only within a narrow region around the discharge electrode tip (with peak intensity below 100 µm from the tip). The study also shows no presence of excited OH*, O*, and other radicals. Full article

SO₂ and H₂S are the two most important gas-phase sulfur species emitted by volcanoes, with a global amount from non-explosive emissions of the order 10 Tg-S/yr. These gases are readily oxidized forming SO₄²⁻ aerosols, which effectively scatter the incoming solar radiation and cool the surface. They also perturb atmospheric chemistry by enhancing the NO_x to HNO₃ heterogeneous conversion via hydrolysis on the aerosol surface of N₂O₅ and Br-Cl nitrates. This reduces formation of tropospheric O₃ and the OH to HO₂ ratio, thus limiting the oxidation of CH₄ and increasing its lifetime. In addition to this tropospheric chemistry perturbation, there is also an impact on the NO_x heterogeneous chemistry in the lower stratosphere, due to vertical transport of volcanic SO₂ up to the tropical tropopause layer. Furthermore, the stratospheric O₃ formation and loss, as well as the NO_x budget, may be slightly affected by the additional amount of upward diffused solar radiation and consequent increase of photolysis rates. Two multi-decadal time-slice runs of a climate-chemistry-aerosol model have been designed for studying these chemical-radiative effects. A tropopause mean global net radiative flux change (RF) of −0.23 W·m⁻² is calculated (including direct and indirect aerosol effects) with a 14% increase of the global mean sulfate aerosol optical depth. A 5–15 ppt NO_x decrease is found in the mid-troposphere subtropics and mid-latitudes and also from pole to pole in the lower stratosphere. The tropospheric NO_x perturbation triggers a column O₃ decrease of 0.5–1.5 DU and a 1.1% increase of the CH₄ lifetime. The surface cooling induced by solar radiation scattering by the volcanic aerosols induces a tropospheric stabilization with reduced updraft velocities that produce ice supersaturation conditions in the upper troposphere. A global mean 0.9% decrease of the cirrus ice optical depth is calculated with an indirect RF of −0.08 W·m⁻². Full article

Three dehydrogenases – (R)-alcohol dehydrogenase from L. kefir, (S)-aromatic alcohol dehydrogenase from T. sp. and (S)-alcohol dehydrogenase from T. brockii – were tested for the preparation of enantiopure hydroxyl metabolites of pentoxifylline (PTX), propentofylline (PPT) and denbufylline (DBF). These metabolites have an important pharmacological significance. The experimental conditions were optimized for biocatalytic reactions. LKADH produced the chiral secondary alcohols: (R)-OHPTX, (R)-OHPPT and (R)-OHDBF, in an anti- Prelog’s rule configuration. In contrast, TBADH and SAADH also generated chiral secondary alcohols, but according to Prelog’s rule, giving (S)-OHPTX, (S)-OHPPT and (S)-OHDBF respectively. All the ADHs tested were characterized by a high enantioselectivity (ees of 99–100%), but the yield of bioconversion was only satisfactory for the reactions performed using LKADH, being in the 96–98% range for PPT and PTX respectively. Full article