On the formation of hydrogen peroxide in water microdroplets

Recent reports on the formation of hydrogen peroxide (H₂O₂) in water microdroplets produced via pneumatic spraying or capillary condensation have garnered significant attention. How covalent bonds in water could break under such mild conditions challenges our textbook understanding of physical chemistry and water. While there is no definitive answer, it has been speculated that ultrahigh electric fields at the air–water interface are responsible for this chemical transformation. Here, we report on our comprehensive experimental investigation of H₂O₂ formation in (i) water microdroplets sprayed over a range of liquid flow-rates, (shearing) air flow rates, and air composition, and (ii) water microdroplets condensed on hydrophobic substrates formed via hot water or humidifier under controlled air composition. Specifically, we assessed the contributions of the evaporative concentration and shock waves in sprays and the effects of trace O₃(g) on the H₂O₂ formation. Glovebox experiments revealed that the H₂O₂ formation in water microdroplets was most sensitive to the air–borne ozone (O₃) concentration. In the absence of O₃(g), we could not detect H₂O₂(aq) in sprays or condensates (detection limit ≥250 nM). In contrast, microdroplets exposed to atmospherically relevant O₃(g) concentration (10–100 ppb) formed 2–30 µM H₂O₂(aq), increasing with the gas–liquid surface area, mixing, and contact duration. Thus, the water surface area facilitates the O₃(g) mass transfer, which is followed by the chemical transformation of O₃(aq) into H₂O₂(aq). These findings should also help us understand the implications of this chemistry in natural and applied contexts.

A. Gallo Jr, H. Mishra et al., pinpoint the origins of the spontaneous H₂O₂ formation in water microdroplets formed via spraying or condensation, i.e., without the addition of electrical energy, catalyst, or co-solvent.     

Surface Interaction of Ionic Liquids: Stabilization of Polyethylene Terephthalate-Degrading Enzymes in Solution

The effect of aqueous solutions of selected ionic liquids solutions on Ideonella sakaiensis PETase with bis(2-hydroxyethyl) terephthalate (BHET) substrate were studied by means of molecular dynamics simulations in order to identify the possible effect of ionic liquids on the structure and dynamics of enzymatic Polyethylene terephthalate (PET) hydrolysis. The use of specific ionic liquids can potentially enhance the enzymatic hydrolyses of PET where these ionic liquids are known to partially dissolve PET. The aqueous solution of cholinium phosphate were found to have the smallest effect of the structure of PETase, and its interaction with (BHET) as substrate was comparable to that with the pure water. Thus, the cholinium phosphate was identified as possible candidate as ionic liquid co-solvent to study the enzymatic hydrolyses of PET.     

Formation of 8-nitroguanine and 8-oxoguanine due to reactions of peroxynitrite with guanine

Reactions of peroxynitrite with guanine were investigated using density functional theory (B3LYP) employing 6-31G** and AUG-cc-pVDZ basis sets. Single point energy calculations were performed at the MP2/AUG-cc-pVDZ level. Genuineness of the calculated transition states (TS) was tested by visually examining the vibrational modes corresponding to the imaginary vibrational frequencies and applying the criterion that the TS properly connected the reactant and product complexes (PC). Genuineness of all the calculated TS was further ensured by intrinsic reaction coordinate (IRC) calculations. Effects of aqueous media were investigated by solvating all the species involved in the reactions using the polarizable continuum model (PCM). The calculations reveal that the most stable nitro-product complex involving the anion of 8-nitroguanine and a water molecule i.e. 8NO(2)G(-) + H(2)O can be formed according to one reaction mechanism while there are two possible reaction mechanisms for the formation of the oxo-product complex involving 8-oxoguanine and anion of the NO(2) group i.e. 8OG + NO(2)(-). The calculated relative stabilities of the PC, barrier energies of the reactions and the corresponding enthalpy changes suggest that formation of the complex 8OG + NO(2)(-) would be somewhat preferred over that of the complex 8NO(2)G(-) + H(2)O. The possible biological implications of this result are discussed.     

Reduction of Oxide Minerals by Hydrogen Plasma: An Overview

Carbothermic reduction of oxide minerals is one of the major routes to obtain the corresponding metals. This process produces a lot of CO₂, which is responsible for greenhouse effect. Alternatively, hydrogen plasma containing hydrogen in atomic, ionic, and excited states can reduce almost every metal oxide even at lower temperatures. Besides this advantage, plasma processing also offers kinetic advantages. Further, hydrogen-water cycle does not pose any environmental problems. However, reduction of metal oxides in hydrogen plasma is not so straightforward—there are issues relating to introduction of material into the plasma zone, residence time, reverse reaction, and scale-up that must be resolved—yet, it holds the key to future environmental challenges particularly with respect to CO₂ emission. This paper provides an overview of reduction of oxide minerals by hydrogen plasma. The influences of various reaction conditions particularly with respect to reduction of oxides are discussed and some aspects of both thermal and non-thermal cold plasma linking oxidative as well as dissociative reduction are presented.     

Static and Kinetic Studies on the Adsorption Behavior of Sulfadiazene

To investigate the nature of interactive forces between sulfadiazene molecules and alumina surface the experiments were performed for the adsorption of sulfadiazene (SD) from its aqueous sulution onto the alumina surfaces at 25 ± 0.2°C and the influence of factors such as increasing concentration of SD (4.0–20.0 × 10^–3 mol cm^–3), the time required for adsorption equilibrium, pH (2.0–12.0) and temperature (5–45°C) of the adsorption medium, the presence of ions like Cl^–, SO^2– ₄ and PO^3– ₄ (0.01–0.30 M) and organic solvents (5% v/v) were observed on the course of adsorption of SD. Various adsorption and kinetic parameters such as adsorption coefficient, the rate constants for adsorption and desorption were also evaluated. The results of the above cited studies facilitated to formulate the mechanisms of interaction between SD and alumina surfaces. From application view point the present work may be a potential tool for an effective chromatographic separation of sulfa drugs from industrial effluents.     

Reactivity of M(en)Cl2 (M = Pd/Pt,en = 1,2-diaminoethane) with N,N′-bis(salicylidene)-p-phenylenediamine: Binding with hexafluorobenzene

Schiff base N,N′-bis(salicylidene)-p-phenylenediamine (LH₂) complexed with Pt(en)Cl₂ and Pd(en)Cl₂ provided [Pt(en)L]₂ · 4PF₆ (1) and Pd(Salen) (2) (Salen = N,N′-bis(salicylidene)-ethylenediamine), respectively, which were characterized by their elemental analysis, spectroscopic data and X-ray data. A solid complex obtained by the reaction of hexafluorobenzene (hfb) with the representative complex 1 has been isolated and characterized as 3 (1 · hfb) using UV–Vis, NMR (¹H, ¹³C and ¹⁹F) data. A solid complex of hfb with a reported Zn-cyclophane 4 has also been prepared and characterized 5 (4 · hfb) for comparison with complex 3. The association of hfb with 1 and 4 has also been monitored using UV–Vis and luminescence data.     

Homotopy analysis Sumudu transform method for time—fractional third order dispersive partial differential equation

In this article, we apply the newly introduced numerical method which is a combination of Sumudu transforms and Homotopy analysis method for the solution of time fractional third order dispersive type PDE equations. It is also discussed generalized algorithm, absolute convergence and analytic result of the finite number of independent variables including time variable.