Presence Of Oxygen In Water Research Articles

The case for reporting PO2 (partial pressure of oxygen), in addition to DO (dissolved oxygen), in studies of aquatic systems

In this essay, we question the sole use of mg/L (ppm) and the term DO (dissolved oxygen) when referring to oxygen supply in water, and discuss reasons for also reporting the partial pressure of oxygen (PO2). Oxygen moves from water into organisms by diffusion only, and the rate and direction of diffusion is solely dependent upon partial pressure gradients, not concentration gradients. However, the amount of oxygen moved into an organism is both a function of DO and PO2. Therefore, to have physiological and ecological relevance, the presence of oxygen in water, when reported as DO, should also include PO2.

Transformations of shungite in aqueous media (pH from 1 to 12)

The kinetics of leaching of Karelian shungites (types I–III) with water at pH in the interval 1–12 was studied. Changes in the chemical composition and structure of the shungite substance were revealed by X-ray fluorescence analysis and scanning electron microscopy. The catalytic properties of shungite were studied in relation to the presence of oxygen in water. The optimum design of a shungite–carbonate installation for potable water treatment was substantiated.

Prevention of Transition Metal Dichalcogenide Photodegradation by Encapsulation with h-BN Layers.

Transition metal dichalcogenides (TMDs) have recently received increasing attention because of their potential applications in semiconducting and optoelectronic devices exhibiting large optical absorptions in the visible range. However, some studies have reported that the grain boundaries of TMDs can be easily degraded by the presence of oxygen in water and by UV irradiation, ozone, and heating under ambient conditions. We herein demonstrate the photodegradation of WSe2 and MoSe2 by laser exposure (532 nm) and the subsequent prevention of this photodegradation by encapsulation with hexagonal boron nitride (h-BN) layers. The photodegradation was monitored by variation in peak intensities in the Raman and photoluminescence spectra. The rapid photodegradation of WSe2 under air occurred at a laser power of ≥0.5 mW and was not observed to any extent at ≤0.1 mW. However, in the presence of a water droplet, the photodegradation of WSe2 was accelerated and took place even at 0.1 mW. We examined the encapsulation of WSe2 with h-BN and found that this prevented photodegradation. However, a single layer of h-BN was not sufficient to fully prevent this photodegradation, and so a triple layer of h-BN was employed. We also demonstrated that the photodegradation of MoSe2 was prevented by encapsulation with h-BN layers. On the basis of X-ray photoelectron spectroscopy and scanning photoemission microscopy data, we determined that this degradation was caused by the photoinduced oxidation of TMDs. These results can be used to develop a general strategy for improving the stability of 2D materials in practical applications.

Heteropolyanion-based ionic liquids catalysed conversion of cellulose into formic acid without any additives

Heteropolyanion-based ionic liquids with –SO3H functionalized cations and PMo11VO404− anions were synthesized and applied in the conversion of cellulose into formic acid (FA). It was demonstrated that the as-prepared ILs showed enhanced activity for catalysing cellulose conversion to FA in the presence of oxygen in water compared to H4PMo11VO40. A high FA yield over 50% accompanied by a FA concentration of ∼10% in reaction solution was obtained at 180 °C and in an oxygen pressure of 1.0 MPa. The possible pathway of FA production from cellulose was investigated. It was indicated that the resulting ILs served as bifunctional catalysts with cations catalysing the cellulose hydrolysis to glucose and anions catalysing glucose oxidation to FA. These ILs may find more applications in cellulose conversion.

Action of pyrroloquinolinequinol as an antioxidant against lipid peroxidation in solution.

The activities of pyrroloquinoline quinone (PQQ), a coenzyme of methanol dehydrogenase and amine oxidase, and its reduced form pyrroloquinoline quinol (PQQH2) as an antioxidant have been measured in solution. PQQH2 was stable in the absence of oxygen but rapidly auto-oxidized to PQQ in the presence of oxygen in water. PQQH2 was stable in an aprotic solvent such as acetonitrile, even in air. PQQ did not exert appreciable antioxidant activity, whereas PQQH2 exerted higher reactivity than alpha-tocopherol toward galvinoxyl radical and peroxyl radical. PQQH2 acted as a potent antioxidant against the oxidation of methyl linoleate in acetonitrile induced by azo compound and produced a clear induction period, from which the apparent stoichiometric number was obtained as 1.1. PQQH2 reduced the alpha-tocopheroxyl radical and spared alpha-tocopherol in the oxidation of methyl linoleate. These results suggest that PQQH2 may act as a potent antioxidant, particularly in combination with alpha-tocopherol.

The reaction of S-nitrosothiols with thiols at high thiol concentration

Reactions of S-nitrosothiols (RSNO) with their corresponding thiols (RSH) present in a large excess (>20-fold) proceed readily to give the disulfide. Ammonia is formed together with some nitrite anion, and these constitute >90% of the "nitrogen" products. This is in marked contrast with the reaction at low thiol concentration, where nitric oxide is the major initial "nitrogen" product, which is rapidly converted in the presence of oxygen in water to nitrite anion. Also in marked contrast to the "low thiol concentration" reaction, the reaction at high thiol concentration is not affected by added Cu2+, nor by the metal-ion scavenger EDTA. Kinetically all reactions were excellent first-order processes, and the reactions were also strictly first order in thiol concentration. A large range of nitrosothiols were studied and the generality of the reaction established. Some reactions of RSNO with other thiols (R'SH) were examined and the results readily interpreted in terms of a prior rapid equilibrium transnitrosation. The pH dependence for the reaction of S-nitrosocysteine with cysteine clearly showed that the reactive species is the cysteine thiolate anion. The results are discussed along with those of two other recent reports of these reactions, in terms of thiolate attack initially at the nitroso nitrogen atom, and subsequently at sulfur atoms, eliminating RSSR and yielding hydroxylamine, which is rapidly reduced by thiolate ion to ammonia. The results are also discussed in connection with the release of NO from nitrosothiols and with the important biological consequences, both for the in vivo reactions of NO and for the potential of nitrosothiols as NO-releasing drugs for medical use.Key words: S-nitrosothiols, thiols, nitric oxide, ammonia, nitrous oxide.