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Optical Nanosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
The NP sensors based on this design include ions (H+, Ca2+, Mg2+, Zn2+, Fe3+, and K+), radicals (•OH radical), small molecules (O2, singlet oxygen, hydrogen peroxide, H2O2), etc. Singlet oxygen is the lowest excited state of the dioxygen molecule, which is less stable than the normal triplet oxygen. Its lifetime in solution is in the microsecond range (3 μs in water to about 700 μs in deuterated benzene, C6D6). It undergoes several reactions with organic molecules (the ene reaction and the Diels–Alder reaction).
Carbon, Nitrogen, and Sulfur in Air Pollution
Published in Jerome Greyson, Carbon, Nitrogen, and Sulfur Pollutants and Their Determination in Air and Water, 2020
Triplet oxygen atoms produced from the photodissociation of ozone are known to rapidly recombine with molecular oxygen to reform ozone in the troposphere. Singlet oxygens, however, react with water to form two units of the highly reactive hydroxyl free radical [Graedel 1980, 109] H2O+O(1D)=2HO.
NMR and EPR Spectroscopy as a Tool for the Studies of Intermediates of Transition Metal–Catalyzed Oxidations
Published in Evgenii Talsi, Konstantin Bryliakov, Applications of EPR and NMR Spectroscopy in Homogeneous Catalysis, 2017
Evgenii Talsi, Konstantin Bryliakov
The direct reaction of triplet oxygen 3O2 with singlet organic molecules to give singlet products is a spin-forbidden process. In terms of chemical kinetics, this means that uncatalyzed reaction of 3O2 with organic substrates will proceed very slowly. At the same time, such reactions may be facilitated by transition metal complexes; the role of the metal center is (1) to “activate” the dioxygen molecule and convert it to reactive metal–oxygen species, which will then (2) transfer the oxygen atom to the organic substrate. In this chapter, we will particularly focus on the second process; typically, it is conducted by metal–oxygen intermediates (such as superoxo, peroxo, hydroperoxo, alkylperoxo, and oxo complexes of transition metals). The unfading interest in experimental and theoretical investigations of metal–oxygen reactive species and oxidation reactions they conduct is to a large degree accounted for by the participation of related metal–oxygen intermediates in reactions occurring in living organisms in the presence of metalloenzymes. The corresponding branch of catalytic science, focused on the investigation of synthetic metal complexes, modeling the catalytic functions of natural metalloenzymes, is called biomimetic catalysis. On the other hand, the attention to metal-catalyzed oxidations is caused by the growing demand in novel, more efficient, and “green” catalyst systems for chemo-, regio-, and stereoselective oxidation of organic substrates, which is mostly dictated by toughening economic and environmental constraints. Nowadays, it is generally accepted that the design of novel catalyst systems should be based on the understanding of the detailed mechanism of their catalytic action, which in turn requires deep insight into the nature of the reactive species.
Theoretical investigation for the reactions of triplet oxygen atom with dimethyl sulphide, ethyl methyl sulphide: mechanism and kinetics properties
Published in Molecular Physics, 2022
In recent years, the research on the oxidation mechanism of sulfur-containing compounds has also attracted widespread interest. Sulphur is one of the most abundant elements on earth and is an essential component of all living cells. Atmospheric sulphur compounds mainly were produced from burning of fossil fuels and in smaller amounts from the action of anaerobic bacteria and volcanic activity [1,2]. Alkylsulphides and their derivates, for example, are used as coke and CO inhibiting additives during the steam cracking of crude oil fractions to olefins [3]. In free radical polymerisation, sulphur compounds are frequently used to control the molecular mass of the polymer [4] and used in other applications [5]. Gas phase sulphur compounds represent only a small fraction of the Earth’s atmospheric composition, comprising less than 1 ppm by volume in air. However, the chemistry of sulphur compounds has a significant impact on the atmosphere and the biosphere: acid rain, visibility reduction and climate modification [6,7]. As an important sulphur-containing compounds, dimethyl sulphide (CH3SCH3) and ethyl methyl sulphide (CH3CH2SCH3) can react with Cl, BrO, NO3, N2O5, O3, OH, H, HOO [8–20] and eventually form stratospheric sulphate aerosols and the sulphur constituent of troposphere. Triplet oxygen atoms (O(3P)) are member of the odd oxygen family and are present in almost all atmospheric layers. Atomic oxygen is formed by the photodissociation of ozone resulting in excited singlet state oxygen atom O(‘D). This excited state O(‘D), after reacting with nitrogen molecule and with oxygen molecule forms [21,22]: