Experimental and Density Functional Theory Studies on 1,1,1,4,4,4-Hexafluoro-2-Butene Pyrolysis

A series of thermal decomposition experiments were conducted over a temperature range of 873-1073 K to evaluate the thermal stability of 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz(Z)) and the production of hydrogen fluoride (HF). According to the detected products and experimental phenomena, the thermal decomposition of HFO-1336mzz(Z) could be divided into three stages. Our experimental results showed that HF concentration gradually increased with the elevation of thermal decomposition temperature. In this present study, a total of seven chemical reaction pathways of HFO-1336mzz(Z) pyrolysis were proposed to explore the generated mechanism on products through density functional theory (DFT) with M06-2X/6-311++(d,p) level theory. The thermal decomposition mechanism of pure HFO-1336mzz(Z) was discussed and the possible formation pathways of HF and other main products were proposed.

Detailed Investigation of the Outstanding Peroxyl Radical Scavenging Activity of Two Novel Amino-Pyridinol-Based Compounds

The ability of two novel amino-pyridinol based compounds (NPyr6 and NPyr7) as peroxyl radical scavengers was investigated in silico. The gathered data indicate that they are exceptionally efficient in that role. However, solvent polarity influences their relative efficiency for that purpose. NPyr6 was identified as the best peroxyl radical scavenger in lipid solution, while NPyr7 takes that place in aqueous solution. Both compounds present two acid-base equilibria, which influence their reactivity in aqueous solution. The associated pKa values were estimated. Several reaction mechanisms were explored. Hydrogen transfer from the phenolic group was identified as the chemical route with the highest contribution to the antioxidant behavior of the investigated compounds in both, nonpolar medium and aqueous solution (at 2 ≤ pH ≤ 10). At higher pH other reaction pathways become the most relevant ones. In addition, their bioavailability, cell permeability, safety, and manufacturability were evaluated. According to these, particularly toxicity, NPyr7 seems to be a better candidate for use as an oral drug to fight oxidative stress than NPyr6.

The reaction pathway analysis of phosphoric acid with the active radicals: a new insight of the fire-extinguishing mechanism of ABC dry powder

Dry powder fire-extinguishing agent is one of Halon substitutes due to its superior fire-extinguishing performance, non-toxicity, and environmental friendliness. As one of the most widely used dry powders, ABC dry powder has attracted wide attention. Understanding its reaction mechanism is important to the design of more efficient compound dry powder based on it. When ABC dry powder was applied to the flame, ammonium dihydrogen phosphate (the main fire-extinguishing component of ABC dry powder) would rapidly decompose into phosphoric acid (H₃PO₄) and ammonia. Therefore, in order to figure out the chemical reaction mechanism of ABC dry powder and active radicals, the main focus of this paper is on the H₃PO₄. Analysis of the electrostatic potential on van der Waals surface of H₃PO₄ was carried out. Besides, detailed theoretical investigation has been performed on the mechanism, kinetics, and thermochemistry of the reactions of H₃PO₄ with H, OH, and CH₃ radicals and further decomposition of H₃PO₄ using M06-2X/6-311G(d,p)//CCSD(T)/cc-pVTZ level of theory. Mayer bond order for all intrinsic reaction coordinate points was also calculated. Finally, it is theoretically proved that ABC dry powder extinguishes the fire mainly by chemical inhibition on H and OH radicals. Grapical Abstract .

Dual antioxidant/pro-oxidant behavior of the tryptophan metabolite 3-hydroxyanthranilic acid: a theoretical investigation of reaction mechanisms and kinetics

Potent antioxidant in the absence of metal ions, responsible for the activity usually attributed to tryptophan. Pro-oxidant in the presence of metal ions; this effect increases with the pH.

A theoretical insight into atmospheric chemistry of HFE-7100 and perfluoro-butyl formate: reactions with OH radicals and Cl atoms and the fate of alkoxy radicals

The calculated rate constants for C₄F₉OCH₃ + OH/Cl reactions are found to be 1.94 × 10⁻¹⁴ and 1.74 × 10⁻¹² cm³ molecule⁻¹ s⁻¹, respectively, at 298 K. The atmospheric lifetime and global warming potential for HFE-7100 are computed to be 2.12 years and 155.3, respectively.

Atmospheric chemistry of ethers, esters, and alcohols on the lifetimes, temperature dependence, and kinetic isotope effect: an example of CF3CX2CX2CX2OX with OX reactions (X = H, D)

Mechanisms and kinetics of the reaction of CF₃CX₂CX₂CX₂OX with OX (X= H, D) radical are investigated on a sound theoretical basis.

Assessing the Protective Activity of a Recently Discovered Phenolic Compound against Oxidative Stress Using Computational Chemistry

The protection exerted by 3,5-dihydroxy-4-methoxybenzyl alcohol (DHMBA), a phenolic compound recently isolated from the Pacific oyster, against oxidative stress (OS) is investigated using the density functional theory. Our results indicate that DHMBA is an outstanding peroxyl radical scavenger, being about 15 times and 4 orders of magnitude better than Trolox for that purpose in lipid and aqueous media, respectively. It was also found to react faster with HOO(•) than other known antioxidants such as resveratrol and ascorbic acid. DHMBA is also predicted to be able to sequester Cu(II) ions, consequently inhibiting the OS induced by Cu(II)-ascorbate mixtures and downgrading the (•)OH production via the Haber-Weiss reaction. However, it is proposed that DHMBA is more efficient as a primary antioxidant (free radical scavenger), than as a secondary antioxidant (metal ion chelator). In addition, it was found that DHMBA can be efficiently regenerated in aqueous solution, at physiological pH. Such regeneration is expected to contribute to increase the antioxidant protection exerted by DHMBA. These results suggest that probably synthetic routes for this compound should be pursued, because albeit its abundance in nature is rather low, its antioxidant activity is exceptional.

Adrenaline and noradrenaline: protectors against oxidative stress or molecular targets?

Density functional theory was used to investigate the potential role of neurotransmitters adrenaline and noradrenaline regarding oxidative stress. It is predicted that they can be efficient as free radical scavengers both in lipid and aqueous media, with the main reaction mechanism being the hydrogen transfer and the sequential proton loss electron transfer, respectively. Despite the polarity of the environment, adrenaline and noradrenaline react with (•)OOH faster than Trolox, which suggests that they are better peroxyl radical scavengers than the reference compound. Both catecholamines are also proposed to be capable of efficiently inhibiting the oxidative stress induced by copper(II)-ascorbate mixtures, and the (•)OH production via Haber-Weiss reaction, albeit the effects on the later are only partial. They exert such beneficial effects by sequestering Cu(II) ions. In summary, these catecholamines can be capable of reducing oxidative stress, by scavenging free radicals and by sequestering metal ions. However, at the same time they might lose their functions in the process due to the associated structural modifications. Consequently, adrenaline and noradrenaline can be considered as both protectors and molecular targets of oxidative stress. Fortunately, under the proper conditions, both catecholamines can be regenerated to their original form so their functions are restored.

Theoretical investigation on the atmospheric fate of CF3C(O)OCH 2O radical: alpha-ester rearrangement vs oxidation at 298 K

A theoretical study on the mechanism of the thermal decomposition of CF(3)C(O)OCH(2)O radical is presented for the first time. Geometry optimization and frequency calculations were performed at the MPWB1K/6-31 + G(d, p) level of theory and energetic information further refined by calculating the energy of the species using G2(MP2) theory. Three plausible decomposition pathways including α-ester rearrangement, reaction with O(2) and thermal decomposition (C-O bond scission) were considered in detail. Our results reveal that reaction with O(2) is the dominant path for the decomposition of CF(3)C(O)OCH(2)O radical in the atmosphere, involving the lowest energy barrier, which is in accord with experimental findings. Our theoretical results also suggest that α-ester rearrangement leading to the formation of trifluoroacetic acid TFA makes a negligible contribution to decomposition of the title alkoxy radical. The thermal rate constants for the above decomposition pathways were evaluated using canonical transition state theory (CTST) at 298 K.

Theoretical studies on kinetics, mechanism and thermochemistry of gas-phase reactions of HFE-449mec-f with OH radicals and Cl atom

A theoretical study on the mechanism and kinetics of the gas phase reactions of CF3CHFCF2OCH2CF3 (HFE-449mec-f) with the OH radicals and Cl atom have been performed using meta-hybrid modern density functional M06-2X using 6-31+G(d,p) basis set. Two conformers have been identified for CF3CHFCF2OCH2CF3 and the most stable one is considered for detailed study. Reaction profiles for OH-initiated hydrogen abstraction are modeled including the formation of pre-reactive and post-reactive complexes at entrance and exit channels. Our calculations reveal that hydrogen abstraction from the CH2 group is thermodynamically and kinetically more facile than that from the CHF group. Using group-balanced isodesmic reactions, the standard enthalpies of formation for HFE-449mecf and radicals generated by hydrogen abstraction, are also reported. The calculated bond dissociation energies for CH bonds are in good agreement with experimental results. The rate constants of the two reactions are determined for the first time in a wide temperature range of 250-450K. The calculated rate constant values are found to be 9.10×10(-15) and 4.77×10(-17)cm(3)molecule(-1)s(-1) for reactions with OH radicals and Cl atom, respectively. At 298K, the total calculated rate coefficient for reactions with OH radical is in good agreement with the experimental results. The atmospheric life time of HFE-449mec-f is estimated to be 0.287 years.