Water OH Bond Activation by Gas-Phase Plutonium Atoms: Reaction Mechanisms and Ab Initio Molecular Dynamics Study

Unveiling the Reduction Mechanism of Pu(IV) by Acetaldoxime

The separation of plutonium (Pu) from spent nuclear fuel was achieved by effectively adjusting the oxidation state of Pu from +IV to +III in the plutonium uranium reduction extraction (PUREX) process. Acetaldoxime (CH3CHNOH) as a free salt reductant can rapidly reduce Pu(IV), but the reduction mechanism remains indistinct. Herein, we explore the reduction mechanism of two Pu(IV) ions by one CH3CHNOH molecule, where the second Pu(IV) reduction is the rate-determining step with the energy barrier of 19.24 kcal mol-1, which is in line with the experimental activation energy (20.95 ± 2.34 kcal mol-1). Additionally, the results of structure and spin density analyses demonstrate that the first and second Pu(IV) reduction is attributed to hydrogen atom transfer and hydroxyl ligand transfer, respectively. Analysis of localized molecular orbitals unveils that the reduction process is accompanied by the breaking of the Pu-OOH bond and the formation of the OOH-H and C-OOH bonds. The reaction energies confirm that the reduction of Pu(IV) by acetaldoxime is both thermodynamically and kinetically accessible. In this work, we elucidate the reduction mechanism of Pu(IV) with CH3CHNOH, which provides a theoretical understanding of the rapid reduction of Pu(IV).

Oxidative stress state inhibits exosome secretion of hPDLCs through a specific mechanism mediated by PRMT1

BACKGROUND AND OBJECTIVES

Periodontitis, the most common chronic inflammation characterized by persistent alveolar bone resorption in the periodontitis, affects almost half of the adult population worldwide. Oxidative stress is one of the pathophysiological mechanisms underlying periodontitis, which affects the occurrence and development of periodontitis. Exosomes are increasingly recognized as vehicles of intercellular communication and are closely related to periodontitis. However, the effects of oxidative stress on exosome secretion and the specific mechanisms remain elusive in human periodontal ligament cells (hPDLCs). The relationship between exosome secretion and the osteogenic differentiation of hPDLCs also needs to be investigated.

METHODS

Isolated PDLSCs were identified using flow cytometry. Osteogenesis was measured using alizarin red staining and ALP staining. Expression of exosomal markers and PRMT1 was analyzed using western blot. Immunofluorescence was used to measure exosome uptake and the expression of EEA1.

RESULTS

The secretion capacity of exosomes was markedly suppressed under oxidative stress. Protein arginine methyltransferase 1 (PRMT1) has been strongly associated with both oxidative stress and inflammation, and PRMT1 was significantly upregulated under oxidative stress conditions. Lentivirus-mediated overexpression of PRMT1 caused a significant reduction in the secretion of exosomes, but multivesicular bodies (MVBs) containing a large number of intraluminal vesicles (ILVs) were increased. Rab11a and Rab27a expression, which mediate MVBs fusion with cell membranes, decreased, although this phenomenon was restored after knocking down PRMT1 expression under oxidative stress.

CONCLUSIONS

These results indicated that PRMT1 mediated a decrease in exosome secretion of hPDLCs. The decrease in Rab11a and Rab27a leads to a large accumulation of MVBs in cells and is one of the main reasons for impaired exosome secretion. The decrease in osteogenic differentiation of hPDLCs caused by H₂ O₂ may originate in part from the inhibition of exosome secretion.

The formation mechanism of uranium and thorium hydride phosphorus: a systematically theoretical study

Activation of prototypical bonds by actinide atoms is an important aspect of material activity, and the results can be used for the study of nuclear material storage. In this study, the activation of the P–H bonds of the PH₃ molecule by U or Th to form uranium or thorium hydride phosphorus has been systematically explored using density functional theory. A detailed description of the reaction mechanism which includes the potential energy profiles and the properties of bond evolution is presented. There are two types of reaction channels, isomerization and dehydrogenation in U + PH₃ and Th + PH₃. The difference between the two reactions is the process of the first P–H bond dissociation. The evolution characteristics of the chemical bonds along reaction pathways is analyzed by using electron localization functions, quantum theory of atoms in molecules, Mayer bond orders and natural bond orbitals. The reaction rate constants are calculated at the variational transition state level, and rate-determining steps are predicted.

The reactions of U, Th with PH₃ to form the uranium and thorium hydride phosphorus have been systematically explored.

Mechanochemical formation of chlorinated phenoxy radicals and their roles in the remediation of hexachlorobenzene contaminated soil

Mechanochemical degradation (MCD) is a promising eco-friendly method to dispose persistent organic pollutants (POPs). Mechanically induced free-radical attack was thought to be one of the key elements in initiating and accelerating the dechlorination and degradation of POPs. In this study, mechanochemical formation of free-radicals and their roles in the remediation of hexachlorobenzene (HCB) contaminated soil were explored using both of experimental analysis and quantum chemical calculations. It was found that chlorinated phenoxy radicals(CB-O) can be produced in the milling process and they played a vital role in the dechlorination of HCB, based on the results of electron spin-resonance (ESR) and X-ray photoelectron spectra (XPS). Two transition states of mechanochemical reaction along the formation of pentachlorinated phenoxy radical (PeCB-O) were located, with the energy barriers of 39.4 and 3.4 kJ/mol. The localized orbital locator (LOL), Mayer bond order and topological analysis were also implemented to depict the process in detail. Free-radical attack dominated dechlorination pathway of HCB in the MCD process was also verified by the Fukui function analysis. The study on the mechanically-induced generation of free-radicals and their associated modes of action on the degradation of HCB will provide a deep insight into mechanochemical remediation mechanism of POPs contaminated soil.

New Insights into Adsorption Behaviour of NH3 Molecules on Small (SiO2)n (n=2–7) Clusters Through Systematic Analysis of Structural and Topological Properties

The adsorption of NH3 molecules on (SiO2)n (n = 2–7) clusters was explored using various theoretical methods. The stable structures, interaction energies, and bonding properties for the various methods were evaluated in detail. Reactivity analysis and optimization results showed that a single NH3 molecule preferentially adheres to the Si atom at the edge of the clusters. It was also observed that the energy gap and hardness of the complexes decreased with an increase in the number of NH3 molecules. Topological, electron localization function, and atoms-in-molecules analyses were performed to investigate the bonding characteristics of these complexes. In addition, the results of this study were compared with those obtained for a similar system (H2O molecules adsorbed onto SiO2 clusters), and the similarities and differences between the two systems were discussed.

Can water continuously oxidize the PuO molecule? Mechanisms, topological analysis and rate constant calculations

A detailed description of the PuO continuously oxidized by water in the gas-phase.

Ab initio molecular dynamics study of the interaction of plutonium with oxygen in the gas phase

There are two kinds of plutonium surface corrosion, one of which is oxidation between plutonium and oxygen or oxygen compounds.

Systematic analysis of structural and topological properties: new insights into PuO2(H2O)n2+ (n = 1–6) complexes in the gas phase

In this study, the equilibrium, electronic structures, bonding and topological properties of PuO₂(H₂O)_n²⁺ (n = 1–6) complexes were systematically investigated.