Catalytic Effect of Aqueous Solution in Water-Assisted Proton-Transfer Mechanism of 8-Hydroxy Guanine Radical

Uncovering the reduction mechanism of Np(VI) with N,N-diethyl hydroxylamine: a scalar-relativistic DFT investigation

Salt-free reductants have been extensively studied in the plutonium uranium reduction extraction (PUREX) process for Np(VI) reduction. Hydroxylamine derivatives as a class of promising salt-free reductants can reduce Np(VI) to Np(V) in nitric acid solution. The reduction reaction and kinetic behavior of Np(VI) to Np(V) by diethylhydroxylamine (DEHA) were studied experimentally. Herein, we explored the reduction mechanism of Np(VI) by DEHA in aqueous solution using scalar-relativistic density functional theory. Four stages are included in the process of Np(VI) reduction to Np(V) by DEHA. The intermediate C2H5N(O)C2H4 is hydrolyzed to C2H5NHOH. The third and fourth stages of Np(VI) reduction are via two pathways due to different H atoms participating successively in the reduction process. The largest energy barrier for the four Np(VI) reduction processes is 12.3 kcal mol-1 for the third stage of Pathway I, consistent with the experimental observations. The Np-Oyl bond distances and spin density on Np elucidate the reduction essence including outer-sphere electron transfer or hydrogen atom transfer. The analyses of bonding nature reveal the bonding evolution during the reduction process. This work elucidates the reduction mechanism of Np(VI) by DEHA and provides new insights into the reduction of Np(VI) by hydroxylamine derivatives.

Theoretical investigation of the SN2 mechanism of X- [X = SH, PH2] + CH3Y [Y = F, Cl, Br, I] reactions in water

We investigated the S_N2 Walden-inversion mechanism of X^- (X = SH, PH₂) + CH₃Y (Y = F, Cl, Br, I) reactions in water using multi-level quantum mechanics (ML-QM) and molecular mechanics (MM) methods. The potentials of the mean force were mapped using not only the density functional theory (DFT)/MM method but also a high-level, accurate CCSD(T)/MM method using the aug-cc-pVTZ basis set. In particular, for the PH₂^- + CH₃I reaction, although the backside attack Walden-inversion mechanics were not observed in the gas phase, we found that this mechanism takes place in water. The atomic-level dynamics of the concerted S_N2 mechanism and the stationary points along the reaction paths were characterized. For these reactions in water, their Walden-inversion barriers are higher than their corresponding ones in the gas phase, indicating that the aqueous solution hinders their reactivity. For the reactions with the same nucleophile X^- in water, the reaction barrier heights with different leaving groups are in the order of F > Cl > Br > I. For the same leaving group Y with different nucleophiles SH^- and PH₂^-, the reaction barrier with SH^- is greater than that of PH₂^- due to the former having higher electronegativity than the latter.

Infrared photodissociation spectroscopic studies of ScO(H2O)n=1–3Ar+ cluster cations: solvation induced reaction of ScO+ and water

We investigate the gaseous ScO(H₂O)_1–3Ar⁺ cations prepared by laser vaporization coupled with supersonic molecular beam using infrared photodissociation spectroscopy in the O–H stretching region.

Reactions of water with radical cations of guanine, 9-methylguanine, 2′-deoxyguanosine and guanosine: keto–enol isomerization, C8-hydroxylation, and effects of N9-substitution

The reactions of D₂O with guanine radical cations in nucleobases and nucleosides were studied in the gas phase using the guided-ion-beam experiment and computational modeling.