Quantum tunneling of hydrogen atom transfer affects mandrel degradation in inertial confinement fusion target fabrication

Confinement effects of mandrel degradation in ICF target fabrication

Understanding and further regulating the degradation of mandrel materials is a key aspect of target fabrication in inertial confinement fusion (ICF). Here, a quasi-one-dimensional confinement model is developed using a series of single-walled carbon nanotubes with varying diameters (Dm), and the degradation of poly-α-methylstyrene (PAMS) as a typical mandrel material is investigated under such confined conditions by using the combined method of quantum mechanics and molecular mechanics. In comparison to the isolated system, the calculations show that confinement can decrease or increase the energy barriers of PAMS degradation, which directly depends on Dm. Following which a clear exponential relationship between the degradation rate of PAMS and its own density is derived, indicating that the density of PAMS can be used to regulate mandrel degradation. This work highlights the important effects of confinement on degradation and provides a valuable reference for further development of polymer degradation technologies in ICF target fabrication and other fields.

Rapid Thalidomide Racemization Is Related to Proton Tunneling Reactions via Water Bridges

Quantum mechanical tunneling (QMT) can play an important role in light element-related chemical reactions; however, its influence on racemization is not fully understood. Herein, we demonstrate that the role of QMT is decisive for rapid racemization of the well-known thalidomide molecule in aqueous environments, increasing the reaction rate constants of the most likely racemization pathways by 87-149 times at approximately body temperature and achieving good agreement between theoretical calculations and experimental observations. In addition, the kinetic isotope effect values fit well with those of previous experiments. These results are attributed to enhanced tunneling probability due to the alteration of potential barriers for proton transfer reactions via water bridges. This work highlights the significance of the QMT effect in racemization and its potential impact on drug safety, providing a fundamental perspective for understanding chirality-related issues in biological systems.

Initiator enhancement of mandrel degradation for ICF target fabrication

Poly-α-methylstyrene (PAMS), as an ideal mandrel material used in the fabrication of inertial confinement fusion (ICF) targets, its efficient degradation is the key to the quality of targets. However, there is a great challenge to achieve enhanced degradation. Here, we proposed the strategy to optimize the degradation of PAMS microspheres using di-tert-butyl peroxide (DTBP) as a degradation initiator. Experimentally, monodisperse PAMS microspheres with DTBP were controllably prepared by a microfluidic-based microencapsulation technique. Thermogravimetric results show that DTBP largely decreases the initial degradation temperature from 550 K to 450 K, which effectively promotes the thermal degradation of PAMS microspheres. Theoretically, DTBP can reduce the activation energy of degradation. Moreover, the potential energy surfaces were used to describe the degradation process at the atomic level. Our work brings a new direction for the study of mandrel degradation in ICF targets fabrication, and also provides a valuable reference for solving the pollution of waste plastics.

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Di-tert-butyl peroxide enhances the thermal degradation performance of mandrel

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Di-tert-butyl peroxide decreases the degradation activation energy of mandrel

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Thermogravimetric study and DFT calculation prove the enhanced degradation

How Does Electronic Activity Drive Chemical Reactions? Insights from the Reaction Electronic Flux for the Conversion of Dopamine into Norepinephrine

Hydrogen atom transfer (HAT) is a crucial step in the physiological conversion of dopamine into norepinephrine catalyzed by dopamine β-monooxygenase. The way the reaction takes place is unclear, and a rational explanation on how the electronic activity drives the HAT seems to be necessary. In this work, we answer this question using the reaction electronic flux (REF), a DFT-based descriptor of electronic activity. Two reaction mechanisms will be analyzed using the REF's decomposition in polarization and electron transfer effects. Results show that both mechanisms proceed as follows: (1) polarization effects initiate the reactions producing structural distortions; (2) electron transfer processes take over near the transition states, triggering specific chemical events such as bond forming and breaking which are responsible to push the reactions toward the products; (3) after passing the transition state, polarization shows up again and drives the relaxation process toward the product. Similar polarization effects were observed in both reactions, but they present an opposite behavior of the electronic transfer flux disclosing the fact that electron transfer phenomena govern the reaction mechanisms.