Computational investigation of the kinetic and thermodynamic parameters governing polytetrafluoroethylene chain shortening.

Mechanisms of fluoropolymer pyrolysis are poorly understood. Oversimplifications in both experimental and computational studies related to high temperature decomposition of PTFE have led to the elucidation of potentially incomplete and inaccurate pathways. While most conflicts within the literature claim that individual decomposition occurs through either CF elimination or CF elimination, one mechanism that is largely ignored is the thermodynamically favored 1,2-F atom transfer.

Role of explicit solvation and level of theory in predicting the aqueous reduction potential of carbonate radical anion by DFT.

Chemical oxidation reactions, a key class of electron transfer processes, have broad applications, including the treatment of persistent and mobile pollutants. Marcus theory, paired with density functional theory (DFT) simulations, enables quantification of thermodynamic properties in these reactions. However, accurately modeling species with complex solvent interactions, especially radicals, requires careful selection of computational methods.

Persistent Luminescence Nanosensors: A Generalized Optode-Based Platform for Autofluorescence-Free Sensing in Biological Systems.

Fluorescent nanosensors have revolutionized diagnostics and our ability to monitor cellular dynamics. Yet, distinguishing sensor signals from autofluorescence remains a challenge. Here, we merged optode-based sensing with near-infrared-emitting ZnGaO:Cr persistent luminescence nanoparticles (PLNPs) to create nanocomposites for autofluorescence-free "glow-in-the-dark" sensing.

Kinetic Model for Predicting Perfluoroalkyl Acid Degradation During UV-Sulfite Treatment.

Hydrated electron () treatment processes show great potential in remediating recalcitrant water contaminants, including perfluoroalkyl and polyfluoroalkyl substances (PFAS). However, treatment efficacy depends upon many factors relating to source water composition, UV light source characteristics, and contaminant reactivity. Here, we provide critical insights into the complex roles of solution parameters on contaminant abatement through application of a UV-sulfite kinetic model that incorporates first-principles information on photogeneration and reactivity.

Chemical bonding in potential PFAS products from the thermal degradation of energetic devices, a DFT analysis.

This work investigates stability and chemical bonding in possible per- and polyfluoroalkyl substances (PFAS) generated through the disposal of munitions in controlled detonations and open burns. Density functional theory (DFT) calculations were used to determine bond dissociation enthalpies (BDEs), activation energies, and other chemical properties. Calculated parameters were used to determine the functional groups most likely to be present based on the level of fluorination and the position of fluorines.

Influence of Carbonate Speciation on Hydrated Electron Treatment Processes.

Advanced reduction processes (ARPs) that generate hydrated electrons (e; e.g., UV-sulfite) have emerged as a promising remediation technology for recalcitrant water contaminants, including per- and polyfluoroalkyl substances (PFASs).

Ultra-short chain fluorocarboxylates exhibit wide ranging reactivity with hydrated electrons.

Recent reports demonstrate that technologies generating hydrated electrons (e; e.g., UV-sulfite) are a promising strategy for destruction of per- and polyfluoroalkyl substances, but fundamental rate constants are lacking.

Phototriggered Desorption of Hydrogen, Ethylene, and Carbon Monoxide from a Cu(I)-Modified Covalent Organic Framework.

Materials that are capable of adsorbing and desorbing gases near ambient conditions are highly sought after for many applications in gas storage and separations. While the physisorption of typical gases to high surface area covalent organic frameworks (COFs) occurs through relatively weak intermolecular forces, the tunability of framework materials makes them promising candidates for tailoring gas sorption enthalpies. The incorporation of open Cu(I) sites into framework materials is a proven strategy to increase gas uptake closer to ambient conditions for gases that are capable of π-back-bonding with Cu.

High-temperature decomposition chemistry of trimethylsiloxane surfactants, a potential Fluorine-Free replacement for fire suppression.

Per- and polyfluoroalkyl substances (PFAS) have become global environmental contaminants due to being notoriously difficult to degrade, and it has become increasingly important to employ suitable PFAS alternatives, especially in aqueous film-forming foams (AFFF). Trimethylsiloxane (TriSil) surfactants are potential fluorine-free replacements for PFAS in fire suppression technologies. Yet because these compounds may be more susceptible to high-temperature decomposition, it is necessary to assess the potential environmental impact of their thermal degradation products.

Conformational distributions of helical perfluoroalkyl substances and impacts on stability.

Per- and polyfluoroalkyl substances (PFAS) have been widely used the past 70 years in numerous applications due to their chemical and thermal stability. Due to their robust stability, they are environmentally recalcitrant which made them one of the most persistent environmental contaminants. In addition to strong CF bond strength, oleophobicity, hydrophobicity, and high reduction-oxidation (redox) potential of PFAS has led to their inefficient degradation by traditional means.

Computational protocol for predicting F NMR chemical shifts for PFAS and connection to PFAS structure.

Per- and polyfluoroalkyl substances (PFAS) are robust "forever" chemicals that have become global environmental contaminants due to their inability to degrade using traditional techniques. In addition to the persistent nature of PFAS, the structural and functional diversity in PFAS creates a unique challenge in identification and remediation. Their identification is further complicated by the absence of standards for many PFAS.

Role of Explicit Hydration in Predicting the Aqueous Standard Reduction Potential of Sulfate Radical Anion by DFT and Insight into the Influence of pH on the Reduction Potential.

Sulfate radical anion (SO) is a potent oxidant capable of destroying recalcitrant environmental contaminants such as perfluoroalkyl carboxylic acids. In addition, it is thought to participate in important atmospheric reactions. Its standard reduction potential (°) is fundamental to its reactivity.

Diazaborines oxidize slowly with HO but rapidly with peroxynitrite in aqueous buffer.

Reactive oxygen species (ROS) such as hydrogen peroxide (HO) and peroxynitrite (ONOO) oxidize arylboronic acids to their corresponding phenols. When used in molecular imaging probes and in ROS-responsive molecules, however, simple arylboronic acids struggle to discriminate between HO and ONOO because of their fast rate of reaction with both ROS. Here, we show that diazaborines (DABs) react slowly with HO but rapidly with peroxynitrite in an aqueous buffer.

Periodic Trends behind the Stability of Metal Catalysts Supported on Graphene with Graphitic Nitrogen Defects.

This study explored the fundamental chemical intricacies behind the interactions between metal catalysts and carbon supports with graphitic nitrogen defects. These interactions were probed by examining metal adsorption, specifically, the location of adsorption and the electronic structure of metal catalysts as the basis for the metal-support interactions (MSIs). A computational framework was developed, and a series of 12 transition metals was systematically studied over various graphene models with graphitic nitrogen defect(s).

Understanding Fragmentation of Organic Small Molecules in Atom Probe Tomography.

In atom probe tomography of molecular organic materials, field ionization of either entire molecules or molecular fragments can occur, but the mechanism governing this behavior was not previously understood. This work explains when a doubly ionized small molecule organic material is expected to undergo fragmentation. We find that multiple detection events arising from post-ionization fragmentation of a parent molecular dication into two daughter ions is well explained by the free energy and geometries of the molecules computed using density functional theory.

Structure and Reactivity of Alloxan Monohydrate in the Liquid Phase.

Alloxan is an important toxic glucose analogue used to induce diabetes in lab test animals. Once regarded as a "problem structure," the condensed-phase structure of anhydrous alloxan has largely been settled, but literature inconsistencies remain for the structure of the typically employed reagent alloxan monohydrate. Due to the criticality of structure-function relationships, we have used H/C{H} NMR, IR spectroscopy, as well as quantum mechanical (QM) calculations to probe the liquid-phase structure and reactivity of alloxan monohydrate.

Intermolecular fluoroamination of allenes towards substituted vinyl fluorides.

A synthetic method towards fluorinated allylamines using allene precursors is reported. A variety of heterocyclic amines were employed as nucleophiles in a Selectfluor promoted intermolecular fluoroamination reaction. This strategy provides a novel synthetic route to access vinyl fluorides with a vicinal amine moiety.

Reactive Molecular Dynamics Simulations and Quantum Chemistry Calculations To Investigate Soot-Relevant Reaction Pathways for Hexylamine Isomers.

Sooting tendencies of a series of nitrogen-containing hydrocarbons (NHCs) have been recently characterized experimentally using the yield sooting index (YSI) methodology. This work aims to identify soot-relevant reaction pathways for three selected CHN amines, namely, dipropylamine (DPA), diisopropylamine (DIPA), and 3,3-dimethylbutylamine (DMBA) using ReaxFF molecular dynamics (MD) simulations and quantum mechanical (QM) calculations and to interpret the experimentally observed trends. ReaxFF MD simulations are performed to determine the important intermediate species and radicals involved in the fuel decomposition and soot formation processes.

Investigating the Photochemistry of C7 and C8 Functionalized N(5)-Ethyl-flavinium Cation: A Computational Study.

Flavins are a diverse set of compounds with a wide variety of biological and nonbiological applications. Applications of flavins receiving attention recently consist of electro- and photocatalytic oxidation of substrates for organic synthesis, bioengineered nanotechnology, and water splitting catalysts, among others. While there is vast knowledge regarding the structure-property relationships of flavins and their electrochemistry, there is much less work elucidating the structure property relationships as they pertain to flavinium photochemistry.

Characterization of the ALSEP Process at Equilibrium: Speciation and Stoichiometry of the Extracted Complex.

We have determined the identity of the complexes extracted into the ALSEP process solvent from solutions of nitric acid. The ALSEP process is a new solvent extraction separation designed to separate americium and curium from trivalent lanthanides in irradiated nuclear fuel. ALSEP employs a mixture of two extractants, 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) and ,,','-tetra(2-ethylhexyl)diglycolamide (TEHDGA) in -dodecane, which makes it difficult to ascertain the nature of the extracted metal complexes.

Dynamic and Solvation Behaviors of ALSEP Organic Ligands.

The Actinide-Lanthanide Separation Process (ALSEP) is a solvent extraction approach for separating relevant trivalent minor actinides (e.g., americium and curium) from used nuclear fuel.

1,2-H Atom Rearrangements in Benzyloxyl Radicals.

The rate constants for solvent-assisted 1,2-H atom rearrangements in para-substituted benzyloxyl radicals were studied with density functional theory. The rate of the radical rearrangement, calculated through transition state theory with Eckhart tunneling corrections, was shown to be drastically impacted by the presence of both implicit and explicit solvent molecules, with a quantitative agreement with laser flash photolysis studies for a variety of electron-donating and -withdrawing substituents. The rate of rearrangement was found to be correlated to the distance between the rearranging hydrogen atom and the α-carbon in the transition state, which could be modified through the para substituent and the type of assisting solvent molecule (e.

Solvation Dynamics of HEHEHP Ligand at the Liquid-Liquid Interface.

Actinide-lanthanide separation (ALSEP) has been a topic of interest in recent years as it has been shown to selectively extract problematic metals from spent nuclear fuel. However, the process suffers from slow kinetics, prohibiting it from being applied to nuclear facilities. In an effort to improve the process, many fundamental studies have been performed, but the majority have only focused on the thermodynamics of separation.