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Uranium Takes an Alternate Pathway
Under normal working conditions, radioactive materials such as uranium react in a predictable manner. However, under extreme conditions of high temperature, a short timescale, and rapid cooling, the reaction pathways and kinetics change dramatically. Until recently, scientists lacked a good understanding of the chemistry associated with the thermal decomposition of these reactive compounds under extreme conditions since their reaction rates are so fast and so different from equilibrium processes.
The October 21, 2022, Inorganic Chemistry cover story presents how Lawrence Livermore scientists have synthesized uranium-based compounds that are extremely air- and water-sensitive. The team was able to characterize the behavior of these compounds under extreme conditions using a custom-built laser chamber capable of handling radioactive material. The process used laser irradiation to thermally decompose UI4(1,4-dioxane)2 to form a thin layer of material containing a mixture of decomposition products. The extreme nature of the irradiation process is then observed in the production of vapor during the intense temperature cycling. This effort was the first application of laser-driven chemistry with a uranium-based compound containing organic ligands as the precursor.
“The knowledge can potentially be applied to materials manufacturing, stockpile stewardship, or even waste consolidation, processing, or storage,” says Livermore radiochemist Maryline Kerlin, first author of the paper. “We could imagine storing a metal-containing compound under a stable configuration, and then react it under lasers to obtain a new product.”
Contact: Maryline Kerlin (925) 423-3675 (kerlin4@llnl.gov).
Model Instantly Predicts Polymer Properties
Development of suitable polymer materials for use in a growing application space relies on accurately predicting the properties of candidate materials. Quantitative understanding of the relationship between chemical structure and observable properties is particularly challenging for polymers, due to their complex 3D structures. The molecular structure of polymers consists of numerous repeating chemical subunits, a characteristic known as periodicity.
A team of Lawrence Livermore materials and computer scientists developed a machine-learning (ML) model to demonstrate how subtle changes in a polymer’s connectivity and periodicity can dramatically affect its predicted properties. The team developed a new method, described in the October 31, 2022, Journal of Chemical Information and Modeling, for explicitly encoding the polymer’s periodicity into the ML model. “The results show that inclusion of periodicity in the model enables state-of-the-art accuracy for predicting polymer properties,” says Livermore researcher Evan Antoniuk. The ML model can generate property predictions almost immediately. “The success of the model lies in a new polymer representation that compactly captures the polymers’ structure, in combination with powerful graph-based ML techniques that autonomously learn how to describe the structure of the polymer,” says Antoniuk. The team has also developed an interactive web interface to allow quick access to the ML models. Adds project co-leader Anna Hiszpanski, “This interactive model will allow polymer chemists to understand the properties of new polymer materials, enabling new concepts in polymer chemistry to be rapidly tested and iterated.”
Contact: Evan Antoniuk (925) 423-9107 (antoniuk1@llnl.gov).
New Technique to Analyze Fentanyl
A team of Lawrence Livermore scientists has developed a new method, published in the November 2, 2022, PLOS One, to analyze and confirm the presence of fentanyl and a related analog—acetyl fentanyl, a potent opioid as well—to aid in chemical forensics, toxicology, and medical diagnoses. The Livermore technique detects fentanyl in blood and urine at low levels still lethal enough to cause an overdose. Specifically, the researchers detected intact fentanyl in biological tissues to confidently identify and confirm fentanyl’s presence in the sample by chemically modifying the opioid.
The team spiked blood and urine samples with levels of fentanyl and acetyl fentanyl obtained from human overdose cases. An organic solvent was used to extract the opioid from the samples. That organic extract was treated with the chemical reagent 2,2,2-trichloroethoxycarbonyl chloride (troc chloride). “The reaction between troc chloride and fentanyl breaks the compound into two products from the opioid: the first is 2-chloroethyl benzene and the second is troc-norfentanyl, both of which are easily detectable using standard forensic science equipment,” says lead investigator Carlos Valdez. “The strength of this approach is that both products can be pieced together to identify any fentanyl-related substances, even unknown ones, that have been absorbed into the body.” Along with applications for blood and urine analysis, the new fentanyl identification technique could be used for other biological tissues, including liver, kidney, and heart tissue.
Contact: Carlos A. Valdez (925) 423-1804 (valdez11@llnl.gov).
