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1. Generation of Diazomethyl Radicals by Hydrogen Atom Abstraction and Their Cycloaddition with Alkenes

   https://doi.org/10.1002/anie.202105472  

   Su, Yong‐Liang; Dong, Kuiyong; Zheng, Haifeng; Doyle, Michael P. (July 2021, Angewandte Chemie International Edition)

   Abstract A general catalytic methodology for the synthesis of pyrazolines from α‐diazo compounds and conjugated alkenes is reported. The direct hydrogen atom transfer (HAT) process of α‐diazo compounds promoted by thetert‐butylperoxy radical generates electrophilic diazomethyl radicals, thereby reversing the reactivity of the carbon atom attached with the diazo group. The regiocontrolled addition of diazomethyl radicals to carbon‐carbon double bonds followed by intramolecular ring closure on the terminal diazo nitrogen and tautomerization affords a diverse set of pyrazolines in good yields with excellent regioselectivity. This strategy overcomes the limitations of electron‐deficient alkenes in traditional dipolar [3+2]‐cycloaddition of α‐diazo compounds with alkenes. Furthermore, the straightforward formation of the diazomethyl radicals provides umpolung reactivity, thus opening new opportunities for the versatile transformations of diazo compounds. 

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2. Particle-phase accretion forms dimer esters in pinene secondary organic aerosol

   https://doi.org/10.1126/science.adi0857  

   Kenseth, Christopher M.; Hafeman, Nicholas J.; Rezgui, Samir P.; Chen, Jing; Huang, Yuanlong; Dalleska, Nathan F.; Kjaergaard, Henrik G.; Stoltz, Brian M.; Seinfeld, John H.; Wennberg, Paul O. (November 2023, Science)

   Secondary organic aerosol (SOA) is ubiquitous in the atmosphere and plays a pivotal role in climate, air quality, and health. The production of low-volatility dimeric compounds through accretion reactions is a key aspect of SOA formation. However, despite extensive study, the structures and thus the formation mechanisms of dimers in SOA remain largely uncharacterized. In this work, we elucidate the structures of several major dimer esters in SOA from ozonolysis of α-pinene and β-pinene—substantial global SOA sources—through independent synthesis of authentic standards. We show that these dimer esters are formed in the particle phase and propose a mechanism of nucleophilic addition of alcohols to a cyclic acylperoxyhemiacetal. This chemistry likely represents a general pathway to dimeric compounds in ambient SOA. 

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3. Natural organic matter composition determines the molecular nature of silver nanomaterial-NOM corona

   https://doi.org/10.1039/c8en00018b  

   Baalousha, Mohammed; Afshinnia, Kamelia; Guo, Laodong (January 2018, Environmental Science: Nano)

   Adsorption of natural organic matter (NOM) on nanomaterials (NMs) results in the formation of interfacial area between NMs and the surrounding environment (referred to as NOM-corona), giving rise to NMs' unique surface identity. This unique surface identity is determined by the ligands and their interactions with NM surfaces. Since the chemical structure and functionality is heterogeneous and polydisperse, the molecular composition of NOM-corona is the result of competitive adsorption of NOM molecules on the NM surface. Here, we investigate the molecular composition of NOM-corona formed from two different NOM samples (isolated from the Yukon River and Milwaukee River) on the surface of AgNMs using electrospray ionization-Fourier-transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS). The composition of AgNM-NOM corona varied with the composition of the original NOM. In general, AgNM-NOM corona is rich with N- and S-containing compounds. Furthermore, AgNM-NOM corona is rich with compounds with high molecular weight, high unsaturation, and high number of oxygenated groups. However, CHOS (carbon, hydrogen, oxygen and sulfur) compounds adsorbed on AgNMs from the Yukon River NOM have low molecular weight (LMW) and low saturation index, which might be due to selective adsorption via chemical complexation (Ag–S). On the other hand, NOM compounds with LMW and low unsaturation or compounds containing few oxygenated groups (mainly alcohols and ethers) are preferentially maintained in solution phase. The results here provide evidence of molecular interactions between NOM and NMs, which are critical to understanding NM behavior and toxicity in natural environments. 

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4. Quantum chemical exercise linking computational chemistry to general chemistry topics

   https://doi.org/10.1515/cti-2019-0014  

   Simpson, Scott; Evanoski-Cole, Ashley; Gast, Kellie; Wedvik, Madeleine C.; Schneider, Patrick W.; Klingensmith, Isaac (March 2020, Chemistry Teacher International)

   Abstract Students in a second semester general chemistry course used quantum chemical calculations to investigate and reinforce general chemistry concepts. Students explored the isomers of hypochlorous acid, made predictions of miscibility via dipole moments calculated from ab-initio means, experimentally validated/disqualified their miscibility predictions, and used molecular models to visualize intermolecular attraction forces between various compounds. Student responses in pre-/post-exercise assessments show evidence of student learning. Responses in pre-/post-exercise surveys showed an increase in student understanding of basic concepts and of the importance of quantum mechanics in common general chemistry topics. 

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5. Artificial intelligence-enhanced quantum chemical method with broad applicability

   https://doi.org/10.1038/s41467-021-27340-2  

   Zheng, Peikun; Zubatyuk, Roman; Wu, Wei; Isayev, Olexandr; Dral, Pavlo O. (December 2021, Nature Communications)

   Abstract High-level quantum mechanical (QM) calculations are indispensable for accurate explanation of natural phenomena on the atomistic level. Their staggering computational cost, however, poses great limitations, which luckily can be lifted to a great extent by exploiting advances in artificial intelligence (AI). Here we introduce the general-purpose, highly transferable artificial intelligence–quantum mechanical method 1 (AIQM1). It approaches the accuracy of the gold-standard coupled cluster QM method with high computational speed of the approximate low-level semiempirical QM methods for the neutral, closed-shell species in the ground state. AIQM1 can provide accurate ground-state energies for diverse organic compounds as well as geometries for even challenging systems such as large conjugated compounds (fullerene C 60 ) close to experiment. This opens an opportunity to investigate chemical compounds with previously unattainable speed and accuracy as we demonstrate by determining geometries of polyyne molecules—the task difficult for both experiment and theory. Noteworthy, our method’s accuracy is also good for ions and excited-state properties, although the neural network part of AIQM1 was never fitted to these properties. 

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