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We report the development of a method to parameterize and predict the performance of structurally flexible β-turn-containing peptide catalysts, using the atroposelective bromination of 3-arylquinazolin-4(3H)- ones as a case study. The multivariate correlations obtained for tetrapeptides of two β-turn types, type I′ pre-helical and type II′ β-hairpin, indicate that although one conformer may be associated with a more dominant contribution to the observed enantioselectivity, it is possible that multiple conformers contribute to a complex transition state ensemble. [ABSTRACT FROM AUTHOR]

Diarylmethylamido bis(phenols) have been subjected to peptide-catalyzed, enantioselective bromination reactions. Desymmetrization of compounds in this class has been achieved such that enantioenriched products may be isolated with up to 97:3 er. Mechanistically, the observed enantioselectivity was shown to be primarily a function of differential functionalization of enantiotopic arenes, although additional studies unveiled a contribution from secondary kinetic resolution of the product (to afford the symmetrical dibromide) under the reaction conditions. Variants of the tetrapeptide catalyst were also evaluated and revealed a striking observation--enantiodivergent catalysis is observed upon changing the achiral amino acid residue in the catalyst (at the i+2 position) from an aminocyclopropane carboxamide residue (97:3 er) to an aminoisobutyramide residue (33:67 er) under a common set of conditions. An expanded set of catalysts was also evaluated, enabling structure/selectivity correlations to be considered in a mechanistic light. [ABSTRACT FROM AUTHOR]

Primary and secondary sources contributing to atmospheric organic aerosol during the months of July and August were quantitatively assessed in three North American urban areas: Cleveland, Ohio, and Detroit, Michigan, in the Midwest region and Riverside, California, in the Los Angeles Air Basin. Organic molecular marker species unique to primary aerosol sources and secondary tracers derived from isoprene, α-pinene, β-caryophyllene, and toluene were measured using gas chromatography-mass spectrometry. Source contributions from motor vehicles, biomass burning, vegetative detritus, and secondary organic aerosol (SOA) were estimated using chemical mass balance (CMB) modeling. In Cleveland, primary sources accounted for 37 ± 2% of ambient organic carbon, measured biogenic and anthropogenic secondary sources contributed 46 ± 6%, and other unknown sources contributed 17 ± 4%. Similarly, Detroit aerosol was determined to be 44 ± 5% primary and 37 ± 3% secondary, while 19 ± 7% was unaccounted for by measured sources. In Riverside, 21 ± 3% of organic carbon came from primary sources, 26 ± 5% was attributed to measured secondary sources, and 53 ± 3% came from other sources that were expected to be secondary in nature. The comparison of samples across these two regions demonstrated that summertime SOA in the Midwestern United States was substantially different from the summertime SOA in the Los Angeles Air Basin and indicated the need to exert caution when generalizing about the sources and nature of SOA across different urban areas. Furthermore, the results of this study suggest that the contemporary understanding of SOA sources and formation mechanisms is satisfactory to explain the majority of SOA in the Midwest Additional SOA sources and mechanisms of formation are needed to explain the majority of SOA in the Los Angeles Air Basin. [ABSTRACT FROM AUTHOR]

Ambient sampling was conducted in Riverside, California during the 2005 Study of Organic Aerosols in Riverside to characterize the composition and sources of organic aerosol using a variety of state-of-the-art instrumentation and source apportionment techniques. The secondary organic aerosol (SOA) mass is estimated by Organic Aerosols and carbon monoxide tracer methods, water soluble organic carbon content, chemical mass balance of organic molecular markers, and positive matrix factorization of high-resolution aerosol mass spectrometer data. Estimates obtained from each of these methods indicate that the organic fraction in ambient aerosol is overwhelmingly secondary in nature during a period of several weeks with moderate ozone concentrations and that SOA is the single largest component of PM1 aerosol in Riverside. Average SONOA contributions of 70-90% were observed during midday periods, whereas minimum SOA contributions of ∼45% were observed during peak morning traffic periods. These results are contraryto previous estimates of SOA-throughout the Los Angeles Basin which reported that, other than during severe photochemical smog episodes, SOA was lower than primary OA. Possible reasons for these differences are discussed. [ABSTRACT FROM AUTHOR]

Chemistry, a field focused on the molecular scale, provides important contributions in understanding global-scale phenomena, including climate and climate change. This editorial focuses on chemistry's contributions to our understanding of atmospheric science and climate from both research and chemical education perspectives. [ABSTRACT FROM AUTHOR]

Viscosity, or the "thickness," of aerosols plays a key role in atmospheric processes like ice formation, water absorption, and heterogeneous kinetics. However, the viscosity of sea spray aerosols (SSA) has not been widely studied. This research explored the relationship between particle size and viscosity of authentic SSA particles through particle bounce, atomic force microscopy analysis, and predictive viscosity modeling from molecular composition. The study found that 40 nm SSA particles had estimated viscosities around 10 4 Pa·s and bounce fractions three times higher than 100 and 200 nm particles with less than 10 2 Pa·s at a relative humidity (RH) of 60%. Additional studies revealed the Kelvin effect and particle density, influenced by particle size, have a greater impact on size-dependent bounce fractions than changes in RH across impactor stages. While changes in the level of surfactants can impact particle bounce, the increased viscosity in smaller SSA is attributed to the formation of gel-like phase states caused by cation-organic cross-links between divalent calcium ions and organic anions enriched in the smaller particles. This work shows the smallest gel-like SSA particles observed in the field are highly viscous, which has implications for cloud formation, secondary aerosol growth, and pollutant transport in coastal environments.

Decamethylcyclopentasiloxane (D 5 ), a common ingredient in many personal care products (PCPs), undergoes oxidation in the atmosphere, leading to the formation of secondary organic aerosol (SOA). Yet, the specific contributions of D 5 -derived SOA on ambient fine particulate matter (PM 2.5 ) have not been characterized. This study addresses this knowledge gap by introducing a new analytical method to advance the molecular characterization of oxidized D 5 and its detection in ambient aerosol. The newly developed reversed phase liquid chromatography method, in conjunction with high-resolution mass spectrometry, separates and detects D 5 oxidation products, enabling new insights into their molecular and isomeric composition. Application of this method to laboratory-generated SOA and urban PM 2.5 in New York City expands the number of D 5 oxidation products observed in ambient aerosol and informs a list of molecular candidates to track D 5 -derived SOA in the atmosphere. An oxidation series was observed in which one or more methyl groups in D 5 (C 10 H 30 O 5 Si 5 ) is replaced by a hydroxyl group, which indicates the presence of multistep oxidation products in ambient PM 2.5 . Because of their specificity to PCPs and demonstrated detectability in ambient PM 2.5 , several oxidation products are proposed as molecular tracers for D 5 -derived SOA and may prove useful in assessing the impact of PCPs-derived SOA in the atmosphere., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

The Kathmandu valley experiences an average wintertime PM 1 concentration of ∼100 μg m -3 and daily peaks over 200 μg m -3 . We present ambient nonrefractory PM 1 chemical composition, and concentration measured by a mini aerosol mass spectrometer (mAMS) sequentially at Dhulikhel (on the valley exterior), then urban Ratnapark, and finally suburban Lalitpur in winter 2018. At all sites, organic aerosol (OA) was the largest contributor to combined PM 1 (C-PM 1 ) (49%) and black carbon (BC) was the second largest contributor (21%). The average background C-PM 1 at Dhulikhel was 48 μg m -3 ; the urban enhancement was 120% (58 μg m -3 ). BC had an average of 6.1 μg m -3 at Dhulikhel, an urban enhancement of 17.4 μg m -3 . Sulfate (SO 4 ) was 3.6 μg m -3 at Dhulikhel, then 7.5 μg m -3 at Ratnapark, and 12.0 μg m -3 at Lalitpur in the brick kiln region. Chloride (Chl) increased by 330 and 250% from Dhulikhel to Ratnapark and Lalitpur on average. Positive matrix factorization (PMF) identified seven OA sources, four primary OA sources, hydrocarbon-like (HOA), biomass burning (BBOA), trash burning (TBOA), a sulfate-containing local OA source (sLOA), and three secondary oxygenated organic aerosols (OOA). OOA was the largest fraction of OA, over 50% outside the valley and 36% within. HOA (traffic) was the most prominent primary source, contributing 21% of all OA and 44% of BC. Brick kilns were the second largest contributor to C-PM 1 , 12% of OA, 33% of BC, and a primary emitter of aerosol sulfate. These results, though successive, indicate the importance of multisite measurements to understand ambient particulate matter concentration heterogeneity across urban regions., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

To better understand the impact of plastic burning on atmospheric fine particulate matter (PM 2.5 ), we evaluated two methods for the quantification of 1,3,5-triphenylbenzene (TPB), a molecular tracer of plastic burning. Compared to traditional solvent-extraction gas chromatography mass spectrometry (GCMS) techniques, thermal-desorption (TD) GCMS provided higher throughput, lower limits of detection, more precise spike recoveries, a wider linear quantification range, and reduced solvent use. This method enabled quantification of TPB in fine particulate matter (PM 2.5 ) samples collected at rural and urban sites in the USA and Bangladesh. These analyses demonstrated a measurable impact of plastic burning at 5 of the 6 study locations, with the largest absolute and relative TPB concentrations occurring in Dhaka, Bangladesh, where plastic burning is expected to be a significant source of PM 2.5 . Background-level contributions of plastic burning in the USA were estimated to be 0.004-0.03 μg m -3 of PM 2.5 mass. Across the four sites in the USA, the lower estimate of plastic burning contributions to PM 2.5 ranged 0.04-0.8%, while the median estimate ranged 0.3-3% (save for Atlanta, Georgia, in the wintertime at 2-7%). The results demonstrate a consistent presence of plastic burning emissions in ambient PM 2.5 across urban and rural sites in the USA, with a relatively small impact in comparison to other anthropogenic combustion sources in most cases. Much higher TPB concentrations were observed in Dhaka, with estimated plastic burning impacts on PM 2.5 ranging from a lower estimate of 0.3-1.8 μg m -3 (0.6-2% of PM 2.5 ) and the median estimate ranging 2-35 μg m -3 (5-15% of PM 2.5 ). The methodological advances and new measurements presented herein help to assess the air quality impacts of burning plastic more broadly., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Non-covalent inhibitors of the main protease (M pro ) of SARS-CoV-2 having a pyridinone core were previously reported with IC 50 values as low as 0.018 μM for inhibition of enzymatic activity and EC 50 values as low as 0.8 μM for inhibition of viral replication in Vero E6 cells. The series has now been further advanced by consideration of placement of substituted five-membered-ring heterocycles in the S4 pocket of M pro and N-methylation of a uracil ring. Free energy perturbation calculations provided guidance on the choice of the heterocycles, and protein crystallography confirmed the desired S4 placement. Here we report inhibitors with EC 50 values as low as 0.080 μM, while remdesivir yields values of 0.5-2 μM in side-by-side testing with infectious SARS-CoV-2. A key factor in the improvement is enhanced cell permeability, as reflected in PAMPA measurements. Compounds 19 and 21 are particularly promising as potential therapies for COVID-19, featuring IC 50 values of 0.044-0.061 μM, EC 50 values of ca. 0.1 μM, good aqueous solubility, and no cytotoxicity., Competing Interests: The authors declare the following competing financial interest(s): Yale University has submitted a preliminary patent application on the compounds., (© 2021 American Chemical Society.)

Ice nucleating particles (INPs) influence weather and climate by their effect on cloud phase state. Fatty alcohols present within aerosol particles confer a potentially important source of ice nucleation activity to sea spray aerosol produced in oceanic regions. However, their interactions with other aerosol components and the influence on freezing were previously largely unknown. Here, we report quantitative measurements of fatty alcohols in model sea spray aerosol and examine the relationships between the composition and structure of the surfactants and subphase in the context of these measurements. Deposited mixtures of surfactants retain the ability to nucleate ice, even in fatty acid-dominant compositions. Strong refreezing effects are also observed, where previously frozen water-surfactant samples nucleate more efficiently. Structural sources of refreezing behavior are identified as either kinetically trapped film states or three-dimensional (3D) solid surfactant particles. Salt effects are especially important for surfactant INPs, where high salt concentrations suppress freezing. A simple water uptake model suggests that surfactant-containing aerosol requires either very low salt content or kinetic trapping as solid particles to act as INPs in the atmosphere. These types of INPs could be identified through comparison of different INP instrument responses.

Although theories have been developed that describe surface activity of organic molecules at the air-water interface, few studies have tested how surface activity impacts the selective transfer of molecules from solution phase into the aerosol phase during bubble bursting. The selective transfer of a series of organic compounds that differ in their solubility and surface activity from solution into the aerosol phase is quantified experimentally for the first time. Aerosol was produced from solutions containing salts and a series of linear carboxlyates (LCs) and dicarboxylates (LDCs) using a bubble bursting process. Surface activity of these molecules dominated the transport across the interface, with enrichment factors of the more surface-active C4-C8 LCs (55 ± 8) being greater than those of C4-C8 LDCs (5 ± 1). Trends in the estimated surface concentrations of LCs at the liquid-air interface agreed well with their relative concentrations in the aerosol phase. In addition, enrichment of LCs was followed by enrichment of calcium with respect to other inorganic cations and depletion of chloride and sulfate.

Understanding the interactions of water with atmospheric aerosols is crucial for determining the size, physical state, reactivity, and climate impacts of this important component of the Earth's atmosphere. Here we show that water uptake and hygroscopic growth of multicomponent, atmospherically relevant particles can be size dependent when comparing 100 nm versus ca. 6 μm sized particles. It was determined that particles composed of ammonium sulfate with succinic acid and of a mixture of chlorides typical of the marine environment show size-dependent hygroscopic behavior. Microscopic analysis of the distribution of components within the aerosol particles show that the size dependence is due to differences in the mixing state, that is, whether particles are homogeneously mixed or phase separated, for different sized particles. This morphology-dependent hygroscopicity has consequences for heterogeneous atmospheric chemistry as well as aerosol interactions with electromagnetic radiation and clouds.

Organosulfates have been proposed as contributors to aerosol growth and have been detected in both chamber and atmospheric aerosol samples. We present a simple method for the synthesis of quantitative analytical standards of two small hydroxycarboxylic acid-derived organosulfates, glycolic and lactic acid sulfate. Additionally, we discuss the stability of hydroxycarboxylic acid-derived organosulfates and their previously proposed sulfate hemiacetal isomers in commonly used solvents for filter extraction. The hydroxycarboxylic acid-derived organosulfates were found to be stable under acidic conditions comparable to those found in ambient aerosol. By using synthesized standards, quantitative organosulfate concentrations were measured from ambient particulate matter (PM(2.5)) collected in urban locations in the United States, Mexico City, and Pakistan. Lactic acid sulfate and glycolic acid sulfate concentrations ranged 0.4-3.8 ng/m(3) and 1.9-11.3 ng/m(3), respectively. We propose that glycolic acid sulfate represents an important tracer for atmospheric processes that form organosulfates in ambient particulate matter.