More Like this

1. Organosulfates from Dark Aqueous Reactions of Isoprene-Derived Epoxydiols Under Cloud and Fog Conditions: Kinetics, Mechanism, and Effect of Reaction Environment on Regioselectivity of Sulfate Addition

   https://doi.org/10.1021/acsearthspacechem.0c00293  

   Petters, Sarah S.; Cui, Tianqu; Zhang, Zhenfa; Gold, Avram; McNeill, V. Faye; Surratt, Jason D.; Turpin, Barbara J. (February 2021, ACS Earth and Space Chemistry)

   Blum, Joel (Ed.)

   Atmospheric oxidation of isoprene yields large quantities of highly water-soluble isoprene epoxydiols (IEPOX) that partition into fogs, clouds, and wet aerosols. In aqueous aerosols, the acid-catalyzed ring-opening of IEPOX followed by nucleophilic addition of inorganic sulfate or water forms organosulfates and 2-methyltetrols, respectively, contributing substantially to secondary organic aerosol (SOA). However, the fate of IEPOX in clouds, fogs, and evaporating hydrometeors is not well understood. Here we investigate the rates, product branching ratios, and stereochemistry of organosulfates from reactions of dilute IEPOX (5–10 mM) under a range of sulfate concentrations (0.3–50 mM) and pH values (1.83–3.38) in order to better understand the fate of IEPOX in clouds and fogs. From these aqueous dark reactions of β-IEPOX isomers (trans- and cis-2-methyl-2,3-epoxybutane-1,4-diols), which are the predominant IEPOX isomers, products were identified and quantified using hydrophilic interaction liquid chromatography coupled to an electrospray ionization high-resolution quadrupole time-of-flight mass spectrometer operated in negative ion mode (HILIC/(−)ESI-HR-QTOFMS). We found that the regiochemistry and stereochemistry were affected by pH, and the tertiary methyltetrol sulfate (C5H12O7S) was promoted by increasing solution acidity. Furthermore, the rate constants for the reaction of IEPOX under cloud-relevant conditions are up to 1 order of magnitude lower than reported in the literature for aerosol-relevant conditions due to a markedly different solution activities. Nevertheless, the contribution of cloud and fog water reactions to IEPOX SOA may be significant in cases of lower aqueous-phase pH (model estimate) or during droplet evaporation (not studied). 

   more » « less
2. Ultraviolet absorption spectra of acrylic acid and its conjugate base, acrylate, in aqueous solution

   https://doi.org/10.1016/j.jphotochem.2023.115371  

   Xue, Lei; Kieber, David J. (April 2024, Journal of Photochemistry and Photobiology A: Chemistry)

   Acrylic acid is an important compound widely used in industry with multiple commercial applications, and it is also a key intermediate in the marine organosulfur cycle. However, the fundamental ultraviolet (UV) absorption spectrum of acrylic acid or its conjugate base, acrylate (pKa = 4.25 at 20 oC) have not been determined in water. In this paper, we determined the absorption spectrum of acrylate in aqueous solution at pH 7.2 and 20 oC between 207 and 400 nm. The molar absorptivity decreased rapidly from 3958 M‒1 cm‒1 at 207 nm to a non-detectable value at wavelengths greater than 330 nm, with weak absorption at wavelengths greater than 290 nm (e.g., ɛ290nm 2.7 M‒1 cm‒1). No discernable absorption bands were observed in the absorption spectrum. Excellent agreement was observed when comparing absorption spectra obtained (1) with two different spectrophotometers and (2) with standards prepared from either newly purchased sodium acrylate or from the base hydrolysis of dimethylsulfoniopropionate. Wavelength-dependent molar absorptivities were constant at pH 7.2 over a range of acrylate concentrations from 25 to 135 μM. The absorption spectrum red shifted when the solution pH increased from 2.8 to 8.2, with an isosbestic point observed at 214 nm indicating two exchangeable species in solution. Our study provides the first detailed UV absorption spectra of acrylic acid and acrylate in aqueous solution, with important implications regarding the detection and study of these compounds in environmental settings and commercial applications. 

   more » « less
3. Photolysis Products of Fluorinated Pharmaceuticals: A Combined Fluorine Nuclear Magnetic Resonance Spectroscopy and Mass Spectrometry Approach

   https://doi.org/10.1002/etc.5773  

   Mundhenke, Thomas F.; Bhat, Akash P.; Pomerantz, William C. K.; Arnold, William A. (November 2023, Environmental Toxicology and Chemistry)

   Abstract The aqueous photolysis of four pharmaceuticals with varying fluorinated functional groups was assessed under neutral, alkaline, advanced oxidation, and advanced reduction conditions with varying light sources. Solar simulator quantum yields were 2.21 × 10⁻¹ mol Ei⁻¹for enrofloxacin, 9.36 × 10⁻³ mol Ei⁻¹for voriconazole, and 1.49 × 10⁻² mol Ei⁻¹for flecainide. Florfenicol direct photolysis was slow, taking 150 h for three degradation half‐lives. Bimolecular rate constants between pharmaceuticals and hydroxyl radicals were 10⁹to 10¹⁰ M⁻¹ s⁻¹. Using a combined quantitative fluorine nuclear magnetic resonance spectroscopy (¹⁹F‐NMR) and mass spectrometry approach, fluorine mass balances and photolysis product structures were elucidated. Enrofloxacin formed a variety of short‐lived fluorinated intermediates that retained the aryl F motif. Extended photolysis time led to complete aryl F mineralization to fluoride. The aliphatic F moiety on florfenicol was also mineralized to fluoride, but the resulting product was a known antibiotic (thiamphenicol). For voriconazole, the two aryl Fs contributed more to fluoride production compared with the heteroaromatic F, indicating higher stability of the heteroaromatic F motif. The two aliphatic CF₃moieties in the flecainide structure remained intact under all conditions, further supporting the stability of these moieties found in per‐ and polyfluoroalkyl substances under a variety of conditions. The advanced treatment conditions generating hydroxyl radicals or hydrated electrons accelerated the degradation, but not the defluorination, of flecainide. The combination of¹⁹F‐NMR and mass spectrometry proved powerful in allowing identification of fluorinated products and verifying the functional groups present in the intermediates and products. The results found in the present study will aid in the understanding of which fluorinated functional groups should be incorporated into pharmaceuticals to ensure organofluorine byproducts are not formed in the environment and help determine the water‐treatment processes that effectively remove specific pharmaceuticals and more generally fluorinated motifs.Environ Toxicol Chem2023;00:1–12. © 2023 The Authors.Environmental Toxicology and Chemistrypublished by Wiley Periodicals LLC on behalf of SETAC. 

   more » « less
4. Sunlight photolysis of SARS-CoV-2 N1 gene target in the water environment: considerations for the environmental surveillance of wastewater-impacted surface waters

   https://doi.org/10.2166/wh.2023.091  

   Dunn, Fiona B.; Silverman, Andrea I. (August 2023, Journal of Water and Health)

   Abstract Wastewater surveillance of SARS-CoV-2 has been used around the world to supplement clinical testing data for situational awareness of COVID-19 disease trends. Many regions of the world lack centralized wastewater collection and treatment infrastructure, which presents additional considerations for wastewater surveillance of SARS-CoV-2, including environmental decay of the RT-qPCR gene targets used for quantification of SARS-CoV-2 virions. Given the role of sunlight in the environmental decay of RNA, we evaluated sunlight photolysis kinetics of the N1 gene target in heat-inactivated SARS-CoV-2 with a solar simulator under laboratory conditions. Insignificant photolysis of the N1 target was observed in a photosensitizer-free matrix. Conversely, significant decay of the N1 target was observed in wastewater at a shallow depth (<1 cm). Given that sunlight irradiance is affected by several environmental factors, first-order decay rate models were used to evaluate the effect of water column depth, time of the year, and latitude on decay kinetics. Decay rate constants were found to decrease significantly with greater depth of the well-mixed water column, at high latitudes, and in the winter. Therefore, sunlight-mediated decay of the N1 gene target is likely to be minimal, and is unlikely to confound results from wastewater-based epidemiology programs utilizing wastewater-impacted surface waters. 

   more » « less
5. Formation of Stilbene Azo‐Dimer by Direct Irradiation of p‐Azidostilbene ^†

   https://doi.org/10.1111/php.13659  

   Osisioma, Onyinye; Patton, Leanna J.; Merugu, Rajkumar; Govorov, Dmitrii; Milbrandt, Margaret A.; Jarus, Cassandra; Karney, William L.; Gudmundsdottir, Anna D. (July 2022, Photochemistry and Photobiology)

   ABSTRACT Triplet arylnitrenes may provide direct access to aryl azo‐dimers, which have broad commercial applicability. Herein, the photolysis ofp‐azidostilbene (1) in argon‐saturated methanol yielded stilbene azo‐dimer (2) through the dimerization of tripletp‐nitrenostilbene (³1N). The formation of³1Nwas verified by electron paramagnetic resonance spectroscopy and absorption spectroscopy (λ_max ~ 375 nm) in cryogenic 2‐methyltetrahydrofuran matrices. At ambient temperature, laser flash photolysis of1in methanol formed³1N(λ_max ~ 370 nm, 2.85 × 10⁷ s⁻¹). On shorter timescales, a transient absorption (λ_max ~ 390 nm) that decayed with a similar rate constant (3.11 × 10⁷ s⁻¹) was assigned to a triplet excited state (T) of1. Density functional theory calculations yielded three configurations for T of1, with the unpaired electrons on the azido (T_A) or stilbene moiety (T_Tw, twisted and T_Fl, flat). The transient was assigned to T_Twbased on its calculated spectrum. CASPT2 calculations gave a singlet–triplet energy gap of 16.6 kcal mol⁻¹for1 N; thus, intersystem crossing of¹1Nto³1Nis unlikely at ambient temperature, supporting the formation of³1Nfrom T of1. Thus, sustainable synthetic methods for aryl azo‐dimers can be developed using the visible‐light irradiation of aryl azides to form triplet arylnitrenes. 

   more » « less