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1. New mass spectrometry concepts for characterization of synthetic polymers and additives

   https://doi.org/10.1002/rcm.8768  

   Inutan, Ellen D. ; Meher, Anil K. ; Karki, Santosh ; Fischer, Joshua L. ; Imperial, Lorelie F. ; Foley, Casey D. ; Jarois, Dean R. ; El‐Baba, Tarick J. ; Lutomski, Corinne A. ; Trimpin, Sarah ( August 2020 , Rapid Communications in Mass Spectrometry)

   New ionization processes have been developed for biological mass spectrometry (MS) in which the matrix lifts the nonvolatile analyte into the gas phase as ions without any additional energy input. We rationalized that additional fundamental knowledge is needed to assess analytical utility for the field of synthetic polymers and additives.

   Different mass spectrometers (Thermo Orbitrap (Q‐)Exactive (Focus); Waters SYNAPT G2(S)) were employed. The formation of multiply charged polymer ions upon exposure of the matrix/analyte(/salt) sample to sub‐atmospheric pressure directly from the solid state and surfaces facilitates the use of advanced mass spectrometers for detection of polymeric materials including consumer products (e.g., gum).

   Astonishingly, using nothing more than a small molecule matrix compound (e.g., 2‐methyl‐2‐nitropropane‐1,3‐diol or 3‐nitrobenzonitrile) and a salt (e.g., mono‐ or divalent cation(s)), such samples upon exposure to sub‐atmospheric pressure transfer nonvolatile polymersandnonvolatile salts into the gas phase as multiply charged ions. These successes contradict the conventional understanding of ionization in MS, because can nonvolatile polymers be lifted in the gas phase as ions not only by as little as a volatile matrix but also by the salt required for ionizing the analyte through noncovalent metal cation adduction(s). Prototypevacuummatrix‐assisted ionization (vMAI) and automated sources using a contactless approach are demonstrated for direct analyses of synthetic polymers and plasticizers, minimizing the risk of contamination using direct sample introduction into the mass spectrometer vacuum.

   Direct ionization methods from surfaces without the need of high voltage, a laser, or even applied heat are demonstrated for characterization of detailed materials using (ultra)high‐resolution and accurate mass measurements enabled by the multiply charged ions extending the mass range of high‐performance mass spectrometers and use of a split probe sample introduction device. Our vision is that, with further development of fundamentals and dedicated sources, both spatial‐ and temporal‐resolution measurements are within reach if sensitivity is addressed for decreasing sample‐size measurements.

    

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2. Enzymatic Knoevenagel condensation in dual‐functionalized water‐mimicking ionic liquids and tertiary amide solvents

   https://doi.org/10.1002/jctb.7603  

   Zhao, Hua ; Campbell, Chante' D. ( February 2024 , Journal of Chemical Technology & Biotechnology)

   Knoevenagel condensation is an important tool for building carbon–carbon (CC) bonds, especially when catalyzed by enzymes to enable a potentially high chemo‐, regio‐ and/or stereoselectivity. Although many Knoevenagel condensation reactions are carried out in aqueous solutions, insoluble hydrophobic substrates often lead to poor catalytic efficiencies. The use of water‐miscible organic solvents improves the substrate solubilization, but usually induces activity suppression or inactivation of enzymes. There is a great need to develop alternative solvents for both substrate dissolution and enzyme compatibility in CC bond formation reactions.

   Our group previously developed dual‐functionalized water‐mimicking ionic liquids (ILs) for the activation and stabilization of hydrolases (e.g. lipase and protease). In the present study, we evaluated the Knoevenagel condensation of 4‐chlorobenzaldehyde with acetylacetone, and found that porcine pancreas lipase in water‐mimicking ILs carrying ammonium, imidazolium and benzimidazolium cations enabled higher reaction rates (up to 3.22 μmol min⁻¹ g⁻¹lipase) and better yields thantert‐butanol, glymes and [BMIM][Tf₂N]. Interestingly, tertiary amide solvents such asN‐methyl‐2‐pyrrolidone (NMP),N,N‐dimethylformamide (DMF) andN,N‐dimethylacetamide (DMAc) led to 8.2‐ to 11.1‐fold increases in the initial rate (up to 35.66 μmol min⁻¹ g⁻¹lipase) when compared with dual‐functionalized ILs, which is likely due to some synergistic effect of these tertiary amides with the lipase.

   Dual‐functionalized ILs based on ammonium, imidazolium and benzimidazolium cations improved Knoevenagel condensation reaction rates and yields when compared withtert‐butanol and glymes. Tertiary amides (NMP, DMF and DMAc) significantly increased the reaction rate. © 2024 The Authors.Journal of Chemical Technology and Biotechnologypublished by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

    

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3. Perspective on the Recent Measurements of Reduced Nitrogen Compounds in the Atmosphere

   https://doi.org/10.3389/fenvs.2022.868534  

   Lee, S.-H. ( April 2022 , Frontiers in Environmental Science)

   Reduced-nitrogen compounds (RNC), such as ammonia and amines, play important roles in atmospheric aerosol nucleation, secondary organic aerosol (SOA), and cloud formation processes. Fast measurements of ammonia and amines are made with a chemical ionization mass spectrometer (CIMS). Clusters containing RNC are measured with an atmospheric pressure interface time of flight mass spectrometer (APi-TOF) or chemical ionization APi-TOF (CI-APi-TOF). Aerosol-phase amines can be detected with a single particle mass spectrometer at real-time, or with offline chemical analytical methods using filter samples. However, the application of these instruments in real atmospheric measurements is still very limited. This perspective article highlights recent measurements of RNC in the atmosphere and discusses their implications in new particle formation (NPF). 

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4. Knudsen cell studies of the uptake of gaseous ammonia and amines onto C3–C7 solid dicarboxylic acids

   https://doi.org/10.1039/C7CP05252A  

   Fairhurst, Michelle C. ; Ezell, Michael J. ; Finlayson-Pitts, Barbara J. ( January 2017 , Phys. Chem. Chem. Phys.)

   While atmospheric particles affect health, visibility and climate, the details governing their formation and growth are poorly understood on a molecular level. A simple model system for understanding the interactions between the gas and particle phases is the reaction of bases with acids, both of which are common constituents of atmospheric particles. In the present study, uptake coefficients for the reactions of gas phase ammonia, methylamine, ethylamine, dimethylamine and trimethylamine with a series of solid dicarboxylic acids (diacids) were measured at 296 ± 1 K using a Knudsen cell interfaced to a quadrupole mass spectrometer. The uptake coefficients ( γ ) for a given amine follow an odd–even trend in carbon number of the diacid, and are larger for the odd carbon diacids. Values range from γ = 0.4 for ethylamine on malonic acid (C3) to less than ∼10 −6 for ammonia and all amines on adipic (C6) and pimelic (C7) acids. Basicity or structure of the amines/ammonia alone do not explain the effect of the base on uptake. The crystal structures of the diacids also play a key role, which is especially evident for malonic acid (C3). Evaporation of aqueous mixtures of amines/ammonia with odd carbon diacids show the formation of ionic liquids (ILs) or in some cases, metastable ILs that revert back to a stable solid salt upon complete evaporation of water. The trends with amine and diacid structure provide insight into the mechanisms of uptake and molecular interactions that control it, including the formation of ionic liquid layers in some cases. The diversity in the kinetics and mechanisms involved in this relatively simple model system illustrate the challenges in accurately representing such processes in atmospheric models. 

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5. Effects of particle phase acidity and gaseous ammonia on the heterogenous interactions between amines and ambient aerosol

   Hang, Y.-J. ; Newberry, C. ; DeMayo, R. ; Qiu, C. ( August 2021 , The 262nd American Chemical Society National Meeting & Exposition)

   Recent research in atmospheric chemistry suggested that gaseous amines may rapidly react with the acidic components in the aerosol to be incorporated in the particle phase. However, laboratory experiments suggested that these heterogeneous processes may be sensitive to the reaction conditions, such as relative humidity (RH), the initial aerosol acidity and the initial concentration of gaseous ammonia which is ubiquitous in the atmosphere. We studied the heterogenous reactions between several amines and ammonium sulfate using a series of thermodynamic simulations under varying initial conditions, including RH, particle-phase acidity and gaseous amine and ammonia concentrations. Several distinctively different trends in the particle-phase ammonium, amines and water content were observed, depending significantly on the particle-phase acidity and the initial amine to ammonia mole ratio. One notable observation was that alkylamines may facilitate the water uptake of ammonium sulfate even in the presence of 1000 times more ammonia gas. Such change in aerosol water content may alter the surface tension, uptake coefficient and could formation properties of aerosol and influence the radiative forcing of the particles. 

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