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1. Current Status of AMOEBA–IL: A Multipolar/Polarizable Force Field for Ionic Liquids

   https://doi.org/10.3390/ijms21030697  

   Vázquez-Montelongo, Erik Antonio; Vázquez-Cervantes, José Enrique; Cisneros, G. Andrés (February 2020, International Journal of Molecular Sciences)

   Computational simulations of ionic liquid solutions have become a useful tool to investigate various physical, chemical and catalytic properties of systems involving these solvents. Classical molecular dynamics and hybrid quantum mechanical/molecular mechanical (QM/MM) calculations of IL systems have provided significant insights at the atomic level. Here, we present a review of the development and application of the multipolar and polarizable force field AMOEBA for ionic liquid systems, termed AMOEBA–IL. The parametrization approach for AMOEBA–IL relies on the reproduction of total quantum mechanical (QM) intermolecular interaction energies and QM energy decomposition analysis. This approach has been used to develop parameters for imidazolium– and pyrrolidinium–based ILs coupled with various inorganic anions. AMOEBA–IL has been used to investigate and predict the properties of a variety of systems including neat ILs and IL mixtures, water exchange reactions on lanthanide ions in IL mixtures, IL–based liquid–liquid extraction, and effects of ILs on an aniline protection reaction. 

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2. Identifying thermal phase transitions of lignin–solvent mixtures using electrochemical impedance spectroscopy

   https://doi.org/10.1039/C5GC02342D  

   Klett, Adam S.; Gamble, Jordan A.; Thies, Mark C.; Roberts, Mark E. (January 2016, Green Chemistry)

   Lignin is unique among renewable biopolymers in having significant aromatic character, making it potentially attractive for a wide range of uses from coatings to carbon fibers. Recent research has shown that hot acetic acid (AcOH)–water mixtures can be used to recover “ultraclean” lignins of controlled molecular weight from Kraft lignins. A key feature of this discovery is the existence of a region of liquid–liquid equilibrium (LLE), with one phase being rich in the purified lignin and the other rich in solvent. Although visual methods can be used to determine the temperature at which solid lignin melts in the presence of AcOH–water mixtures to form LLE, the phase transition can be seen only at lower AcOH concentrations due to solvent opacity. Thus, an electrochemical impedance spectroscopy (EIS) technique was developed for measuring the phase-transition temperature of a softwood Kraft lignin in AcOH–water mixtures. In electrochemical cells, the resistance to double-layer charging ( i.e. , polarization resistance R p ) is related to the concentration and mobility of free ions in the electrolyte, both of which are affected by the phases present. When the lignin–AcOH–water mixture was heated through the phase transition, R P was found to be a strong function of temperature, with the maximum in R P corresponding to the transition temperature obtained from visual observation. As the system is heated, acetate ions associate with the solid lignin, forming a liquefied, lignin-rich phase. This association increases the overall impedance of the system, as mobile acetate ions are stripped from the solvent phase and thus are no longer available to adsorb on the polarizing electrode surfaces. The maximum in R P occurs once the new lignin-rich phase has completely formed, and no further association of the lignin polymer with AcOH is possible. Except at sub-ambient temperatures, the phase-transition temperature was a strong function of solvent composition, increasing linearly from 18 °C at 70/30 AcOH/water to 97 °C at 10/90 wt% AcOH/water. 

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3. On the liquid demixing of water + elastin-like polypeptide mixtures: bimodal re-entrant phase behaviour

   https://doi.org/10.1039/d0cp05013j  

   Lindeboom, Tom; Zhao, Binwu; Jackson, George; Hall, Carol K.; Galindo, Amparo (March 2021, Physical Chemistry Chemical Physics)

   null (Ed.)

   Water + elastin-like polypeptides (ELPs) exhibit a transition temperature below which the chains transform from collapsed to expanded states, reminiscent of the cold denaturation of proteins. This conformational change coincides with liquid–liquid phase separation. A statistical-thermodynamics theory is used to model the fluid-phase behavior of ELPs in aqueous solution and to extrapolate the behavior at ambient conditions over a range of pressures. At low pressures, closed-loop liquid–liquid equilibrium phase behavior is found, which is consistent with that of other hydrogen-bonding solvent + polymer mixtures. At pressures evocative of deep-sea conditions, liquid–liquid immiscibility bounded by two lower critical solution temperatures (LCSTs) is predicted. As pressure is increased further, the system exhibits two separate regions of closed-loop of liquid–liquid equilibrium (LLE). The observation of bimodal LCSTs and two re-entrant LLE regions herald a new type of binary global phase diagram: Type XII. At high-ELP concentrations the predicted phase diagram resembles a protein pressure denaturation diagram; possible “molten-globule”-like states are observed at low concentration. 

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4. Increasing the selectivity of optical anion sensors with cationic extracting agents

   https://doi.org/10.1080/10610278.2024.2426547  

   González, Mario J; Rathnaweera, Uththara MC; Le, Ellie M; Sowell, Hannah L; Singh, Anmol; Busschaert, Nathalie (December 2024, Supramolecular Chemistry)

   Anions play an important role in our life, from storing our genetic code on the polyanion DNA, to being the active ingredient in agricultural fertilizers and other industrial processes. Consequently, chemists have been designing systems that can sense anionic species through a variety of methods, such as unimolecular chromophores or sensor arrays. Nonetheless, most existing sensing approaches still have some drawbacks, particularly related to obtaining adequate selectivity and achieving sensing of anions in aqueous environments. In this manuscript, we report a liquid-liquid extraction (LLE)-based sensing approach that allows the conversion of non-selective optical anion sensors that only work in organic media, into selective sensing systems that allow detection of anions in water. We tested this approach on deprotonation-based anion sensors (alizarin, naphthol AS, 4-nitrophenol, BI-Lawsone, and chromophore 1) and hydrogen bonding-based anion sensors (1,2-diaminoanthraquinone and 4-nitro-1,2-phenylenediamine). In general, the deprotonation-based sensors could be converted from a non-selective sensor for basic anions (NCO¯, H2PO4¯, AcO¯ and F¯) to a selective sensing system for NCO¯ with the aid of carefully chosen tetraalkylammonium salts as extracting agents. On the other hand, the hydrogen-bonding based sensors could be converted to a selective sensing system for the hydrophobic anion ClO4¯ using similar tetraalkylammonium salts. 

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5. Formation of insoluble brown carbon through iron-catalyzed reaction of biomass burning organics

   https://doi.org/10.1039/d2ea00141a  

   Hopstock, Katherine S.; Carpenter, Brooke P.; Patterson, Joseph P.; Al-Abadleh, Hind A.; Nizkorodov, Sergey A. (January 2023, Environmental Science: Atmospheres)

   Biomass burning organic aerosol (BBOA) is one of the largest sources of organics in the atmosphere. Mineral dust and biomass burning smoke frequently co-exist in the same atmospheric environment. Common biomass burning compounds, such as dihydroxybenzenes and their derivatives, are known to produce light-absorbing, water-insoluble polymeric particles upon reaction with soluble Fe( iii ) under conditions characteristic of aerosol liquid water. However, such reactions have not been tested in realistic mixtures of BBOA compounds. In this study, model organic aerosol (OA), meant to replicate BBOA from smoldering fires, was generated through the pyrolysis of Canary Island pine needles in a tube furnace at 300, 400, 500, 600, 700, and 800 °C in nitrogen gas, and the water-soluble fractions were reacted with iron chloride under dark, acidic conditions. We utilized spectrophotometry to monitor the reaction progress. For OA samples produced at lower temperatures (300 and 400 °C), particles (P300 and P400) formed in solution, were syringe filtered, and extracted in organic solvents. Analysis was conducted with ultrahigh pressure liquid chromatography coupled to a photodiode array spectrophotometer and a high-resolution mass spectrometer (UHPLC-PDA-HRMS). For OA samples formed at higher pyrolysis temperatures (500–800 °C), water-insoluble, black particles (P500–800) formed in solution. In contrast to P300 and P400, P500–800 were not soluble in common solvents. Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and transmission electron microscopy (TEM) were used to image P600 and determine bulk elemental composition. Electron microscopy revealed that P600 had fractal morphology, reminiscent of soot particles, and contained no detectable iron. These results suggest that light-absorbing aerosol particles can be produced from Fe( iii )-catalyzed reactions in aging BBOA plumes produced from smoldering combustion in the absence of any photochemistry. This result has important implications for understanding the direct and indirect effects of aged BBOA on climate. 

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