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1. Solute–Solvent Interactions of 2,2,6,6-Tetramethylpiperidinyloxyl and 5-Tert-Butylisophthalic Acid in Polyethylene Glycol as Observed by Measurements of Density, Viscosity, and Self-Diffusion Coefficient

   https://doi.org/10.1007/s10953-023-01265-4  

   Hoffmann, Markus M.; Randall, Nathaniel P.; Apak, Miray H.; Paddock, Nathaniel A.; Gutmann, Torsten; Buntkowsky, Gerd (June 2023, Journal of Solution Chemistry)

   This study is seeking a better understanding of polyethylene glycol (PEG) as a solvent to promote its use in chemical synthesis. The effect of adding two solutes of interest, 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) and 5-tert-butylisophthalic acid (5-TBIPA) to PEG200 (average molar weight of 200 g·mol−1) on the solution density, viscosity, and selfdiffusion coefficients is monitored in a temperature range of 298.15–358.15 K to deduce how these solutes interact with the PEG200 solvent. The effect of water, the most common impurity in PEGs, is also monitored and found to be nearly negligibly small. Addition of (5-TBIPA) increases solution density and viscosity. Combined with the observation that 5-TBIPA consistently self-diffuses at about half the rate as PEG200 at all investigated experimental conditions, this suggests strong attractive solute–solvent interactions likely through hydrogen bonding interactions. In contrast, addition of TEMPO causes lower solution densities and viscosities suggesting that the solute–solvent interactions of TEMPO lead to an overall weakening of the intermolecular interactions present compared to neat PEG200. Inspection of the viscosity and self-diffusion temperature dependence reveals slight deviations from the Arrhenius equation. Interestingly, the activation energies obtained from the viscosity and the self-diffusion data are essentially identical in values suggesting that the same dynamic processes and thus the same activation barriers govern translational motion and momentum transfer in these PEG200 solutions. 

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2. A computational investigation of aromatic oligoamide foldamer binding to sugar molecules

   https://doi.org/10.1039/D5OB00908A  

   Horowitz, Samantha; Bryan, Taylor; Guzman, Joshua E; Radichel, Sarah; Pickell, Ella C; Golebiewski, Olivia; Zhong, Yulong; Miller, Daniel P; Gong, Bing (October 2025, Organic & Biomolecular Chemistry)

   Helical aromatic oligoamide foldamers (1a–c) with tunable lengths were computationally examined for their ability to bind selected sugars and sugar alcohols. These helices feature cylindrically shaped inner cavities lined with multiple inward-facing amide carbonyl oxygens acting as hydrogen-bond acceptors, enabling sugar binding via hydrogen bonding. Each of the helical foldamers has an overall dipole moment that increases with the length of the helix. The binding of a guest typically results in a reduction of the overall helix dipole moment within the complex, although there are several exceptions. The strength of host–guest interactions correlated positively with the number of hydrogen bonds formed. Longer helix 1c showed stronger interaction energies (up to −84.45 kcal mol−1), particularly with disaccharides, while shorter helix 1a bound sugars more weakly due to fewer established hydrogen bonds. The helical hosts exhibit structural adaptibility upon binding guests, with host distortion upon binding decreased with increasing helix length. Despite reduced binding energies, the complexes retained binding capability in aqueous environments, demonstrating their viability for aqueous-phase applications. This study underscores the critical roles of helical length and dipole alignment in optimizing sugar binding, providing a theoretical foundation for designing synthetic receptors for sugars and sugar alcohols based on aromatic oligoamide foldamers. 

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3. Charge‐transfer Adducts vs Iodine(I) Complexes: Dual Role of Halogen Bonding in Reactions of Diiodine with N‐donor Bases

   https://doi.org/10.1002/cphc.202500076  

   Burnell, Amanda; Hardin, Maison; Zeller, Matthias; Rosokha, Sergiy_V (March 2025, ChemPhysChem)

   Abstract The interaction of diiodine with quinuclidine (QN) and 4‐dimethylaminopyridine (DMAP) in solutions with 1 : 1 molar ratio of reactants at room temperature produced (in essentially quantitative yields) pure charge‐transfer QN⋅I₂adducts and iodine(I) salt [DMAP‐I‐DMAP]I₃, respectively. In comparison, the quantitative formation of pure iodine (I) salt [QN‐I‐QN]I₅was observed for the room‐temperature reactions of QN with a 50 % excess of I₂, and the charge‐transfer adducts of I₂with DMAP (and other pyridines) were formed when reactions were carried out at low temperatures. Computational analysis related the switch from the formation of charge‐transfer adducts to iodine(I) complexes in these systems to the strength of the halogen bonding of diiodine to the N‐donor bases. It shows that while the halogen‐bonded adducts represent critical intermediates in the formation of iodine(I) complexes, exceedingly strong halogen bonding between diiodine and the base prevents any subsequent transformations. In other words, while halogen bonding usually facilitates electron and halogen transfer, the halogen‐bonded complexes may serve as “black holes” hindering any follow‐up processes if this intermolecular interaction is too strong. 

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4. Radial–axial transport coordination enhances sugar translocation in the phloem vasculature of plants

   https://doi.org/10.1093/plphys/kiac231  

   Nakad, Mazen; Domec, Jean-Christophe; Sevanto, Sanna; Katul, Gabriel (May 2022, Plant Physiology)

   Abstract Understanding mass transport of photosynthates in the phloem of plants is necessary for predicting plant carbon allocation, productivity, and responses to water and thermal stress. Several hypotheses about optimization of phloem structure and function and limitations of phloem transport under drought have been proposed and tested with models and anatomical data. However, the true impact of radial water exchange of phloem conduits with their surroundings on mass transport of photosynthates has not been addressed. Here, the physics of the Munch mechanism of sugar transport is re-evaluated to include local variations in viscosity resulting from the radial water exchange in two dimensions (axial and radial) using transient flow simulations. Model results show an increase in radial water exchange due to a decrease in sap viscosity leading to increased sugar front speed and axial mass transport across a wide range of phloem conduit lengths. This increase is around 40% for active loaders (e.g. crops) and around 20% for passive loaders (e.g. trees). Thus, sugar transport operates more efficiently than predicted by previous models that ignore these two effects. A faster front speed leads to higher phloem resiliency under drought because more sugar can be transported with a smaller pressure gradient. 

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5. Mechanistic Understanding on Difluoromethane Absorption Thermodynamics on Novel Deep Eutectic Solvents by COSMO-Based Molecular Simulation

   https://doi.org/10.3390/app13106182  

   Quaid, Thomas; Reza, M. Toufiq (May 2023, Applied Sciences)

   Hydrofluorocarbons (HFC) are fluorinated compounds used globally for refrigeration. These gases have been shown to contain a greenhouse potential of up to 22,000 times that of CO2. Thus, 1298 type-5 deep eutectic solvents (DES) were examined for the absorption and interaction mechanisms of difluoromethane (R32), due to their non-polar attributes. Of these solvents, quaternary ammonium salts mixed with various species of hydrogen bond donators (HBD) produced the most favorable interactions, with ln activity coefficients predicted to be as low as −1.39 at 1:1 compositional ratio. These DES were further studied for compositional analysis where pure tetrabutylammonium bromide showed the strongest interaction potential. The pressure study showed a linear solubility increase with a pressure increase reaching up to 86 mol/mol% in a methyltrioctylammonium bromide and polyethylene glycol mixture at 9 bar. The van der Waals interaction is the driving force of absorption with ~3x enthalpic release over hydrogen bonding. All chemicals contain strong potential for an environmentally friendly solution, as is evident through an environmental health and safety analysis. 

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