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In previous work with thermally robust salts [Cassity et al., Phys. Chem. Chem. Phys. , 2017, 19 , 31560] it was noted that an increase in the dipole moment of the cation generally led to a decrease in the melting point. Molecular dynamics simulations of the liquid state revealed that an increased dipole moment reduces cation–cation repulsions through dipole–dipole alignment. This was believed to reduce the liquid phase enthalpy, which would tend to lower the melting point of the IL. In this work we further test this principle by replacing hydrogen atoms with fluorine atoms at selected positions within the cation. This allows us to alter the electrostatics of the cation without substantially affecting the sterics. Furthermore, the strength of the dipole moment can be controlled by choosing different positions within the cation for replacement. We studied variants of four different parent cations paired with bistriflimide and determined their melting points, and enthalpies and entropies of fusion through DSC experiments. The decreases in the melting point were determined to be enthalpically driven. We found that the dipole moment of the cation, as determined by quantum chemical calculations, is inversely correlated with the melting point of the given compound. Molecular dynamics simulations of the crystalline and solid states of two isomers showed differences in their enthalpies of fusion that closely matched those seen experimentally. Moreover, this reduction in the enthalpy of fusion was determined to be caused by an increase in the enthalpy of the crystalline state. We provide evidence that dipole–dipole interactions between cations leads to the formation of cationic domains in the crystalline state. These cationic associations partially block favourable cation–anion interactions, which are recovered upon melting. If, however, the dipole–dipole interactions between cations is too strong they have a tendency to form glasses. This study provides a design rule for lowering the melting point of structurally similar ILs by altering their dipole moment. 

Recent work by Wasserscheid, et al. suggests that PPh 4 + is an organic molecular ion of truly exceptional thermal stability. Herein we provide data that cements that conclusion: specifically, we show that aliphatic moieties of modified PPh 4 + -based cations incorporating methyl, methylene, or methine C–H bonds burn away at high temperatures in the presence of oxygen, forming CO, CO 2 , and water, leaving behind the parent ion PPh 4 + . The latter then undergoes no further reaction, at least below 425 °C. 

Previously, a boronium salt possessing a terminal benzyl group was reported to have greater antibacterial activity than a commercial quaternary ammonium disinfectant solution againstEscherichia coli,Pseudomonas aeruginosa, andStaphylococcus aureus. Results of the current study indicate that the same boronium salt without a benzyl group, exhibited equal or better antifungal activity against actively growingCandida albicansyeast andAspergillus fumigatusmold when compared to the same quat disinfectant. This same compound also displayed antifungal activity against dormantA. fumigatusspores comparable to the quat disinfectant. In contrast, the boronium ion with a benzyl group was 4–16X less effective than either the non‐benzylated form or quat disinfectant for all 3 fungal test conditions. The observation that the boronium salt without a benzyl group exhibited substantial antifungal activity in the current study but did not display any antibacterial activity in the previous study is of particular interest. This finding represents a flip‐flop outcome from the previous bacterial testing. It suggests that the presence of a terminal benzyl group greatly influences the boronium ion's ability to interact with fungal membranes.

 

Drugs containing amine groups react with CO 2 to form crystalline ammonium carbamates or carbamic acids. In this approach, both the cation and anion of the salt, or the neutral CO 2 adduct, are derived from the parent drug, generating new crystalline versions in a ‘masked’ or prodrug form. It is proposed that this approach may serve as a valuable new tool in engineering the physical properties of drugs for formulation purposes. 

Plastids contain their own genomes, which are transcribed by two types of RNA polymerases. One of those enzymes is a bacterial‐type, multi‐subunit polymerase encoded by the plastid genome. The plastid‐encoded RNA polymerase (PEP) is required for efficient expression of genes encoding proteins involved in photosynthesis. Despite the importance of PEP, its DNA binding locations have not been studied on the genome‐wide scale at high resolution. We established a highly specific approach to detect the genome‐wide pattern of PEP binding to chloroplast DNA using plastid chromatin immunoprecipitation–sequencing (ptChIP‐seq). We found that in matureArabidopsis thalianachloroplasts, PEP has a complex DNA binding pattern with preferential association at genes encoding rRNA, tRNA, and a subset of photosynthetic proteins. Sigma factors SIG2 and SIG6 strongly impact PEP binding to a subset of tRNA genes and have more moderate effects on PEP binding throughout the rest of the genome. PEP binding is commonly enriched on gene promoters, around transcription start sites. Finally, the levels of PEP binding to DNA are correlated with levels of RNA accumulation, which demonstrates the impact of PEP on chloroplast gene expression. Presented data are available through a publicly available Plastid Genome Visualization Tool (Plavisto) athttps://plavisto.mcdb.lsa.umich.edu/.