Effects of Methylating Imidazolium-Based Ionic Liquids on Viscosity: New Insights from the Compensated Arrhenius Formalism

Methylation of the C(2) carbon on imidazolium-based room temperature ionic liquids (RTILs) causes an unexpected increase in viscosity when paired with the anion bis(trifluoromethylsulfonamide) [Tf₂N]^-, but the viscosity decreases when the methylated imidazolium is paired with a tetracyanoborate [B(CN)₄]^- anion. This paper investigates these different observations in viscosity using the compensated Arrhenius formalism (CAF) for fluidity (inverse viscosity), which assumes fluidity to be a thermally activated process. CAF activation energies are determined for imidazolium [Tf₂N]^- and methylated imidazolium [Tf₂N]^- and compared to imidazolium [B(CN)₄]^- and methylated imidazolium [B(CN)₄]^-. The results show that the activation energy increases with methylation for [Tf₂N]^-, but it decreases with methylation for [B(CN)₄]^-. The CAF results also yield information concerning the entropy of activation, which are compared for the two systems.

An inquiry-based exercise in medicinal chemistry: Synthesis of a molecular library and screening for potential antimalarial and anti-inflammatory compounds

The development of new medicines holds particular fascination for chemistry, biochemistry, and biology students interested in a career in medicine or the life sciences. The identification and refinement of lead compounds to treat diseases requires researchers to be facile in a number of different disciplines including organic synthesis, biochemistry, cell biology, and molecular biology. We have developed an interdisciplinary, inquiry-based laboratory spanning both organic chemistry and biochemistry classes that acquaints students with research in medicinal chemistry. The first part of the exercise takes place in the second semester of organic chemistry, where pairs of students design and execute their own multistep synthesis of a novel compound with anti-inflammatory and/or antimalarial potential. Later, in first semester biochemistry, many of the same students then test these synthesized compounds for cytotoxicity, inhibition of the enzyme nitric oxide synthase, and inhibition of the transcription factor NF-kB. Learning outcomes, measured by the Classroom Undergraduate Research Experience (CURE) survey, suggest that students participating in both classes had higher gains than an average student. © 2018 International Union of Biochemistry and Molecular Biology, 46(5):424-434, 2018.

Open Source Drug Discovery: Highly Potent Antimalarial Compounds Derived from the Tres Cantos Arylpyrroles

The development of new antimalarial compounds remains a pivotal part of the strategy for malaria elimination. Recent large-scale phenotypic screens have provided a wealth of potential starting points for hit-to-lead campaigns. One such public set is explored, employing an open source research mechanism in which all data and ideas were shared in real time, anyone was able to participate, and patents were not sought. One chemical subseries was found to exhibit oral activity but contained a labile ester that could not be replaced without loss of activity, and the original hit exhibited remarkable sensitivity to minor structural change. A second subseries displayed high potency, including activity within gametocyte and liver stage assays, but at the cost of low solubility. As an open source research project, unexplored avenues are clearly identified and may be explored further by the community; new findings may be cumulatively added to the present work.

The iconoclastic dynamics of the 1,2,6-heptatriene rearrangement

CASSCF(8,8)/6-31G* and AM1-SRP direct dynamics trajectory calculations have been run on the rearrangement of 1,2,6-heptatriene to 3-methylene-1,5-hexadiene. They show that the experimental results of Roth et al. on this reaction can be explained without the need to invoke a concerted, pericyclic mechanism. Instead, bifurcation occurs at the transition state for conversion of the reactant to 2-methylenecyclohexane-1,4-diyl. Some trajectories leaving the transition state do enter the PES local minimum for the intermediate, but others, differing only in the phases of the real-frequency vibrational modes, bypass the intermediate and proceed over a second transition state to the product. A significant fraction of the trajectories that do enter the biradical local minimum proceed on to the product in <500 fs, despite the fact that the minimum is some 12 kcal/mol deep at the CASSCF level. This nonstatistical behavior seems to be due in part to a resonance between key C-H bending and C-C stretching vibrations in the intermediate.