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Specifications and mastery grading schemes have been growing in popularity in higher education over the past several years, and reports of specifications grading and other alternative grading systems are emerging in the chemistry education literature. The general goal of these alternative grading approaches is to reduce the reliance on high-stakes exams and give students a more transparent pathway to achieving the course learning outcomes. More importantly, relying less on infrequent high-stakes exams may help reduce historical equity gaps in introductory gateway STEM courses. Herein, we describe the implementation of two versions of mastery grading systems in large enrollment general chemistry courses at a public R1 institution. Class-wide course outcomes, equity gaps in performance on a common final exam, and student feedback on their experience navigating these grading schemes are presented. We show that combining mastery grading with interactive courseware tools improved the average performance on a common final assessment for under-represented minority (URM) students by 7.1 percentage points relative to an active control course that used infrequent high-stakes exams. 

An NMR-guided procedure for refining crystal structures has recently been introduced and shown to produce unusually high resolution structures. 

Water-soluble deep cavitands with cationic functions at the lower rim can selectively bind iodide anions in purely aqueous solution. By pairing this lower rim recognition with an indicator dye that is bound in the host cavity, optical sensing of anions is possible. The selectivity for iodide is high enough that micromolar concentrations of iodide can be detected in the presence of molar chloride. Iodide binding at the “remote” lower rim causes a conformational change in the host, displacing the bound dye from the cavity and effecting a fluorescence response. The sensing is sensitive, selective, and works in complex environments, so will be important for optical anion detection in biorelevant media. 

Crystals composed of photoreactive molecules represent a new class of photomechanical materials with the potential to generate large forces on fast timescales. An example is the photodimerization of 9- tert -butyl-anthracene ester ( 9TBAE ) in molecular crystal nanorods that leads to an average elongation of 8%. Previous work showed that this expansion results from the formation of a metastable crystalline product. In this article, it is shown how a novel combination of ensemble oriented-crystal solid-state NMR, X-ray diffraction, and first principles computational modeling can be used to establish the absolute unit cell orientations relative to the shape change, revealing the atomic-resolution mechanism for the photomechanical response and enabling the construction of a model that predicts an elongation of 7.4%, in good agreement with the experimental value. According to this model, the nanorod expansion does not result from an overall change in the volume of the unit cell, but rather from an anisotropic rearrangement of the molecular contents. The ability to understand quantitatively how molecular-level photochemistry generates mechanical displacements allows us to predict that the expansion could be tuned from +9% to −9.5% by controlling the initial orientation of the unit cell with respect to the nanorod axis. This application of NMR-assisted crystallography provides a new tool capable of tying the atomic-level structural rearrangement of the reacting molecular species to the mechanical response of a nanostructured sample.