Emily C. Heider

An NMR-guided procedure for refining crystal structures has recently been introduced and shown to produce unusually high resolution structures. Herein, this procedure, is modified to include ¹⁵N shift tensors instead of the ¹³C values employed previously. This refinement involves six benchmark structures and 45 ¹⁵N tensors. All refined structures show a statistically significant improvement in NMR fit over energy based refinements. Metrics other than NMR agreement indicate that NMR refinement does not introduce errors with no significant changes observed in atom positions or diffraction patterns. However, refinement does change bond lengths by more than experimental uncertainty with most bond types become shorter than diffraction values. Although this decrease is small (1–4 pm), it significantly alters computed ¹⁵N tensors. The NMR refinement was further evaluated by refining two tripeptides. These structures rapidly converged and achieved an NMR agreement equivalent to benchmark values. To ensure accurate comparisons, a complete atomic structure of the tripeptide AGG was determined by single crystal neutron diffraction at 0.58 Å resolution, allowing unambiguous determination of all hydrogen positions. To verify that all NMR refinements represent genuine improvements rather than artifacts of DFT methods, an independent approach was included to evaluate the final NMR refined coordinates. This analysis employs cluster methods and the PBE0 functional. The unusually small ¹⁵N NMR root-mean-square error of the final refined structures (3.6 ppm) supports the conclusion that the changes made represent improvements over both diffraction coordinates and lattice-including DFT energy refined coordinates.

Recent research has demonstrated the unambiguous positive effects of active learning in a variety of college-level courses. We report the implementation and assessment of a 50 minute active-learning in-class activity to conceptualize light absorbance, reflectance, and transmittance, coupled with a writing-to-learn exercise. The activity is suitable in a classroom setting using portable hand-held sensors and samples, including textiles and food-dye solutions. The assessment of the activity included a quasi-experimental design, in which 116 students in an introductory university chemistry course completed the activity, with outcomes compared to a different section, including 322 students, without the active-learning exercise. To determine the efficacy of the activity, students’ written reports and exam assessment items relating to reflectance, transmittance, and absorbance were evaluated. With the assessment questions showing statistically significant improvement, it was concluded that the hands-on activity was effective in helping the students better understand the relationships among the three properties of light.

Sales of low-calorie sweeteners are increasing in the Unites States, with sucralose representing the second largest of the U.S. market share. Since >99% of ingested sucralose is excreted as the parent compound, it represents a contaminant of emerging concern and has been proposed as an indicator of pollution of natural waters by anthropogenic waste. Many report that it is increasingly omnipresent in surface, coastal, and drinking water. Given the increasing consumption of low-calorie sweeteners, changes in influent and effluent sucralose concentrations presage their concentrations in natural waters. The aim of this research was to quantify sucralose at a constructed treatment wetland that was designed to remove nutrients (nitrogen and phosphorus) from secondary treated wastewater. We report the concentrations of sucralose in the surface water, sediment, and porewater throughout the flow train of the wetlands over a period of three years and include surface water sampling following an extreme weather event. The average influent surface water concentration of sucralose was 24 ± 2 ppb, and the average outfall concentration was 20 ± 6 ppb, indicating the sucralose is not subjected to chemical or physical adsorption in the sediment within the wetland.

Informal learning (IL) venues such as museums, zoos, scouting, national parks, and community activities are increasingly recognized for their important role in enhancing the public understanding of science. Many benefits to students who participate in rich informal learning experiences are reported in the literature, including improvements in scientific reasoning skills, percentages of students enrolling in science, technology, engineering, and math (STEM) majors, and completion of college degrees. The research reported herein analyzes potential benefits of including informal learning experiences in college general chemistry courses, using the School Museum Learning Framework to structure the informal learning experiences. Assessment of outcomes of the informal learning activities are scaffolded upon the U.S. National Research Council's Strands of Informal Learning. Gains in science learning as they related to formal chemistry course content were quantified using pre- and post-assessment measures. Additional outcomes quantifying student motivation were evaluated using the Science Motivation Questionnaire. Results show improvement in some course-related outcomes as well as affective expressions of motivation by students who participated in informal learning experiences.

Herein, we report on the experimental measurements for estimated relative mobility shifts caused by changes in mass distribution from isotopic substitutions in isotopologues and isotopomers with high-resolution cyclic ion mobility separations. By utilizing unlabeled and fully labeled isotopologues with the same isotopic substitutions (i.e., ²H or ¹³C), we created a highly precise mobility scale for each set analyzed to determine the magnitude of such mass distribution shifts and thus calculate estimated deviations from expected, theoretical reduced mass contributions. We observed relative mobility shifts in various isotopologues (e.g., hexadecyltrimethylammonium, sucrose, and palmitic acid species) that deviated from reduced mass theory, according to the Mason–Schamp relationship, ranging in estimated magnitude from ∼0.007% up to ∼0.1% in relative mobility. More interestingly, it was found that two deuterated palmitic acid isotopomers also differed by ∼0.03% from one another in their respective relative mobility shifts. Our results are the first report of isotopologue and isotopomer separations on a commercially available cyclic ion mobility spectrometry-mass spectrometry platform. We envision that our presented mobility scale methodology will have broad applicability in studying the effect of mass distribution changes from isotopic substitutions in other biomolecules and help pave the way for the improvement of ion mobility theory and collision cross section calculators.

Shape selectivity is important in reversed-phase liquid chromatographic separations, where stationary phases are capable of separating geometric isomers, thereby resolving solutes based on their three-dimensional structure or shape rather than other chemical differences. Numerous chromatographic studies have been carried out using n-alkyl-chain-modified columns to understand how molecular shape affects retention. For polycyclic aromatic hydrocarbons (PAHs), it was found that planar compounds were selectively retained over nonplanar structures of comparable molecular weight on surfaces with longer n-alkyl chains, higher chain-density, or at lower temperatures, where selectivity likely arises with greater ordering of the n-alkyl chains. A limitation of these studies, however, is the small range of chain ordering that can be achieved and lack of a direct measure of the n-alkyl-chain order of the stationary phases. In this work, we employ a C₁₈ stationary phase modified with a monolayer of phospholipid as a means of significantly varying the n-alkyl chain order. These hybrid-supported lipid bilayers, which have previously been employed as membrane-like stationary phases for measuring lipophilicity, provide a unique approach to control n-alkyl chain ordering by varying the acyl chain length and degree of unsaturation of the phospholipid modifier. The degree of alkyl-chain order of the resulting modified surfaces is determined from the ratio of trans- versus gauche-conformers, measured in situ within individual porous particles by confocal Raman microscopy. This methodology was also used to assess the affinity of these surfaces for planar versus nonplanar PAH molecules. The retention selectivity for the planar versus nonplanar compounds, thus determined, was found to vary significantly and systematically with the degree of order of the acyl/alkyl chains in the hybrid-supported lipid bilayers. The investigation also demonstrates the utility of confocal Raman microscopy for interrogating the impact of solute partitioning on stationary-phase structure within porous chromatographic particles.

Artificial water-treatment wetlands can reduce nitrogen and phosphorous nutrient concentrations in wastewater effluent to improve water quality and decrease eutrophication in natural waters. The Orlando Easterly Wetlands (OEW) is an engineered wetland that polishes 57 million liters of wastewater per day, lowering the total nitrogen and phosphorous concentrations through biological, physical, and chemical processes. In addition to purifying the water, the wetlands provide habitat for avian, mammalian, reptilian and macroinvertebrate species. Previous research has shown that avian species affect the eutrophication of agricultural reservoirs near their roost. The research herein quantifies uric acid in avian and reptilian excretory product and tracks its concentration profile throughout the OEW over a seven-month period. This measure of the non-anthropogenic contribution to nitrogen within the park includes winter months when large numbers of migratory birds occupy the wetland. The enzymatic decomposition of uric acid and the subsequent fluorimetric analysis were used to quantify uric acid throughout the flow train of the OEW. High concentrations of 2–4 mg/L uric acid were found in the influent, but drastically declined to concentrations below 0.2 mg/L in the effluent.

Utilizing organisms as sources of fluorophores relieves the demand for petroleum feedstock in organic synthesis of fluorescent products, and endophytic fungi provide a promising vein for natural fluorescent products. We report the characterization of a pH‐responsive fluorophore from an endophytic fungus isolated from sand pine. The endogenous fluorescence of the live organism was measured using fluorescence microscopy. Computational interpretation of the spectra was accomplished with time‐dependent density functional theory methods. The combined use of experimental and theoretically predicted spectra revealed the pH equilibria and photoexcited tautomerization of the natural product, 5‐methylmellein. This product shows promise both as a stand‐alone pH‐indicating fluorophore, with alkaline pK_a, and as "green" feedstock for synthesis of custom fluorophores.