The Scientific Method as a Scaffold to Enhance Communication Skills in Chemistry

Scientific success in the field of chemistry depends upon the mastery of a wide range of soft skills, most notably scientific writing and speaking. However, training for scientific communication is typically limited at the undergraduate level, where students struggle to express themselves in a clear and logical manner. The underlying issue is deeper than basic technical skills; rather, it is a problem of students’ unawareness of a fundamental and strategic framework for writing and speaking with a purpose. The methodology has been implemented for individual mentorship and in our regional summer research program to deliver a blueprint of thought and reasoning that endows students with the confidence and skills to become more effective communicators. Our didactic process intertwines undergraduate research with the scientific method and is partitioned into six steps, referred to as “phases”, to allow for focused and deep thinking on the essential components of the scientific method. The phases are designed to challenge the student in their zone of proximal development so they learn to extract and ultimately comprehend the elements of the scientific method through focused written and oral assignments. Students then compile their newly acquired knowledge to create a compelling and logical story, using their persuasive written and oral presentations to complete a research proposal, final report, and formal 20 min presentation. We find that such an approach delivers the necessary guidance to promote the logical framework that improves writing and speaking skills. Over the past decade, we have witnessed both qualitative and quantitative gains in the students’ confidence in their abilities and skills (developed by this process), preparing them for future careers as young scientists

Do Models beyond Hybrid Density Functionals Increase the Agreement with Experiment for Predicted NMR Chemical Shifts or Electric Field Gradient Tensors in Organic Solids?

Ab initio predictions of chemical shifts and electric field gradient (EFG) tensor components are frequently used to help interpret solid-state nuclear magnetic resonance (NMR) experiments. Typically, these predictions employ density functional theory (DFT) with generalized gradient approximation (GGA) functionals, though hybrid functionals have been shown to improve accuracy relative to experiment. Here, the performance of a dozen models beyond the GGA approximation are examined for the prediction of solid-state NMR observables, including meta-GGA, hybrid, and double-hybrid density functionals and second-order Møller–Plesset perturbation theory (MP2). These models are tested on organic molecular crystal data sets containing 169 experimental 13C and 15N chemical shifts and 114 17O and 14N EFG tensor components. To make these calculations affordable, gauge-including projector augmented wave (GIPAW) Perdew–Burke–Ernzerhof (PBE) calculations with periodic boundary conditions are combined with a local intramolecular correction computed at the higher level of theory. Within the context of typical NMR property calculations performed on a static, DFT-optimized crystal structure, the benchmarking finds that the double-hybrid DFT functionals produce errors versus experiment that are no smaller than those of hybrid functionals in the best cases, and they can be larger. MP2 errors versus experiment are even bigger. Overall, no practical advantages are found for using any of the tested double-hybrid functionals or MP2 to predict experimental solid-state NMR chemical shifts and EFG tensor components for routine organic crystals, especially given the higher computational cost of those methods. This finding likely reflects error cancellation benefiting the hybrid functionals. Improving the accuracy of the predicted chemical shifts and EFG tensors relative to experiment would probably require more robust treatments of the crystal structures, their dynamics, and other factors

Do Models beyond Hybrid Density Functionals Increase the Agreement with Experiment for Predicted NMR Chemical Shifts or Electric Field Gradient Tensors in Organic Solids?

Ab initio predictions of chemical shifts and electric field gradient (EFG) tensor components are frequently used to help interpret solid-state nuclear magnetic resonance (NMR) experiments. Typically, these predictions employ density functional theory (DFT) with generalized gradient approximation (GGA) functionals, though hybrid functionals have been shown to improve accuracy relative to experiment. Here, the performance of a dozen models beyond the GGA approximation are examined for the prediction of solid-state NMR observables, including meta-GGA, hybrid, and double-hybrid density functionals and second-order Møller–Plesset perturbation theory (MP2). These models are tested on organic molecular crystal data sets containing 169 experimental 13C and 15N chemical shifts and 114 17O and 14N EFG tensor components. To make these calculations affordable, gauge-including projector augmented wave (GIPAW) Perdew–Burke–Ernzerhof (PBE) calculations with periodic boundary conditions are combined with a local intramolecular correction computed at the higher level of theory. Within the context of typical NMR property calculations performed on a static, DFT-optimized crystal structure, the benchmarking finds that the double-hybrid DFT functionals produce errors versus experiment that are no smaller than those of hybrid functionals in the best cases, and they can be larger. MP2 errors versus experiment are even bigger. Overall, no practical advantages are found for using any of the tested double-hybrid functionals or MP2 to predict experimental solid-state NMR chemical shifts and EFG tensor components for routine organic crystals, especially given the higher computational cost of those methods. This finding likely reflects error cancellation benefiting the hybrid functionals. Improving the accuracy of the predicted chemical shifts and EFG tensors relative to experiment would probably require more robust treatments of the crystal structures, their dynamics, and other factors

Measuring And Modeling Highly Accurate \u3csup\u3e15\u3c/sup\u3eN Chemical Shift Tensors In A Peptide.

NMR studies measuring chemical shift tensors are increasingly being employed to assign structure in difficult-to-crystallize solids. For small organic molecules, such studies usually focus on 13C sites, but proteins and peptides are more commonly described using 15N amide sites. An important and often neglected consideration when measuring shift tensors is the evaluation of their accuracy against benchmark standards, where available. Here we measure 15N tensors in the dipeptide glycylglycine at natural abundance using the slow-spinning FIREMAT method with SPINAL-64 decoupling. The accuracy of these 15N tensors is evaluated by comparing to benchmark single crystal NMR 15N measurements and found to be statistically indistinguishable. These FIREMAT experimental results are further used to evaluate the accuracy of theoretical predictions of tensors from four different density functional theory (DFT) methods that include lattice effects. The best theoretical approach provides a root mean square (rms) difference of ±3.9 ppm and is obtained from a fragment-based method and the PBE0 density functional

Critical Analysis of Cluster Models and Exchange-Correlation Functionals for Calculating Magnetic Shielding in Molecular Solids

Calculations of the principal components of magnetic-shielding tensors in crystalline solids require the inclusion of the effects of lattice structure on the local electronic environment to obtain significant agreement with experimental NMR measurements. We assess periodic (GIPAW) and GIAO/symmetry-adapted cluster (SAC) models for computing magnetic-shielding tensors by calculations on a test set containing 72 insulating molecular solids, with a total of 393 principal components of chemical-shift tensors from ¹³C, ¹⁵N, ¹⁹F, and ³¹P sites. When clusters are carefully designed to represent the local solid-state environment and when periodic calculations include sufficient variability, both methods predict magnetic-shielding tensors that agree well with experimental chemical-shift values, demonstrating the correspondence of the two computational techniques. At the basis-set limit, we find that the small differences in the computed values have no statistical significance for three of the four nuclides considered. Subsequently, we explore the effects of additional DFT methods available only with the GIAO/cluster approach, particularly the use of hybrid-GGA functionals, meta-GGA functionals, and hybrid meta-GGA functionals that demonstrate improved agreement in calculations on symmetry-adapted clusters. We demonstrate that meta-GGA functionals improve computed NMR parameters over those obtained by GGA functionals in all cases, and that hybrid functionals improve computed results over the respective pure DFT functional for all nuclides except ¹⁵N

Redetermination of 1,4-dimethoxybenzene

The structure of the centrosymmetric title compound, C8H10O2, originally determined by Goodwin et al. [Acta Cryst.(1950), 3, 279–284], has been redetermined to modern standards of precision to aid in its use as a model compound for 13C chemical-shift tensor measurements in single-crystal NMR studies. In the crystal structure, a C—H...O interaction helps to establish the packing

Study of Perfluorophosphonic Acid Surface Modifications on Zinc Oxide Nanoparticles

In this study, perfluorinated phosphonic acid modifications were utilized to modify zinc oxide (ZnO) nanoparticles because they create a more stable surface due to the electronegativity of the perfluoro head group. Specifically, 12-pentafluorophenoxydodecylphosphonic acid, 2,3,4,5,6-pentafluorobenzylphosphonic acid, and (1H,1H,2H,2H-perfluorododecyl)phosphonic acid have been used to form thin films on the nanoparticle surfaces. The modified nanoparticles were then characterized using infrared spectroscopy, X-ray photoelectron spectroscopy, and solid-state nuclear magnetic resonance spectroscopy. Dynamic light scattering and scanning electron microscopy-energy dispersive X-ray spectroscopy were utilized to determine the particle size of the nanoparticles before and after modification, and to analyze the film coverage on the ZnO surfaces, respectively. Zeta potential measurements were obtained to determine the stability of the ZnO nanoparticles. It was shown that the surface charge increased as the alkyl chain length increases. This study shows that modifying the ZnO nanoparticles with perfluorinated groups increases the stability of the phosphonic acids adsorbed on the surfaces. Thermogravimetric analysis was used to distinguish between chemically and physically bound films on the modified nanoparticles. The higher weight loss for 12-pentafluorophenoxydodecylphosphonic acid and (1H,1H,2H,2H-perfluorododecyl)phosphonic acid modifications corresponds to a higher surface concentration of the modifications, and, ideally, higher surface coverage. While previous studies have shown how phosphonic acids interact with the surfaces of ZnO, the aim of this study was to understand how the perfluorinated groups can tune the surface properties of the nanoparticles