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  1. Abstract

    This paper reports the principal values of the13C chemical shift tensors for five nitrogen‐dense compounds (i.e., cytosine, uracil, imidazole, guanidine hydrochloride, and aminoguanidine hydrochloride). Although these are all fundamentally important compounds, the majority do not have13C chemical shift tensors reported in the literature. The chemical shift tensors are obtained from1H→13C cross‐polarization magic‐angle spinning (CP/MAS) experiments that were conducted at a high field of 18.8 T to suppress the effects of14N‐13C residual dipolar coupling. Quantum chemical calculations using density functional theory are used to obtain the13C magnetic shielding tensors for these compounds. The best agreement with experiment arises from calculations using the hybrid functional PBE0 or the double‐hybrid functional PBE0‐DH, along with the triple‐zeta basis sets TZ2P or pc‐3, respectively, and intermolecular effects modeled using large clusters of molecules with electrostatic embedding through the COSMO approach. These measurements are part of an ongoing effort to expand the catalog of accurate13C chemical shift tensor measurements, with the aim of creating a database that may be useful for benchmarking the accuracy of quantum chemical calculations, developing nuclear magnetic resonance (NMR) crystallography protocols, or aiding in applications involving machine learning or data mining. This work was conducted at the National High Magnetic Field Laboratory as part of a 2‐week school for introducing undergraduate students to practical laboratory experience that will prepare them for scientific careers or postgraduate studies.

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    Free, publicly-accessible full text available January 17, 2025
  2. Abstract

    The ongoing COVID-19 pandemic highlights the necessity for a more fundamental understanding of the coronavirus life cycle. The causative agent of the disease, SARS-CoV-2, is being studied extensively from a structural standpoint in order to gain insight into key molecular mechanisms required for its survival. Contained within the untranslated regions of the SARS-CoV-2 genome are various conserved stem-loop elements that are believed to function in RNA replication, viral protein translation, and discontinuous transcription. While the majority of these regions are variable in sequence, a 41-nucleotide s2m element within the genome 3′ untranslated region is highly conserved among coronaviruses and three other viral families. In this study, we demonstrate that the SARS-CoV-2 s2m element dimerizes by forming an intermediate homodimeric kissing complex structure that is subsequently converted to a thermodynamically stable duplex conformation. This process is aided by the viral nucleocapsid protein, potentially indicating a role in mediating genome dimerization. Furthermore, we demonstrate that the s2m element interacts with multiple copies of host cellular microRNA (miRNA) 1307-3p. Taken together, our results highlight the potential significance of the dimer structures formed by the s2m element in key biological processes and implicate the motif as a possible therapeutic drug target for COVID-19 and other coronavirus-related diseases.

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  3. Free, publicly-accessible full text available December 31, 2024
  4. Colleges are becoming increasingly diverse, including strengthening representation of students with disabilities in STEM (Science, Teaching, Engineering, and Math) fields; however, representation still lags behind national trends. To adapt to this changing demographic and improve representation, STEM college professors must be prepared to grant equitable access to the STEM curriculum and enhance scientific communication skills. This practice brief outlines how a college science faculty applied the Universal Design for Learning (UDL) framework to improve scientific communication skills equitably among college students with diverse needs during a 10-week NSF-REU (National Science Foundation – Research Experiences for Undergraduates) at the host institution summer program during the COVID-19 pandemic. It also provides recommendations about how students with disabilities (i.e., chronic illness, chronic pain, depression, anxiety, and attention deficit hyperactivity disorder [ADHD]) which may have been exacerbated by the COVID-19 pandemic. Applying the UDL framework increased student confidence in applying the scientific method and led to gains in students' perception of their ability to use their skills to solve scientific problems. STEM faculty can use the lessons from the NSF-REU summer program outlined in this work to develop inclusive and accessible STEM programs for students with diverse needs across the country. Moreover, this work highlights the need for STEM faculty to involve Disability Services coordinators as active members in research programs to ensure equity and inclusion. 
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  5. A series of boron, aluminum, gallium, and indium chelates containing the underexplored bis(phenolate) aza-dipyrromethene (aza-DIPY) core were prepared. These compounds were found to possess near-infrared absorption and emission profiles in the 710 to 770 nm domain and exhibit quantum yield values up to 14%. X-ray diffraction analysis revealed that heavier group 13 bis(phenolate) aza-DIPY chelates possessed octahedral geometries with either THF or pyridine groups occupying the axial positions as opposed to the tetrahedral geometry of the boron chelate. 
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