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The composition of fluorescent polymer nanoparticles, commonly referred to as carbon dots, synthesized by microwave‐assisted reaction of citric acid and ethylenediamine was investigated by 13C, 13C{1H}, 1H─13C, 13C{14N}, and 15N solid‐state nuclear magnetic resonance (NMR) experiments. 13C NMR with spectral editing provided no evidence for significant condensed aromatic or diamondoid carbon phases. 15N NMR showed that the nanoparticle matrix has been polymerized by amide and some imide formation. Five small, resolved 13C NMR peaks, including an unusual ═CH signal at 84 ppm (1H chemical shift of 5.8 ppm) and ═CN2 at 155 ppm, and two distinctive 15N NMR resonances near 80 and 160 ppm proved the presence of 5‐oxo‐1,2,3,5‐tetrahydroimidazo[1,2‐a]pyridine‐7‐carboxylic acid (IPCA) or its derivatives. This molecular fluorophore with conjugated double bonds, formed by a double cyclization reaction of citric acid and ethylenediamine as first shown by Y. Song, B. Yang, and coworkers in 2015, accounts for the fluorescence of the carbon dots. Cross‐peaks in a 1H─13C HETCOR spectrum with brief 1H spin diffusion proved that IPCA is finely dispersed in the polyamide matrix. From quantitative 13C and 15N NMR spectra, a high concentration (18 ± 2 wt%) of IPCA in the carbon dots was determined. A pronounced gradient in 13C chemical‐shift perturbations and peak widths, with the broadest lines near the COO group of IPCA, indicated at least partial transformation of the carboxylic acid of IPCA by amide or ester formation.
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Automated Chemical Profiling of Wine by Solution NMR Spectroscopy: A Demonstration for Outreach and Education
Profiling complex chemical mixtures provides a unique opportunity for outreach and education. Here, we develop a teaching module using one-dimensional 1H nuclear magnetic resonance (NMR) spectroscopy to study wine. The demonstration is delivered at the Georgia Tech NMR Center during the Atlanta Science Festival to 127 visitors from diverse backgrounds, including families with K–12 children. Participants interact with wine samples through cognitive and sensory experiences. Visitors engage with a live demonstration of a high-field NMR spectrometer, including real-time measurement and automated analysis of 1H NMR spectra for 14 wines. The module enables instructors to showcase how an NMR spectrometer works, quantify 70 wine metabolites, and discuss how chemical composition relates to wine characteristics. Practical examples highlight how 1H NMR can detect wine fraud. An exit survey suggests that the module increases public interest and excitement for research. Adults report learning factors affecting wine characteristics and the basics for how NMR is applied to research. K–12 students retain information about wine composition and enjoy sensory aspects of the activity. A description of the demonstration’s design and implementation is provided to facilitate its adoption in outreach efforts and introductory chemistry courses.
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- Award ID(s):
- 2442018
- PAR ID:
- 10663124
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- Journal of Chemical Education
- ISSN:
- 0021-9584
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1021/acs.jchemed.5c00652
