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¹⁹F NMR fingerprints: identification of neutral organic compounds in a molecular container.

Zhao Y, Markopoulos G, Swager TM - J. Am. Chem. Soc. (2014)

Bottom Line: We report a new approach to effectively "fingerprint" neutral organic molecules by using (19)F NMR and molecular containers.Spatial proximity of the analyte to the (19)F is important to induce the most pronounced NMR shifts and is crucial in the differentiation of analytes with similar structures.This new scheme allows for the precise and simultaneous identification of multiple analytes in a complex mixture.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.

ABSTRACT
Improved methods for quickly identifying neutral organic compounds and differentiation of analytes with similar chemical structures are widely needed. We report a new approach to effectively "fingerprint" neutral organic molecules by using (19)F NMR and molecular containers. The encapsulation of analytes induces characteristic up- or downfield shifts of (19)F resonances that can be used as multidimensional parameters to fingerprint each analyte. The strategy can be achieved either with an array of fluorinated receptors or by incorporating multiple nonequivalent fluorine atoms in a single receptor. Spatial proximity of the analyte to the (19)F is important to induce the most pronounced NMR shifts and is crucial in the differentiation of analytes with similar structures. This new scheme allows for the precise and simultaneous identification of multiple analytes in a complex mixture.

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19F NMR spectra (64 scans) of complex 3 alone and mixturesof complex 3 (1.0 mM in CDCl3) and differentanalytes (2.0 mM): (a) complex 3 alone, (b) four aromaticnitriles and propionitrile added to a solutionof 3 in CDCl3, (c) superimposition of thespectra of complex 3 with each of the five nitriles from(b) collected independently, (d)–(o) complex 3 bound to various nitriles.
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fig4: 19F NMR spectra (64 scans) of complex 3 alone and mixturesof complex 3 (1.0 mM in CDCl3) and differentanalytes (2.0 mM): (a) complex 3 alone, (b) four aromaticnitriles and propionitrile added to a solutionof 3 in CDCl3, (c) superimposition of thespectra of complex 3 with each of the five nitriles from(b) collected independently, (d)–(o) complex 3 bound to various nitriles.

Mentions: To achieve better resolutionof benzonitriles, we examined complexes 3 and 4 with −OCF3 and −CF3 groups inthe meta-position, respectively(Scheme 2). By design, the fluorine atoms inthese complexes are closer to the para-substituentof the nitrile guests, which allows discrimination of this remotestructural difference that was not achieved by 1 and 2. As shown in Figures 4 and 5, the differences in 19F NMR of freeand bound complexes are within the range of <0.3 ppm, which issmaller than those observed with 1 and 2, suggesting spatial proximity is crucial to induce shifts. Minimum 19F NMR shifts are observed for acetonitrile as a result ofits smaller size (Figures 4d and 5d). Interestingly, despite the smaller shifts produced, complexes 3 and 4 display improved resolution of benzonitrilesrelative to complexes 1 and 2 as shown inFigures 4k–o and 5k–o. Our collective results indicate it is possible to rationallydesign sensors with the desired selectivity by optimizing the positionof the fluorine atoms. Simultaneous discrimination of diverse benzonitrilesin a mixture is further demonstrated by the well-dispersed peaks shownin Figures 4b and 5b.


¹⁹F NMR fingerprints: identification of neutral organic compounds in a molecular container.

Zhao Y, Markopoulos G, Swager TM - J. Am. Chem. Soc. (2014)

19F NMR spectra (64 scans) of complex 3 alone and mixturesof complex 3 (1.0 mM in CDCl3) and differentanalytes (2.0 mM): (a) complex 3 alone, (b) four aromaticnitriles and propionitrile added to a solutionof 3 in CDCl3, (c) superimposition of thespectra of complex 3 with each of the five nitriles from(b) collected independently, (d)–(o) complex 3 bound to various nitriles.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4120996&req=5

fig4: 19F NMR spectra (64 scans) of complex 3 alone and mixturesof complex 3 (1.0 mM in CDCl3) and differentanalytes (2.0 mM): (a) complex 3 alone, (b) four aromaticnitriles and propionitrile added to a solutionof 3 in CDCl3, (c) superimposition of thespectra of complex 3 with each of the five nitriles from(b) collected independently, (d)–(o) complex 3 bound to various nitriles.
Mentions: To achieve better resolutionof benzonitriles, we examined complexes 3 and 4 with −OCF3 and −CF3 groups inthe meta-position, respectively(Scheme 2). By design, the fluorine atoms inthese complexes are closer to the para-substituentof the nitrile guests, which allows discrimination of this remotestructural difference that was not achieved by 1 and 2. As shown in Figures 4 and 5, the differences in 19F NMR of freeand bound complexes are within the range of <0.3 ppm, which issmaller than those observed with 1 and 2, suggesting spatial proximity is crucial to induce shifts. Minimum 19F NMR shifts are observed for acetonitrile as a result ofits smaller size (Figures 4d and 5d). Interestingly, despite the smaller shifts produced, complexes 3 and 4 display improved resolution of benzonitrilesrelative to complexes 1 and 2 as shown inFigures 4k–o and 5k–o. Our collective results indicate it is possible to rationallydesign sensors with the desired selectivity by optimizing the positionof the fluorine atoms. Simultaneous discrimination of diverse benzonitrilesin a mixture is further demonstrated by the well-dispersed peaks shownin Figures 4b and 5b.

Bottom Line: We report a new approach to effectively "fingerprint" neutral organic molecules by using (19)F NMR and molecular containers.Spatial proximity of the analyte to the (19)F is important to induce the most pronounced NMR shifts and is crucial in the differentiation of analytes with similar structures.This new scheme allows for the precise and simultaneous identification of multiple analytes in a complex mixture.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.

ABSTRACT
Improved methods for quickly identifying neutral organic compounds and differentiation of analytes with similar chemical structures are widely needed. We report a new approach to effectively "fingerprint" neutral organic molecules by using (19)F NMR and molecular containers. The encapsulation of analytes induces characteristic up- or downfield shifts of (19)F resonances that can be used as multidimensional parameters to fingerprint each analyte. The strategy can be achieved either with an array of fluorinated receptors or by incorporating multiple nonequivalent fluorine atoms in a single receptor. Spatial proximity of the analyte to the (19)F is important to induce the most pronounced NMR shifts and is crucial in the differentiation of analytes with similar structures. This new scheme allows for the precise and simultaneous identification of multiple analytes in a complex mixture.

Show MeSH