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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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Related in: MedlinePlus

X-ray structuresof 1, 2, and 5a (1:1 cocrystalwith CH3CN or PhCN): black, carbon; green,fluorine; blue, nitrogen; red, oxygen; purple, tungsten. Note: Themethyl groups of the acetonitriles in 1:CH3CN and 2:CH3CN are disordered about the crystallographic2-fold axis.
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fig11: X-ray structuresof 1, 2, and 5a (1:1 cocrystalwith CH3CN or PhCN): black, carbon; green,fluorine; blue, nitrogen; red, oxygen; purple, tungsten. Note: Themethyl groups of the acetonitriles in 1:CH3CN and 2:CH3CN are disordered about the crystallographic2-fold axis.

Mentions: To gain more insight intothe transduction of the current method,the X-ray single-crystal structures of 1, 2, and 5a were obtained. Interestingly, 2:CH3CN is found to be perfectly isostructural to 1:CH3CN, and the only difference is the OCF3 group is replaced by a CF3 group (Figure 11). This result suggests that it is valid to estimatethe structures of related complexes. Although the nonlinear geometryof acetonitrile in 2:CH3CN is unusual, itis not unprecedented and has been observed in a variety of metal complexes.20 Another observation is that fluorinated groupsface inward for the cavity in 2:CH3CN whereasthe opposite is true for 2:PhCN. Probably as a resultof the larger size of benzonitrile, the cavity of calixarene expandsto fit the analyte. The discrete behaviors found in 2:CH3CN and 2:PhCN in the crystal structurealso shed light on the chemical shift induced with 2 whereinalkyl nitrile produces a downfield shift whereas aromatic nitrileinduces an upfield shift (Figure 2). The distanceof tungsten to the nitrogen of the nitrile in 2:PhCNis significantly longer than that of 2:CH3CN (2.310 Å vs 2.287 Å), suggesting a weaker bonding ofPhCN. This observation is consistent with the trend of associationconstants found in Table 1. It should be mentionedthat the NMR signals are collected in solution; therefore, the shiftsare largely dependent on the average distance between the fluorineatom and the analyte in all of the conformational isomers.


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

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

X-ray structuresof 1, 2, and 5a (1:1 cocrystalwith CH3CN or PhCN): black, carbon; green,fluorine; blue, nitrogen; red, oxygen; purple, tungsten. Note: Themethyl groups of the acetonitriles in 1:CH3CN and 2:CH3CN are disordered about the crystallographic2-fold axis.
© Copyright Policy
Related In: Results  -  Collection

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

fig11: X-ray structuresof 1, 2, and 5a (1:1 cocrystalwith CH3CN or PhCN): black, carbon; green,fluorine; blue, nitrogen; red, oxygen; purple, tungsten. Note: Themethyl groups of the acetonitriles in 1:CH3CN and 2:CH3CN are disordered about the crystallographic2-fold axis.
Mentions: To gain more insight intothe transduction of the current method,the X-ray single-crystal structures of 1, 2, and 5a were obtained. Interestingly, 2:CH3CN is found to be perfectly isostructural to 1:CH3CN, and the only difference is the OCF3 group is replaced by a CF3 group (Figure 11). This result suggests that it is valid to estimatethe structures of related complexes. Although the nonlinear geometryof acetonitrile in 2:CH3CN is unusual, itis not unprecedented and has been observed in a variety of metal complexes.20 Another observation is that fluorinated groupsface inward for the cavity in 2:CH3CN whereasthe opposite is true for 2:PhCN. Probably as a resultof the larger size of benzonitrile, the cavity of calixarene expandsto fit the analyte. The discrete behaviors found in 2:CH3CN and 2:PhCN in the crystal structurealso shed light on the chemical shift induced with 2 whereinalkyl nitrile produces a downfield shift whereas aromatic nitrileinduces an upfield shift (Figure 2). The distanceof tungsten to the nitrogen of the nitrile in 2:PhCNis significantly longer than that of 2:CH3CN (2.310 Å vs 2.287 Å), suggesting a weaker bonding ofPhCN. This observation is consistent with the trend of associationconstants found in Table 1. It should be mentionedthat the NMR signals are collected in solution; therefore, the shiftsare largely dependent on the average distance between the fluorineatom and the analyte in all of the conformational isomers.

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
Related in: MedlinePlus