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Other Nuclides: 31P, 19F, 15N NMR01:16

Other Nuclides: 31P, 19F, 15N NMR

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Many organic, inorganic, and biological molecules contain spin-half nuclei such as nitrogen-15, fluorine-19, and phosphorus-31. As a result, NMR studies of these nuclei have found extensive applications in chemical and biological research.
While fluorine-19 and phosphorous-31 have high natural abundances (100%) and positive gyromagnetic ratios, nitrogen-15 has a low natural abundance and a negative gyromagnetic ratio. However, nitrogen-15 is still preferred over nitrogen-14 (which has a...
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The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
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In an NMR sample, precise measurement of the absolute absorption frequencies of nuclei is difficult. A standard internal reference compound is added, and the frequency difference between the reference signal and sample signals is measured.
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Atomic fluorescence spectroscopy (AFS) is an analytical technique that involves the electronic transitions of atoms in a flame, furnace, or plasma being excited by electromagnetic (EM) radiation. When these atoms absorb energy, they become excited and subsequently release energy as they return to their original state. This emitted light, or "fluorescence," is observed at a right angle to the incident beam. Both absorption and emission processes transpire at distinct wavelengths, which...
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At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
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Application and Methodology of the Non-destructive 19F Time-domain NMR Technique to Measure the Content in Fluorine-containing Drug Products
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Solid-state NMR study of fluorinated steroids.

Kai-Jay Yang1, Su-Ching Lin1, Shing-Jong Huang2

  • 1Institute of Chemistry, Academia Sinica, Nankang, Taipei 11529, Taiwan, ROC.

Steroids
|December 10, 2013
PubMed
Summary

Fluorinated steroids like betamethasone (BMS) exhibit distinct multiple ring conformations compared to non-fluorinated analogs. This difference, detectable via NMR spectroscopy, highlights the impact of fluorine on steroid structure.

Keywords:
Anisotropic chemical shiftBetamethasoneFludrocortisone acetateSolid-state NMRSteroidal ring conformation

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Area of Science:

  • Solid-state NMR Spectroscopy
  • Organic Chemistry
  • Medicinal Chemistry

Background:

  • Fluorinated steroids are widely used in medicine.
  • Understanding their structural properties is crucial for drug development.
  • Fluorine substitution can significantly alter molecular conformation and biological activity.

Purpose of the Study:

  • To investigate the impact of fluorine substitution on the steroidal ring conformation.
  • To compare the conformational behavior of fluorinated steroids (betamethasone, fludrocortisone acetate) with their non-fluorinated analogs (prednisolone, hydrocortisone 21-acetate).

Main Methods:

  • Solid-state {(1)H}(13)C cross-polarization/magic angle spinning (CP/MAS) NMR spectroscopy was employed.
  • Analysis focused on (13)C NMR signal patterns and chemical shift deviations.

Main Results:

  • Betamethasone (BMS) showed multiplet (13)C signals, indicating multiple ring conformations.
  • Fludrocortisone acetate (FCA), prednisolone (PRD), and hydrocortisone 21-acetate (HCA) exhibited singlet (13)C signals, suggesting a unique conformation.
  • BMS and FCA displayed significant (13)C chemical shift deviations compared to PRD and HCA, particularly at C9.

Conclusions:

  • Fluorine substitution at C9 induces distinct steroidal ring conformations.
  • Fluorinated steroids possess unique conformational properties compared to their non-fluorinated counterparts.
  • NMR spectroscopy is a valuable tool for differentiating steroid conformations based on fluorination.