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The probability of having two carbon-13 atoms next to each other is negligible because of the low natural abundance of carbon-13. Consequently, peak splitting due to carbon-carbon spin-spin coupling is not observed in spectra. However, protons up to three sigma bonds away split the carbon signal according to the n+1 rule, resulting in complicated spectra.
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Resolving alternative structure determinations of indapamide using 13C solid-state NMR.

Caitlin L Evans1, Ivana Radosavlijević Evans1, Paul Hodgkinson1

  • 1Department of Chemistry, Durham University, Stockton Road, Durham, DH1 3LE, UK. paul.hodgkinson@durham.ac.uk.

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|March 28, 2022
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Summary
This summary is machine-generated.

Solid-state NMR resolved crystal structure conflicts for indapamide hemihydrate (IND). IND has multiple molecules in its asymmetric unit, not disordered sulfonamide groups, showcasing NMR crystallography

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Area of Science:

  • Solid-state NMR spectroscopy
  • Crystallography
  • Pharmaceutical science

Background:

  • Conflicting crystal structure data exists for indapamide hemihydrate (IND) in the Cambridge Structural Database.
  • Distinguishing between true structural multiplicity and disorder is crucial for drug characterization.

Purpose of the Study:

  • To resolve the ambiguity between alternative crystal structures reported for indapamide hemihydrate.
  • To demonstrate the utility of solid-state NMR spectroscopy in structural elucidation.

Main Methods:

  • Utilized 13C solid-state Nuclear Magnetic Resonance (NMR) spectroscopy.
  • Applied NMR crystallography to analyze the crystal structure of indapamide hemihydrate.
  • Compared NMR findings with crystallographic refinement factors.

Main Results:

  • Solid-state NMR confirmed the presence of multiple distinct molecules (Z' = 4) in the asymmetric unit of indapamide hemihydrate.
  • The study ruled out disorder in the orientation of sulfonamide groups as the cause of structural ambiguity.
  • NMR crystallography proved more effective than refinement agreement factors for distinguishing alternative crystal structures.

Conclusions:

  • The crystal structure of indapamide hemihydrate has been definitively determined using solid-state NMR.
  • NMR crystallography offers a robust method for resolving structural conflicts in crystalline solids.
  • This approach enhances the reliability of structural data in databases like the Cambridge Structural Database.