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Related Concept Videos

¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

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Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
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¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

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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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¹H NMR of Labile Protons: Temporal Resolution01:10

¹H NMR of Labile Protons: Temporal Resolution

1.6K
Protons bonded to heteroatoms such as nitrogen and oxygen exhibit a range of chemical shift values. This is due to the varying degree of hydrogen bonding between the proton and the heteroatom in other molecules. The extent of hydrogen bonding affects the electron density around the proton, thereby giving different chemical shift values for the protons in the proton NMR spectrum.
The –OH proton in alcohols typically appears in the range of δ 2 to 5 ppm but can vary depending on the specific...
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Proton (¹H) NMR: Chemical Shift01:07

Proton (¹H) NMR: Chemical Shift

3.0K
Organic molecules primarily contain carbon and hydrogen atoms. While all the hydrogen isotopes are NMR-active, protium or hydrogen-1 is the most abundant. It has a significant energy separation between its nuclear spin states due to its large gyromagnetic ratio. As per Boltzmann's distribution, an increase in the energy separation implies a greater excess population of nuclei available for excitation, resulting in a strong NMR absorption signal.
Absorption signals of all the protium nuclei...
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¹H NMR of Labile Protons: Deuterium (²H) Substitution00:48

¹H NMR of Labile Protons: Deuterium (²H) Substitution

1.2K
This lesson illustrates the role of deuterium substitution in simplifying the NMR spectrum of compounds comprising labile protons. One method employed is the use of deuterium. Amongst the three isotopes of hydrogen, deuterium (2H) has a nucleus composed of one proton and one neutron. When the D2O solvent is added to a pure dry ethanol solution, its labile proton is substituted with deuterium.
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Two-Dimensional (2D) NMR: Overview01:12

Two-Dimensional (2D) NMR: Overview

1.3K
The 1D NMR spectrum of large and complex molecules like natural products has complicated splitting patterns and overlapping signals, which can be easily interpreted using 2-dimensional (2D) NMR. Unlike 1D NMR, 2D NMR has two frequency axes that provide the coupling information between the nucleus A and nucleus B in a molecule. The process from which 2D spectra are obtained has four steps.
The first step is the preparation period, during which nucleus A is excited with a radiofrequency pulse....
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Quantifying Pharmaceutical Formulations from Proton Detected Solid-State NMR under Ultrafast Magic Angle Spinning.

Mingyue Li1, Xingyu Lu1, Wei Xu1

  • 1Pharmaceutical Sciences, Merck & Co., Inc., Kenilworth, NJ 07033, USA.

Journal of Pharmaceutical Sciences
|July 18, 2020
PubMed
Summary

Ultrafast magic angle spinning solid-state NMR effectively quantifies pioglitazone forms in drug formulations. This advanced technique offers high resolution and sensitivity for pharmaceutical stability analysis.

Keywords:
Phase transformation(s)PreformulationSolid-state NMR (SSNMR) spectroscopyStability, polymorph(s)

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Area of Science:

  • Pharmaceutical Science
  • Analytical Chemistry
  • Materials Science

Background:

  • Assessing physicochemical stability of active pharmaceutical ingredients in solid dosages is crucial.
  • Challenges exist in quantifying phase stability and low drug content in complex formulations using routine methods.
  • Proton-detected solid-state NMR (ssNMR) with ultrafast magic angle spinning (UF-MAS) offers enhanced resolution and sensitivity.

Purpose of the Study:

  • To demonstrate the application of 60 kHz UF-MAS ssNMR for quantifying pioglitazone free base (PIO-FB) in binary and multicomponent pharmaceutical systems.
  • To establish the limit of detection for PIO-FB in the presence of its hydrochloride salt (PIO-HCl).
  • To showcase the capability of 2D 1H-1H ssNMR for analyzing complex formulations.

Main Methods:

  • Implementation of 60 kHz UF-MAS proton-detected ssNMR.
  • Utilized one-dimensional 1H ssNMR to differentiate pioglitazone free base and its hydrochloride salt.
  • Employed two-dimensional 1H-1H correlation ssNMR for complex mixture analysis.

Main Results:

  • One-dimensional 1H ssNMR successfully differentiated PIO-FB from PIO-HCl with a limit of detection at 1.77% (w/w).
  • Two-dimensional 1H-1H ssNMR quantified approximately 2.0% (w/w) PIO-FB in a multicomponent formulation.
  • The 1H ssNMR method provided higher resolution and faster acquisition compared to conventional 13C techniques.

Conclusions:

  • 60 kHz UF-MAS 1H ssNMR is a powerful and novel method for quantifying drug substances in solid dosages.
  • This technique addresses the limitations of conventional methods for analyzing low drug loading and multicomponent formulations.
  • UF-MAS ssNMR enhances the understanding of pharmaceutical material stability and quality control.