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Related Concept Videos

Carbon-13 (¹³C) NMR: Overview01:10

Carbon-13 (¹³C) NMR: Overview

6.6K
Carbon-13 is a naturally occurring NMR-active isotope of carbon with a low natural abundance of 1.1%. In contrast, carbon-12 is the most abundant isotope of carbon with zero nuclear spin. Therefore, it is NMR inactive. The gyromagnetic ratio of carbon-13 is smaller than that of protons. As a result, carbon-13 resonance is about 6000 times weaker than proton resonance. For a given magnetic field strength, the resonance frequency of carbon-13 is about one-fourth of the resonance frequency for...
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Electron Paramagnetic Resonance (EPR) Spectroscopy: Organic Radicals01:17

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Ideally, an unpaired electron shows a single peak in the EPR spectrum due to the transition between the two spin energy states. However, coupling interactions can occur between the spins of the unpaired electron and any neighboring spin-active nuclei. This hyperfine coupling results in hyperfine splitting, where the EPR signal is split into multiplets. The signals split into 2nI + 1 peaks, where n is the number of equivalent nuclei and I is the nuclear spin. These splitting patterns provide...
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¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR01:15

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1.4K
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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¹³C NMR: ¹H–¹³C Decoupling01:04

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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.
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...
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Updated: May 6, 2026

In Vivo EPR Assessment of pH, pO2, Redox Status, and Concentrations of Phosphate and Glutathione in the Tumor Microenvironment
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EPR Viscometric Measurements Using a 13C-Labeled Triarylmethyl Radical in Protein-based Biotherapeutics and Human

Murugesan Velayutham1,2, Martin Poncelet1,3, Jessica A Perini4

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Electron paramagnetic resonance (EPR) viscometry effectively measures the viscosity of biological fluids and biotherapeutics. This method aids in developing safe and effective protein-based drugs and assessing joint health.

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Area of Science:

  • Biophysics
  • Materials Science
  • Biochemistry

Background:

  • Viscosity is critical for evaluating biological lubricants like synovial fluid and for formulating protein-based therapeutics.
  • High-concentration biotherapeutics (e.g., insulin, monoclonal antibodies) for chronic diseases require viscosity assessment to ensure patient self-administration.
  • Uncontrolled viscosity in drug formulations can lead to manufacturing challenges and painful injections.

Purpose of the Study:

  • To demonstrate the utility of electron paramagnetic resonance (EPR) viscometry using a 13C-labeled trityl spin probe (13C1-dFT) for microviscosity measurements.
  • To assess the applicability of EPR viscometry for analyzing commercial insulin, antibody solutions, and human synovial fluids.
  • To highlight EPR viscometry as a valuable tool for biopharmaceutical formulation control and clinical diagnostics.

Main Methods:

  • Utilized electron paramagnetic resonance (EPR) viscometry with a viscosity-sensitive 13C-labeled trityl spin probe (13C1-dFT).
  • Measured microviscosity in small sample volumes (5-50 μL).
  • Applied the method to commercial insulin samples, antibody solutions, and human synovial fluids.

Main Results:

  • Successfully demonstrated EPR viscometry's capability to measure microviscosity of various biological and pharmaceutical fluid samples.
  • Validated the use of 13C1-dFT spin probe for accurate viscosity determination in microliter volumes.
  • Showcased the method's effectiveness for both biopharmaceutical quality control and clinical assessment of synovial fluid.

Conclusions:

  • EPR viscometry using 13C1-dFT is a practical and effective method for microviscosity measurements.
  • This technique supports the development and administration of high-concentration protein therapeutics.
  • EPR viscometry offers a valuable tool for clinical evaluation of synovial fluid and biopharmaceutical characterization.