Related Experiment Video
Updated: Jun 12, 2026
08:01
Rapid Scan Electron Paramagnetic Resonance Opens New Avenues for Imaging Physiologically Important Parameters In Vivo
Published on: September 26, 2016
The effect of structure on nitroxide EPR spectral linewidth
Scott R Burks1, Mallory A Makowsky, Zachary A Yaffe
1Center for Biomedical Engineering and Technology, and Center for EPR Imaging In Vivo Physiology, University of Maryland, Baltimore, Maryland 21201, USA.
The Journal of Organic Chemistry
|June 15, 2010
Summary
Researchers discovered that a carbonyl double bond in nitroxides leads to narrow Electron Paramagnetic Resonance (EPR) spectral lines. This finding enables the design of new nitroxides for advanced EPR spectroscopy and imaging applications.
Area of Science:
- Chemistry
- Spectroscopy
- Biomedical Imaging
Background:
- Narrow-linewidth nitroxides are crucial for low-frequency Electron Paramagnetic Resonance (EPR) spectroscopy and in vivo EPR imaging.
- Designing such nitroxides requires understanding the structural factors influencing their spectral properties.
Purpose of the Study:
- To investigate the structural basis for the narrow linewidth of 4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxyl (5).
- To design and synthesize novel nitroxides with narrow linewidths for enhanced EPR applications.
Main Methods:
- Computational modeling was employed to analyze the conformational dynamics of nitroxide 5.
- Synthesis of new nitroxides, including 4-methoxycarbonylmethylidene-2,2,6,6-tetramethyl-1-piperidinyloxyl (7) and 4-acetoxymethoxycarbonylmethylidene-2,2,6,6-tetramethyl-1-piperidinyloxyl (9), was performed.
Main Results:
- Computational modeling indicated that the carbonyl double bond in nitroxide 5 promotes conformational diversity, leading to spectral line narrowing.
- Synthesized nitroxides 7 and 9 also exhibited narrow linewidths, consistent with the computational findings.
- Nitroxide 8 served as a versatile prototype for further structural modifications.
Conclusions:
- The presence of a carbonyl double bond is key to achieving narrow EPR linewidths in nitroxides.
- The developed framework facilitates the design of tailored nitroxides for specific EPR spectroscopy and in vivo imaging needs.
- New nitroxides with exocyclic double bonds show promise for targeted in vivo EPR imaging.
Related Concept Videos
01:17Electron Paramagnetic Resonance (EPR) Spectroscopy: Organic Radicals
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...
01:14NMR Spectrometers: Resolution and Error Correction
When magnetic nuclei in a sample achieve resonance and undergo relaxation, the signal detected in NMR is an approximately exponential free induction decay. Fourier transform of an exponential decay yields a Lorentzian peak in the frequency domain. Lorentzian peaks in an NMR spectrum are defined by their amplitude, full width at half maximum, and position, where the peak width is governed by the spin-spin relaxation time alone. In real experiments, however, the applied magnetic field is rendered...
01:02¹H NMR: Interpreting Distorted and Overlapping Signals
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 slanted or...
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 slanted or...
01:13¹H NMR: Complex Splitting
A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
02:52Resonance
The Lewis structure of a nitrite anion (NO2−) may actually be drawn in two different ways, distinguished by the locations of the N-O and N=O bonds.
01:08IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations
Identical bonds within a polyatomic group can stretch symmetrically (in-phase) or asymmetrically (out-of-phase). Similar to hydrogen bonding, these vibrations also influence the shape of the IR peak. Generally, asymmetric stretching frequencies are higher than symmetric stretching frequencies. For example, primary amines exhibit two distinct IR peaks between 3300–3500 cm−1 corresponding to the symmetric and asymmetric N-H stretching, while secondary amines exhibit a single stretching vibration...