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Related Concept Videos

Electron Paramagnetic Resonance (EPR) Spectroscopy: Organic Radicals01:17

Electron Paramagnetic Resonance (EPR) Spectroscopy: Organic Radicals

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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

¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR

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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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Atomic Nuclei: Nuclear Spin State Population Distribution01:14

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Near absolute zero temperatures, in the presence of a magnetic field, the majority of nuclei prefer the lower energy spin-up state to the higher energy spin-down state. As temperatures increase, the energy from thermal collisions distributes the spins more equally between the two states. The Boltzmann distribution equation gives the ratio of the number of spins predicted in the spin −½ (N−) and spin +½ (N+) states.
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π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds01:14

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In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as...
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Paramagnetism01:30

Paramagnetism

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Paramagnets are materials with unpaired electrons that possess a finite magnetic moment. In the absence of a magnetic field, these moments are randomly oriented, and thus the net moment is zero. Under an external field, a torque acting on the moments tends to align them along the field's direction. However, the random thermal motion of electrons produces a torque opposite to the external field and tries to disorient the moments. These two competing effects align only a few moments along the...
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Atomic Spectroscopy: Effects of Temperature01:27

Atomic Spectroscopy: Effects of Temperature

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Atomization, converting samples into gas-phase atoms and ions, is essential for atomic spectroscopy. The flame temperature required for atomization affects the efficiency of the atomic spectroscopic methods by increasing the atomization efficiency and the relative population of the excited and ground states.
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Updated: Dec 23, 2025

Use of Electron Paramagnetic Resonance in Biological Samples at Ambient Temperature and 77 K
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Temperature-cycle electron paramagnetic resonance.

E Gabriele Panarelli1, Peter Gast, Edgar J J Groenen

  • 1Department of Physics, Huygens-Kamerlingh Onnes Laboratory, Leiden University, PO Box 9504, 2300 RA Leiden, The Netherlands. groenen@physics.leidenuniv.nl.

Physical Chemistry Chemical Physics : PCCP
|April 22, 2020
PubMed
Summary

This study introduces temperature-cycle Electron Paramagnetic Resonance (EPR) for studying fast reactions with paramagnetic species. The novel method allows detailed kinetic analysis of short-lived intermediates using pulsed laser heating and intermittent EPR measurements.

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Area of Science:

  • Chemical Kinetics
  • Spectroscopy
  • Biochemistry

Background:

  • Studying fast reactions with paramagnetic species is challenging.
  • Existing methods have limitations in time resolution and sample handling.

Purpose of the Study:

  • To develop a novel technique for studying fast (bio)chemical reactions involving paramagnetic species.
  • To enable the characterization of short-lived intermediates.
  • To provide a flexible method for kinetic studies.

Main Methods:

  • Temperature-cycle Electron Paramagnetic Resonance (EPR) using pulsed near-infrared laser irradiation.
  • Intermittent sample characterization by 275 GHz EPR at low temperatures.
  • Demonstration using TEMPOL reduction with sodium dithionite in aqueous solution.

Main Results:

  • The technique achieves sub-second time scale resolution.
  • A single sample yields a complete kinetic trace.
  • Laser pulse parameters offer flexibility in experimental time scale and temperature.
  • A method for sample loading in water/glycerol mixtures at low temperatures was developed.

Conclusions:

  • Temperature-cycle EPR is a powerful new tool for kinetic studies of paramagnetic reactions.
  • The method allows for detailed investigation of reaction mechanisms and intermediates.
  • The technique offers significant advantages in flexibility and efficiency.