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Related Concept Videos

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

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...
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR01:15

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

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.
Nuclear Overhauser Enhancement (NOE)01:06

Nuclear Overhauser Enhancement (NOE)

Irradiation of a spin-active nucleus causes an increase or decrease in the signal intensity of neighboring nuclei that are not necessarily chemically bonded or involved in J-coupling. This phenomenon, called the nuclear Overhauser enhancement (NOE), results from through-space interactions between the nuclear spins. The NOE effect decreases with increasing internuclear distance and is generally not observed beyond 4 angstroms. In NOE, dipole-dipole interactions between neighboring spin-active...
Stability of Substituted Cyclohexanes02:30

Stability of Substituted Cyclohexanes

This lesson discusses the stability of substituted cyclohexanes with a focus on energies of various conformers and the effect of 1,3-diaxial interactions.
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...
2D NMR: Overview of Homonuclear Correlation Techniques01:16

2D NMR: Overview of Homonuclear Correlation Techniques

Homonuclear correlation spectroscopy (COSY) is a powerful technique used in Nuclear Magnetic Resonance (NMR) spectroscopy to study the correlations between nuclei of the same type within a molecule. It provides information about scalar couplings between adjacent nuclei, which helps determine connectivity and structural information. There are several COSY variants, each with its unique strengths and experimental parameters.
COSY90 is the standard two-dimensional (2D) COSY experiment that...
Electron Paramagnetic Resonance (EPR) Spectroscopy: Organic Radicals01:17

Electron 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...

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Related Experiment Video

Updated: May 10, 2026

Site Directed Spin Labeling and EPR Spectroscopic Studies of Pentameric Ligand-Gated Ion Channels
11:19

Site Directed Spin Labeling and EPR Spectroscopic Studies of Pentameric Ligand-Gated Ion Channels

Published on: July 4, 2016

Structural equilibrium in new nitroxide-capped cyclodextrins: CW and pulse EPR study.

Olesya A Krumkacheva1, Matvey V Fedin, Dmitry N Polovyanenko

  • 1International Tomography Center SB RAS, Institutskaya 3a, Novosibirsk 630090, Russia.

The Journal of Physical Chemistry. B
|June 18, 2013
PubMed
Summary

New spin-labeled cyclodextrins enhance nitroxide functionality. Researchers synthesized and studied complexes of methylated cyclodextrin (TRIMEB) with nitroxides, revealing conformational equilibria and identifying a promising linker for specific applications.

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Rapid Scan Electron Paramagnetic Resonance Opens New Avenues for Imaging Physiologically Important Parameters In Vivo
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Transport Properties of Ibuprofen Encapsulated in Cyclodextrin Nanosponge Hydrogels: A Proton HR-MAS NMR Spectroscopy Study
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Transport Properties of Ibuprofen Encapsulated in Cyclodextrin Nanosponge Hydrogels: A Proton HR-MAS NMR Spectroscopy Study

Published on: August 15, 2016

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Last Updated: May 10, 2026

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Published on: July 4, 2016

Rapid Scan Electron Paramagnetic Resonance Opens New Avenues for Imaging Physiologically Important Parameters In Vivo
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Transport Properties of Ibuprofen Encapsulated in Cyclodextrin Nanosponge Hydrogels: A Proton HR-MAS NMR Spectroscopy Study
10:10

Transport Properties of Ibuprofen Encapsulated in Cyclodextrin Nanosponge Hydrogels: A Proton HR-MAS NMR Spectroscopy Study

Published on: August 15, 2016

Area of Science:

  • Supramolecular Chemistry
  • Organic Chemistry
  • Physical Chemistry

Background:

  • Cyclodextrins are versatile hosts with applications in drug delivery and sensing.
  • Nitroxides are stable free radicals used as spin labels in Electron Paramagnetic Resonance (EPR) spectroscopy.
  • Covalent modification of cyclodextrins with nitroxides offers opportunities to create novel functional materials.

Purpose of the Study:

  • To synthesize and characterize novel spin-labeled cyclodextrin complexes.
  • To investigate the influence of linker properties and radical type on complex structure and dynamics.
  • To evaluate the potential applications of these complexes, particularly in guest recognition and sensing.

Main Methods:

  • Synthesis of cyclodextrin-nitroxide conjugates using various nitroxide types (piperidine, pyrroline, pyrrolidine, imidazoline) and linkers.
  • Characterization using pulse and continuous wave Electron Paramagnetic Resonance (EPR) spectroscopy.
  • Quantitative analysis of radical accessibility to solvent using electron spin echo envelope modulation (ESEEM).

Main Results:

  • Successful synthesis of new cyclodextrin-nitroxide complexes.
  • Observation of conformational equilibria between external and cavity-capping radical conformations.
  • Identification of the -NH-CO- linker as optimal for applications requiring proximity between the nitroxide and TRIMEB inclusion complex.
  • Demonstration that pH-sensitive nitroxides retain sensitivity upon complexation without reduced reduction rates.

Conclusions:

  • Spin-labeled cyclodextrins offer extended functionality for nitroxides.
  • Complex structure and dynamics are tunable via linker and radical choice.
  • These novel complexes show promise for applications in molecular recognition and sensing, with specific linkers enabling tailored interactions.