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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 Labile Protons: Temporal Resolution01:10

¹H NMR of Labile Protons: Temporal Resolution

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...
¹H NMR of Labile Protons: Deuterium (²H) Substitution00:48

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

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.
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved in...
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.
Raman Spectroscopy: Overview01:20

Raman Spectroscopy: Overview

The underlying principle of Raman spectroscopy is based on the interaction between light and matter, specifically molecules' inelastic scattering of photons. When a monochromatic beam of light, typically from a laser source, interacts with a sample, most scattered light has the same frequency as the incident light. This is known as Rayleigh scattering.
However, a small fraction of the scattered light exhibits a frequency shift due to the exchange of energy between the incident photons and the...

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Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
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Molecular dynamics in solid riboflavin as studied by 1H NMR.

E R Andrew1, S Glowinkowski

  • 1Department of Physics, University of Florida, Gainesville 32611, USA.

Solid State Nuclear Magnetic Resonance
|March 29, 2001
PubMed
Summary

Molecular dynamics of riboflavin (vitamin B2) were studied using NMR. Methyl group motion, including tunneling, and hydroxyl proton motion were identified as key relaxation mechanisms across a wide temperature range.

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Area of Science:

  • Solid-state Nuclear Magnetic Resonance (NMR) Spectroscopy
  • Molecular Dynamics
  • Biophysics

Background:

  • Riboflavin (vitamin B2) is essential for various biological processes.
  • Understanding the molecular dynamics of riboflavin is crucial for elucidating its function.

Purpose of the Study:

  • To investigate the molecular dynamics of riboflavin using Nuclear Magnetic Resonance (NMR).
  • To identify and characterize the specific motions contributing to relaxation processes.

Main Methods:

  • Measurement of spin-lattice relaxation times (Tl and Tld) and NMR second moment.
  • Analysis of data across a temperature range of 55-350 K.
  • Application of Haupt's theory and Davidson-Cole distribution for motion analysis.

Main Results:

  • A broad, flat Tl minimum at low temperatures indicates motion of two distinct methyl groups.
  • Tunneling-assisted relaxation mechanisms were observed for methyl group motion.
  • Proton motion within a hydroxyl group contributes to relaxation at higher temperatures.

Conclusions:

  • The study elucidates the complex molecular dynamics of riboflavin.
  • NMR relaxation studies reveal distinct methyl and hydroxyl group motions.
  • These dynamics are critical for riboflavin's biological activity.