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Related Concept Videos

Double Resonance Techniques: Overview01:12

Double Resonance Techniques: Overview

Double resonance techniques in Nuclear Magnetic Resonance (NMR) spectroscopy involve the simultaneous application of two different frequencies or radiofrequency pulses to manipulate and observe two distinct nuclear spins. One important application of double resonance is spin decoupling, which selectively suppresses coupling with one type of nucleus while observing the NMR signal from another nucleus, simplifying the spectrum and enhancing resolution.
Spin decoupling is usually achieved by...
¹H NMR: Complex Splitting01:13

¹H 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.
Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule01:10

Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule

In the AX proton spin system, proton A can sense the two spin states of a coupled proton X, resulting in a doublet NMR signal with two peaks of equal (1:1) intensity. When proton A is coupled to two equivalent protons (AX2 spin system), the spin states of each X can be aligned with or against the external field, creating three possible scenarios. This results in a 1:2:1  triplet signal, where the central peak corresponds to the chemical shift of A and is twice as large or intense as the others.
¹H NMR Signal Multiplicity: Splitting Patterns01:13

¹H NMR Signal Multiplicity: Splitting Patterns

When protons A and X are coupled, their nuclear spin energy levels are slightly modified. This is because the energy required to excite proton A to a spin state parallel to proton X is slightly different from the energy required for it to become anti-parallel to spin X. Consequently, there are two possible excitation frequencies for A (A1 and A2), depending on the spin state of X, and vice versa. The mutual nature of coupling implies that the difference between frequencies A1 and A2, indicated...
¹³C NMR: ¹H–¹³C Decoupling01:04

¹³C NMR: ¹H–¹³C Decoupling

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...
Tandem Mass Spectrometry01:21

Tandem Mass Spectrometry

Tandem mass spectrometry is a technique that uses multiple mass analyzers in series to obtain a higher selectivity and reduce chemical noise during analyte detection. Instruments with multiple analyzers separated by an interaction cell enable secondary fragmentation and selected study of the fragment ions.Secondary fragmentations occur in the interaction cell and can be induced by various factors. Fragmentation induced by collision with inert gases, such as N2, Ar, He, etc., is called...

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Dissolution Dynamic Nuclear Polarization Instrumentation for Real-time Enzymatic Reaction Rate Measurements by NMR
10:54

Dissolution Dynamic Nuclear Polarization Instrumentation for Real-time Enzymatic Reaction Rate Measurements by NMR

Published on: February 23, 2016

Numbers and time doubly dissociate.

Marinella Cappelletti1, Elliot D Freeman, Lisa Cipolotti

  • 1Institute of Cognitive Neuroscience, University College London, London, UK. m.cappelletti@ucl.ac.uk

Neuropsychologia
|August 3, 2011
PubMed
Summary
This summary is machine-generated.

Neuropsychological patients with parietal lesions reveal a double dissociation between number and time processing. Task-irrelevant numbers selectively impaired time perception, suggesting a shared, hierarchical magnitude system.

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Area of Science:

  • Cognitive Neuroscience
  • Neuropsychology

Background:

  • Magnitude dimensions like number, time, and space are hypothesized to share common processing mechanisms.
  • Previous research suggested potential symmetric interactions among these dimensions.

Observation:

  • Two patients with parietal lesions (JT: left, CB: right) exhibited selective impairments in number and time processing.
  • Both patients showed task-irrelevant numbers influencing time processing but not spatial processing.
  • Patient JT's preserved time processing was impaired by task-irrelevant numbers.
  • Patient CB's impaired time estimation was further affected by number magnitude.

Findings:

  • A double dissociation was observed between number and time processing.
  • An asymmetric interaction was found where numbers influenced time perception, but not vice versa.
  • Numerical estimation remained unaffected by time in controls and both patients.

Implications:

  • Results support a partly shared magnitude system rather than a single, fully shared or independent system.
  • The findings suggest a stable hierarchy of magnitude dimensions, with numbers potentially being dominant.
  • This challenges symmetric interaction models and highlights asymmetric influences in magnitude processing.