nuclear magnetic resonance

Examples of nuclear magnetic resonance in the following topics:

• Structural Determination

  • Structural determination using isotopes is often performed using nuclear magnetic resonance spectroscopy and mass spectrometry.
  • Structural determination utilizing isotopes is often performed using two analytical techniques: nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS).
  • Mass spectrometry and nuclear magnetic resonance detect the difference in an isotope's mass, while infrared spectroscopy detects the difference in the isotope's vibrational modes.
  • Nuclear magnetic resonance and mass spectrometry are used to investigate the mechanisms of chemical reactions.

• NMR and MRIs

  • Magnetic resonance imaging is a medical imaging technique used in radiology to visualize internal structures of the body in detail.
  • Magnetic resonance imaging (MRI), also called nuclear magnetic resonance imaging (NMRI) or magnetic resonance tomography (MRT), is a medical imaging technique used in radiology to visualize internal structures of the body in detail.
  • MRI utilized the property of nuclear magnetic resonance (NMR) to image the nuclei of atoms inside the body.
  • When a person is inside the scanner's powerful magnetic field, the hydrogen protons in their body align with the direction of the field.
  • This electromagnetic field has just the right frequency (known as the resonance frequency) to become absorbed and then reverse the rotation of the hydrogen protons in the magnetic field.

• Basic Techniques in Protein Analysis

  • Another protein imaging technique, nuclear magnetic resonance (NMR), uses the magnetic properties of atoms to determine the three-dimensional structure of proteins.
  • This technique depends on the fact that certain atomic nuclei are intrinsically magnetic.

• Medical Imaging

  • A magnetic resonance imaging instrument (MRI), or "nuclear magnetic resonance (NMR) imaging" scanner as it was originally known, uses powerful magnets to polarize and excite hydrogen nuclei (single proton) in water molecules in human tissue, producing a detectable signal which is spatially encoded, resulting in images of the body scanner .
  • This is the "resonance" part of MRI.
  • Nuclear medicine uses certain properties of isotopes and the energetic particles emitted from radioactive material to diagnose or treat various pathology.
  • Different from the typical concept of anatomic radiology, nuclear medicine enables assessment of physiology.
  • A magnetic resonance imaging instrument (MRI scanner), or "nuclear magnetic resonance (NMR) imaging" scanner as it was originally known, uses powerful magnets to polarize and excite hydrogen nuclei (single proton) in water molecules in human tissue, producing a detectable signal which is spatially encoded, resulting in images of the body.

• Proton NMR Spectroscopy

  • This important and well-established application of nuclear magnetic resonance will serve to illustrate some of the novel aspects of this method.
  • A solution of the sample in a uniform 5 mm glass tube is oriented between the poles of a powerful magnet, and is spun to average any magnetic field variations, as well as tube imperfections.
  • If the magnetic field is smoothly increased to 2.3488 T, the hydrogen nuclei of the water molecules will at some point absorb rf energy and a resonance signal will appear.
  • Since protons all have the same magnetic moment, we might expect all hydrogen atoms to give resonance signals at the same field / frequency values.
  • This secondary field shields the nucleus from the applied field, so Bo must be increased in order to achieve resonance (absorption of rf energy).

• Introduction

  • Over the past fifty years nuclear magnetic resonance spectroscopy, commonly referred to as nmr, has become the preeminent technique for determining the structure of organic compounds.
  • The resulting spin-magnet has a magnetic moment (μ) proportional to the spin.
  • Strong magnetic fields are necessary for nmr spectroscopy.
  • The international unit for magnetic flux is the tesla (T).
  • These moments are in nuclear magnetons, which are 5.05078•10-27 JT-1.

• Detection and Observation of Radicals

  • The same unpaired or odd electron that renders most radical intermediates unstable and highly reactive may be induced to leave a characteristic "calling card" by a magnetic resonance phenomenon called "electron spin resonance" (esr) or "electron paramagnetic resonance" (epr).
  • Just as a proton (spin = 1/2) will occupy one of two energy states in a strong external magnetic field, giving rise to nmr spectroscopy; an electron (spin = 1/2) may also assume two energy states in an external field.
  • Because the magnetic moment of an electron is roughly a thousand times larger than that of a proton, the energy difference between the spin states falls in the microwave region of the spectrum (assuming a moderate magnetic field strength).
  • The lifetime of electron spin states is much shorter than nuclear spin states, so esr absorptions are much broader than nmr signals.
  • This complexity is the result of hyperfine splitting of the resonance signal by protons and other nuclear spins, an interaction similar to spin-spin splitting in nmr spectroscopy.

• Examples and Applications

  • To achieve this, the voltage frequency must match the particle's cyclotron resonance frequency,
  • Additionally, cyclotrons are a good source of high-energy beams for nuclear physics experiments.
  • A magnetic field parallel to the filament is imposed by a permanent magnet.
  • The sizes of the cavities determine the resonant frequency, and thereby the frequency of emitted microwaves.
  • A cross-sectional diagram of a resonant cavity magnetron.

• The Chemical Shift

  • Unlike infrared and uv-visible spectroscopy, where absorption peaks are uniquely located by a frequency or wavelength, the location of different nmr resonance signals is dependent on both the external magnetic field strength and the rf frequency.
  • Since no two magnets will have exactly the same field, resonance frequencies will vary accordingly and an alternative method for characterizing and specifying the location of nmr signals is needed.
  • The first feature assures that each compound gives a single sharp resonance signal.
  • Since the deuterium isotope of hydrogen has a different magnetic moment and spin, it is invisible in a spectrometer tuned to protons.
  • The shielding effect in such high electron density cases will therefore be larger, and a higher external field (Bo) will be needed for the rf energy to excite the nuclear spin.

• Emission Topography

  • Positron emission tomography is a nuclear medical imaging technique that produces a three-dimensional image of processes in the body.
  • Positron emission tomography (PET) is a nuclear medical imaging technique that produces a three-dimensional image or picture of functional processes in the body.
  • PET scans are increasingly read alongside CT or magnetic resonance imaging (MRI) scans, with the combination giving both anatomic and metabolic information.