Finals

• Nuclear Magnetic Resonance (NMR)


  A physical phenomenon based upon the magnetic property of the nucleus of an atom

  
• Basic Instrumentation of NMR

  • Magnet
  • Stable radiofrequency transmitter
  • Radio receiver and detector
  • A coil of wire surrounding the sample (sensor)
  • Cell containing the sample
  • Method of sweeping through the spectrum
  • Recorder to display absorption peaks
• Chemical Shift


  • Specific correlation between resonance frequency and chemical structure
  • Used to describe the unique magnetic field strength required to achieve resonance for any given proton
  • Tetramethylsilane (TMS) is used as a reference in proton NMR and is assigned a chemical shift of zero
  • δ Delta scale is frequently used to measure chemical shift
• Resonance


  • A condition resulting from the absorption of energy that causes the nuclei in the lower energy level to be excited into a higher energy level
  • It occurs when the frequency of the rotational magnetic field and the frequency of the precessing nucleus becomes equal allowing the nucleus to flip from a parallel to an antiparallel orientation

  
• Saturation


  A condition in which the lower and the higher energy levels are equally populated resulting to the complete disappearance of the NMR signals
• Relaxation


  A radiationless process when the downward transitions occur at a rate greater than the upward transitions, resulting to the appearance of useful NMR signals
• NMR


  • It studies a magnetic nucleus (hydrogen) by aligning it with a very powerful external magnetic field
  • Perturbing this alignment using an electromagnetic field
  • NMR involves the observation of resonance frequencies of a molecule, to allow the analyst to discover structural information about the molecule

  
• Spin


  • The spin of a nuclei is based on the nuclei's charge and mass
  • A nuclei with an odd mass number possess mechanical spin
  • A nuclei with an even mass number do not possess mechanical spin
  • Only nuclei with spin are useful in NMR studies

  
• Magnetic Moment


  • It refers to the strength of the magnetic field
  • 2 orientations of protons in a magnetic field: +1/2 spin state (aligned with field) and -1/2 spin state (opposed to field)

  
• Precession


  1. Protons spinning in an applied magnetic field exhibit precessional motion about a vertical axis

  2. The frequency of precession (Larmour frequency) increases with the strength of the magnetic field

  3. If a proton is exposed to electromagnetic radiation matching its precessional frequency, it will transition (flip) to the higher energy state, absorbing the radiation

  
• Relaxation


  • Spin-spin Relaxation (Transverse) - involves exchange of energy between two proximal processing nuclei
  • Spin-Lattice Relaxation (Longitudinal) - transfer of energy to lattice components as nuclei returns from higher to lower spin state
• Spin-Lattice Relaxation


  • Nuclei in the higher energy state lose energy to the lattice (sample), increasing the lattice's vibrational and rotational motion
  • The relaxation time (T1) depends on the magnetogyric ratio of the nucleus and the mobility of the lattice

  
• Spin-Spin Relaxation


  Neighbouring nuclei with identical precessional frequencies but differing magnetic quantum states can exchange quantum states, decreasing the average lifetime of nuclei in the excited state and resulting in line-broadening

  
• Chemical Shift


  • The difference between the applied magnetic field and the field at the nucleus due to electron shielding
  • Upfield shift due to diamagnetic effect of s-electrons
  • Chemical shift is the difference between the resonant frequency of the spinning protons and the signal of the reference standard

  
• Spin-Spin Coupling


  A magnetic interaction between individual nuclear spins transmitted by the bonding electrons through which the nuclear spins are indirectly connected
• NMR is the pre-eminent technique for determining the structure of organic compounds
• NMR is the only spectroscopic method for which a complete analysis & interpretation of the entire spectrum is normally expected
• NMR Characteristics and Applications

  • Larger amounts of samples are used in older models
  • A typical 1 mg sample can be used in more modern models
  • Non-destructive method
  • Strong magnetic fields are required (1 to 20 T)
  • Provide detailed information on the exact 3D structure of biological molecules in solution
  • One of the techniques used to build elementary quantum computers
• NMR is the most powerful tool used for elucidating the identification of chemical substances
• NMR


  • Pre-eminent technique for determining the structure of organic compounds
  • The only spectroscopic method for which a complete analysis & interpretation of the entire spectrum is normally expected
• NMR


  • Larger amounts of samples are used (in older models)
  • A typical 1 mg sample can be used (in more modern models)
• NMR


  • Non-destructive method
  • Strong magnetic fields are required (1 to 20 T)
  • Provide detailed information on the exact 3D structure of biological molecules in solution

  
• NMR


  • One of the techniques used to build elementary quantum computers
• Identification of chemical substance

  Most powerful tool used for elucidating the structure of organic molecules
• NMR


  • Data acquisition in petroleum industry and gas exploration/recovery
  • Real-time processing and process optimization in oil refineries & petrochemical plants
• NMR Spectra


  • Benzene
  • Toluene
  • Proteins in 3D
• NMR


  • Imaging in medical diagnosis
• NMR


  • In X-ray crystallography & electron microscopy for the analysis of membrane proteins and amyloid fibrils
• NMR


  • Used in the diagnosis of Alzheimer's disease and Parkinsonism
• Isotopes useful in NMR analysis

  • 3He
  • 13C
  • 15N
  • 14N
  • 19F
  • 31P
  • 17O
  • 10B
  • 11B
  • 35Cl and 37Cl
  • 43Ca
  • 195Pt
• NMR Spectroscopy


  • A technique which exploits the magnetic properties of certain nuclei
  • Provides useful information in qualitative and quantitative studies [physical, chemical, electronic and structural information] of medicinal agents and other organic compounds

  
• NMR Spectrometer


  • An instrument designed to allow observation of the nuclei as they relax from resonance

  
• Components of NMR Spectrometer

  • Magnet with a strong, stable, homogeneous field
  • Radiofrequency transmitter
  • Radio receiver and detector
  • Coil of wire surrounding the sample
  • Cell compartment
  • Method of sweeping through the spectrum
  • Recorder
• Components of NMR Assay

  • Sample/analyte (solid or liquid)
  • Solvent (CCl4, CS2, CdCl3)
  • Tetramethylsilane (TMS or the reference standard)
  • Internal Standard (required only for quantitative NMR studies)
• Magnetic Resonance Imaging (MRI)


  • A medical technique primarily used in radiology to visualize the structure and function of the body
  • Provides much greater contrast between the different soft tissues of the body than computed tomography (CT scan)

  
• Specialized MRI Techniques


  • Diffusion MRI
  • Magnetic Resonance Angiography (MRA)
  • Magnetic Resonance Spectroscopy (MRS)
  • Functional MRI (fMRI)
  • Interventional MRI (iMRI)
  • Radiation Therapy Simulation
  • Magnetic Resonance Guided Focused Ultrasound (MRgFUS)
  • Multinuclear Imaging
  • Susceptibility Weighted Imaging (SWI)
• Nuclear magnetic resonance (NMR) is a property that magnetic nuclei have in a magnetic field and applied electromagnetic (EM) pulse or pulses, which cause the nuclei to absorb energy from the EM pulse and radiate this energy back out

  
• The energy radiated back out is at a specific resonance frequency which depends on the strength of the magnetic field and other factors

  
• NMR allows the observation of specific quantum mechanical magnetic properties of an atomic nucleus

  
• Many scientific techniques exploit NMR phenomena to study molecular physics, crystals and non-crystalline materials through NMR spectroscopy