NMR spectroscopy (1).pptx by analytical chemistry

NMR

1. NMR spectroscopy Lecture Taimoor Khan Dept. of Biotechnology, University of Swabi

2. NMR Nuclear Magnetic Resonance Spectroscopy OR Magnetic Resonance Spectroscopy(MRS)

3. NMR Spectroscopy NMR is a powerful spectroscopy technique used in analytical chemistry , biochemistry, and physics to study the properties of atomic nuclei , or used to observe local magnetic fields around atomic nuclei .

4. Natural Frequency. External Force. Magnetic Resonance. Resonance A phenomenon where an object or system oscillates or vibrates at a specific frequency when subjected to an external force or stimulus that matches its natural frequency.

5. NMR spectroscopy is an advanced characterization technique used to determine the molecular structure at the atomic level of a sample.  NMR spectroscopy has been primly employed to perform experiments on nuclei of atoms, not the electrons. Mukesh et al., 2021

6. Principle The fundamental concept behind NMR spectroscopy is that all nuclei are electrically charged and have multiple spins. Under this situation, the external magnetic field creates the possibility of an energy transfer (Hodgkinson and Emsley, 2000). Generally, this energy transfer occurs from lower to higher energy levels, usually in a single step. This energy transfer or absorption becomes possible at a radio frequency ( Pykett et al., 1982).

7. provides information about the structure , composition , and dynamics of molecules , including organic compounds, inorganic compounds, and biomolecules like; proteins and nucleic acids . Study the nuclei of an atom.

8. History 1940s and early 50s    Isidor Isaac Rabi Noble prize  physics 1944 Jointly developed by Harvard and Stanford University .

9. Principle NMR based upon spin of the nucleus as it generate magnetic field, without external applied magnetic field the nuclear spin are random in direction. Based on the measurement of absorption of electromagnetic radiations in the radio frequency region (4 to 900MHz).

10. Electromagnetic spectrum

11. Radio waves Part of electromagnetic spectrum; produced by alternating electric current. Longest wavelength Low frequency

12. Mechanism A magnetic field generated as result, electron revolves around the nucleus. Nucleus– positive charge( P+N). Electron– negative charge. No. of protons in nuclei are arranged randomly. External field applied– protons will arrange accordingly.

13. Alpa spin-state Most stable state

14. When the spin return to its ground state, the absorbed radio frequency energy is emitted at same frequency level.

15. Alpa spin state – lower energy + highly stable Beta spin state – higher energy + less stable The magnet will tend to reverse about 180 degree when external magnetic field is applied. Reversing of magnets varies with type of molecule. Depending upon presence of electrons.

16. Used to study variety of nuclei. NMR active nuclei  nuclei whose atomic mass and atomic number are odd or either having odd atomic mass and even atomic no. 2. NMR inactive nuclei  nuclei whose atomic mass or atomic number are even.

17. Magnetic shielding Shielding: M agnetic property prevented by surrounded electrons. Surrounded by electrons Molecules shielded by electrons– require less energy to reverse to beta spin state. Deshielding: If not shielded– require lot of energy.

18. energy s DS intensity

19. Modern NMR spectrometers  large and expensive liquid helium-cooled superconducting magnet, because resolution directly depends on magnetic field strength.

20. Protein NMR spectroscopy 3-dimensional structures of the protein. Proteins smaller than 35  Kda . H igh resolution information intrinsically unstructured proteins. Nucleic acid NMR spectroscopy To get information about the structure and dynamics of nucleic acids, such as DNA or  RNA

21. Because of the much higher number of atoms present in a protein molecule in comparison with a small organic compound, the basic 1D spectra become crowded with overlapping signals to an extent where direct spectral analysis becomes untenable. Therefore , multidimensional (2, 3 or 4D) experiments have been devised to deal with this problem