wo main techniques including mass spectrometry (MS) and atomic nucleus magnetic resonance, are applied in metabolic studies. Nuclear magnetic resonance (NMR) spectroscopy is a strong and non-destructive technique used to rapidly analysis of biological samples at the molecular level without the need for the separation and purification of compounds.
This technique has had a significant impact on various sciences such as biology, medicine, imaging, NMR microscopy (a variety of usages such as diamond localization to prevent breakings, the detection of microscopic defects in plastic tubes, the fruits ripening, the best conditions for food handling, and the best cooking temperature conditions), food analysis (including creamery products, vegetables, meat, oils, lipids, and beverages), physics, chemistry (chemical structure determination, in both solution and solid form), and biology.
An example:
NMR microscopy of a fresh fruit (on the left) and of a frozen one (on the right). The effect of the magnetic field B0 on the orientation of the spin magnetic moments. Nuclear magnetic resonance (NMR) spectroscopy: basic principles and phenomena, and their applications to chemistry, biology and medicine, Ioannis P et al, Chem. Educ. Res. Pract. Eur. DOI: 10.1039/B2RP90018A. 2002.
In the field of medicine, various diseases such as obesity, types of cancers, cardiovascular diseases, and celiac disease have been studied using NMR.
The advantages of NMR
- No requirement for the raw samples to separate analytes
- Recycling samples after spectrometry
- High reproducibility of data
- High ability to identify unknown compounds
- Tracing metabolomic pathways
- Identification of compounds that are difficult to ionize or derivatize
- Identification of important cellular components
The most important stages of NMR
- Study design
- Sample collection/storage
- Sample preparation
- Spectral processing
- Data preprocessing
- And application of statistical analysis
The workflow below can better illustrate the steps of NMR.
History and principles
NMR was discovered after World War II and at the end of the 20th century, high-resolution NMR studies of liquid and solid compounds were used dramatically for a wide range of purposes, especially in chemistry. NMR is a physical phenomenon based on quantum mechanics. In fact, in the presence of a strong magnetic field, the energy of the nuclei of certain elements is split into two or more quantized levels due to the magnetic properties of these particles. Transitions between the resulting levels of magnetic energy can be achieved by absorbing electromagnetic radiation with an appropriate frequency. The difference in energy between the quantum magnetic levels of atomic nuclei lies between 0.1 and 100 MHz. NMR is widely used for quantitative analysis and qualitative identification of very complex organic and biological compounds. In the normal state, the energy difference between the nuclear spin levels is zero, but when the atoms are placed in the presence of a magnetic field, based on the Zeeman characteristic, the degeneracy state of the system decreases. With the disappearance of the field, the atom intensifies and exhibits radiations, which are called nuclear magnetic resonance.
NMR spectroscopy is based on measuring electromagnetic radiation in the radio frequency (RF) range of about 4 to 600 MHz. So that the nucleus to find the energy states required for absorption, it is necessary to place the sample in a strong magnetic field. The primary goal of using NMR spectroscopy is to determine and recognize the structure of molecules. The information required for this work is obtained through the measurement, analysis, and interpretation of NMR spectra with high resolution.
In nuclear magnetic resonance spectroscopy; in the absence of an external magnetic field, all magnetic nuclei have equal energy. When an external field is applied, aligned and misaligned orientations will correspond to different energies. The nucleus of some atoms has a nuclear spin. In the absence of a magnetic field, all the spin states of a nucleus have the same energy level, but in the presence of a magnetic field, the spin states will not be the same. Among the important nuclei that have spin, we can mention phosphorus 31, hydrogen 1, and carbon 13.
The phenomenon of nuclear magnetic resonance occurs when the nuclei absorb energy in the direction of the applied field B۰ and changes their spin direction relative to that field. This action is called resonance.
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