Language
Country/Area
No result found
hy is NQR called "zero-field nuclear magnetic resonance"? Explore its uniqueness
Nuclear quadrupole resonance spectroscopy (NQR) is a chemical analysis technique related to nuclear magnetic resonance (NMR). Unlike NMR, the nuclear transitions of NQR can be detected without a magnetic field, so NQR spectroscopy is called "zero-field NMR." This characteristic gives NQR unparalleled advantages when analyzing solid materials.
The NQR resonance is mediated through the interaction of the electric field gradient (EFG) with the quadrupole moment of the nuclear charge distribution.
NQR works on the basis that any nucleus with more than one unpaired nuclear particle (such as a proton or neutron) will have an uneven charge distribution, resulting in the generation of its quadrupole moment. When the density of the electron cloud present around the nucleus is not uniform, the supplied electric field gradient causes the energy level of the nucleus to change unequally. This allows the nucleus to absorb a certain amount of energy under RF (radio frequency) electromagnetic radiation, which is very similar to NMR but different in that the absorption of NQR occurs in an environment without an external magnetic field.
In NQR, many transition frequencies are strongly dependent on temperature, making it a tool for studying phase changes in solid matter.
NQR technology can sensitively detect the interaction between the nuclear quadrupole moment and the electric field gradient around the nucleus, which makes NQR important for analyzing the bonding, structural characteristics, phase changes and molecular dynamics of solid compounds.
Application scope of NQR
NQR is particularly prominent in pharmaceutical science, and in particular the application of 14N-NQR enables the differentiation of enantiomeric compounds from drugs that appear similar in appearance. For example, in the study of D-serine and L-serine, although the two compounds have similar compositions, they have different properties.
D-serine is considered a potential biomarker for Alzheimer's disease, while L-serine is currently in FDA-approved human clinical trials.
In addition, NQR can also distinguish crystal heterogeneity, which is crucial for identifying the authenticity of drugs. For example, drugs containing sulfonamides often occur in polymorphic forms, and differences in NQR frequencies and associated quadrupole coupling constants and asymmetry parameters make this identification feasible.
Technical challenges and limitations
Although NQR has significant advantages, its technical challenges cannot be ignored. NQR requires the sample to be of sufficient size since the signal intensity is usually very low. In addition, the low isotope abundance of NQR active cores makes it more difficult to obtain effective signals experimentally.
In the technical context of NQR, the requirements for measured frequency and sample size limit the popularity of this technology.
Similar to traditional NMR technology, NQR can also be used to measure the water/gas/oil mixture in oil wells in real time, helping to calculate the well's remaining capacity and optimize the extraction process.
Finally, the zero-field characteristics of NQR open up several possible future directions for its application, including the detection of explosives. Although devices claiming to be able to use NQR to detect explosives have appeared in the past, real scientific progress is still progressing steadily.
In summary, NQR is not just a chemical analysis tool, but an in-depth study of the interaction between the nucleus and its environment. With the advancement of technology, NQR may show its unique potential and applications in more fields in the future. What new possibilities will such development bring?
