Projects / Programmes
A spectrometer for automatic 14N nuclear quadrupole resonance characterization of new substances
| Code |
Science |
Field |
Subfield |
| 7.00.00 |
Interdisciplinary research |
|
|
| Code |
Science |
Field |
| P180 |
Natural sciences and mathematics |
Metrology, physical instrumentation |
| Code |
Science |
Field |
| 1.03 |
Natural Sciences |
Physical sciences |
nuclear quadrupole resonance, nitrogen, pharmaceutical substances, polymorphism
Researchers (10)
Organisations (3)
Abstract
Nuclear quadrupole resonance (NQR) is a several decades old technique for the observation of energy level transitions in quadrupole nuclei, which is nowadays far less widespread compared to its sister method nuclear magnetic resonance, mainly due to a very broad spectrum of characteristic resonance frequencies. In this project we will attempt to solve this problem for the nucleus 14N and some other nuclei by developing a new NQR spectrometer with a working range up to 5 MHz. The advantage of this new spectrometer over the commercial and some non-commercial systems available today will be a fully automatic operation, in particular including the usually tedious and time consuming adaptation of hardware for different frequencies. The new spectrometer will primarily allow a much easier NQR characterization of new substances, compared to all current solutions. The spectrometer will also allow for a quick confirmation of selected, already NQR characterized substances in unknown samples under investigation.
There are two major problems involved in the development of such a spectrometer:
a huge dispersion of the characteristic frequencies, which for 14N span
from 0 – 5 MHz,
big differences of the NQR parameters, mainly those related to relaxation, among various substances.
The dispersion of frequencies is probably the main technical issue and prevents the acquisition of the whole spectrum in a »single step« as for example in NMR or many other spectroscopic techniques. The resonances have to be literally searched for, which is very time consuming. Another issue with this spread is hardware. The today available commercial NMR hardware, which is mainly used for NQR, cannot handle such a frequency range by default, so that significant manual modifications are required throughout the experiments.
The work in this project will be organized around the two problems in two parts. Part I (equipment) will involve the activities for the development and construction of the spectrometer, with the main emphasis on the Tx/Rx switch between probe, amplifier, and preamplifier with a broad (500 kHz – 5 MHz) working range. In the here proposed approach we will use several stepper motor controlled variable components to automatically adjust/tune the hardware to the required operating frequency, with special requirement of a low-noise implementation. The result should be a spectrometer with all modules, the newly developed and the previously developed, integrated in one case and controlled by a single program. Part II will be devoted to the development of efficient NQR detection pulse sequences and protocols for a time efficient inspection of an unknown sample.
The development of the new spectrometer will be targeted at the polymorphic analysis of solid pharmaceutical substances. It is well known that the NQR frequencies are very sensitive to the local environment, e.g. distribution of charge in the molecule, as well as on a more distant environment, the crystal structure. And polymorphs, although with the same molecular structure, have sufficiently different NQR frequencies to be easily separated. However, the new spectrometer will not be limited to the study of polymorphism, many solid phase changes are associated with a change in the NQR frequency as well and can be thus easily detected or studied. Also, the nucleus for the investigation is not necessary nitrogen, but any quadrupole nucleus with NQR frequencies below 5 MHz could be used as well. We here focus on nitrogen, because it is a very common element, but also unsuitable for high-resolution NMR, unlike most other quadrupole nuclei.
This type of spectrometer will significantly upgrade our NQR laboratory and allow for a shift of our focus towards material science. In addition, the results of this project will expand the product catalogue of the Jeklotehna-Teho company (co-financer), which was already involved in the development of a similar system for nuclear magnetic resonance.
Significance for science
The 14N NQR spectrometer for automatic characterization of new substances was being developed with two uses in mind: 1.) The applied use for the characterization of new substances, especially for pharmaceutical needs. 2.) To help the basic research on organic systems with 14N NQR spectroscopy. Although 14N NQR is an old spectroscopic technique, nowadays there are still many open questions. In the past, the 14N NQR research was mainly focused on the resonance frequency, where the typical questions were: How is the resonance frequency connected with the crystal structure, or how to calculate the frequency using various models and approximations. The reason for using only frequency was the experimental equipment (CW spectrometers), which allowed to easy determine the frequency but not other resonance parameters. Modern spectrometers (pulse spectrometers) allow to relatively easy determine also relaxation parameters and accurately determine intensity. Both type of parameters are related with the sample physical properties, and can therefore also aid the research if the relationships are well understood. There are two problems which seem particularly interesting and important: 1.) The relationship between resonance intensity and crystallite size? A typical 14N NQR sample is polycrystalline, where the size of the crystallites depends on the method of material preparation. Very often, the goal is to have a large sample surface, which is obtained by fine grinding the sample. But this can/will influence also the NQR parameters. Namely, the NQR resonance is a property of the ordered region, but a small crystallite has a large surface area, which is only partially ordered, as the nuclei luck their neighbors. Because of these, we expect that the resonance of the surface region will be very broad, and my not be observed. Therefore some intensity will be lost. For very fine powders, this effect may be so large to reduce the reliability of the measurement significantly. So far, the crystallite size where surface effects become important is not known yet, but certainly this will be an important topic in the future. 2.) So far, the relaxation parameters are almost never used for analysis. We expect, that these parameters will be also significantly affected by the size of the crystallites, but we do not yet know at what size these effects will become important A similar situation is true also when the sample is being exposed to pressure, and when some other techniques are used for sample preparation. In principle, the answers for the above questions, could be provided without the new spectrometer, but we foresee that many different samples and materials will be required to elucidate the behavior, every time finding the resonance frequency first. Our spectrometer for automatic characterization, will help us a lot, as the task of finding the frequency is now just a routine, and on top of that, much faster than before. Because of this, we will be able to spend much more time on the actual parameters under study and give us an important advantage over other competing groups.
Significance for the country
The 14N NQR spectrometer for automatic characterization o fnew substances is a standalone instrument, which does not need additional components for its operation. Because of this, it can be directly used as an analytical tool in various laboratories. We therefore foresee a huge marketing potential. The plan is to use this product as a basis for a new spin-off company which will first offer commercial 14N NQR analysis regionally, and later, sell the spectrometer worldwide. As a high-tech company, the planned added value will be high, which would be very beneficial for Slovenia and its further development. The product will be advertised on all important conferences in this field and thus promote Slovenia and its technological development.
Most important scientific results
Annual report
2011,
2012,
2013,
final report,
complete report on dLib.si
Most important socioeconomically and culturally relevant results
Annual report
2011,
2012,
2013,
final report,
complete report on dLib.si
