Nitrogen-14 Nuclear Quadrupole Resonance Research Articles

On the Observation of 14N Quadrupole Resonance Transitions in Water Proton NMR Relaxometry Dispersion Curves: The Case of a Labile NH Grouping in a Semirigid Molecular Moiety.

The electric field gradient tensor (considered here at the level of a nitrogen nucleus) can be described by two parameters: the largest element in the (X,Y,Z) principal axis system, denoted by VZZ (leading to the nuclear quadrupole coupling), and the asymmetry parameter η = (|VYY| - |VXX|)/|VZZ| with |VZZ| > |VYY| > |VXX|. The frequencies of the three nitrogen-14 nuclear quadrupole resonance (NQR) transitions depend on both parameters but, for sensitivity reasons, their determination may be especially difficult and time consuming. For a partly rigid NH grouping with a labile proton, water nuclear magnetic resonance (NMR) relaxometry curves may exhibit these three transitions (dubbed quadrupolar dips or quadrupole relaxation enhancement (QRE)), provided that the NH grouping belongs to a moiety possessing a sufficient degree of ordering. Their line shape leads to the correlation time describing mainly the motion of the NH grouping (the proton of which being in exchange with water protons), and their amplitude can be interpreted in terms of an effective NH distance. This approach is applied to a hydrogel, where separate NQR lines are observed for the different types of water existing in this system. Furthermore, the analysis of experimental data allows one to determine the nuclear quadrupole coupling in the protonated and deprotonated forms of this molecular moiety involving a labile NH grouping.

Toward nitrogen-14 nuclear quadrupole resonance imaging by nutation experiments performed with a radio-frequency field gradient

Until now, NQR imaging has been considered mainly in the case of Chlorine-35. This is a spin 3/2 resonating at relatively high frequency (around 30MHz) thus affording a favorable sensitivity. Conversely, Nitrogen-14 (spin 1) NQR is much less sensitive because its resonances frequencies are below 6MHz. In contrast to already existing methodologies for object localization by 14N NQR, we present here a new, more straightforward, approach and the principles of space dependent 14N Quadrupole Resonance are laid down. The method is based on nutation curves obtained with an inhomogeneous radio-frequency field produced by a dedicated transmit-receive coil. The gradient created that way does not need to be uniform although more accurate results would be obtained with a uniform gradient. Nutation curves have been simulated by a specially designed algorithm which takes into account the 14N Quadrupole Resonance particularities including the so-called powder average. Preliminary experiments were carried out with the highest resonance frequency (4.64MHz) of sodium nitrite (NaNO2). A cylindrical sample of powder sodium nitrite containing a spacer was used. Simulations of the corresponding nutation curves not only demonstrate the existence of this spacer but, in addition, provide its position and its thickness. This clearly ascertains the feasibility of 14N Quadrupole Resonance imaging.

Batch-specific discrimination using nuclear quadrupole resonance spectroscopy.

In this paper, we report on the identification of batches of analgesic paracetamol (acetaminophen) tablets using nitrogen-14 nuclear quadrupole resonance spectroscopy ((14)N NQR). The high sensitivity of NQR to the electron charge distribution surrounding the quadrupolar nucleus enables the unique characterization of the crystal structure of the material. Two hypothesis were tested on batches of the same brand: the within the same batch variability and the difference between batches that varied in terms of their batch number and expiry date. The multivariate analysis of variance (MANOVA) did not provide any within-batches variations, indicating the natural deviation of a medicine manufactured under the same conditions. Alternatively, the statistical analysis revealed a significant discrimination between the different batches of paracetamol tablets. Therefore, the NQR signal is an indicator of factors that influence the physical and chemical integrity of the material. Those factors might be the aging of the medicine, the manufacturing, or storage conditions. The results of this study illustrate the potential of NQR as promising technique in applications such as detection and authentication of counterfeit medicines.

Design and testing of a low impedance transceiver circuit for nitrogen-14 nuclear quadrupole resonance

A low impedance transceiver circuit consisting of a transmit–receive switch circuit, a class-D amplifier and a transimpedance amplifier (TIA) was newly designed and tested for a nitrogen-14 NQR. An NQR signal at 1.37MHz from imidazole was successfully observed with the dead time of ~85µs under the high Q transmission (Q~120) and reception (Q~140). The noise performance of the low impedance TIA with an NQR probe was comparable with a commercial low noise 50Ω amplifier (voltage input noise: 0.25 nV/Hz) which was also connected to the probe. The protection voltage for the pre-amplifier using the low impedance transceiver was ~10 times smaller than that for the pre-amplifier using a 50Ω conventional transceiver, which is suitable for NQR remote sensing applications.

Tautomeric transformations and reactivity of isoindole and sila-indole: A computational study

In this work, the tautomeric transformations and reactivity of isoindole and sila-isoindole molecules has been explored using the B3LYP/6-311G(d,p) level of theory in gas and solution phases. These calculations show that isoindole isomer has more stability rather than 1-h-isoindole. There is identical trend in silated species. The frontier molecular orbitals (FMO) and band gap energy calculations were performed at the B3LYP/6-311G(d,p) level in gas and various solvent. Solvent effects have been analyzed by using the self-consistent reaction field (SCRF) method based on polarizable continuum model (PCM) in chloroform, chlorobenzene, dichloromethane and tetrahydrofurane. Thermodynamic parameters calculated at room temperature have been analyzed. Also, electron affinities were computed. Local reactivity descriptors as Fukui functions [Formula: see text] local softness [Formula: see text] and electrophilicity indices [Formula: see text] analyses are performed to find out the reactive sites within molecule. Density functional theory (DFT) calculations were performed to compute nitrogen-14 nuclear quadrupole resonance (NQR) spectroscopy parameters.

The Detection of Concealed Targets Based on NQR of Nitrogen-14

Nuclear quadrupole resonance (NQR) is an advanced radio frequency (RF) spectroscopic technique, widely used to analyse substances containing quadrupole nuclei, such as2H,14N,17O,35Cl and39K. In this paper, we focus on the NQR detection of nitrogenous compounds including nucleus Nitrogen-14 or14N. We will briefly introduce its fundamental principles, namely, nuclear quadrupole moment and NQR detection mechanism, and then provide some experimental results based on these theories, such as sodium nitrite, methenamine, urea and thiourea. At last, according to these results, we will make some discussion about the properties of NQR detection.

Nitrogen-14 Nuclear Quadrupole Resonance Spectroscopy: A Promising Analytical Methodology for Medicines Authentication and Counterfeit Antimalarial Analysis

We report the detection and analysis of a suspected counterfeit sample of the antimalarial medicine Metakelfin through developing nitrogen-14 nuclear quadrupole resonance ((14)N NQR) spectroscopy at a quantitative level. The sensitivity of quadrupolar parameters to the solid-state chemical environment of the molecule enables development of a technique capable of discrimination between the same pharmaceutical preparations made by different manufacturers. The (14)N NQR signal returned by a tablet (or tablets) from a Metakelfin batch suspected to be counterfeit was compared with that acquired from a tablet(s) from a known-to-be-genuine batch from the same named manufacturer. Metakelfin contains two active pharmaceutical ingredients, sulfalene and pyrimethamine, and NQR analysis revealed spectral differences for the sulfalene component indicative of differences in the processing history of the two batches. Furthermore, the NQR analysis provided quantitative information that the suspected counterfeit tablets contained only 43 ± 3%, as much sulfalene as the genuine Metakelfin tablets. Conversely, conventional nondestructive analysis by Fourier transform (FT)-Raman and FT-near infrared (NIR) spectroscopies only achieved differentiation between batches but no ascription. High performance liquid chromatography (HPLC)-UV analysis of the suspect tablets revealed a sulfalene content of 42 ± 2% of the labeled claim. The degree of agreement shows the promise of NQR as a means of the nondestructive identification and content-indicating first-stage analysis of counterfeit pharmaceuticals.

Variable-pitch rectangular cross-section radiofrequency coils for the nitrogen-14 nuclear quadrupole resonance investigation of sealed medicines packets.

The performance of rectangular radio frequency (RF) coils capable of being used to detect nuclear quadrupole resonance (NQR) signals from blister packs of medicines has been compared. The performance of a fixed-pitch RF coil was compared with that from two variable-pitch coils, one based on a design in the literature and the other optimized to obtain the most homogeneous RF field over the whole volume of the coil. It has been shown from 14N NQR measurements with two medicines, the antibiotic ampicillin (as trihydrate) and the analgesic medicine Paracetamol, that the latter design gives NQR signal intensities almost independent of the distribution of the capsules or pills within the RF coil and is therefore more suitable for quantitative analysis.

Off-resonance effects and selectivity profiles in pulsed nitrogen-14 nuclear quadrupole resonance

In order to alleviate base-line distortions in nitrogen-14 NQR spectra originating from pulse breakthrough, low power radio-frequency (rf) pulses were applied. It is recalled that the required power is four times lower than that for an equivalent NMR experiment. This is easily explained by the fact that, in NMR, half the amplitude of the rf field is active. Moreover, the selectivity profile (i.e. the peak amplitude as a function of the difference between the carrier frequency and the resonance frequency) exhibits a shape which is, in most cases, more favorable in NQR than in NMR. An appropriate theory has been developed for explaining these experimental observations. It is concluded that low power NQR is perfectly feasible and should even be recommended for most applications, provided that the line-width of the NQR signal is not too large.

B24N24 nanocages: a GIAO density functional theory study of 14N and 11B nuclear magnetic shielding and electric field gradient tensors

AbstractDensity functional theory (DFT) calculations were performed to determine boron-11 and nitrogen-14 nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) spectroscopy parameters in the three most stable B 24 N 24 fullerenes for the first time. The considered samples were first allowed to relax entirely, and then the NMR and NQR calculations were performed on the geometrically optimized models. The calculations of the 11 B and 14 N nuclear magnetic shielding tensors and electric field gradient tensors employed the Gaussian 98 software implementation of the gauge-including atomic orbital (GIAO) method using the Becke3, Lee-Yang-Parr (B3LYP) DFT level and 6-311G** and 6-311++G** standard basis sets in each of the three optimized forms, and converted the results to experimentally measurable NMR parameters.The calculated NMR chemical shieldings of the three cages show significant differences, providing a way to identify these clusters. The evaluated NQR parameters of the 11 B and 14 N nuclei in the clusters are also reported and discussed.Graphical abstract[IMAGE]

Optimised NQR pulse technique for the effective detection of Heroin Base

The nuclear quadrupole resonance (NQR) method has been applied to Heroin Base (HB) to find an optimised multi-pulse technique for effective detection of HB. Experimental results of applying the proposed spin-locking multi-pulse (SLMP) technique to nitrogen-14 NQR in this sample are presented and convincingly demonstrate as a path towards efficient detection. A detection using a sequence of this character could be achieved over real-world scan volumes for screening of goods. All experiments were carried out at room temperature.

Density functional calculations of 14N and 11B NQR parameters in the H-capped (6,0) and (4,4) single-walled BN nanotubes

Density functional theory (DFT) calculations were performed to calculate nitrogen-14 and boron-11 nuclear quadrupole resonance (NQR) spectroscopy parameters in the representative considered models of zigzag and armchair boron nitride nanotubes (BNNTs) for the first time. The considered models consisting of 1 nm length of H-capped (6,0) and (4,4) single-walled BNNT were first allowed to fully relax and then the NQR calculations were performed on the geometrically optimized models. The evaluated nuclear quadrupole coupling constants and asymmetry parameters for the mentioned nuclei reveal that the considered models can be divided into four layers of nuclei with an equivalent electrostatic environment where those nuclei at the ends of tubes have a very strong electrostatic environment compared to the other nuclei along the length of tubes. Those nuclei at the center of the tube length also have an equivalent electrostatic environment. The calculations were performed based on the B3LYP DFT method and 6-311G** and 6-311++G** standard basis sets using the Gaussian 98 package of program.

Nitrogen-14 nuclear quadrupole resonance (NQR): Dramatic sensitivity enhancement by large and fast temperature lowering

We have observed that, when going rapidly from ambient temperature down to liquid nitrogen temperature, the nitrogen-14 NQR signal (for transitions involving the m = 0 spin state, nitrogen-14 being a quadrupolar nucleus of spin I = 1) is increased by a factor of ca. 10 2. While Boltzmann statistics cannot explain this enhancement, the strong temperature dependence of the quadrupolar interaction is very likely to be at the origin of this phenomenon. Indeed, the quadrupolar Hamiltonian becomes time dependent and is prone to induce transitions toward the spin state associated with m = 0. Its binding and slow relaxing properties result in a durable increased population and consequently in an increased intensity of NQR lines originating from the state m = 0.

Modified multipulse technique for the effective detection of pure nuclear quadrupole resonance

Modification of the steady-state free precession (SSFP) multipulse technique for the effective detection of nuclear quadrupole resonance (NQR) signals was studied. This modification is based on the use of the preparatory pulse in the SSFP pulse sequences. It was shown that under certain conditions the total intensity of accumulated NQR signal can be increased. Experimental results of applying the proposed technique to nitrogen-14 NQR in the sample of sodium nitrite (NaNO2) are presented and convincingly demonstrate the technique’s effectiveness.

Modified steady-state free precession pulse sequences for the detection of pure nuclear quadrupole resonance

Modifications of the steady-state free precession multi-pulse technique for the effective detection of the nuclear quadrupole resonance (NQR) signals are proposed. These modifications are based on the use of composite pulses and enable the suppression of the coherent noise signals such as the magneto-acoustic and piezo-electric signals or the ringing signal from the NQR probe. Experimental results of applying the proposed technique to nitrogen-14 NQR in the sample of C 6H 12N 4 are also presented and convincingly demonstrate its effectiveness.

Modifications of the steady-state free-precession sequence for the detection of pure nuclear quadrupole resonance

Modifications of the steady-state free-precession (SSFP) sequence are proposed for the effective detection of pure nuclear quadrupole resonance (NQR). These modifications enable the suppression of the effect of intensity anomalies observed under steady-state conditions. The steady-state signals in SSFP-type sequences strongly depend on the frequency offset from resonance and the pulse spacing. This dependence has some peculiarities which were taken into consideration. Experimental results of modified SSFP sequence applications are reported for nitrogen-14 NQR in a plastic explosive.

A novel probe design for pulsed nitrogen-14 nuclear quadrupole resonance spectrometer

A fast recovery probe circuit, which involves an active damping unit, is proposed in this paper. Because of its simplicity and high efficiency in converting radio-frequency power into an oscillating magnetic field, the suggested probe configuration is suitable for operation at low frequency (below 10 MHz), such as 14N nuclear quadrupole resonance where the ringing of a conventional probe usually lasts quite long.

Radiation Response of Hydrated Urea Evaluated Using 14N Nuclear Quadrupole Resonance

In this paper Nitrogen-14 nuclear quadrupole resonance is utilized to detect radiation-induced changes in urea over the 0- to 300-Gy dose range. The spin-spin relaxation time exhibits a consistent change as a function of delivered dose in hydrated urea under exposure to [sup 60]Co gamma radiation. No changes to the spin-spin relaxation time are observed in urea samples that were not hydrated. The radiation-induced changes are attributed to indirect radiation interactions with the water surrounding the urea molecules and are explained by the formation of subtle changes in the electron bonding configurations surrounding the [sup 14]N nuclei, not major structural rearrangements. These subtle changes may provide additional insight into the effects of ionizing radiation on biological systems.

Nitrogen-14 nuclear quadrupole resonance study of bonding in transition-metal cyanides

Nitrogen-14 n.q.r. frequencies were measured for K4[Mo(CN)8]·2H2O, K3[Fe(CN)6], K4[Fe(CN)6]·3H2O, Ba2[Fe(CN)6]·3H2O, K4[Ru(CN)6]·3H2O, K2[Ni(CN)4], Na2[Ni(CN)4], K2[Pd(CN)4], Na2[Pd(CN)4], K[Ag(CN)2], and K[Au(CN)2] at 77 K. Two sets of cyanides with different σ- but equal π-orbital populations were found in K4[Mo(CN)8]·2H2O. Changing from Mn to Co in hexacyanides produced an increase in back bonding and a decrease in σ bonding. In the nickel to platinum group cyanides no back bonding was found and the changes in the principal quantum number produced variations only in the nitrogen σ population. In the zinc to mercury group cyanides almost no change was found with variation of the principal quantum number in either σ or π populations. In dicyanides of Hg, Ag, and Au, back bonding increased in that order. It was found also that the variations in the metal charge caused important modifications in the population of the σ and π orbitals of the –CN group.

Glassy Crystals VI. Nitrogen-14 Quadrupole Resonance in Glassy Crystalline Thiazole

Crystalline thiazole has been studied by nitrogen-14 nuclear quadrupole resonance in the 77 - 206 K temperature interval that contains a glass transition at 174 K. The temperature dependences of the relaxation time T1 , of the frequencies and the amplitudes of the NQR signals have been determined for lines ν+ and ν-. No crystal-crystal phase transition has been observed, so that the glass transition at T'g can be observed on heating and on cooling. The T1 measurements have shown the existence of a large-amplitude motion which is different from that which is “frozen” at T'g: it corresponds to a secondary relaxation process which is still active in the glassy crystalline phase. Further studies will attempt to assign it to a definite molecular motion.