Nuclear Quadrupole Resonance Parameters Research Articles

The 1H [formula omitted] dispersion curve of fentanyl citrate to identify NQR parameters

We report the 1H T1 dispersion curve between 0 and 5 ​MHz for the synthetic opioid fentanyl citrate (C28H36N2O8). The structures in the curve can be used to estimate the 14N nuclear quadrupole resonance (NQR) frequencies of the material. Density functional theory predictions of the NQR parameters of several fentanyl citrate compounds are also reported. The predictions for the aniline nitrogen are consistent with structures in the observed T1 data. To help interpret the fentanyl citrate results the T1 dispersion curve for the explosive ammonium nitrate is also presented.

First-Order Metal–Semiconductor Transition Triggered by Rattling Transition in Tetrahedrite Cu12Sb4S13: Cu-Nuclear Magnetic Resonance Studies

Tetrahedrite Cu12Sb4S13 shows a metal–semiconductor transition (MST) at TMST = 85 K. We have studied the mechanism of the MST by measurements of Cu-NMR. Above TMST, the Cu-NMR spectrum consists of signals from a tetrahedral Cu(1) 12d site and a trigonally coordinated Cu(2) 12e site. Analyses of the spectra at 95 and 20 K yield NMR and nuclear quadrupole resonance (NQR) parameters above and below TMST. The Cu(1) signal does not show clear quadrupole splitting, which remains unchanged on cooling across TMST. On the other hand, the Cu(2) signal at T > TMST clearly shows the quadrupole splitting characterized by a quadrupole frequency νQ(2) ≈ 18.6 MHz and an asymmetry parameter η(2) ≈ 0.03. Below TMST, the values of νQ(2) and η(2) change markedly. Such marked changes in NQR parameters provide evidence of a remarkable change in the local electronic structure around the Cu(2) site. Together with νQ from NMR spectra and that from first-principles calculation, we conclude that the Cu(2) atoms are displaced from the sulfur triangles below TMST. We also found that the NMR Knight shift and the spin–lattice relaxation rate divided by temperature, 1/T1T, for the Cu(1) signal markedly change below TMST, which is ascribable to the reduction in the electronic density of states at the Fermi level. We further discuss the relationship among the MST, structural transformation, and crystal structure below TMST.

Assessment of substituent effects on the parameters of 35Cl nuclear quadrupole resonance in para‐substituted benzene‐sulphenyl chloride via quantum chemical calculations

In this research, substituent effects on the parameters of 35Cl nuclear quadrupole resonance (NQR) in para‐substituted benzene‐sulphenyl chloride were studied at M062X/6‐311G(d,p) theory level. The 35Cl NQR parameters of the quadrupole coupling constant (QCC) and electric‐field gradient (EFG) tensor, as well as an asymmetric parameter, were shown to be correlated with Hammett constant following their calculations. The frontier orbital energy levels, HOMO‐LUMO gaps, hardness, electrophilicity, and chemical potential values of these molecules were calculated as well. natural bond orbital (NBO) analysis was applied for calculating natural populations at chlorine atoms.

Predicting quadrupole relaxation enhancement peaks in proton R1-NMRD profiles in solid Bi-aryl compounds from NQR parameters

ABSTRACTWe propose a simple method to calculate and predict quadrupole relaxation enhancement (QRE) features in the spin-lattice nuclear magnetic relaxation dispersion (-NMRD) profile of protons (1H) in solids. The only requirement is the knowledge of the nuclear quadrupole resonance (NQR) parameters of the quadrupole nuclei in a molecule. These NQR parameters – the quadrupole coupling constant and the asymmetry parameter η – can be determined by NQR spectroscopy or using quantum chemistry calculations. As there is an increasing interest in using molecules producing high field QRE features as, e.g. for contrast enhancing agents in magnetic resonance imaging, the experimental efforts of seeking for suitable compounds can be reduced by pre-selecting molecules via calculations. Also, the method can be used to extract NQR parameter, and thus structural information, from -NMRD profiles showing QRE features. In this article, we describe the calculation procedure and present examples of comparing the result to experimental -NMRD data of two different solid 209Bi-aryl compounds.

Design of a Novel Series of Donor-Acceptor Frameworks via Superalkali-Superhalogen Assemblage to Improve the Nonlinear Optical Responses.

Presently, many researches are directed toward the design of novel superatoms with high nonlinear optical responses. Inspired by a fascinating finding of superatoms which were designed by bonding superhalogen (Al13 nanocluster) with superalkalis (M3O, M = Na and K), we suggest an effective strategy to form a series of typical donor-acceptor frameworks with high nonlinear optical responses via bonding the superalkalis M3O (Li3O, Na3O, K3O, Li2NaO, Li2KO, Na2LiO, Na2KO, K2LiO, K2NaO, and LiNaKO) with low ionization potential to the superhalogen Al13 with large electron affinity. The ionization potential, electronic spatial extent, electric field gradient tensors of 17O nuclei, and natural bond orbital charge values of the superalkalis M3O were also calculated. We found that the M ligands have the remarkable effect on the ionization potential as well as 17O nuclear quadrupole resonance parameters of the superalkalis M3O. Our results also represented that the bonding superalkalis can efficiently narrow wide HOMO-LUMO gap and considerably enhance first hyperpolarizability of the pristine Al13, due to electron transfer in this type of superatom. Also, the effect of oriented external electric fields on the nonlinear optical responses of the superatoms M3O-Al13 has been systematically explored. We found that the first hyperpolarizability of the superatom compounds can be gradually increased by increasing the imposed oriented external electric field from zero to the critical external electric field along the charge transfer direction (M3O → Al13). In this respect, this work reveals an effective approach to gradually enhance the nonlinear optical responses of the superatoms through applying oriented external electric fields.

Single ferromagnetic fluctuations in UCoGe revealed by Ge73 - and Co59 -NMR studies

$^{73}$Ge and $^{59}$Co nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements have been performed on a $^{73}$Ge-enriched single-crystalline sample of the ferromagnetic superconductor UCoGe in the paramagnetic state. The $^{73}$Ge NQR parameters deduced from NQR and NMR are close to those of another isostructural ferromagnetic superconductor URhGe. The Knight shifts of the Ge and Co sites are well scaled to each other when the magnetic field is parallel to the $b$ or $c$ axis. The hyperfine coupling constants of Ge are estimated to be close to those of Co. The large difference of spin susceptibilities between the $a$ and $b$ axes could lead to the different response of the superconductivity and ferromagnetism with the field parallel to these directions. The temperature dependence of the nuclear spin-lattice relaxation rates $1/T_1$ at the two sites is similar to each other above 5 K. These results indicate that the itinerant U-$5f$ electrons are responsible for the ferromagnetism in this compound, consistent with previous studies. The similarities and differences in the three ferromagnetic superconductors are discussed.

Theoretical investigation of NMR–NQR tensors of hallucinogenic harmine in monomeric and cluster states

In the present study, density functional theory was employed to analyze the structure and nuclear magnetic resonance (NMR) — nuclear quadrupole resonance (NQR) spectra of hallucinogenic harmine in monomeric, dimeric, trimeric, and tetrameric states in the gas phase. Furthermore, the effects of hydrogen and resonance interactions on the values of NMR and NQR parameters of nitrogen nuclei in the four states mentioned above were investigated. The computations at the B3LYP/6-311[Formula: see text]G** level of theory indicated that NQR — NMR parameters of nitrogen nuclei varied for each of the four states and were strongly affected by chemical environment, molecular cluster size and molecular interactions. Accordingly, by increasing the participation of lone pair electrons in resonance interactions and aromaticity development, the values of NMR chemical shielding around them increased, whereas their NQR parameters ([Formula: see text] and [Formula: see text] decreased. In contrast, it could be observed that resonance interaction was not the only effective factor influencing changes in values and trends of NMR — NQR parameters by passing from monomeric state to other ones. Moreover, the negative charge on nitrogen atoms and the possibility of hydrogen bond formation were other important factors influencing NMR — NQR parameters.

Detection of extremely weak NQR signals using stochastic resonance and neural network theories

Nuclear Quadrupole Resonance (NQR) signal detection is widely used for searching related substances of interest, such as explosives, petroleum, drugs, etc. NQR responses from these substances are usually very weak compared to background noise. Moreover, in some applications such as landmine detection, NQR responses decay with time quickly, and the required scanning times are usually prohibitively long. This paper presents a novel approach which can detect NQR signals of very low SNRs in such scenarios, by combining a stochastic resonance framework and neural network theory. Firstly, the approach relies on the design of a stochastic resonance (SR) system which can transform the original data into a nonlinear waveform with special SR features. Secondly, a (feedforward) robust neural network is trained to discern this nonlinear waveform accurately, in order to identify the NQR signal. Our results demonstrate that the neural network approach outer-performs traditional signal processing detection and estimation methods. Moreover, this stochastic resonance neural network approach (SRNN) can be designed to detect a variety of NQR signals which have similar NQR parameters. The SRNN approach can also be effective in cases where both noise and radio frequency interference are strong relative to the NQR response.

Nuclear magnetic and nuclear quadrupole resonance parameters of β-carboline derivatives calculated using density functional theory

A density functional theory (DFT) calculations using B3LYP/6-311++G(d,p) method were carried out to investigate the relative stability of the molecules of β-carboline derivatives such as harmaline, harmine, harmalol, harmane and norharmane. Calculated nuclear quadrupole resonance (NQR) parameters were used to determine the 14N nuclear quadrupole coupling constant χ, asymmetry parameter η and EFG tensor (q zz ). For better understanding of the electronic structure of β-carboline derivatives, natural bond orbital (NBO) analysis, isotropic and anisotropic NMR chemical shieldings were calculated for 14N nuclei using GIAO method for the optimized structures. The NBO analysis shows that pyrrole ring nitrogen (N9) atom has greater tendency than pyridine ring nitrogen (N2) atom to participate in resonance interactions and aromaticity development in the all of these structures. The NMR and NQR parameters were studied in order to find the correlations between electronic structure and the structural stability of the studied molecules.

Theoretical study addressing the effects of tautomerism and explicit/implicit water molecules on NQR and NMR parameters of tetrazole-5-thione.

DFT/B3LYP calculations were employed to study the effects of tautomerism and explicit/implicit water molecules on Nuclear Quadrupole Resonance (NQR) and Nuclear Magnetic Resonance (NMR) tensors of nitrogen nuclei in tetrazole-5-thione structure. The obtained results revealed that nuclear quadrupole coupling constant (χ) and isotropic chemical shielding (σiso ) values of nitrogen nuclei in tetrazole ring of five possible tautomeric forms of tetrazole-5-thione, i.e. two thione forms called tautomers A and E and three thiol forms called tautomers B, C, and D, were functions of resonance energy(E2 ) values of nitrogen lone pairs. Furthermore, it was observed that by increasing participation of lone pairs of nitrogen atoms in the ring resonance interactions, the σiso values around them were increased, while their χ and qzz values were decreased. However, the results indicated that with exception of tautomer B, the order of qzz and χ values of nitrogen nuclei in tetrazole ring was exactly opposite of the order of resonance energy values for the same nitrogen nuclei in all tautomers and their mono-hydrated complexes. In addition, a significant decrease was noticed in χ and qzz values when a water molecule was put in different positions near the tetrazole ring in tautomers A-E. The mentioned result can be attributed to hydrogen bond formation between nitrogen nuclei and the oxygen of water. In mono-hydrated complexes, the σiso values around nitrogen atoms acting as hydrogen donors in hydrogen bond formation (N-H….OH2 ) were decreased, while its values were increased for nitrogen atoms acting as hydrogen acceptors in hydrogen bond formation(N….H-OH). Copyright © 2016 John Wiley & Sons, Ltd.

DFT Studies of NH-Cl Hydrogen Bond of Amino Acid Hydrochloride Salts in Ion Channels.

Quantum chemical calculations were made, to study NH-Cl hydrogen bonds of two amino acid hydrochloride salts called alanine and threonine. The Nuclear Magnetic Resonance and Nuclear Quadrupole Resonance parameters for nitrogen and chlorine were calculated via four functionals such as, B3LYP, M062X, M06L, and CAM-B3LYP and by applying the 6-311++G(d,p) basis set. One of the functionals produced more accurate results. Geometry optimization was performed using the M062X/6-31++G(d,p) method, and Natural Bond Orbitals analysis was performed by applying the M062X/6-311++G(d,p) level. This study examined Nuclear Magnetic Resonance and Nuclear Quadrupole Resonance parameters with changes in structure from monomer to pentamer and investigated correlations between Natural Bond Orbitals parameters and Nuclear Magnetic Resonance or Nuclear Quadrupole Resonance parameters. The Natural Bond Orbitals parameters were used to investigate changes in structural parameters along with crystal development.

Analysis of 27Al- and 93Nb-NMR spectra of PrNb2Al20 single crystal

We report the results of 27Al- and 93Nb- nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements in PrNb2Al20 single crystals. The field angle dependence of the observed 93Nb-NMR lines for the single crystal at around 5 T and at 50 K is reproduced by a simulation using previously reported NQR parameters νQ,Nb ≈ 1.82 MHz and ηNb ≈ 0, while 27Al-NMR lines were not reproduce by the previously reported NQR parameters νQ,Al(3) ≈ 1.53 MHz and ηAl(3) ≈ 0.17. By reexamining and reconsidering the NMR and NQR lines for powder samples, we obtained a correct NQR parameters for Al(3) site to be νQ,Al(3),new ≈ 1 MHz and ηAl(3),new ≈ 0.4.

Interaction between F2 gas with the pristine and 3C-doped(4, 4) armchair boron phosphide nanotubes: a DFT study

In this research, the structure, quantum and NQR (Nuclear quadrupole resonance)parameters of F2 gas adsorption on the pristine and 3C-doped (4,4) armchair models of boron phosphide nanotubes (BPNTs) have been investigated in the framework of density functional theory. For this purpose, at the first step, four models for F2 adsorption on the inner and outer surfaces of pristine and 3Cdoped BPNTS are considered and then all structures are optimized by using Gaussian 03 program package. The optimized structures are used to calculate the quantum and NQR parameters. The calculated results reveal that the adsorption energy of pristine and 3Cdoped models of BPNTs are exothermic and adsorption process is a physisorption process due to the weak Van der Waals interaction. The substitution of three carbons with three B atoms of nanotube decreases significantly the adsorption energies. The F2 adsorption and 3C-doping decrease the band gap, global hardness, and ionization potential of the pristine BPNTs. The calculated NQR parameters of all the models show that CQ and ηQ values of the first layer are larger than those of the other layers.

93Nb- and 27Al-NMR/NQR studies of the praseodymium based PrNb2Al20

We report a study of 93Nb- and 27Al-nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) in a praseodymium based compound PrNb2Al20. The observed NMR line at around 3 T and 30 K shows a superposition of typical powder patterns of one Nb signal and at least two Al signals. 93Nb-NMR line could be reproduced by using the previously reported NQR frequency νQ ≊ 1.8MHz and asymmetry parameter η ≊ 0 [Kubo T et al 2014 JPS Conf. Proc. 3 012031]. From 27Al-NMR/NQR, NQR parameters are obtained to be νQ,A ≊ 1.53 MHz, and ηA ≊ 0.20 for the site A, and νQ,B ≊ 2.28 MHz, and ηB ≊ 0.17 for the site B. By comparing this result with the previous 27Al-NMR study of PrT2Al20 (T = Ti, V) [Tokunaga Y et al 2013 Phys. Rev. B 88 085124], these two Al site are assigned to the two of three crystallographycally inequivalent Al sites.

Ab initio study of two quinoline derivatives as corrosion inhibitor in acidic media: electronic structure, inhibitor–metal interaction, and nuclear quadrupole resonance parameters

Density functional theory B3LYP and Hartree–Fock methods with 6-311++G** basis set were utilized to study the relationship between electronic structure and corrosion inhibition efficiencies of protonated and non-protonated forms of 3-formyl 8-hydroxy quinoline and 5-naphthylazo-8-hydroxyquinoline (5NA8HQ) in acidic media in gas and solvent phase. Quantum chemical parameters including highest molecular orbital energy, lowest unoccupied molecular orbital energy, energy gap (ΔE g), the fraction of electrons transferred (ΔN), and energy change during charge transfer (ΔE) were calculated. Protonation energy calculations showed that the favorite protonation site of 5NA8HQ is the N12 position, which is confirmed by the result of previously reported experimental investigations. Calculations on the inhibitor/iron system were performed using the B3LYP/6-311++G** method and found that azo nitrogens of 5NA8HQ have better interaction with iron. Also, nuclear quadrupole resonance parameters indicate that azo nitrogens (N11 and N12) are the best sites for interaction with iron.

A computational exploration into isomorphously substituted effects on hydrogen electric field gradient and chemical shielding tensors in the H‐ZSM‐5 zeolite

ABSTRACTDensity functional theory calculations have been performed at the B3LYP/6‐31++G** level to investigate the effect of the isomorphously substituted ZSM‐5 zeolite with trivalent elements B, Al, and Ga on the hydrogen atom of the Brönsted acid site via nuclear quadrupole resonance (NQR) and nuclear magnetic resonance (NMR) parameters. ZSM‐5 clusters were modeled as ((H)3SiO)3–Si–O(H)–M–(OSi(H)3)3 (M = B, Al, and Ga). Variations of isotropic chemical shifts, δiso, of 1H atom in the Brönsted acid site as well as quadrupole coupling constant, CQ, and asymmetry parameter, ηQ, of 2H atom in the Brönsted acid site are well correlated with the trend in acidic strength of isomorphously substituted H‐ZSM‐5, estimated from the experimental results: B‐ZSM‐5 < Ga‐ZSM‐5 < Al‐ZSM‐5. The CQ value of 2H atom in the Brönsted acid site decreases in the order: B‐ZSM‐5, Ga‐ZSM‐5, Al‐ZSM‐5, respectively; eventually, their ηQ values of 2H atom in the Brönsted acid site increase concluding models with high CQ have a lower Brönsted acidity than those with low CQ. In addition, the calculated chemical shifts of the Brönsted proton increase in the sequence: B‐ZSM‐5 < Ga‐ZSM‐5 < Al‐ZSM‐5. All the results show a high consistency among NQR and NMR parameters and relative acidity of the isomorphously substituted ZSM‐5 zeolite. © 2014 Curtin University of Technology and John Wiley & Sons, Ltd.

Theoretical study of substituents effects on characteristics of resonance-assisted hydrogen bond in (Z)-(thionitrosomethylene)hydrazine and its derivatives in ground and electronic excited state

The molecular geometry, intramolecular hydrogen bond strength, vibrational frequencies, 1H NMR chemical shift, and nuclear quadrupole resonance parameters of 14N, 35S and 2H atoms and several well-established indices of aromaticity in (Z)-(thionitrosomethylene)hydrazine molecule and its derivatives were studied by density functional theory method. The results of calculations were obtained at B3LYP/6-311++G** level of approximation on model species, with the resonance-assisted hydrogen bonds. A set of simple and mostly common substituents having different properties in resonance effect according to values of substituents constants were chosen to simulate the influence of substitution in R position of title molecule on the quasi-delocalization and H-bonding. The following substituents have been taken into consideration: F, Cl, NO2, OCH3, OCF3, SCH3, SH, and OH. The excited-state properties of intramolecular hydrogen bonding in substituted systems have been investigated theoretically using the time-dependent density functional theory method. Also, the possible charge transfer and the topological properties of investigated molecule and its derivatives were studied by means of natural bond orbital and atoms in molecules (AIM) theory. The energy of the N–H···S interactions studied here was found medium in strength ( $$ E_{\text{HB}}^{*} $$ = −36.5 to −45.3 kJ mol−1). The electron density (ρ), Laplacian (∇2 ρ) properties and the total electron energy density (HC), estimated by AIM calculations, indicate that H···S bond possesses low ρ, positive ∇2 ρ and HC < 0 which are in agreement with partially covalent character of HB.

Investigation of the electronic structure and the structural stability of selected penicillins by density functional calculations of 14N nuclear quadrupole resonance parameters

A computational study was carried out by density functional theory (DFT) to investigate the relative stability and reactivity in three selected penicillins: penicillin-G, penicillin-V and carbenicillin. The geometry of the investigated molecules was optimized at the B3LYP/6-31G(d) level of theory. Then, the nuclear quadrupole resonance (NQR) parameters of 14N and 2H nuclei and natural bond orbital (NBO) analysis in these molecules were calculated on the geometrically optimized models at the B3LYP level using 6-311++G(d,p) basis sets in the gas phase. The NBO analysis shows that the occupancy of the LP(N) decreases with increasing p character of the lone pair of nitrogen. A comparison between the results obtained for these penicillins and related 6-APA structures of them indicates that the presence of a bulky side group in the acyl side chain can lead to more stability of the β-lactam ring. On the other hand, NBO analysis was applied to rationalize the 14N NQR parameters in the charge distribution around nitrogen atoms. Inspection of the present results illustrates that the largest component of EFG tensor (q zz ), the nuclear quadrupole coupling constant, C Q, and the NQR frequency values of nitrogens decrease with decreasing occupancy values of LP(N). We suggest that the reason for this trend can be found in increasing contribution of delocalized electrons of nitrogen in the intramolecular interactions and hence stability of these structures increases in the order: PG < PV < CA. Finally, a good relationship is found between most of the calculated 2H NQR parameters and the related intramolecular hydrogen bonds.

A DFT Computation for Comparison of NQR of O&lt;sub&gt;2&lt;/sub&gt;, N&lt;sub&gt;2&lt;/sub&gt; and CO over the Surface of Single-Walled Carbon Nanotubes

In this study we assumed Single-Walled Carbon Nano Tubes (SWCNTs) as ideal candidates for various applications of gas sensors due to their amazing physical adsorption properties. The adsorption behavior of selected nitrogen, oxygen and CO molecules on the surface of the Single-Walled Carbon Nano Tubes (SWCNTs) was studied by the Density Functional Theory (DFT) (B3LYP/6-311G*) using the Gaussian 98 software. We studied the Nuclear Quadrupole Resonance (NQR) of the armchair (4, 4) SWCNTs with the optimal diameter of 5.6 Å and the length of 9.8 Å. For the first time, DFT calculations were performed to calculate oxygen and nitrogen the interaction of quadrupole moment with Electric Field Gradient (EFG) in NQR in the representative considered model of the (N2-CNTs), (O2-CNTs) and (CO-CNTs). The evaluated NQR parameters reveal that the EFG tensors of Oxygen-17, Nitrogen-14 and Carbon-13 are influenced and show particular trends from gas molecules in the SWCNTs due to the contribution of N-N, O-O and C-O gas molecules of SWCNTs.

Influence of Carbon-Doping by Boron/Nitrogen Substitution in Boron Nitride Nanotube, a Density Functional Theory Study of Nuclear Quadrupole Resonance Parameters

Influence of Carbon-Doping by Boron/Nitrogen Substitution in Boron Nitride Nanotube, a Density Functional Theory Study of Nuclear Quadrupole Resonance Parameters