Spin-lattice Relaxation Time T1 Research Articles

Detrimental Increase of Spin-Phonon Coupling in Molecular Qubits on Substrates.

Molecular qubits are a promising platform for quantum information systems. Although single molecule and ensemble studies have assessed the performance of S = 1/2 molecules, it is understood that to function in devices, regular arrays of addressable qubits supported by a substrate are needed. The substrate imposes mechanical and electronic boundary conditions on the molecule; however, the impact of these effects on spin-lattice relaxation times is not well understood. Here we perform electronic structure calculations to assess the effects of a graphene (Cgr) substrate on the molecular qubit copper phthalocyanine (CuPc). We use a progressive Hessian approach to efficiently calculate and separate the substrate contributions. We also use a simple thermal model to predict the impact of these changes on the spin-phonon coupling from 0 to 200 K. Further analysis of the individual vibrational modes with and without Cgr shows that an overall increase in SPC between the vibrations modes of CuPc with the surface reduces the spin-lattice relaxation time T1. We explain these changes by examining how the substrate lifts symmetries of CuPc in the absorbed configuration. Our work shows that a surface can have a large unintentional impact on SPC and that ways to reduce this coupling need to be found to fully exploit arrays of molecular qubits in device architectures.

Understanding Ion Dynamics in Closoborate-Type Lithium-Ion Conductors on Different Time-Scales.

The lithium-ion transport mechanism in 0.7Li(CB9H10)-0.3Li(CB11H12) complex hydride solid electrolyte was studied over a wide time-scale (ns-ms) by choosing appropriate techniques for assessing ionic motion on the desired time-scale using nuclear magnetic resonance (NMR) relaxation, AC impedance, and pulsed field gradient-NMR (PFG-NMR) measurements. The 7Li NMR line width decreased with increasing temperature, and the spin-lattice relaxation time T1 for the cation and anions showed a minimum near 303 K, indicating that the lithium ions and the anions were highly mobile. The activation energy estimated from the analysis of the NMR relaxation time matched well with the values estimated from the AC impedance and PFG-NMR. This confirms that the lithium-ion motion in 0.7Li(CB9H10)-0.3Li(CB11H12) is the same over a wide time-scale, suggesting steady Li-ion motion over a wide transport range. This understanding offers insights into strategies for designing complex hydride lithium superionic conductors.

COMPLEX FORMATION IN THE SYSTEM ZINC (II)-CHROMIUM (III) -COBALT (II)-GLYCINE-WATER

The study of complex formation processes is the scientific basis for the development of electrolytes in electroplating. The data on complexation in the zinc (II)–chromium (III)–cobalt (II)–glycine–water system were obtained. The study of complex formation in the zinc (II)-chromium (III)-cobalt (II)-glycine-water system is relevant due to the possibility of developing electrolytic galvanizing processes and obtaining appropriate coatings with high corrosion resistance. In addition, the alloying of zinc electroplating coatings with chromium, cobalt makes it possible to replace the use of toxic cadmium coatings and use their smaller thicknesses. The solutions were thermostated at 25 °C. The HI 2215 pH/ORPMeter was used to measure pH. The spin-lattice relaxation time T1 was measured on a pulsed NMR spectrometer "Minispecmq20" with a frequency of 19.75 MHz. The constants of the formation of complexes and their accumulation shares were calculated according to the CPESSP program. The paper presents data on previously conducted studies of chromium(III)–water, zinc(II)–glycine–water, chromium(III)–glycine–water and zinc(II)–chromium(III)–glycine–water systems. Data on complexation in the chromium (III)-cobalt (II)-glycine-water system were obtained. The formation of a heteronuclear complex CrCoGly83- has been established. The compositions of heteronuclear compounds, their accumulation fractions and formation constants were established: CrCoZn(HGly)5Gly34+ (lgK= 2.31±0.01); CrCoZn(HGly)3Gly52+ (lgK= -1.36±0.05) and CrCoZn(HGy)2Gly6+ (lgK= -4.23±0.09). The maximum proportion of accumulation of heteronuclear complexes, as studies have shown, is observed in the pH range of 2...6. In this paper, considerations are made about the electrochemical reactivity of heteronuclear compounds. In particular, it is noted that the electrochemical reduction of more electronegative metals, if they are in a heteronuclear complex, should occur with less overvoltage of the reaction. For citation: Berezin N.B., Chevela V.V., Mezhevich Zh.V., Ivanova V.Yu. Complex formation in the system zinc (II)-chromium (III) -cobalt (II)-glycine-water. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 6. P. 31-36. DOI: 10.6060/ivkkt.20236606.6789.

An NMR study of hexamethylbenzene (HMB) incorporated in 2,4,6-tris(4-chlorophenoxy)-1,3,5-triazine (CLPOT) framework

Molecular motion of hexamethylbenzene (HMB) incorporated in 2,4,6-tris(4-chlorophenoxy)-1,3,5-triazine (CLPOT) was investigated by 1H NMR spin-lattice relaxation time T1 measurements. In the porous space of one-dimensional (1D) CLPOT nanochannels, HMB molecules reorientate more freely compared to bulk HMB crystals. With low concentrations x < 0.5 of CLPOT-(HMB)x, the distribution of HMB seems to be quite inhomogeneous in 1D nanochannel. The activation energy of the in-plane reorientation of HMB is 5 kJ mol−1 due to the interaction with nanochannel-wall and 10 - 18 kJ mol−1 depending on the separation distance when the interaction between the adjacent HMB molecules determines the activation energy.

Towards Luminescent Vanadium(II) Complexes with Slow Magnetic Relaxation and Quantum Coherence.

Molecular entities with doublet or triplet ground states find increasing interest as potential molecular quantum bits (qubits). Complexes with higher multiplicity might even function as qudits and serve to encode further quantum bits. Vanadium(II) ions in octahedral ligand fields with quartet ground states and small zero-field splittings qualify as qubits with optical read out thanks to potentially luminescent spin-flip states. We identified two V2+ complexes [V(ddpd)2 ]2+ with the strong field ligand N,N'-dimethyl-N,N'-dipyridine-2-yl-pyridine-2,6-diamine (ddpd) in two isomeric forms (cis-fac and mer) as suitable candidates. The energy gaps between the two lowest Kramers doublets amount to 0.2 and 0.5 cm-1 allowing pulsed EPR experiments at conventional Q-band frequencies (35 GHz). Both isomers possess spin-lattice relaxation times T1 of around 300 μs and a phase memory time TM of around 1 μs at 5 K. Furthermore, the mer isomer displays slow magnetic relaxation in an applied field of 400 mT. While the vanadium(III) complexes [V(ddpd)2 ]3+ are emissive in the near-IR-II region, the [V(ddpd)2 ]2+ complexes are non-luminescent due to metal-to-ligand charge transfer admixture to the spin-flip states.

Calculation of the spin-lattice relaxation time and the activation energy near the IV–III phase transition in pyridinium fluorosulfonate (C5NH6)FSO3

The spin-lattice relaxation time T1 H for protons nuclei is calculated in term of the pseudospin–phonon (PS) coupled and the energy fluctuation (EF) models close to the IV–III solid–solid phase transition of in (C5NH6)FSO3. This calculation was performed by associating the observed second moment of the 1H as the order parameter below T C and the disorder parameter above T C. Values of the activation energy for the cation reorientation in this crystal are also deduced by using both models. In addition, the observed dielectric permittivity of this crystal is analyzed within the framework of the Landau theory and values of the spontaneous polarization (P S) are determined as a function of temperature. The normalized values of P S are used in the PS and EF models to extract the activation energy for the reorientation of the dipole moment of this compound arising from cation–anion interaction. Our results show that the PS and EF models can describe the observed behavior of the spin-lattice relaxation time adequately for the IV–III solid–solid transition in (C5NH6)FSO3.

Molecular motion of imidazolium cations and phase transitions in (ImH)2KCo(CN)6 with double perovskite structure

Temperature dependence of 1H nuclear magnetic resonance spin–lattice relaxation time T1 of (ImH)2KCo(CN)6, ImH+: imidazolium cation, is reported. The asymmetric T1 minimum observed in intermediate-temperature phase between 198 and 112 K is analyzed assuming the Cole-Davidson distribution of correlation time. Temperature dependences of 14N nuclear quadrupole resonance frequencies and spin–lattice relaxation times are also reported. The phase transitions at 198 and 112 K are shown to be of second and first order, respectively. The 14N relaxation is shown to be governed by the electric field gradient fluctuation due to the in-plane reorientational motion of the imidazolium cations.

Solid-state MAS NMR at ultra low temperature of hydrated alanine doped with DNP radicals

Magic angle spinning (MAS) nuclear magnetic resonance (NMR) experiments at ultra low temperature (ULT) (≪ 100 K) have demonstrated clear benefits for obtaining large signal sensitivity gain and probing spin dynamics phenomena at ULT. ULT NMR is furthermore a highly promising platform for solid-state dynamic nuclear polarization (DNP). However, ULT NMR is not widely used, given limited availability of such instrumentation from commercial sources. In this paper, we present a comprehensive study of hydrated [U-13C]alanine, a standard bio-solid sample, from the first commercial 14.1 Tesla NMR spectrometer equipped with a closed-cycle helium ULT-MAS system. The closed-cycle helium MAS system provides precise temperature control from 25 K to 100 K and stable MAS from 1.5 kHz to 12 kHz. The 13C CP-MAS NMR of [U-13C]alanine showed 400% signal gain at 28 K compared with at 100 K. The large sensitivity gain results from the Boltzmann factor, radio frequency circuitry quality factor improvement, and the suppression of its methyl group rotation at ULT. We further observed that the addition of organic biradicals widely used for solid-state DNP significantly shortens the 1H T1 spin lattice relaxation time at ULT, without further broadening the 13C spectral linewidth compared to at 90 K. The mechanism of 1H T1 shortening is dominated by the two-electron-one-nucleus triple flip transition underlying the Cross Effect mechanism, widely relied upon to drive solid-state DNP. Our experimental observations suggest that the prospects of MAS NMR and DNP under ULT conditions established with a closed-cycle helium MAS system are bright.

Molecular Motion of Azetidinium Ion and Phase Transition in [(CH2)3NH2]2KCo(CN)6 with Double Perovskite Structure

Abstract Molecular dynamics of azetidinium ion (AzH+), a four-membered-ring ammonium, in a cyano-bridged double perovskite compound (AzH)2KCo(CN)6 is studied by spin-lattice relaxation time measurements of 1H NMR as well as 14N NQR in relation to the phase transition associated with considerable change of dielectric property. AzH+ ions are in static and dynamic disorder, respectively, below and above Tc = 199 K. Below Tc, a ring-puckering motion of AzH+ takes place with the activation energy Ea = 17.5 kJ mol−1 and the correlation time τc/s = 2.8 × 10−14 exp(Ea/RT). On the other hand, from sudden decrease of 1H NMR linewidth above Tc, a C3 reorientation of AzH+ ion is shown to be activated in high-temperature phase. The activation energy of the C3 reorientation is estimated to be 18 kJ mol−1 from the temperature dependences of 1H NMR as well as 14N NQR spin-lattice relaxation times T1 and T1Q.

CHARMM36 Lipid Force Field with Explicit Treatment of Long-Range Dispersion: Parametrization and Validation for Phosphatidylethanolamine, Phosphatidylglycerol, and Ether Lipids.

Long-range Lennard-Jones (LJ) interactions have been incorporated into the CHARMM36 (C36) lipid force field (FF) using the LJ particle-mesh Ewald (LJ-PME) method in order to remove the inconsistency of bilayer and monolayer properties arising from the exclusion of long-range dispersion [Yu, Y.; Semi-automated Optimization of the CHARMM36 Lipid Force Field to Include Explicit Treatment of Long-Range Dispersion. J. Chem. Theory Comput. 2021, 10.1021/acs.jctc.0c01326. (preceding article in this issue)]. The new FF is denoted C36/LJ-PME. While the first optimization was based on three phosphatidylcholines (PCs), this work extends the validation and parametrization to more lipids including PC, phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and ether lipids. The agreement with experimental structure data is excellent for PC, PE, and ether lipids. C36/LJ-PME also compares favorably with scattering data of PG bilayers but less so with NMR deuterium order parameters of 1,2-dimyristoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DMPG) at 303.15 K, indicating a need for future optimization regarding PG-specific parameters. Frequency dependence of NMR T1 spin-lattice relaxation times is well-described by C36/LJ-PME, and the overall agreement with experiment is comparable to C36. Lipid diffusion is slower than C36 due to the added long-range dispersion causing a higher viscosity, although it is still too fast compared to experiment after correction for periodic boundary conditions. When using a 10 Å real-space cutoff, the simulation speed of C36/LJ-PME is roughly equal to C36. While more lipids will be incorporated into the FF in the future, C36/LJ-PME can be readily used for common lipids and extends the capability of the CHARMM FF by supporting monolayers and eliminating the cutoff dependence.

7Li NMR Studies of Short-Range and Long-Range Lithium Ion Dynamics in a Heat-Treated Lithium Iodide-Doped Lithium Thiophosphate Glass Featuring High Ion Conductivity

We combine 7Li field-cycling relaxometry with 7Li field-gradient diffusometry to study both short-range and long-range lithium ion dynamics in a heat-treated 0.33 LiI + 0.67 Li3PS4 glass, which exhibits a high ionic conductivity of 6.5 mS/cm. 7Li field-cycling relaxometry, which provides access to the spin–lattice relaxation time T1 over broad frequency and temperature ranges, allows us to determine the activation energy distribution g(Ea) of the local jumps in a model-free way. We find that g(Ea) has a Gaussian form and is characterized by the mean energy Em = 0.40 eV and the standard deviation σ = 0.08 eV. 7Li field-gradient studies indicate free diffusion and yield self-diffusion coefficients of D ∼ 10–12 m2/s at ambient temperatures. Comparing our results for the short-range and long-range ion dynamics and considering previous knowledge about ionic conductivity, we show that the local jumps characterized by the Gaussian distribution g(Ea) determine the macroscopic transport. We conclude that the high ionic conductivity of the heat-treated glass does not result from the formation of minor crystalline regions during the annealing process but rather from a modification of the predominant amorphous phase.

Sp3-Functionalization of Single-Walled Carbon Nanotubes Creates Localized Spins.

Chemical functionalization-introduced sp3 quantum defects in single-walled carbon nanotubes (SWCNTs) have shown compelling optical properties for their potential applications in quantum information science and bioimaging. Here, we utilize temperature- and power-dependent electron spin resonance measurements to study the fundamental spin properties of SWCNTs functionalized with well-controlled densities of sp3 quantum defects. Signatures of isolated spins that are highly localized at the sp3 defect sites are observed, which we further confirm with density functional theory calculations. Applying temperature-dependent line width analysis and power-saturation measurements, we estimate the spin-lattice relaxation time T1 and spin dephasing time T2 to be around 9 μs and 40 ns, respectively. These findings of the localized spin states that are associated with the sp3 quantum defects not only deepen our understanding of the molecular structures of the quantum defects but could also have strong implications for their applications in quantum information science.

The Role of Titanium Dioxide on the Hydration of Portland Cement: A Combined NMR and Ultrasonic Study.

Titanium dioxide (TiO2) is an excellent photocatalytic material that imparts biocidal, self-cleaning and smog-abating functionalities when added to cement-based materials. The presence of TiO2 influences the hydration process of cement and the development of its internal structure. In this article, the hydration process and development of a pore network of cement pastes containing different ratios of TiO2 were studied using two noninvasive techniques (ultrasonic and NMR). Ultrasonic results show that the addition of TiO2 enhances the mechanical properties of cement paste during early-age hydration, while an opposite behavior is observed at later hydration stages. Calorimetry and NMR spin–lattice relaxation time T1 results indicated an enhancement of the early hydration reaction. Two pore size distributions were identified to evolve separately from each other during hydration: small gel pores exhibiting short T1 values and large capillary pores with long T1 values. During early hydration times, TiO2 is shown to accelerate the formation of cement gel and reduce capillary porosity. At late hydration times, TiO2 appears to hamper hydration, presumably by hindering the transfer of water molecules to access unhydrated cement grains. The percolation thresholds were calculated from both NMR and ultrasonic data with a good agreement between both results.

Nuclear Magnetic Relaxation Mapping of Spin Relaxation in Electrically Stressed Glycerol.

This work discusses nuclear magnetic relaxation effects in glycerol subject to a strong electric field. The methods used are 1.5 T magnetic resonance imaging (MRI), referenced by 9.4 T nuclear magnetic resonance (NMR). While MRI allows a glycerol probe to be sampled with a high voltage (HV) of 16 kV applied to the probe, NMR provides precise molecular data from the sample, but the sample cannot be tested under HV. Using MRI, the recording of magnetic relaxation times was possible while HV was applied to the glycerol. NMR spectroscopy was used to confirm that MRI provides a reasonably accurate estimation of temperature. The applied HV was observed to have a negligible effect on the spin–lattice relaxation time T1, which represents the energy release to the thermal bath or system enthalpy. In contrast to that, the spin–spin relaxation time T2, which does represent the local entropy of the system, shows a lower response to temperature while the liquid is electrically stressed. These observations point toward a proton population in electrically stressed glycerol that is more mobile than that found in the bulk, an observation that is in agreement with previously published results for water.

Noninvasive MRI Native T1 Mapping Detects Response to MYCN-targeted Therapies in the Th-MYCN Model of Neuroblastoma.

Noninvasive early indicators of treatment response are crucial to the successful delivery of precision medicine in children with cancer. Neuroblastoma is a common solid tumor of young children that arises from anomalies in neural crest development. Therapeutic approaches aiming to destabilize MYCN protein, such as small-molecule inhibitors of Aurora A and mTOR, are currently being evaluated in early phase clinical trials in children with high-risk MYCN-driven disease, with limited ability to evaluate conventional pharmacodynamic biomarkers of response. T1 mapping is an MRI scan that measures the proton spin-lattice relaxation time T1. Using a multiparametric MRI-pathologic cross-correlative approach and computational pathology methodologies including a machine learning-based algorithm for the automatic detection and classification of neuroblasts, we show here that T1 mapping is sensitive to the rich histopathologic heterogeneity of neuroblastoma in the Th-MYCN transgenic model. Regions with high native T1 corresponded to regions dense in proliferative undifferentiated neuroblasts, whereas regions characterized by low T1 were rich in apoptotic or differentiating neuroblasts. Reductions in tumor-native T1 represented a sensitive biomarker of response to treatment-induced apoptosis with two MYCN-targeted small-molecule inhibitors, Aurora A kinase inhibitor alisertib (MLN8237) and mTOR inhibitor vistusertib (AZD2014). Overall, we demonstrate the potential of T1 mapping, a scan readily available on most clinical MRI scanners, to assess response to therapy and guide clinical trials for children with neuroblastoma. The study reinforces the potential role of MRI-based functional imaging in delivering precision medicine to children with neuroblastoma. SIGNIFICANCE: This study shows that MRI-based functional imaging can detect apoptotic responses to MYCN-targeted small-molecule inhibitors in a genetically engineered murine model of MYCN-driven neuroblastoma.

Molecular dynamics in polyester resin doped with barium titanate nanoparticles studied by 1H NMR techniques

BaTiO3/polymer composites, which combine the high dielectric constant of ceramics with the high dielectric strength of polymers, are used in modern microelectronics as capacitors, piezoelectric transducers and optoelectronic elements. The aim of the work was to determine the effect of barium titanate (BT) nanoparticles on physical properties of polyester resin (PR). The introduction of nanoparticles into a cross-linked polyester resin induces changes in its molecular structure and dynamics as a result of the particle-polymer interface. Molecular dynamics of polyester resin filled with barium titanate nanoparticles with BT content of 0.1% wt. and 1% wt. was studied. The internal motion of cured polyester resin and new PR/BT composites was investigated by different 1H NMR techniques. The temperature dependences of the spin-lattice relaxation times T1 in the laboratory frame and the frequency dispersions of the spin-lattice off-resonance relaxation times T1ρoff in the rotating frame were determined. Also, the first derivative of the absorption 1H NMR signal was recorded and the second moment of the signal was determined as a function of temperature. Differential Scanning Calorimetry was employed to study the thermal properties of the samples. The results showed that BT nanoparticles influenced the molecular dynamics and thermal properties of polyester resin. The addition of BT nanoparticles leads to a decrease in the correlation times and in the activation energy of internal motion in composites, compared with those for pure polyester resin. What is more, the glass transition temperature Tg and the thermal decomposition temperature TD of polymer composites shift to lower values.

New Approach to Analyze 2D Map T1–T2

Based on the method of two-dimensional (2D) nuclear magnetic resonance (NMR) relaxometry, a technique was developed for determining the joint distribution of the correlation time $$ \tau_{c} $$ and the Van Vleck second moments $$ \Delta \omega^{2} $$. The field of application is the study of slow molecular motions corresponding to the condition of the ratio of nuclear magnetic relaxation times T1/T2 > 1.05 (the relation of spin–lattice relaxation time T1 to spin–spin relaxation time T2). The technique is based on the use of a priori information about the mechanism of nuclear magnetic relaxation in a system. The technique has used this information in the regularization solution of an inverse problem. In contrast to the known method for calculating 2D maps of the joint distribution P2 (T1, T2), the proposed method for constructing a 2D map of the joint distribution $$ Q_{2} \left( {\tau_{c} ,\Delta \omega^{2} } \right) $$ does not depend on the main characteristic of the NMR relaxometer—the resonance frequency $$ \omega_{0} $$. The technique was used to analyze the characteristics of sorbed water in clay rocks–argillite.

Motional freedom of dimethylammonium ions in a cyanoelpasolite, [(CH3)2NH2]2KCo(CN)6, which exhibits phase transition associated with a distinct change in dielectric property.

The temperature dependence of the 1H nuclear magnetic resonance spin-lattice relaxation time T1 of [(CH3)2NH2]2KCo(CN)6 and the partially deuterated analogue [(CD3)2NH2]2KCo(CN)6 has been reported. A change in the molecular motion of organic cations through the first-order phase transition at Tc = 246 K has been discussed. Although this first-order transition has been reported as an isosymmetric transition, in which the space group of the crystal does not change, the number of the 14N nuclear quadrupole resonance line changed from three in the high-temperature phase to twelve in the low-temperature phase indicating the lowering of crystal symmetry.

Spin fluctuations of the uranium 5f-electrons in UN according to 14N-NMR data

The results of the study of the paramagnetic region of uranium mononitride by the method of nuclear magnetic resonance (NMR)of 14N nuclei are presented.The 14N NMR spectra, the Knight shifts K, the spin-lattice relaxation times T1 have been obtained within the temperature range T = 60 – 375 K and at magnetic fields 92.8 kOe and 117.5 kOe. The temperature dependence of the Knight shift of the 14N line is proportional to the spin susceptibility χ of 5f-electrons of uranium. The ratio of the experimentally determined value TT1K2 to the theoretically calculated value of the Korringa contribution is 21.5 (at T = 295 K), which is significantly more than for common metals. This suggests that nuclear relaxation is based on the same mechanism as the Knight shift, namely, the indirect connection between the 14N nuclei and the localized magnetic moments of uranium through conduction electrons. The experimental results on the T-dependence of the spin-lattice relaxation rate of 14N also do not contradict the assumption that uranium mononitride is a concentrated Kondo system.

Sequence for simultaneous measurement of long-limit diffusion and longitudinal relaxation in unilateral NMR.

When unilateral NMR is employed with large gradients (20 T/m), measurements of T1 using standard sequences become affected by Brownian motion of spins, particularly in samples with long spin-lattice relaxation times T1 (>2000 ms) and a large diffusion coefficient D (2*10-6 mm2/ms). In light of this, a modified saturation sequence which we have called GAUSS-SR is proposed that allows direct measurement of both D and T1 to be carried out subject to certain constraints. The evolution of Mz magnetization is the main phenomenon to be modeled. The sequence is composed of three main parts: (i) a saturation train designed to render the Mz profile in Gaussian form, (ii) a main delay where by the simultaneous effects of T1 and D on this profile has been solved analytically and (iii) a detection train to ensure a good signal-to-noise ratio. An NMR-MOUSE was used to acquire the desired measurement through this sequence. By relying on the coherence of the longitudinal rather than the transverse magnetization component, the sequence successfully provides the long-limit value of the diffusion coefficient.