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Energy transfer from Zeeman to dipolar order discovered by Jeener et al. is usually observed in solids with a strong dipole-dipole interaction of nuclear spins. It is not observed in liquids, where fast molecular motion completely averages this interaction. The intermediate case, when the dipole-dipole interaction of nuclear spins is only partially averaged, has been poorly studied. We report on the first measurement of an angular-dependent proton spin relaxation of a dipolar reservoir in mobile water molecules confined in the interlayer pores of a vermiculite single crystal. In this layered crystal, the intramolecular dipole-dipole interactions of nuclear spins are only partially averaged due to the restricted anisotropic molecular motion in nanopores. We show that this allows the formation of dipolar echo. We measured the spin-lattice relaxation times of the dipolar order T 1D at different angles between the normal to the crystal surface and the applied magnetic field and obtained a distinct angular dependence of T 1D . The minimum relaxation rate R 1D was found around the magic angle of 54.74°., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2024 Elsevier Inc. All rights reserved.)

An analysis of our data on 1 H and 13 C spin-lattice and spin-spin relaxation times and rates in aqueous suspensions of purified nanodiamonds produced by detonation technique (DNDs), DNDs with grafted paramagnetic ions, and micro- and nanodiamonds produced by milling bulk high-temperature high-pressure diamonds is presented. It has been established that in all the studied materials, the relaxation rates depend linearly on the concentration of diamond particles in suspensions, the concentration of grafted paramagnetic ions, and surface paramagnetic defects produced by milling, while the relaxation times exhibit a hyperbolic dependence on the concentration of paramagnetic centers. This is a universal law that is valid for suspensions, gels, and solids. The results obtained will expand the understanding of the properties of nano- and microdiamonds and will be useful for their application in quantum computing, spintronics, nanophotonics, and biomedicine.

Purpose: Testing the potential use of saline suspension of polyvinylpyrrolidone (PVP)-coated gadolinium(Gd)-grafted detonation nanodiamonds (DND) as a novel contrast agent in MRI., Methods: Stable saline suspensions of highly purified de-agglomerated Gd-grafted DND particles coated by a PVP protective shell were prepared. T 1 and T 2 proton relaxivities of the suspensions with varying gadolinium concentration were measured at 8 Tesla. A series of ex vivo (phantom) and in vivo dynamic scans were obtained in 3 Tesla MRI using PVP-coated Gd-grafted DND and gadoterate meglumin in equal concentrations of gadolinium, and then T 1 -weighted hyperintensity was compared., Results: The proton relaxivities of PVP-coated Gd-grafted DND were found to be r 1 = 15.9 ± 0.8 s -1 mM -1 and r 2 = 262 ± 15 s -1 mM -1 , respectively, which are somewhat less than those for uncoated Gd-grafted DND but still high enough. Ex vivo MRI evaluation of PVP-coated Gd-grafted DND results with a dose-dependent T 1 -weighted hyperintensity with a significant advantage over the same for gadoterate meglumin. The same was found when the 2 contrast agents were tested in vivo., Conclusion: The novel MRI contrast agent - saline suspensions of PVP-coated Gd-grafted DND - provides significantly higher signal intensities than the common tracer gadoterate meglumin, therefore increasing its potential for a safer use in clinics., (© 2021 International Society for Magnetic Resonance in Medicine.)

Objectives: Detonation nanodiamonds (DND) with Gd 3+ ions directly grafted to the DND surface have recently demonstrated enhanced relaxivity for protons in aqueous suspensions. Herewith, the relaxivity measurements were done on a series of suspensions with the gadolinium content varied by changing number of Gd 3+ ions grafted per each DND particle whereas the DND content in each suspension was kept the same. Such an approach to vary the contrast agent content differs from that commonly used in the relaxivity measurements. In the common approach, contrast agents are directly dissolved/suspended in media. Aiming to test validity of the unconventional approach, in the present study we follow the common way of measurement relaxivity: using variable concentrations of carriers (DND particles) in aqueous suspension keeping the number of Gd 3+ ions per each carrier fixed., Materials and Methods: 1 H NMR relaxation measurements of aqueous suspensions of DND with Gd 3+ ions directly grafted to the DND surface were carried out at room temperature (293 K or 20 °C) in the external magnetic field B 0  = 8.0 T., Results and Conclusions: Comparative study of two approaches for measuring relaxivity in suspensions containing DND as magnetic entities' carriers reveals complete identity of techniques in use.

We developed an approach for determining location of intrinsic paramagnetic defects in nanodiamonds from the data of proton spin-lattice relaxation of the surface hydrogen atoms. The approach was applied to the detonation nanodiamond (DND) of the diameter of 5 nm. We found that dangling bonds with unpaired electron spins are located within the near-surface belt at the distance of 0.3-0.9 nm from the DND surface. The NMR data are compared with the results of EPR measurements., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Kuzmin et al. reported on the application of the 3He NMR relaxometry technique to localization of intrinsic paramagnetic defects in detonation nanodiamond (DND) particles. We found some inconsistencies in the DND characterization, the model of paramagnetic defects' allocation used in that work as well as the estimation of distances between 3He NMR probes and paramagnetic defects, which question the results obtained.

Detonation nanodiamonds (DNDs) have emerged as promising candidates for a variety of biomedical applications, thanks to different physicochemical and biological properties, such as small size and reactive surfaces. In this study, we propose carbon dot decorated single digit (4-5 nm diameter) primary particles of detonation nanodiamond as promising fluorescent probes. Due to their intrinsic fluorescence originating from tiny (1-2 atomic layer thickness) carbonaceous structures on their surfaces, they exhibit brightness suitable for in vitro imaging. Moreover, this material offers a unique, cost effective alternative to sub-10 nm nanodiamonds containing fluorescent nitrogen-vacancy color centers, which have not yet been produced at large scale. In this paper, carbon dot decorated nanodiamonds are characterized by several analytical techniques. In addition, the efficient cellular uptake and fluorescence of these particles are observed in vitro on MDA-MD-231 breast cancer cells by means of confocal imaging. Finally, the in vivo biocompatibility of carbon dot decorated nanodiamonds is demonstrated in zebrafish during the development. Our results indicate the potential of single-digit detonation nanodiamonds as biocompatible fluorescent probes. This unique material will find application in correlative light and electron microscopy, where small sized NDs can be attached to antibodies to act as a suitable dual marker for intracellular correlative microscopy of biomolecules.

We developed an approach for determining distances between carbon nanoparticles and grafted paramagnetic ions and molecules by means of nuclear spin-lattice relaxation data. The approach was applied to copper-, cobalt- and gadolinium-grafted nanodiamonds, iron-grafted graphenes, manganese-grafted graphene oxide and activated carbon fibers that adsorb paramagnetic oxygen molecules. Our findings show that the aforementioned distances vary in the range of 2.7-5.4 Å and that the fixation of paramagnetic ions to nanoparticles is most likely implemented by means of the surface functional groups. The nuclear magnetic resonance data data are compared with the results of electron paramagnetic resonance measurements and density functional theory calculations.

Temperature dependencies of 27 Al and 23 Na nuclear magnetic resonance spectra and spin-lattice relaxations in mordenite have been studied in static and magic angle spinning regimes. Our data show that the spin-lattice relaxations of the 23 Na and 27 Al nuclei are mainly governed by interaction of nuclear quadrupole moments with electric field gradients of the crystal, modulated by translational motion of water molecules in the mordenite channels. At temperatures below 200 K, the dipolar interaction of nuclear spins with paramagnetic impurities becomes an important relaxation mechanism of the 23 Na and 27 Al nuclei.

Behavior of water molecules entrapped in nanochannels of zeolite mordenite has been investigated by (1)H NMR technique. The (1)H spectra and spin-lattice relaxation times in the laboratory and rotating frames, T1 and T1ρ, respectively, as well as the dipolar relaxation time T1D have been measured in the temperature range from 96 to 351K. Diffusion of water molecules along the channels was observed above ~200K. While in bulk liquid the dipolar ordered state of nuclear spins is not formed owing to complete motional average of dipolar interactions, we show that such a state is observed for mobile molecules confined in a restricted geometry. At temperatures below ~140K the relaxation was found to be mainly caused by interaction of (1)H nuclear spins with paramagnetic impurities. Complete lost of the fine structure of (1)H spectra above ~320 K is attributed to isotropic molecular reorientation or/and proton exchange. We show that the dipolar relaxation in mordenite is responsive to slow 180° reorientations of water molecules. The correlation times of nuclear and electron spin fluctuations were determined., (Copyright © 2016 Elsevier Inc. All rights reserved.)

We report on (13)C spin-lattice (R 1) and spin-spin (R 2) relaxation rate dependence on magic-angle-spinning (MAS) rate in highly purified synthetic nanodiamonds. Noticeable slowdown of both relaxation processes and reduction of nuclear spin diffusion coefficient D with increasing MAS rate was obtained. This effect is attributed to suppression of nuclear spin diffusion by MAS. We developed a theoretical approach that describes the MAS rate dependence of R 1, R 2 and D, allows quantitative analysis of the data and shows good compliance with the experiment.

We report on (13)C nuclear spin-lattice relaxation time (T1) dependence on the magic-angle-spinning (MAS) rate in powder nanodiamond samples. We confirm that the relaxation is caused by interaction of nuclear spins with fluctuating electron spins of localized paramagnetic defects. It was found that T1 is practically not affected by MAS for small particles, while for larger particles with lower defect density T1 is different in static and MAS regimes and reveals elongation with increasing MAS rate. This effect is attributed to suppression of nuclear spin diffusion by MAS. We propose an approach that describes T1 dependence on the MAS rate and allows quantitative analysis of this effect., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Size dependence of physical properties of nanodiamond particles is of crucial importance for various applications in which defect density and location as well as relaxation processes play a significant role. In this work, the impact of defects induced by milling of micron-sized synthetic diamonds was studied by magnetic resonance techniques as a function of the particle size. EPR and (13)C NMR studies of highly purified commercial synthetic micro- and nanodiamonds were done for various fractions separated by sizes. Noticeable acceleration of (13)C nuclear spin-lattice relaxation with decreasing particle size was found. We showed that this effect is caused by the contribution to relaxation coming from the surface paramagnetic centers induced by sample milling. The developed theory of the spin-lattice relaxation for such a case shows good compliance with the experiment.

We report on investigation of detonation nanodiamond annealed at 800C°in chlorine atmosphere by means of 1H, 13C and 35Cl nuclear magnetic resonance and X-ray photoelectron spectroscopy. The results of these methods are found to be consistent with each other and evidence formation of chlorine-carbon groups and sp2 carbon shell on the nanodiamond surface. The data obtained provide detailed information about the structure and bonding in this diamond nanoparticle. Interaction of nuclear spins with unpaired electron spins of dangling bonds results in fast 13C nuclear spin-lattice relaxation.

We report on a proton magnetic resonance study of a powder nanodiamond sample. We show that (1)H spin-lattice relaxation in this compound is mainly driven by the interaction of nuclear spins with unpaired electron spins of paramagnetic defects. We measured the spin-lattice relaxation time T1 by means of a saturation comb pulse sequence followed by dipolar dephasing, and plotted T1 as a function of the dephasing time [Formula: see text] in different external magnetic fields. The received T1([Formula: see text]) dependence provides a striking manifestation of the spin diffusion-assisted relaxation regime. The obtained experimental data allow us to estimate the spin diffusion coefficient and spin diffusion barrier radius.

We report on the first nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) study of the high-temperature nanodiamond-to-onion transformation. (1)H, (13)C NMR and EPR spectra of the initial nanodiamond samples and those annealed at 600, 700, 800 and 1800 ° C were measured. For the samples annealed at 600 to 800 ° C, our NMR data reveal the early stages of the surface modification, as well as a progressive increase in sp(2) carbon content with increased annealing temperature. Such quantitative experimental data were recorded for the first time. These findings correlate with EPR data on the sensitivity of the dangling bond EPR line width to air content, progressing with rising annealing temperature, that evidences consequent graphitization of the external layers of the diamond core. The sample annealed at 1800 ° C shows complete conversion of nanodiamond particles into carbon onions.

In this paper we present a simple model to calculate the Hahn-echo decay of the exchange-coupled nuclear spins in solids. Satisfactory agreement between the calculated and experimentally observed echo decay of the exchange-coupled spins of T203l and T205l isotopes in thallium chloride TlCl and thallium tantalum sulfide TlTaS(3) is obtained., (Copyright © 2012 Elsevier Inc. All rights reserved.)

We report on the first NMR study of powder and single crystal samples of thallium indium sulfide, TlInS(2). The crystal under study is a pure single-layer TlInS(2) polytype. Our findings show that transformation from the high temperature paraelectric phase to the low temperature ferroelectric phase occurs via an incommensurate phase that exists in the temperature range from T(c) = 192 K to T(i) = 205 K. On approaching the phase transition at T(i) from above, the crystal exhibits a soft mode behavior. A discrepancy in the literature data on the phase transitions in TlInS(2) is discussed and ascribed to polytypism of the TlInS(2) crystals., (© 2012 IOP Publishing Ltd)

Spin diffusion and spin-lattice relaxation in solids containing paramagnetic impurities under influence of a multiple-pulse spin-locking radio-frequency sequence are studied theoretically and experimentally. The diffusion equation obtained provides a clue for determination of the time dependent magnetization. The spin-lattice relaxation time is calculated as a function of the correlation time and multiple-pulse field parameters. From the experimental data the spin diffusion coefficient, the radius of the spin diffusion barrier, and the correlation time for very slow molecular motion in polycrystalline (C(2)F)(n) system are estimated and found to be D∼7.1×10(-12)cm(2)/s, r(c)∼4.8×10(-10)m, and τ(c)∼10.2μs, respectively., (Copyright © 2010 Elsevier Inc. All rights reserved.)

We report on the first nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) investigation of inorganic fullerene-like MoS(2) nanoparticles. Spectra of bulk 2H-MoS(2) samples have also been measured for comparison. The similarity between the measured quadrupole coupling constants and chemical shielding anisotropy parameters for bulk and fullerene-like MoS(2) reflects the nearly identical local crystalline environments of the Mo atoms in these two materials. EPR measurements show that fullerene-like MoS(2) exhibits a larger density of dangling bonds carrying unpaired electrons, indicative of them having a more defective structure than the bulk sample. The latter observation explains the increase in the spin-lattice relaxation rate observed in the NMR measurements for this sample in comparison with the bulk 2H- MoS(2) ones.

Inorganic fullerene-like nanoparticles of WS2 (IF-WS2), are synthesized by a reaction of tungsten oxide with molecular hydrogen and hydrogen sulfide. The synthesized nanoparticles appear as large agglomerates (>40 microns), each one counting thousands of IF nanoparticles. 1H nuclear magnetic resonance study of these nanoparticles is reported. The measurements show that the prepared product contains water (and possibly some hydrogen) molecules that occupy the voids in the central part of the fullerene-like nanoparticles and the nanopores between the adhering IF-WS2 particles. Defects in the IF-WS2 structure, arising due to the strain release during the folding of the layers, may result in additional sites for the absorbed water. Vacuum annealing of the powder leads to substantial reduction in the amount of absorbed water molecules.

We demonstrate, both theoretically and experimentally, that two-pulse sequence (2n+1) X 90 degrees(Y) - 90 degrees(X) -Acq(t) without delay between pulses, yields the reverse of time evolution of spin system with dipolar and quadrupole interactions. This process results in refocusing of the spin magnetization into magic echo at te = t1/2 after the second pulse, where t1 is the length of the first pulse.

We present a detailed theoretical and experimental NQR multiple-pulse spin-locking study of spin-lattice relaxation and spin diffusion processes in the presence of paramagnetic impurities in solids. The relaxation function of the nuclear spin system at the beginning of the relaxation process is given by exp (-t/T1rho)alpha, where T1rho is spin-lattice relaxation time in rotating frame and alpha = d/6, d is the sample dimensionality. Then the relaxation proceeds asymptotically to an exponential function of time, which was attributed to the spin-diffusion regime. Using the experimental data obtained from the analysis of those two relaxation regimes in gamma-irradiated powdered NaClO3, spin diffusion coefficient has been determined and the radius of the diffusion barrier has been estimated.

The response of a spin system to a long (in comparison to spin-spin relaxation time T2) radiofrequency pulse has been studied. We observed that the magnetization after the long pulse does not fall to zero at time t >> T2 for both on-resonance and off-resonance conditions. The dependencies of the magnetization on frequency offset, linewidth and radiofrequency power are investigated, both theoretically and experimentally. The question of the effective field direction is also discussed.