Том 50, № 4 (2019)

Negatively charged nitrogen vacancy (NV) color centers in diamond crystals have been intensively studied in the last few decades with the use of the optically detected magnetic resonance method which usually implies resonance excitation using a DC or pulsed drive field in the gigahertz range (MW field). Various techniques for multi-frequency MW excitation of magnetic resonance in the nuclear structure of ¹⁴N atoms in NV centers were developed. Most of them use MW excitation in combination with RF modulation or direct RF excitation of nuclear transition. Here, we report on the possibility to detect ultra-narrow resonances in the nuclear structure of ¹⁴N using the ODMR methods with single-frequency DC RF excitation of the nuclear transition at 4.95 MHz. The resonances detected in a bulk sample in weak (0–10 mT) magnetic fields show approximately 7 kHz width HWHM, corresponding to T₂^* = 23 μs, and they seem to be insensitive to the magnetic field direction. These resonances may be of interest for solid-state quantum information processing, as well as for quantum magnetometry, especially in biological and medical applications where a strong MW drive field may be undesirable. We demonstrate that optical pumping can be used to create and detect not only the electron orientation, but also the nuclear one, even in the state with a zero electron spin projection. This allows sensitive non-pulsed detection methods like coherent population trapping to be applied to nuclear spins.

Ionic dynamics in nano-structured 2D superionic conductors LaF₃ obtained by a synthesis at the gas–solution interface has been analyzed using ¹⁹F NMR Static Field Gradient (SFG) diffusometry in a temperature range up to 800 K. The fluorine diffusion in 2D materials is significantly higher as compared to that in bulk LaF₃ and is strongly dependent on the nano-crystalline sheet thickness. Its decrease from 18 nm to 6 nm leads to an increase of mobility by almost two orders of magnitude, resulting in an overall mobility enhancement of more than three orders of magnitude compared to mono-crystalline LaF₃. Moreover, the activation energy is reduced from 1.2 eV for mono-crystals to 0.23 eV for 6 nm thin nano-crystalline powder samples.

Ischemic heart disease (IHD) is the most common cause of death in the world. Metabolic profiling is an innovative and reliable new method to detect more sensitive biomarkers identifying altered health conditions specifically among the variety of patients with different risk factors. We evaluated the metabolic profile of filtered serum of stable IHD patients (ICD10 codes I20 and I25.2, ischemic heart disease without or with previous myocardial infarction respectively) using proton nuclear magnetic resonance spectroscopy (NMR). The filtered venous serum from age- and gender-matched stable IHD patients ICD10 coded I20 (n = 13), I25.2 (n = 6) and control individuals (n = 19) were analyzed using one-dimensional proton nuclear magnetic resonance (¹H NMR) spectroscopy. These spectra were used for metabolic profiling and concentration calibration (Chenomx Inc.) followed by statistical analysis using one-way ANOVA and principal component analysis (PCA). Chemometrics analysis showed a significant distinction between the patients and control individuals. The stable IHD patients were exemplified by the increased concentration of acetylacetate, choline, betaine, formate, pyruvate and by the decreased concentration of alanine, creatine, glycine, histidine, lactate, proline, urea and other biomolecules. The major implications found in the serum of IHD patients are related to energy metabolism and potentially altered microbiome. PCA of ¹H NMR detected serum metabolites exhibit a significant difference of stable IHD patients and control individuals. These data demonstrate that metabolomics approach may be useful for the early detection of stable IHD, for detection of synergistic pathways involved in the development of altered health conditions, and molecular understanding of particular health condition. The differences of the detected metabolic profile of ischemic patients with or without previous myocardial infarction appear to be minor. This relatively inexpensive, non-invasive and reproducible approach may be useful for the molecular understanding and early prevention of IHD, improvement of surveillance and therapy. The study emerges the need for future investigations using larger cohort and possible longitudinal sight.

The ^63,65Cu nuclear quadrupole resonance spectra and spin–lattice relaxation rate (1/T₁) have been measured in the semiconductor compound CuAlO₂. The value of the nuclei quadrupole interaction constant Q_CC = 56.24(6) MHz (T = 298 K) has been obtained. The broad maximum has been found in the temperature dependence of 1/T₁ in the low-temperature region (below 276 K). This maximum can be associated with the presence of energy levels in the forbidden band. The activation energy has been estimated in CuAlO₂ [E_A = 45(2) meV], assuming the activation character of the mobility of holes.

We investigated the influence of gadolinium (Gd)-based upconverting nanoparticles (UCNPs) on water spin–lattice relaxation (T₁) and diffusion at different magnetic field strengths (0.4 T and 9.4 T). Our findings show that smaller NPs (12 nm compared to 19 nm) were more favourable for proton relaxivity. We also demonstrate that using simplified Solomon–Bloembergen–Morgan (SBM) model we can associate two measured diffusion coefficients with processes occurring near the surface of UCNPs and in bulk water. Using the relationship between relaxation and diffusion, we can estimate not only the total impact of NPs on relaxation of water molecules, but also the impact on relaxation of local water molecules, directly connected to paramagnetic Gd³⁺ ions in NPs. Different magnetic field strengths did not alter the spin–lattice relaxivity of NPs. This suggests that Gd-based UCNPs could be developed into high-performance multimodal magnetic resonance imaging contrast agents working over a broad range of imaging field strengths used in clinical routine.