Pulsed NMR Research Articles

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.

Hydrogen storage and mobility determined by NMR to various organically functionalized porous silica synthetized by using the post-grafting method

The results of this study will help in guiding the future design of low-cost and highly performing functionalized mesoporous silica using cationic surfactants as directing agents. Indeed, by properly tuning surface interactions and the textural characteristics, the overall efficiency of H2 capture processes could be improved. Among different synthetized samples, the experimental results show the better interaction with (3-Aminopropyl)triethoxysilane precursor. Furthermore, an NMR investigation aiming at clarifying the internal arrangement and diffusion properties of hydrogen molecules inside functionalized porous silica materials has been performed. The NMR spectral analysis and the T1 relaxation times indicated two different “populations” for H2 sorbate due to the molecules adsorbed in mesopores and in micropores. For the first time, the H2 self-diffusion coefficient in functionalized silica has been experimentally measured by pulsed field gradient NMR. The spin-echo decay revealed two different diffusion mechanisms coexist in the functionalized mesoporous silica, except for the material functionalized with iodopropyl groups, which shows a single diffusion coefficient.

Determination of the Oil Content of Sunflower Seeds Using Natural Samples of Sunflower Oil: on the Example of the Calibration of a Pulsed NMR Analyzer

One of the main parameters of sunflower seeds is its oil content. This characteristic is mandatory for certifica[1]tion of agricultural products and assessment of their value. IR spectroscopy and pulsed NMR methods are widely used to determine the oil content.The purpose of the research was to scientifically and practically substantiate the possibility of using sunflower oil samples for calibrating NMR analyzers, identifying and assessing the quality of oilseeds and products of their processing based on the NMR method. The comparison of the results of various options for the calibration of a pulsed NMR analyzer for determining the oil content of sunflower seeds was carried out. The first option was to measure the NM relaxation characteristics of oil protons from prepared samples of sunflower seeds, followed by determination of their oil content by exhaustive extraction in a Soxhlet apparatus, construction of a calibration equation based on the obtained data, and entering its coefficients into the program of NMR analyzers.The resulting calibration was the base one, with which other calibration options were compared. The second option was to use for calibrating the NMR analyzer various samples of sunflower oil obtained by pressing from sunflower seeds of the same varieties and hybrids, that were used for the first calibration option, as well as sunflower oil samples purchased in a commercial network. Five samples evenly distributed in the range from 2.000 g to 7.000 g with an accuracy of 0.001 g were taken from each oil sample using laboratory scales, and the amplitudes of proton NMR signals were measured in them. The dependency between the oil mass of the analyzed samples and the amplitude of proton NMR signals in them was graphed. Comparison of the obtained calibration dependences showed their close nature. Mathematical calculations have shown that the use of sunflower oil for the calibration of NMR analyzers does not lead to an increase in the error in the measurement results of the oil content of sunflower seeds compared to the first option of the calibration.The practical significance of the research will considerably simplify the calibration process, reduce the calibration time from 3–4 days to 3–4 hours, and eliminate the use of toxic solvents and additional expensive equipment without a significant change in the error in determining the oil content of sunflower seeds by NMR.

On the applicability of cosine-modulated pulses for high-resolution solid-state NMR of quadrupolar nuclei with spin > 3/2

In MQMAS-based high-resolution solid-state NMR experiments of half-integer spin quadrupolar nuclei, the high radiofrequency (RF) field requirement for the MQ excitation and conversion steps with two hard-pulses is often a sensitivity limiting factor in many practical applications. Recently, the use of two cosine-modulated (cos) low-power (lp) pulses, lasting one-rotor period each, was successfully introduced for efficient MQ excitation and conversion of spin-3/2 nuclei with a reduced RF amplitude. In this study, we extend our previous investigations of spin-3/2 nuclei to systems with higher spin values and discuss the applicability of coslp-MQ excitation and conversion in MQMAS and MQ-HETCOR experiments under slow and fast spinning conditions. For the numerical simulations and experiments we used a moderate magnetic field of 14.1 T. Two spin-5/2 nuclei (85Rb and 27Al) are mainly employed with a large variety of CQ values, but we show that the practical set up is also available for higher spin values, such as spin-9/2 with 93Nb in Cs4Nb11O30. We demonstrate for nuclei with spin value larger than 3/2 a preferential use of coslp-MQ acquisition for low-gamma nuclei and/or large CQ values with a much reduced RF-field with respect to that of hard-pulses used with conventional methods.

Digitally Based Precision Time-Domain Spectrometer for NMR Relaxation and NMR Cryoporometry

NMR Relaxation (NMRR) is an extremely useful quantitative technique for material science, particularly for studying polymers and porous materials. NMR Cryoporometry (NMRC) is a powerful technique for the measurement of pore-size distributions and total porosities. This paper discusses the use, capabilities and application of a newly developed compact NMR time-domain relaxation spectrometer suitable for studying both solid and liquid samples (Mk3 NMR Relaxation spectrometer & Cryoporometer, Lab-Tools (nano-science), Ramsgate, Kent, UK. (2019)). This highly compact precision NMR Spectrometer is based on a Field Programmable Gate array (FPGA) module and custom surface mount low-noise NMR receiver and NMR linear transmitter. A high proportion of the RF circuitry is in a digital form, implemented as firmware in the FPGA, which gives the instrument an excellent long-term stability. It also includes an on-chip Linux computer. The FPGA module is credit-card sized, and both the NMR receiver and NMR transmitter are even smaller. The software, including the top-level NMR pulse sequence definitions, are written in an array processing language, Apl. The spectrometer comes complete with a Graphical User Interface (GUI) for control and on- and offline curve fitting and data analysis. The recent development of the Lab-Tools Peltier thermo-electrically cooled NMR variable-temperature (V-T) probe that cools the sample below −60 °C is also discussed. This Peltier cooling gives the precision temperature control and smoothness needed by NMR Cryoporometry (10 mK near the probe liquid bulk melting point). This enables the NMRC measurement of pore-size distributions in porous materials, for the unusually wide pore-size range of sub-nano to over 1 micron-sized pores. The NMR Spectrometer’s unusually small size, ability to measure solids, low noise and high performance make it particularly suitable for material science studies both in the field and in university, research institute, company and even school laboratories. A human portable version now exists. Use of the controlling GUI is described, and results from example NMR Relaxation and NMR Cryoporometric measurements are given.

Low perturbation limit decoherence analyzed by scaling the Double Quantum Hamiltonian

By varying the magnitude of the effective interaction between spins in relation to the perturbations, we study the decoherence behavior in a connected proton system. Making use of the Magnus expansion, we introduce a NMR pulse sequence that generates an average Hamiltonian with Double Quantum terms multiplied by a scaling factor, δ, with the possibility to take positive and negative values. The performance of the pulse sequence for different values of the scaling factors was validated in polycrystalline adamantane, by observing the evolution of the polarization. A time reversal procedure, accessible through the change of sign in the controlled Hamiltonian, was necessary to observe multiple quantum coherences. The spin counting develops a characteristic growth in two species of clusters for the scaled time. The influence of the scaling factor on the reversibility was observed through the behavior of the Loschmidt echoes, which decayed faster as the scaling factor increases. From the analysis of dynamics and its reversibility, we extracted characteristic times for the spin diffusion, T2δ and the intrinsic decoherence decay, T3δ for each scaling factor δ, and perturbation time scale, TΣ. Observing the dependence of reversibility vs. perturbation rates, both normalized with the spin diffusion rate, we find that in the limit of low perturbations, T2δ/T3δ deviates from the linear dependence on T2δ/TΣ that corresponds to strong perturbation. The asymptotic value T2/T3≈0.15 as T2δ/TΣ vanishes, gives evidence that the main source of irreversibility is the intrinsic decoherence associated to the chaotic many-body dynamics of the system.

Mobility of Li+, Na+, and Cs+ cations in Nafion membrane, as studied by NMR techniques

The local mobility and diffusion of Li+, Na+, and Cs+ cations in Nafion 117 membrane were explored by 7Li, 23Na, and 133Cs spin relaxation and pulsed field gradient NMR techniques. It was shown that the macroscopic mass transfer of cations is controlled by ion motion near sulfonate groups. Lithium and sodium cations, whose hydrated energy is higher than the water hydrogen bond energy, are moving together with water molecules, but cesium cations possessing a low hydrated energy are jumping directly between the neighboring sulfonate groups.

Design of NMR Pulses by Iterative Optimization of Phases

Design of NMR Pulses by Iterative Optimization of Phases

NMR Characterization of Polyethylene Glycol Conjugates for Nanoparticle Functionalization.

The molecular weight, purity, and functionalization of polyethylene glycols are often characterized by 1H NMR spectroscopy. Oft-forgotten, the typical 1H NMR pulse sequence is not 13C decoupled. Hence, for large polymers, the 13C coupled 1H peaks arising from the repeating units have integrations comparable to that of the 1H of the terminal groups. Ignoring this coupling leads to erroneous assignments. Once correctly assigned, these 13C coupled 1H peaks can be used to determine both the molecular weight of the polymer and the efficacy of conjugation of a terminal moiety more accurately than the uncoupled 1H of the repeating unit.

Physical and Chemical Properties of Water in the Cytoplasma of Plant Cells

A study is performed of the physicochemical properties of the aqueous component of the cytoplasm of a living cell and the intercellular fluid associated with their structural organization. As a single coherent system, the structure of the water component of a plant plays a crucial role in its water regime, and therefore determines the development and adaptability of the plant to environmental conditions. Low-frequency L-dielcometry is used for the first time in experimental studies of the water regime of plants. The change in the peak intensities in the spectrum of the dependence of the dielectric loss tangent on the EMF frequency under conditions of artificial drought for different phytotest objects is used to show there are two types of water in living plants: free and self-organized bound. Free water is responsible for the mode of evaporation, while bound water participates in the organization of a complex network of intercellular communications, including the transmission of different signals through putative synapse-like contacts. Results correlate fully with others from plant phytomonitoring with pulsed NMR at the Kazan Scientific School of Phytophysiologist. The conclusion that there are two types of water in a living plant simultaneously is substantiated theoretically on the basis of generalized crystallography using Bulienkov’s modular computer design. It is the most important component of the concept of quantum bioenergetics.

Lithium transference in electrolytes with star-shaped multivalent anions measured by electrophoretic NMR.

One approach for improving lithium transference in electrolytes is through the use of bulky multivalent anions. We have studied a multivalent salt containing a bulky star-shaped anion with a polyhedral oligomeric silsesquioxane (POSS) center and lithium counterions dissolved in a solvent. The charge on each anion, z-, is equal to -20. The self-diffusion coefficients of all species were measured by pulsed field gradient NMR (PFG-NMR). As expected, anion diffusion was significantly slower than cation diffusion. An approximate transference number, also referred to as the current fraction (measured by Bruce, Vincent and Watanabe method), was higher than those expected from PFG-NMR. However, the rigorously defined cation transference number with respect to the solvent velocity measured by electrophoretic NMR was negative at all salt concentrations. In contrast, the approximate transference numbers based on PFG-NMR and current fractions are always positive, as expected. The discrepancy between these three independent approaches for characterizing lithium transference suggests the presence of complex cation-anion interactions in solution. It is evident that the slow self-diffusion of bulky multivalent anions does not necessarily lead to an improvement of lithium transference.

Tracking nitrite's deviation from Stokes-Einstein predictions with pulsed field gradient 15N NMR spectroscopy.

Predicting the behavior of oxyanions in radioactive waste stored at the Department of Energy legacy nuclear sites requires the development of novel analytical methods. This work demonstrates 15N pulsed field gradient nuclear magnetic resonance spectroscopy to quantify the diffusivity of nitrite. Experimental results, supported by molecular dynamics simulations, indicate that the diffusivity of free hydrated nitrite exceeds that of free hydrated sodium despite the greater hydrodynamic radius of nitrite. Investigations are underway to understand how the compositional and dynamical heterogeneities of the ion networks at high concentrations affect rheological and transport properties.

ОПРЕДЕЛЕНИЕ СОДЕРЖАНИЯ АРОМАТИЧЕСКИХ УГЛЕВОДОРОДОВ В МИНЕРАЛЬНЫХ МАСЛАХ МЕТОДОМ ЯМР-РЕЛАКСАЦИИ

Molecular group composition analysis of mineral oils is helpful to predict the performance of a future lubricant and to assess the compatibility of plasticizer oil with rubbers. The method of pulsed low-frequency NMR relaxation was used to determine the molecular group composition of 11 mineral oil samples, and the ratio of aromatic and non-aromatic hydrocarbons in them was calculated. NMR measurements were performed on a Chromatec-Proton 20M NMR analyzer with a 1H resonance frequency of 20 MHz. The method used consists in recording free induction decay signals, reconstructing the total signal amplitude, estimating the relative signal amplitude per unit mass of the sample, and calculating the proportion of aromatic hydrocarbons in the sample. The results were compared with those obtained by the standard chromatographic method. A high degree of correlation (R2 = 0.99) was observed between the results.

環境影響を低減したパルス法NMR測定による熱酸化した厚肉ゴムの局所的な引張特性の予測

Prediction of tensile properties by pulsed NMR measurements is improved by swelling the sample with a deuterated solvent. However, in recent years, the use of organic solvents has been avoided from the viewpoint of safety and health risks and the environmental impact of volatile organic compounds. In this study, we investigated a method for predicting the tensile properties of rubber by pulsed NMR measurements without using a swelling solvent. Spin-spin relaxation measurements in dry state and tensile tests were performed on sliced sheets sampled from the surface and interior of thermally oxidized thick-walled rubber. As a result of multivariate analysis using NMR parameters obtained from spin-spin relaxation, it was found that the spin-spin relaxation time of network component (T2HS) and its Weibull coefficient (WHS) are effective as explanatory variables for tensile properties. Regression equations using T2HS and WHS could predict the extension ratio at break (λB) and the stress at 100% strain (S100) of surface and inner layers of thermally oxidized products with high accuracy.

Updates and Original Case Studies Focused on the NMR-Linked Metabolomics Analysis of Human Oral Fluids Part III: Implementations for the Diagnosis of Non-Cancerous Disorders, Both Oral and Systemic.

This communication represents Part III of our series of reports based on the applications of human saliva as a useful and conveniently collectable medium for the discovery, identification and monitoring of biomarkers, which are of some merit for the diagnosis of human diseases. Such biomarkers, or others reflecting the dysfunction of specific disease-associated metabolic pathways, may also be employed for the prognostic pathological tracking of these diseases. Part I of this series set the experimental and logistical groundwork for this report, and the preceding paper, Part II, featured the applications of newly developed metabolomics technologies to the diagnosis and severity grading of human cancer conditions, both oral and systemic. Clearly, there are many benefits, both scientific and economic, associated with the donation of human saliva samples (usually as whole mouth saliva) from humans consenting to and participating in investigations focused on the discovery of biomolecular markers of diseases. These include usually non-invasive collection protocols, relatively low cost when compared against blood sample collection, and no requirement for clinical supervision during collection episodes. This paper is centred on the employment and value of 'state-of-the-art' metabolomics technologies to the diagnosis and prognosis of a wide range of non-cancerous human diseases. Firstly, these include common oral diseases such as periodontal diseases (from type 1 (gingivitis) to type 4 (advanced periodontitis)), and dental caries. Secondly, a wide range of extra-oral (systemic) conditions are covered, most notably diabetes types 1 and 2, cardiovascular and neurological diseases, and Sjögren's syndrome, along with a series of viral infections, e.g., pharyngitis, influenza, HIV and COVID-19. Since the authors' major research interests lie in the area of the principles and applications of NMR-linked metabolomics techniques, many, but not all, of the studies reviewed were conducted using these technologies, with special attention being given to recommended protocols for their operation and management, for example, satisfactory experimental model designs; sample collection and laboratory processing techniques; the selection of sample-specific NMR pulse sequences for saliva analysis; and strategies available for the confirmation of resonance assignments for both endogenous and exogenous molecules in this biofluid. This article also features an original case study, which is focussed on the use of NMR-based salivary metabolomics techniques to provide some key biomarkers for the diagnosis of pharyngitis, and an example of how to 'police' such studies and to recognise participants who perceive that they actually have this disorder but do not from their metabolic profiles and multivariate analysis pattern-based clusterings. The biochemical and clinical significance of these multidimensional metabolomics investigations are discussed in detail.

Origin and remedy for HSQC artifacts in proton-detected INADEQUATE spectra.

NMR pulse sequences visualizing 1JCC and nJCC bond connectivity via an intermediate state of 13C-13C double-quantum coherence and 1H detection are an indispensable tool to solve small-molecule structures at the natural abundance level of 13C. A longstanding issue with these experiments set up to display 2D spectra with single-quantum frequencies is that in addition to the 1H-13C-13C correlations of interest, appearance of HSQC-type artifacts can complicate analysis and obscure JCC connectivities. The origin of these artifacts is described and remedies for their suppression are introduced. They include refocusing of 1JCH couplings prior to creation of 13C-13C double-quantum coherence, which is known to enhance sensitivity by reducing loss into zero-quantum coherence for pairs of two protonated 13C.

Quantitative Polymer Characterizations with NMR Cryoprobes through Spin Echo NMR Pulse Sequences

Quantitative Polymer Characterizations with NMR Cryoprobes through Spin Echo NMR Pulse Sequences

Application for Powder Dispersibility and Interface Characterization Using Low-field NMR

The dispersibility and wettability of the powder can be possible to measure by pulse NMR. The characteristic is being able to measure with good reproducibility in a short time without diluting. As a concrete measurement example of dispersibility, we compared with the particle size distribution measurement depending on the dispersion time on low concentration carbon nanotubes. Which was about 0.02%. Next, we compared the graphene dispersion sample from 10% to 50% by pulse-NMR and diluted sample by laser diffraction measurement. In the example of comparing the results in the diluted state have good correlation. However, in the case of different concentrations, there was no correlation. In addition, as a concrete evaluation example of wettability, surface treatment of powder was performed, and the difference in wettability to pure water and hexane were compared. Furthermore, an example was shown in which the wettability to the resin was also compared. Although it only shows simple applications, we think this valuation method has a high potential by the user’s idea.

(Invited) NMR Investigation of Proton Transport in Concentrated Aqueous and Polymer Electrolytes Based on Polyphosphoric Acid

Concentrated aqueous electrolytes have received much attention in recent years due to their high ionic conductivity and electrochemical window that usually exceeds that of the water electrolysis limitation. In collaboration with Ziyue Li and Fei Wang (Fudan University) we have investigated water/polyphosphoric acid solutions ranging in concentration from 1.25 to 16.6 molar being considered for proton-based batteries. Self-diffusion coefficients measured by pulsed field gradient NMR as well as spin-lattice time relaxation measurements were determined for 31P and 1H. The results shed light on the observed maximum in conductivity at the 5.9 molar concentration.For polymer electrolyte membrane fuel cells (PEMFC), polybenzimidazole (PBI) membranes with high phosphoric acid content have been developed previously by collaborator Brian Benicewicz (University of South Carolina) using the so-called PPA process. Recently, a carefully controlled drying method has been discovered by Benicewicz and co-worker Laura Murdock in which a PBI membrane prepared by the PPA process is transformed into a dense PBI film. Though originally developed for flow battery applications, it was found that this dense film could be re-acidified to yield a mechanically robust PEM. Furthermore this method provides a synthetic route to PBI films without the use of any organic solvents. The re-doped PBI films display high ionic conductivity at elevated temperatures, similar to the starting PBI gel membranes prepared by the PPA process, while containing nearly a factor of two less acid than the latter and also exhibiting enhanced mechanical properties. NMR spectroscopy was used to characterize the structure and dynamics of the modified and the original PBI/PPA membranes. In addition to pulsed field gradient diffusion studies, we have performed solid state one-dimensional 31P, 13C and two-dimensional 31P{1H} and 13C{1H} HETCOR NMR measurements, which yield additional information on structural differences between the membranes and how these differences may affect transport properties.

Simultaneous Determination of the Saponification Value, Acid Value, Ester Value, and Iodine Value in Commercially Available Red Fruit Oil (Pandanus conoideus, Lam.) Using 1H qNMR Spectroscopy

Red fruit oil (RFO) can be extracted from fruits of Pandanus conoideus, Lam., an endogenous plant of Papua, Indonesia. It is a commonly used essential original traditional medicine. By applying a newly developed quantitative 1H NMR (qNMR) spectroscopy method for quality assessment, a simultaneous determination of the saponification value (SV), acid value (AV), ester value (EV), and iodine value (IV) in RFO was possible. Dimethyl sulfone (DMSO2) was used as an internal standard. Optimization of NMR parameters, such as NMR pulse sequence, relaxation delay time, and receiver gain, finally established the 1H NMR-based quantification approach. Diagnostic signals of the internal standard at δ = 2.98 ppm, SV at δ = 2.37–2.20 ppm, AV at δ = 2.27–2.20 ppm, EV at δ = 2.37–2.27 ppm, and IV at δ = 5.37–5.27 ppm, respectively, were used for quantitative analysis. The method was validated concerning linearity (R2 = 0.999), precision (less than 0.83%), and repeatability in the range 99.17–101.17%. Furthermore, this method was successfully applied to crude RFO, crude RFO with palmitic and oleic acid addition, and nine commercial products. The qNMR results for the respective fat values are in accordance with the results of standard methods, as can be seen from the F- and t-test (< 1.65 and < 1.66, respectively). The fundamental advantages of qNMR, such as its rapidity and simplicity, make it a feasible and existing alternative to titration for the quality control of RFO.