Water Proton NMR Relaxation Research Articles

Earth's field NMR relaxation of pre-polarised water protons for real-time detection of free-radical formation.

Real-time imaging of free-radical formation is important in physical chemistry, biochemistry, and radiobiology, especially for the study of radiation dose-rate effects. Herein, we show for the first time that the formation of free radicals during the time course of a chemical reaction can be imaged through NMR relaxation measurements of water protons in the Earth's magnetic field, in an open-coil spectrometer. The relaxation rate constants of water magnetisation are enhanced as reactions leading to the formation of hydroxyl radicals and oxygen proceed on the timescale of tens of minutes. The reaction rate of iodide-catalysed H2O2 decay was followed by Earth-field 1H NMR relaxation in real time. The relaxivities of the reaction product and several other paramagnetic compounds were determined. Spin-trap molecules were then used to capture ˙OH radical species, thus altering the reaction rate in proportion to the formation of new paramagnetic compounds. Thereby, a new experimental method for magnetic resonance imaging of the formation of intermediate and stable radical species in water is proposed.

Water proton NMR relaxation revisited: Ultrahighly diluted aqueous solutions beyond Avogadro’s limit prepared by iterative centesimal dilution under shaking cannot be considered as pure solvent

• Ultramolecular dilutions prepared according to homeopathic pharmacopoeia differ from solvent and from simply diluted samples. • Evidence for an unexpected gradual increase of correlation times of water with dilution in ultrahighly diluted solutions. • Evidence for solute-induced nanostructures in aqueous high dilutions growing with dilution. • Nanostructures result from nucleation between the solute, nanobubbles and elements coming from the medium during preparation. • Nanostructures in ultrahigh dilutions, even ultramolecular, enhance leaching processes in glass containers. The biological activity of ultrahigh dilutions (HDs) as used in homeopathy, especially those beyond Avogadro's limit, is still controversial and an intriguing problem for scientists. Homeopathic remedies are mostly prepared by iterative centesimal dilution under vigorous shaking, called dynamization. Cn corresponds to a dilution factor of 10 -2n , and C12 (10 -24 ) to the theoretical limit of molecular presence. Since the 1990 s, NMR relaxation of water protons has emerged as a potent tool for investigating HDs. This article reviews studies of high methodological quality by five independent teams over more than two decades. They demonstrate an increase in T1 and T1/T2, with a decrease in T2, although less constant, in dynamized aqueous HDs. No variation was observed in the similarly treated solvent controls. The phenomenon seems to be common, regardless of solute, dissolved oxygen, material used (glass or plastic), method of shaking, frequency from 0.02 to 600 MHz. Strikingly, the changes in relaxation times increased gradually with dilution, even in the C12-C30 ultramolecular range and they totally vanished after a heating–cooling cycle directly applied on the sealed NMR tubes. The results were interpreted in terms of increasing correlation times of water, greater than 10 −8 s, resulting from the formation of growing solute-induced nanostructures involving nanobubbles and various elements coming from the medium, the atmosphere and the container. Another unexpected result was that HDs were able to enhance some leaching processes in glass containers.

Monitoring of the sedimentation kinetics of vaccine adjuvants using water proton NMR relaxation.

Suspensions of solid particles find applications in many areas-mining, waste treatment, and in pharmaceutical formulations. Pharmaceutical suspensions include aluminum-adjuvanted vaccines are widely administered to millions of people worldwide annually. Hence, the stability parameters of such suspensions, for example, sedimentation rate and the compactness of the formed sediments, are of great interest to achieve the most optimal and stable formulations. Unlike currently used analytical techniques involving visual observations and/or monitoring of several optical properties using specialized glassware, water proton nuclear magnetic resonance (wNMR) used in this work allows one to analyze samples in their original sealed container regardless of its opacity and/or labeling. It was demonstrated that the water proton transverse relaxation rate could be used to monitor in real time the sedimentation process of two widely used aluminum adjuvants-Alhydrogel® and Adju-Phos®. Using wNMR, we obtained valuable information on the sedimentation rate, dynamics of the supernatant and sediment formation, and the sedimentation volume ratio (SVR) reflecting the compactness of the formed sediment. Results on SVR from wNMR were verified by caliper measurements. Verification of the sedimentation rate results from wNMR by other analytical techniques is challenging due to differences in the measured attributes and even units of the reported rate. Nonetheless, our results demonstrate the practical applicability of wNMR as an analytical tool to study pharmaceutical suspensions, for example, aluminum-adjuvanted vaccines, to provide higher quality and more efficient vaccines. Such analyses could be carried out in the original container of a suspension drug product to study its colloidal stability and to monitor its quality over time without compromising product integrity.

Enhanced NMR relaxation of fluids confined to porous media: A proposed theory and experimental tests.

We propose a theory to account for the NMR relaxation of water protons in situations in which the fluid is confined to porous structures exhibiting a scarce distribution of paramagnetic centers on their surface. Though much of what is stated and assumed concerns the response of water, the model has sufficiently general features to be able to explain proton relaxation of other polar fluids under similar conditions. One of the main results of the paper is to show that the local anisotropy introduced by the dominant dipolar coupling in the relaxation rates of active surface elements induces a measurable dependence on sample orientation in the overall relaxation rates of the saturating fluid provided its confining structure is not statistically isotropic. Measurements of T_{1} proton relaxation on water saturating microcapillary tubes are performed to reveal the effect.

Complex formation, chemical exchange, species structure, and stereoselective effects in the copper(ii)-l/dl-histidine systems

The formation of copper(II) complexes with L- and DL-histidine (HisH) has been studied by means of pH-potentiometry and spectrophotometry over a wide range of pH (2-14), ligand-to-metal ratio (1 : 1-15 : 1), and temperature (15-55 °C) in aqueous solutions with 1.0 mol dm(-3) KNO(3) as background. Formation constants and spectral characteristics of 13 complex types were found. Fine stereoselective effects have been detected with preferential coordination of two ligands with identical configuration in Cu(His)(HisH)(+) and opposite configuration in Cu(His)(2). The stereoselective effect for Cu(His)(HisH)(+) is explained by hydrogen bond formation between the carboxyl and imidazolyl groups of neighboring ligands at cis-arrangement of amino groups (3N(eq)-form). The opposite sign of stereoselective effect for Cu(His)(2) is derived from favourable axial coordination of the imidazole group in meso-form with cis-structure (3N(eq)N(ax)-form). A significant tetrahedral distortion was revealed for the first time in the prevalent cis-isomer of the Cu(L-His)(2) 4N(eq)-form. These findings were confirmed by EPR data and DFT computations at the B3LYP/TZVP level. The prevalence of cis-isomers for these complexes has been assigned to the rather strong trans effect of the amino groups. The structures of other detected complexes are briefly discussed on the basis of spectroscopic data. Chemical exchange reactions in the copper(II)-L/DL-hishidine systems have been investigated by the NMR relaxation of water protons. A unique proton exchange reaction with short-term proton dissociation from the coordinated imidazolyl group catalyzed by hydroxide ion was characterised for the first time. The discovered enantioselective effects in the ligand exchange reactions between Cu(His)(2) and HisH or His(-) species were attributed to the associative substitution mechanism.

The Assembly State between Magnetic Nanosensors and Their Targets Orchestrates Their Magnetic Relaxation Response

The target-induced clustering of magnetic nanoparticles is typically used for the identification of clinically relevant targets and events. A decrease in the water proton transverse NMR relaxation time, or T(2), is observed upon clustering, allowing the sensitive and accurate detection of target molecules. We have discovered a new mechanistically unique nanoparticle-target interaction resulting in a T(2) increase and demonstrate herein that this increase, and its associated r(2) relaxivity decrease, are also observed upon the interaction of the nanoparticles with ligands or molecular entities. Small molecules, proteins, and a 15-bp nucleic acid sequence were chemically conjugated to polyacrylic-acid-coated iron oxide nanoparticles, and all decreased the original nanoparticle r(2) value. Further experiments established that the r(2) decrease was inversely proportional to the number of ligands bound to the nanoparticle and the molecular weight of the bound ligand. Additional experiments revealed that the T(2)-increasing mechanism was kinetically faster than the conventional clustering mechanism. Most importantly, under conditions that result in T(2) increases, as little as 5.3 fmol of Bacillus anthracis plasmid DNA (pX01 and pX02), 8 pmol of the cholera toxin B subunit (Ctb), and even a few cancer cells in blood were detected. Transition from the binding to the clustering mechanism was observed in the carbohydrate-, Ctb-, and DNA-sensing systems, simply by increasing the target concentration significantly above the nanoparticle concentration, or using Ctb in its pentameric form as opposed to its monomer. Collectively, these results demonstrate that the molecular architectures resulting from the interaction between magnetic nanosensors and their targets directly govern water proton NMR relaxation. We attribute the observed T(2) increases to the bound target molecules partially obstructing the diffusion of solvent water molecules through the superparamagnetic iron oxide nanoparticles' outer relaxation spheres. Finally, we anticipate that this novel interaction can be incorporated into new clinical and field detection applications, due to its faster kinetics relative to the conventional nanoparticle-clustering assays.

NMR water proton relaxation in unheated and heated ultrahigh aqueous dilutions of histamine: Evidence for an air-dependent supramolecular organization of water

We measured 20-MHz R1 and R2 water proton NMR relaxation rates in ultrahigh dilutions (range 5.43 · 10 − 8 M–5.43 · 10 − 48 M) of histamine in water (Hist-W) and in saline (Hist-Sal), prepared by iterative centesimal dilutions under vigorous agitation in controlled atmospheric conditions. Water and saline were similarly and simultaneously treated, as controls. The samples were immediately sealed in the NMR tubes after preparation, and then code-labelled. Six independent series of preparations were performed, representing about 7000 blind measurements. R2 exhibited a very broad scatter of values in both native histamine dilutions and solvents. No variation in R1 and R2 was observed in the solvents submitted to the iterative dilution/agitation process. By contrast, histamine dilutions exhibited slightly higher R1 values than solvents at low dilution, followed by a slow progressive return to the values of the solvents at high dilution. Unexpectedly, histamine dilutions remained distinguishable from solvents up to ultrahigh levels of dilution (beyond 10 − 20 in Hist-Sal). A significant increase in R2 with increased R2/R1 was observed in Hist-W. R1 and R2 were linearly correlated in solvents, but uncorrelated in histamine dilutions. After a 10-min heating/cooling cycle of the samples in their sealed NMR tubes (preventing any modification of the chemical composition and gas content), all of the relaxation variations observed as a function of dilution vanished, the R2/R1 ratio and the scatter of the R2 values dropped in all solutions and solvents, and the correlation between R1 and R2 reappeared in the Hist-W samples. All these results pointed to a more organized state of water in the unheated samples, more pronounced in histamine solutions than in solvents, dependent on the level of dilution. It was suggested that stable supramolecular structures, involving nanobubbles of atmospheric gases and highly ordered water around them, were generated during the vigorous mechanical agitation step of the preparation, and destroyed after heating. Histamine molecules might act as nucleation centres, amplifying the phenomenon which was thus detected at high dilution levels.

Quantitative evaluation of polymer concentration profile during swelling of hydrophilic matrix tablets using 1H NMR and MRI methods

Many pharmaceutical tablets are based on hydrophilic polymers, which, after exposure to water, form a gel layer around the tablet that limits the dissolution and diffusion of the drug and provides a mechanism for controlled drug release. Our aim was to determine the thickness of the swollen gel layer of matrix tablets and to develop a method for calculating the polymer concentration profile across the gel layer. MR imaging has been used to investigate the in situ swelling behaviour of cellulose ether matrix tablets and NMR spectroscopy experiments were performed on homogeneous hydrogels with known polymer concentration. The MRI results show that the thickest gel layer was observed for hydroxyethylcellulose tablets, followed by definitely thinner but almost equal gel layer for hydroxypropylcellulose and hydroxypropylmethylcellulose of both molecular weights. The water proton NMR relaxation parameters were combined with the MRI data to obtain a quantitative description of the swelling process on the basis of the concentrations and mobilities of water and polymer as functions of time and distance. The different concentration profiles observed after the same swelling time are the consequence of the different polymer characteristics. The procedure developed here could be used as a general method for calculating polymer concentration profiles on other similar polymeric systems.

Influence of Cellulosic Additives on Tricalcium Silicate Hydration: Nuclear Magnetic Resonance Relaxation Time Analysis

This paper reports a study on the effects of cellulose additives on the setting process of tricalcium silicate (C3S) paste. Cellulose and cellulose derivatives are largely used in the cement industry due to their excellent water carrying capacity that makes these additives essential in the practice of the extrusion processes. However, how they are effective in many processes is not known. We addressed this point investigating the hydration kinetics of C3S in the presence of cellulose derivative by thermal analysis and water proton NMR relaxation. Both these methods provided useful information on the mechanisms of the C3S curing process involving cellulose. The experimental results clearly show that cellulose additives act as a regulator of water release during the whole hydration process. A quantitative description of this process is reported.

Investigation of molecular motions and interprotein interactions in solutions by NMR and TDDS

Non-selective NMR relaxation of protein and water protons at various resonance frequencies as well as Time Domain Dielectric Spectroscopy (TDDS) were applied to study the molecular motions in lysozyme and myoglobin solutions. It was found that the correlation function of the protein motion defined by means of all these methods can be presented as a sum of three components having substantially different correlation times. Both NMR and TDDS experimental data were treated on the basis of approach according to which these components of the correlation function correspond to three different kinds of protein motion, namely 1) internal local motion, 2) anisotropic rotational Brownian diffusion and 3) translational Brownian diffusion. According to the hypothesis proposed earlier we suppose that the reason of anisotropy of protein rotation and possibility to detect experimentally the slowest motion (translational diffusion) is the mutual interprotein electrostatic steering. The qualitative consistency between parameters of correlation function obtained from NMR and TDDS and their concentration dependence confirm the validity of the qualitative model of the interprotein electrostatic interactions.

Monitoring Stress Sensitivity by Water Proton NMR Relaxation Times in Leaves of Azaleas That Originated in Different Ecological Habitats

Monitoring Stress Sensitivity by Water Proton NMR Relaxation Times in Leaves of Azaleas That Originated in Different Ecological Habitats

Synthesis and characterization of a novel DTPA-like gadolinium(III) complex: a potential reagent for the determination of glycated proteins by water proton NMR relaxation measurements

The synthesis of a novel DTPA-like ligand 2 containing two boronic acid phenylamide substituents and its Gd(III) complex 3 is reported. The measurement of the proton relaxation rate over the proton Larmor frequency range from 0.01 to 50 MHz of an aqueous solution of this paramagnetic complex suggests that it contains only one water molecule in its inner coordination sphere, as was previously found for the parent DTPA complex.

Anthocyanin Influence on Water Proton NMR Relaxation Times and Water Contents in Leaves of Evergreen Woody Plants During the Winter

Anthocyanin Influence on Water Proton NMR Relaxation Times and Water Contents in Leaves of Evergreen Woody Plants During the Winter

The response of the kht sarcoma to radiotherapy as measured by water proton nmr relaxation times: Relationships with tumor volume and water content

The potential application of magnetic resonance imaging (MRI) to predict tumor response to radiotherapy is investigated. The water proton spin-lattice and spin-spin relaxation times (T2 and T2, respectively) of murine sarcomas (designated KHT) were measured shortly after excision. This study has demonstrated significantly different responses in T1 and T2 between the control and the irradiated tumors at various times following single doses of X rays. Quite generally, the changes in relaxation times correlated with the changes in tumor water content, indicating that the MR relaxation-time probes are fairly sensitive to radiation-induced edema and dehydration. The possible relationships between the T1 and T2 responses and radiobiological effects such as those on tumor blood flow, vascular permeability, physiological state of cells, and cell death are discussed. It is conceivable that the findings obtained from this investigation could be extended to in situ studies for potential applications in clinical radiotherapy.

Proton nuclear magnetic resonance relaxation rates in aqueous solutions of amino acids

Variations of water-proton NMR relaxation rates induced by amino acids are very different for longitudinal and transverse relaxations. The presence of amino acids increases the longitudinal relaxation rate only slightly, when compared with the increase induced by the oxygen content of the solution. The measured transverse relaxation rate is dependent on the pulse delay of a Carr-Purcell-Meiboom-Gill sequence. Transverse proton relaxation dispersions are shown to be consistent with rapid proton exchange between water and the NH+ 3 groups of the amino acids. The mean exchange time is about 1 ms. The variation of the exchange time with temperature yields the enthalpy and the entropy of the apparent first-order reaction of this exchange. Changes of pH, temperature and oxygen content give rise to opposite effects on relaxation rates of amino acid solutions. The discussion here underlines the fact that, even in such a simple system, relaxation-rate measurements give valuable information only if the physico-chem...

Statistical Studies Using AIC Method to Decide the Question of “Break” or “Straight” in Arrhenius Plots of Water Proton NMR Relaxation Times in Chilling-Sensitive Vigna and Insensitive Pisum Seedlings

Statistical Studies Using AIC Method to Decide the Question of “Break” or “Straight” in Arrhenius Plots of Water Proton NMR Relaxation Times in Chilling-Sensitive Vigna and Insensitive Pisum Seedlings

NMR relaxation of water protons in normal and malignant hyperthermia-susceptible pig muscle

1H-NMR has been used to study the evolution of water proton transversal relaxation times in ageing skeletal muscles of normal and halothane-positive Pietrain pigs. Malignant hyperthermia was confirmed by the caffeine contracture test. Lactic acid, creatine phosphate, and ATP levels in muscle biopsies were measured by biochemical analysis. The NMR dynamic results revealed malignant hyperthermia, but knowledge of animal age and muscle type improved significantly the detection ability. The NMR results revealed large differences between muscles. Halothane sensitivity detection seems to be less affected by animal age, than by muscle effect but discrimination was more efficient in the older animal group. It is concluded that 1 H-NMR is a suitable method for diagnosing halothane sensitivity on a well identified muscle biopsy and that water dynamics might be related to acidosis in muscle fibres.

Water proton NMR relaxation mechanisms in lung tissue.

The NMR relaxation times T'2, T2, and T1 were measured in isolated rat lungs as functions of external magnetic field B0, temperature, and lung inflation. The observed linear dependence on B0 of the tissue-induced free induction decay rate (T'2)-1 provides independent confirmation of the air/water interface model of the lung. Furthermore, measurements of the Larmor frequency dependence of T1 are consistent with a spin-lattice relaxation rate of the form 1/T1 = A omega -1/2 + B as expected for the case in which the relaxation arises from water-biopolymer cross-relaxation, which should be proportional to the surface area of the lung. This prediction was verified by observations of an approximately linear dependence of 1/T1 on transpulmonary pressure and thus on the lung surface area.

Effect of cholesterol solubilised in membranes on the interfacial water structure — a study by water proton NMR relaxation in reverse micelles

Cholesterol solubilised in the reverse micellar system of Aerosol OT in isooctane has been found to decrease the hydrophilicity of the surfactant molecule. This has been studied in detail by water proton NMR relaxation measurements in water—Aerosol OT—isooctane with and without cholesterol. It is concluded that the intermolecular hydrogen bonding between the 3β-OH group of cholesterol and the carbonyl ester of Aerosol OT is responsible for the decrease in hydrogen bonding capacity of the latter.

Effect of induced field inhomogeneity on transverse proton NMR relaxation in tissue water and model systems.

The effect of induced field inhomogeneity (IFI) on transverse NMR relaxation of water protons in tissue has been investigated by examining the field dependence of the effective transverse relaxation rates (1/T2 eff) for in vitro canine brain tissue samples. At fields of 0.47, 2.35, 7.05 T (corresponding to 20, 100, and 300 MHz, respectively) the transverse relaxation rates for both white and gray matter samples follow a field dependence of the form 1/T2 eff = C0 + C1 B0, where B0 is the applied field. The linearly dependent term, C1 B0, which reflects the IFI contribution, does not contribute much (i.e., less than 20%) at fields less than 2.0 T. However, at greater field strengths the contribution is appreciable, e.g., greater than 60% at 7.0 T. Results from model systems of glass beads are also reported to illustrate IFI effects. For both the model systems and canine brain tissue samples, the effects of restricted diffusion are qualitatively evident in Hahn spin-echo experiments.