1H NMR study of water relaxation and self-diffusion in human serum albumin aqueous solutions

Summary Water proton spin-lattice relaxation and self-diffusion in aqueous solutions of human serum albumin have been studied by¹H NMR as a function of the protein concentration. Spin-lattice relaxation data, which display a nonlinear behaviour with the protein concentration, could be fitted with a two-phase model taking into account the experimentally determined hydration (?bound?) water values. Despite a similar trend is registered for the water self-diffusion coefficient, such a model has been found unable to explain the related experimental data taken as a function of the biomolecule concentration. On the other hand, the solute-induced proton self-diffusion decrease could be satisfactorily interpreted by postulating an enhanced probability of hydrogen-bond formation occurring within the ?vicinal? water surrounding the biomolecules for several hydration shells. The consistency within the two models is discussed in connection with the magnetic interactions occurring within the solute-solvent systems.     

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.     

Shift of the proton NMR field in aqueous solutions of paramagnetic ions

In the paper there is discussed the proton NMR field shift in aqueous solutions of transition metal ions, which has to be taken into account in exact measurements of the static magnetic field. Using the results of Luz's and Shulman's measurements (1965) the empirical expression for the field shift is evaluated, which is a function of the sample shape, of the concentration and the susceptibility of paramagnetic ions in the solution. It is shown that in exact field measurements the diamagnetic part of the susceptibility of the solution cannot be neglected and that one may eliminate the field shift by a suitable choice of the paramagnetic-ions concentration in transversely magnetized cylindrical samples.     

Self-association behaviour of alcohols in diluted aqueous solutions

Summary Our recent studies related to the properties of alcohol/water mixtures show the occurrence of some kind of molecular aggregation in the water-rich region of composition beyond a threshold alcohol concentrationx ₂ ^*. The observed behaviour suggests that forx ₂<x ₂ ^* the alcohol molecules are essentially dispersed and surrounded by ?water cages? where the short-range order and microdynamic of water molecules are changed with respect to those of pure water. Alcohol molecules are in mutual contact at higher concentration only when almost all water is involved in hydration shells of alcohol molecules. The structural transition atx ₂ ^* resembles, for some aspect, the micellization process. The main results of these investigations are reviewed and discussed in this paper. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8 1994     

NMR relaxation of protons in tissues and other macromolecular water solutions

Nuclear magnetic resonance (NMR) longitudinal (T₁) and transverse (T₂) relaxation parameters have been evaluated for protein solutions, cellular suspensions and tissues using both data from our laboratory and the extensive literature. It is found that this data can be generalized and explained in terms of three water phases: free water, hydration water, and crystalline water. The proposed model which we refer to as the FPD model differs from similar models in that it assumes that free and hydration water are two phases with distinct relaxation times but that T₁ = T₂ in each phase. In addition there is a single correlation time for each rather than a distribution as assumed in most other models. Longitudinal decay is predicted to be single exponent in character resulting from a fast exchange between the free and hydration compartments. Transverse decay is predicted to be multiphasic with crystalline (T₂ 10 μsec), hydration (T₂ 10 sec) and free (T₂ 100 sec) water normally visible. The observed or effective transverse relaxation times for both the hydration and free water phases are greatly affected by the crystalline phase and are much shorter than the inherent relaxation times.     

General features of proton longitudinal relaxation in proteins in solution

Time courses of the recovery upon nonselective inversion of all individual proton magnetizations in several globular proteins in aqueous (²H₂O) solution were calculated for varying degrees of rotational correlation time of the molecule (10⁻⁹ s ∼ ∞) and compared with the experimental data on various proteins at 400 MHz. In the calculation, the spinrelaxation mechanism was assumed to be solely the dipolar interaction between protons, and the three-site random jumps of the methyl groups, along with the rotation of the whole molecule, were taken into account. The following conclusions were drawn. ( 1 ) For proteins whose molecular weights are below ∼ 10,000, whole-molecule rotation is a dominant source of relaxation, and the longitudinal relaxation times may vary considerably from proton to proton. (2) For proteins whose molecular weights are above ∼20,000, methyl group rotations assisted by spin diffusion are common and major sources of relaxation, producing T₁ values close to 1 s. In the intermediate region (molecular weight 10,000 ∼ 20,000), both whole-molecule rotation and methyl group rotations contribute significantly to relaxation. (3) In some proteins, segmental motions are as important as methyl group rotations in determining relaxation rate.     

Specific features of proton NMR relaxation of hydrocarbons and water in the pore space of silicates

The relaxation of the proton magnetization of water and hydrocarbons in a model medium of glass beads and quartz sand is studied by the NMR method. The spectrum of relaxation times of fluids is one-component in the model environment and three-component in quartz sand. The surface relaxivities measured in the model medium are used to determine the pore size distribution in quartz sand. Estimates of the specific surface area of sand based on the relaxation data are consistent with the values measured by the sorption method. The EPR method is used to determine the chemical nature of the active paramagnetic centers responsible for the surface relaxation of the proton magnetization. Differences in the relaxation behavior of aqueous and hydrocarbon fluids are interpreted within the framework of a simple model of surface relaxation.     

NMR relaxation in binary aqueous mixtures of acetone and tetrahydrofurane

NMR proton relaxation rates of normal and ¹⁷O-enriched water and deuteron relaxation rates of heavy water were measured in mixtures with acetone and tetrahydrofurane at different compositions. The ¹⁷O-induced proton relaxation rate was extracted and from this the rotational correlation time of water was determined. Using these correlation times the composition-dependence of the deuteron quadrupole coupling constant of water was derived. A strong variation was found for the system acetone-water, whereas little variation was observed for tetrahydrofurane-water.     

Determination of the effective correlation time modulating 1H NMR relaxation processes of bound water in protein solutions

The relaxation in protein solutions has mainly been studied by nuclear magnetic relaxation dispersion (NMRD) techniques. NMRD data have mostly been analyzed in terms of fast chemical exchange of water between free water and water bound to proteins. Several approaches were used for the estimation of correlation time modulating the relaxation mechanism of bound water. On the other hand, in a nuclear magnetic resonance experiment, the relaxation rates of protein solutions (1/T1 and 1/T2) and also those of free water (1/T1f and 1/T2f) are measurable. However, the relaxation rates of bound water (1/T1b and 1/T2b) are not. Despite this, equating (1/T1-1/T1f)/2(1/T2-1/T2f) to (1/T1b)/2(1/T2b) leads to an expression involving only an effective tau that is related to the rotational correlation time (tau r) of proteins. Equating the ratios may therefore give a simple alternative method for the determination of tau r even if this method is limited to a single resonance frequency. In this work, a formula was derived for the solution of the effective tau. Then, the 1/T1 and 1/T2 in solutions of two globular proteins (lysozyme and albumin) and one nonglobular protein (gamma-globulin) were measured for different amounts of each protein. Next, the values of 1/T1 and 1/T2 were plotted vs. protein concentrations, and then the slopes of the fits were used in the derived equation for determining the effective tau values. Finally, the rotational correlation time tau r, calculated from tau, was used in the Stokes-Einstein relation to reproduce relevant radii. The effective tau values of lysozyme, albumin and gamma-globulin were found to be 5.89 ns, 7.03 ns and 8.8 ns, respectively. tau r values of albumin and lysozyme produce their Stokes radii. The present data suggest that use of the measurable ratio in the derived formula may give a simple way for the determination of the correlation times of lysozyme and albumin.     

Study of the effect of a low-frequency magnetic field on the spin-lattice relaxation in water and in aqueous solutions

The spin-lattice relaxation times in water and NaCl aqueous solutions in a low-frequency magnetic field have been measured on natural-concentration ¹⁷O nuclei. The activation energies have been calculated. The differences in the temperature dependences of the spin-lattice relaxation time and the changes in the relaxation with the magnetic field frequency are established.     

Proton NMR relaxation of adsorbed water in gelatin and collagen

The dependence of the water self-diffusion coefficients as well as of the proton spin-lattice and spin-spin relaxation rates on the concentration have been studied in the gelatin-water system and in hydrated native collagen. The bound and free water fractions and the corresponding spin-spin and spin-lattice relaxation rates have been determined within the multi-phase water proton exchange model. Various theoretical models for the water proton cross-relaxation to the biopolymer have been studied and the results compared with the observed Larmor frequency dependence of the water proton spin-lattice relaxation rate.     

NMR relaxation of 7Li in concentrated lithium-ammonia solutions

The Knight shift and the spin-lattice relaxation time of ⁷Li in lithium-ammonia solutions have been measured at -57°C over the concentration range X_Li = 0.01–0.20 (X_Li: mole fraction of Li). The Knight shift increases with increasing metal concentration, while the relaxation rate, 1/T₁, shows a broad minimum around X_Li = 0.07.     

Electron paramagnetic relaxation in aqueous solutions of manganese (II) ions

The processes of the electron paramagnetic relaxation, molecular motions and structural changes in aqueous solutions of manganese nitrate have been investigated by direct measurement of spin-lattice (T ₁) and spin-spin (T ₂) relaxation times for a wide range of concentrations, temperatures and viscosities. T ₁ and T ₂ were measured by a non-resonance absorption method.

It was discovered that some structural regions exist at the different concentrations of Mn(II) ions in solution. So, the structure of highly concentrated solutions may be considered as one of the corresponding crystallohydrate. The structural microinhomogeneities were observed also in the intermediate concentration range at definite temperatures. It is shown that the relaxation mechanism proposed by Bloembergen and Morgan is not effective in the concentration range studied by us.

The analysis of relaxation times and E.P.R. spectra has shown the formation of ‘liquid microphases’ at the freezing point of the solution. Such microphases can exist at temperatures a few tenths of a degree below the solvent freezing point, and its composition considerably differs from the initial solution.

The correlation times for intramolecular and intermolecular electron relaxation mechanisms are evaluated and their nature is discussed.     

水溶液中结合水的定义与量化

水溶液中溶质的结合水具有不同于远离溶质的自由水的结构和性质.结合水的存在对水和溶质结构和动力学性质均具有显著甚至决定性的影响.然而,对结合水动力学和热力学性质的定量理解在诸多方面一直存在争议甚至严重分歧,其中重点包括如何定义和量化结合水,如何表征结合水和自由水的动力学差别,结合水如何参与生物大分子各种生物功能过程,以及溶质或界面影响结合水结构与性质的途径等.给出结合水定义的物理学依据和量化方法,是深入理解上述问题的第一步.本文简述了各种不同谱学方法定义结合水的基本原理及量化的困难,强调具有不同时间和空间响应尺度的测试方法所得结合水数不必完全可比.此外,系列水溶液物性随浓度升高会明显改变其浓度依赖关系,相应拐点浓度常被用于量化稀溶液中的溶质结合水数.我们近期研究的水溶液玻璃化转变温度-浓度关系,为结合水的定义、量化和水溶液的三区划分提供了物理依据,同时揭示了上述利用性质-浓度关系拐点浓度量化结合水方法的不足.     

Influence of magnetic impurities on proton spin relaxation of water in clay

The¹H nuclear magnetic spin relaxation of water in slurry of kaolin clay was investigated in the presence of magnetite (black iron oxide, Fe₃O₄) at 0.2 T and room temperature. The water spectra at high magnetite contents showed two different resonances, presumably from surface-associated water and free interstitial water. The difference in observed resonance frequencies increased as much as 200 ppm with increasing magnetite content. The apparent nuclear magnetic resonance intensity decreased biexponentially as a function of magnetite added. The observedT ₂^* values at low magnetite contents were in accordance with the predicted values from the resonance intensities and the estimated magnetic susceptibilities. TheT ₁ relaxation was multiexponential in character, so a uniform penalty program was used for the analysis of distribution. At 0.2 T for¹H, kaolin slurry containing less than 5.5 ppm magnetite did not differ significantly from magnetite-free clay in the longitudinal relaxation rates of water. However, higher concentrations of magnetite produced features in theT ₁ distribution significantly different from those of magnetite-free clay. TheT ₂ could be approximated by monoexponential relaxation, probably because the fast-decaying components relaxed before they could be recorded. The apparent transverse relaxation ratesR ₂ increased linearly as a function of magnetite content. On the basis of the comparison of spin-echo and Carr-Purcell-Meiboom-Gill data, an empirical relation was derived to describe the signal loss due to diffusion. It can be expressed by a power function of magnetite amount, which is multiplied by the sum of volume-dependent and volume-independent terms.     

Control of the longitudinal relaxation timeT 1 of a flowing liquid in NMR flowmeters

The influence of a strong inhomogeneous magnetic field of a magnet-polarizer on the longitudinal relaxation timeT ₁ of a flowing liquid is investigated. The increased inhomogeneity of this field causesT ₁ to decrease. The magnitude of the polarizer field and its inhomogeneity exhibit an optimum whose criteria are the signal/noise ratio in a system for registering the signal of nuclear magnetic resonance (NMR), the mass, and the overall dimensions of the device. St. Petersburg State Technical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 50–53, September 1999.