Multi-Lorentzian representation of deuterium spectrum to study water spin magnetization exchange in MCM-41.

Water behavior on the pore surface of nano-silica MCM-41, at a hydration level corresponding to one water molecule per OH group, is studied using (2)H NMR spectra in the temperature range 213 to 313 K. In an earlier study [J. Hassan, E. Reardon, H. Peemoeller, Microporous Mesoporous Materials, 122 (2009) 121-127] it was shown that at this hydration level, deuterons of water at single OH sites exhibit a Lorentzian line shape and deuterons of water at hydrogen-bonded OH sites exhibit a powder pattern. Here it is shown that magnetization exchange occurs between these two deuteron spin groups. This exchange cannot be described using the common, two-site exchange model, involving two Lorentzians. We successfully apply a multi-Lorentzian exchange model, prompted by Woessner's work [D. E. Woessner, Mol. Phys. 34, 4, (1977) 899-920] on the effects of motion on the shape of water spin resonance lines exhibiting doublet splitting. For this low hydration sample the rate of magnetization exchange out of the hydration site, where the water deuterons exhibit a Lorentzian line in the (2)H spectra, is 1.3 ms(-1) and the activation energy for the exchange is found to be 3.4±0.1 kcal/mole.

Hydration study of homopolypeptides by (2)H NMR.

Deuteron T(1) and T(2) was studied as a function of hydration in homopolyglycine (PG) and homopolyproline (PP). Water deuteron relaxation rates in PG conform to a hydration model involving two types of primary hydration sites where water is directly bonded to the polymer. Once these sites are filled, additional water only bonds to water molecules at the primary sites and in so doing affect their dynamics. PP exhibits an anomalous T(1) and T(2) hydration dependence which has been interpreted in terms of a cooperative water molecule-PP molecule helical conformational rearrangement which occurs once a certain hydration level is reached. The proposal of a water-PP structure is tested using molecular dynamics simulations.

Cross-relaxation bottleneck in water-lysozyme proton magnetization exchange.

The proton spin-lattice relaxation parameters in natural and deuterated lysozyme solutions have been measured as a function of temperature (0-50 degrees C). The variation of the apparent magnitudes of the water proton magnetizations in the solutions with temperature indicates that magnetic coupling mixes protein and water proton magnetizations. The results are consistent with an exchange cross-relaxation model (Hills, B. P., Mol Phys 1992, 76, 489-508) in which the cross-relaxation acts between the labile and nonlabile protons, rather than between water and protein protons. Although this cross-relaxation pathway clearly affects the observed magnetization fractions in this protein solution, its influence on the relaxation rates is less apparent.

Proton spin-spin relaxation study of hydration of a model nanopore.

The hydration pattern of controlled pore glass, with pore diameter of 237 A, was investigated using nuclear magnetic resonance. Water proton spin-spin relaxation decay curves were monitored and modeled as two-component exponential decays as a function of hydration. The results are consistent with a geometric model involving a surface water layer and a bulk-like liquid fraction in the form of a plug. The amount of surface water increases as the sample hydrates, until hydration reached approximately a monolayer, at which point a water plug starts to form in the pore, and grow in length at the expense of the surface layer. The results are also analyzed in terms of, and compared to, a recently developed puddle pore-filling model [S.G. Allen, et al. J. Chem. Phys. 106 (1997) 7802-7809].

High-resolution inelastic neutron scattering from water in mesoporous silica.

High-resolution inelastic neutron scattering measurements of the molecular dynamics of water confined to a porous host, the molecular sieve known as MCM-41, which has a hexagonal array of parallel pores with average pore diameter of 27 A, are reported. Previous neutron measurements probing higher-energy transfers, and thus shorter time scales, have been analyzed with both a rotation-translation diffusion model and a stretched exponential intermediate scattering function. The dynamics on longer time scales presented here are modeled well with a stretched exponential relaxation in a confining geometry. The observed molecular dynamics of water are three orders of magnitude slower than has been previously reported for water confined in MCM-41.

NMR and monte carlo simulation studies of water adsorption dynamics.

Nuclear magnetic resonance water proton spin-spin relaxation time T(2) was measured in wood samples with moisture contents ranging from 0.50 to 26.4%. The experimental results are discussed in terms of Monte Carlo simulations, which determine the correlation times tau for reorientation of the water molecule proton-proton vectors. We demonstrate that 1/T(2) and tau qualitatively follow the same behavior with surface hydration. The common application of the multisite exchange model to hydrated systems is discussed in light of the new results.

Macromolecule and water magnetization exchange modeling in articular cartilage.

Magnetization exchange effects between the matrix macromolecules (e. g., collagen and proteoglycan) and water were examined in normal, deuterated, and proteoglycan-depleted articular cartilage. Relaxation results (T(2), T(1rho), and T(1)) suggested that a four-site exchange scheme provided an accurate model for articular cartilage relaxation and interspin group coupling details. Magnetization exchange within the collagen-bulk-water, proteoglycan-collagen, and collagen fibrillar water-collagen cartilage subsystems were quantified. Although collagen-bulk-water was the largest of the cartilage coupling subsystems ( approximately 90% signal) and is exploited in MRI, the rates of magnetization transfer (MT) within the latter subsystems were appreciably larger. Magnetization exchange rates for proteoglycan-collagen and collagen fibrillar water-collagen were 120 s(-1) and 4.4 s(-1), respectively. The observation of these latter two exchange subsystems suggested potential clinical MRI-MT applications in detecting molecular abnormalities associated with osteoarthritis.

Proton spin-spin relaxation study of molecular dynamics and proteoglycan hydration in articular cartilage.

Spin-spin relaxation of proton magnetization in natural and deuterated articular cartilage is reported over a range of hydration. Information about macromolecular dynamics is deduced and a hydration stabilized macromolecular regime identified. There is good correspondence between NMR results and cartilage stoichiometry. A new measure for hydration of proteoglycans is found.

Intrinsic proton relaxation parameters of hydrated polyglycine from two-dimensional time domain NMR

Proton two-dimensional time domain nmr involving T(1), T(1rho), T(1D), and T(2) measurements was applied to hydrated polyglycine powders. The results were analyzed for magnetization exchange and found to be consistent with a general three-site (glycine-water-glycine) exchange model. The intrinsic glycine and water proton relaxation parameters as well as the three exchange rates were obtained. Estimates of correlation times for water molecule motion at hydration sites are presented. Copyright 1999 John Wiley & Sons, Inc.

A preliminary study of magnetic resonance relaxation times (T1 and T2) in inflammatory and degenerative synovial fluids.

Multiple synovial fluid samples from 21 patients were analysed using standard synovial analysis techniques and by nuclear magnetic resonance spectroscopy. Significant negative correlations were noted between both T1 (P less than 0.01) and T2 (P less than 0.0006) relaxation times and synovial fluid total protein. No differences in T1 or T2 relaxation times were noted in synovial fluid between 16 patients with inflammatory forms of arthritis and five patients with degenerative arthritis. In a single rheumatoid arthritis patient with concurrent staphylococcal arthritis, T1 and T2 relaxation times did not vary between the active phase and the recovery phase. The lack of any significant differences in the measured relaxation times as a function of joint condition suggest that in vivo magnetic resonance measurements of T1 or T2 for joint analysis may not reveal information of either a diagnostic or pathophysiological nature.

Nature of lysozyme-water interactions by proton NMR.

Proton spin-lattice relaxation measurements were performed in 10 mM lysozyme solution as a function of temperature and degree of substitution of solvent H2O with D2O. The results show that in the temperature range from 274 to 323 K, the intermolecular lysozyme proton water proton coupling contributes appreciably to the observed water proton relaxation rate. In this system exchange between water protons and labile protein protons does not dominate the behaviour with temperature of the water-lysozyme intermolecular contribution to the spin-lattice relaxation.

An in vivo animal model to study chronic adriamycin cardiotoxicity: a P-31 nuclear magnetic resonance spectroscopy investigation.

The mechanism responsible for adriamycin induced cardiotoxicity is unknown. We have developed an in vivo rabbit model for use with P-31 nuclear magnetic resonance spectroscopy which allows serial investigations of the drug's effects on myocardial metabolism. Eleven animals were studied over a 10 week period and changes in intracellular pH and phosphate metabolites were observed. The magnitude of changes in pH and inorganic phosphate were the best indicators of the severity of the cardiomyopathy. The results are consistent with an adriamycin induced degeneration of myofibrils rather than a severe metabolic impairment.

Water molecule dynamics in hydrated lysozyme. A deuteron magnetic resonance study.

Proton nuclear magnetic resonance relaxation investigations of water dynamics in hydrated protein powders have the serious drawback that protein-water intermolecular dipolar interactions make the unambiguous interpretation of the results difficult. To circumvent this difficulty, deuteron spin-lattice and spin-spin relaxation times in lysozyme powder hydrated with deuterium oxide were measured as a function of temperature and at two frequencies. Although the deuteron relaxation results are compatible with a water molecule dynamics model based on either a bimodal distribution of correlation times or anisotropic motion, a comparison of the present results with proton data suggests than an anisotropic motion model is more likely to provide a reasonable description of the water molecule motion. An analysis based on an anisotropic motion model that uses two correlation times to characterize the motion shows that most of the water molecules rotate about their twofold axis of symmetry at a rate that is only approximately 100 times smaller than the rate of isotropic diffusion in the bulk liquid. The reorientation of the twofold axis of symmetry itself is characterized by a correlation time of approximately 10(-7) s.

Composition and relaxation of the proton magnetization of human enamel and its contribution to the tooth NMR image.

The spin-spin, T2, and spin-lattice, T1, relaxation times and the magnetization of protons were measured in human enamel. The proton free induction decay was analyzed into solid-like interstitial water, enamel apatite, and semiliquid-like water components. The solid-like interstitial water was evaluated to be approximately 5 wt% and the semiliquid-like water to be approximately 1 to 2%. Neither in wet nor in dry natural enamel does the solid water exchange upon deuteration nor can it be extracted in vacuum. The semiliquid natural water, which is in the closed pores of the structure in the two samples above also remains unexchanged upon an 8 hr deuteration and cannot be extracted in a vacuum. With the lineshape-relaxation correlation NMR the free induction decays from heads and tails of the enamel rods were resolved. The solid-like water with T2 of approximately 14 microseconds and the apatite with a T2 of approximately 61 microseconds have T2's too short to be observed in an NMR zeugmatogram. Therefore only the semiliquid water component having an apparent T*2 of about 240 microseconds would contribute to the NMR image of human enamel. Since the relative intensity of this proton magnetization component in tooth is quite small the NMR image of tooth would show primarily the dentin and liquids within the tooth and on its surface.

Improved characterization of healthy and malignant tissue by NMR line-shape relaxation correlations.

We performed a relaxation-line-shape correlation NMR experiment on muscle, liver, kidney, and spleen tissues of healthy mice and of mouse tumor tissue. In each tissue studied, five spin groups were resolved and characterized by their relaxation parameters. We report a previously uncharacterized semi-solid spin group and discuss briefly the value of this method for the identification of malignant tissues.

Nuclear magnetic resonance analysis of water in natural and deuterated mouse muscle above and below freezing.

Measurements of absolute proton signal intensities, free induction decays, spin-spin relaxation times, and local fields in the rotating frame in natural and fully deuterated mouse muscle at five temperatures in the range 293-170 K are reported. The analysis is carried out at three time windows on the free induction decay. The contribution to the magnetization from protons on large molecules and water are analyzed.

Nuclear magnetic resonance multiwindow analysis of proton local fields and magnetization distribution in natural and deuterated mouse muscle.

The proton free-induction decays, spin-spin relaxation times, local fields in the rotating frame, and spin-lattice relaxation times in the laboratory and rotating frames, in natural and fully deuterated mouse muscle, are reported. Measurements were taken above and below freezing temperature and at two time windows on the free-induction decay. A comparative analysis show that the magnetization fractions deduced from the different experiments are in good agreement. The main conclusion is that the resolution of the (heterogeneous) muscle nuclear magnetic resonance (NMR) response is improved by the multiwindow analysis.

Proton T1 study of coverage parameter changes in tissues from tumor-bearing mice.

measurements of water proton spin-lattice relaxation time, T1, at 20 and -15 degrees C have been performed in spleen, kidney, liver, and muscle tissues from tumor-bearing mice, as well as in tumors grown in their dorsal subcutaneous tissues. All mice used were either from the C3H/HeJ or BALB/c strain. At - 15 degrees C the T1's of tissues of a given type from tumor-bearing and healthy mice are essentially the same. It is shown that in spleen the increased T1 from tumor-bearing mice can only be explained in terms of a large change in the water coverage parameter of macromolecules. In liver, muscle, and tumors the increased water content accounts for the changes in T1, while kidney represents an intermediate case.

A study of molecular dynamics and freezing phase transition in tissues by proton spin relaxation.

Muscle, spleen, and kidney tissues from 4-wk-old C57 black mice were studied by proton magnetic resonance. Spin-lattice relaxation times at high fields and in the rotating frame, as well as the spin-spin relaxation times, are reported as a function of temperature in the liquid and frozen phase. Motions of large molecules and of water molecules and their changes at the freezing phase transition are studied. The shortcomings of the two-state fast-exchange relaxation model are discussed.