Proton Cross-relaxation Research Articles

Specific Ions Modulate Diffusion Dynamics of Hydration Water on Lipid Membrane Surfaces

Effects of specific ions on the local translational diffusion of water near large hydrophilic lipid vesicle surfaces were measured by Overhauser dynamic nuclear polarization (ODNP). ODNP relies on an unpaired electron spin-containing probe located at molecular or surface sites to report on the dynamics of water protons within ∼10 Å from the spin probe, which give rise to spectral densities for electron–proton cross-relaxation processes in the 10 GHz regime. This pushes nuclear magnetic resonance relaxometry to more than an order of magnitude higher frequencies than conventionally feasible, permitting the measurement of water moving with picosecond to subnanosecond correlation times. Diffusion of water within ∼10 Å of, i.e., up to ∼3 water layers around the spin probes located on hydrophilic lipid vesicle surfaces is ∼5 times retarded compared to the bulk water translational diffusion. This directly reflects on the activation barrier for surface water diffusion, i.e., how tightly water is bound to the hydrophilic surface and surrounding waters. We find this value to be modulated by the presence of specific ions in solution, with its order following the known Hofmeister series. While a molecular description of how ions affect the hydration structure at the hydrophilic surface remains to be answered, the finding that Hofmeister ions directly modulate the surface water diffusivity implies that the strength of the hydrogen bond network of surface hydration water is directly modulated on hydrophilic surfaces.

Effect of the frequency of intramolecular motions on the NMR relaxation in liquid state temperature regime

Equations for the spectral densities of complex motion of a spin pair undergoing internal motion and isotropic/anisotropic overall rotation have been considered. The fluctuations of the interproton distances, caused by internal motion, have been taken into account in the theoretical equations. A method allowing a distinction between the isotropic and the anisotropic overall rotation of molecules has been proposed. The effect of the activation parameters of internal motions (known from the solid state study) on the measured T 1 relaxation of the 13C and 1H–1H cross-relaxation rates has been analysed for methyl-β-D-galactopyranoside in DMSO-d6 solution. The conformational trans-gauche jumps of the methylene group are not fast enough to affect the T 1 value of carbon C6 in the liquid state temperatures regime. Only the methyl group rotation is a very fast internal motion. This motion influences the carbon C7 relaxation and methyl protons–anomeric proton cross-relaxation. The values of interatomic distances between anomeric H(C1) and H(C5) as well as the three methyl protons H(C7) have been calculated from the cross-relaxation rates. The distance H(C1)–H(C7) fluctuates due to the rotation of methyl group. The application of the ‘model-free approach’ to study molecular dynamics in solutions is discussed.

Interactions of Charged Porphyrins with Nonionic Triblock Copolymer Hosts in Aqueous Solutions

The extent and locus of solubilization of guest and self-assembling surfactant host molecules in aqueous solutions are influenced by a variety of hydrophobic and hydrophilic interactions, as well as by more specific interactions between the various species present. By using a combination of two-dimensional heteronuclear 13C[1H] NMR correlation experiments with pulsed-gradient NMR diffusion and proton cross-relaxation measurements, the locations and distributions of porphyrin guest molecules have been established unambiguously with respect to the hydrophobic and hydrophilic moieties of a triblock copolymer species in solution. The interactions of tetra(4-sulfonatophenyl)porphyrin with the poly(propylene oxide) (PPO) and the poly(ethylene oxide) (PEO) segments of amphiphilic PEO-PPO-PEO triblock copolymer species have been measured as functions of solution conditions, including temperature and pH. The porphyrin/PEO-PPO-PEO interactions are established to be selective and adjustable according to the different temperature-dependent hydrophilicities or hydrophobicities of the PEO and PPO triblock copolymer components. Furthermore, such interactions influence the self-assembly properties of the block-copolymer amphiphiles in solution by stabilizing molecular porphyrin/PEO-PPO-PEO complexes well above the critical micellization temperature of the triblock copolymer species under otherwise identical conditions.

NMR Cross-Relaxation Study of Ultraslow Motion of the DomainWall in Channel Inclusion Compound

We report on an NMR study of ultraslow motions in the channel thiourea-hexachloroethane inclusion compound, [2.95(NH2)2CS] C2Cl6. Temperature dependent 1H NMR relaxation measurements of the powder thiourea-hexachloroethane at different resonance frequencies, from 23 to 55.5 MHz, have been carried out. Significant reduction of the spin-lattice relaxation time at 38 and 47 MHz is caused by the cross-relaxation of protons via the quadrupole chlorine nuclei. We show that the effective 1H-35Cl cross-relaxation observed in a powder sample is due to a slow mode process, when the molecules of the domain wall exhibit a correlated translational and rotational motion over the channel. Such propagation of the domain wall is confirmed by atom-atomic potential calculation. - Pacs: 76.60-k, 76.60.Es, 61.44.Fw, 61.66.Hq

Solution Structure of a Type 1 H Antigen Trisaccharide at a Micellar Surface: NMR Relaxation and Molecular Dynamics Simulation Studies

The conformation and dynamics of the type 1 H trisaccharide α-l-Fucp-(1→2)-β-d-Galp-(1→3)-β-d-GlcpNAc has been studied as a glycolipid (GL) in a micellar sodium dodecyl sulfate-d25 (SDS)/D2O solution. Carbon-13 spin−lattice (T1) and spin−spin (T2) relaxation time measurements of the GL in the SDS micelles were carried out at two magnetic field strengths, namely, 11.7 and 14.1 T employing 2D NMR techniques. 1H,1H NOESY spectra at the higher field were used to obtain proton−proton cross-relaxation rates. A molecular dynamics simulation of the trisaccharide with explicit water was performed for 3 ns to generate a 3D molecular model. From the 13C NMR relaxation data, a reorientational correlation time was derived for the GL with τM = 1.7 ns as well as a generalized order parameter, S2 = 0.86, using the “model-free” formalism of Lipari and Szabo. Proton−proton distances were calculated from the experimental NMR data. A comparison based on these distances between the GL at the micellar surface and the trisaccharide simulated in water revealed a similar trans-glycosidic distance at the (1→2)-linkage whereas for the corresponding proton pair at the (1→3)-linkage a larger difference was present. On the basis of the Stokes−Einstein relationship for the SDS micelle and the assumption that the GL has a lateral diffusion coefficient similar to that of the SDS molecules on the micellar surface, a reorientational correlation time was estimated close to that found by experiment. The latter finding stresses that lateral diffusion contributes an important part in the reorientational motion of the GL.

Ultraslow motion of domain wall in channel inclusion compound studied by means of NMR cross-relaxation

We report temperature dependent 1H NMR relaxation measurements of the powder thiourea-hexachloroethane inclusion compound, [2.95(NH 2) 2CS]·C 2Cl 6, at different resonance frequencies, from 23 to 55.5 MHz. Significant reduction of spin–lattice relaxation time at 38–47 MHz is caused by the cross-relaxation of protons via the quadrupole chlorine nuclei. We conclude that the effective 1H– 35Cl cross-relaxation observed in powder sample is due to a slow mode process, when the molecules of the domain wall exhibit a correlated translational and rotational motion over the channel. Such a propagation of the domain wall was predicted by atom-atomic potential calculation. We show that the NMR cross-relaxation effect is an effective tool in studying ultraslow motions, in particular in incommensurate structures.

Multiple‐field carbon‐13 and proton relaxation in sucrose in viscous solution

Measurements of carbon-13 spin–lattice and spin–spin relaxation rates as well as nuclear Overhauser enhancement (NOE) were combined with selected proton cross-relaxation measurements for sucrose in a viscous cryosolvent, D2O–DMSO, at several magnetic fields and two temperatures. The results, which were outside the extreme narrowing regime, were interpreted using the Lipari–Szabo formalism. All the carbon relaxation data and the proton cross-relaxation rates give a consistent description, demonstrating that the two sugar residues display a similar and highly limited internal mobility and that the hydroxymethyl groups are more mobile. Our combined carbon and proton data do not give evidence for flexibility of the glycosidic linkage in sucrose. Copyright © 2000 John Wiley & Sons, Ltd.

Molecular characterization around a glassy transition of starch using (1)H cross-relaxation nuclear magnetic resonance.

The aim of this work was to characterize the glassy-rubbery transition in starch gels using molecular (NMR) techniques. Proton cross-relaxation ((1)H CR) NMR spectra of gelatinized starch ( approximately 50% mc) were obtained by cooling stepwise from 20 to -30 degrees C. A significant line broadening was observed in the CR spectra between 0 and -10 degrees C. Deconvolution of the spectra into its component curves (broad and narrow) yielded a peak amplitude, width at half-height, and peak area for each curve. Between 0 and -10 degrees C (temperatures around T(g)), a significant line width change in the broad component (rigid solid) was apparent. These observed qualitative changes may be evidence of a glassy-rubbery transition at a molecular (short-range) level which are strengthened by a similar transition temperature range found previously with (13)C CP-MAS and DMA tan delta(T) measurements. However, the increase in the relative quantity of rigid protons observed by (1)H CR NMR spectra could also be attributed to ice. The (1)H CR NMR method showed its potential application for probing solid components in gels using a simple and economical NMR spectrometer, without the need for a solid-state instrument.

Multiple-field carbon-13 and proton relaxation in sucrose in viscous solution

Measurements of carbon-13 spin–lattice and spin–spin relaxation rates as well as nuclear Overhauser enhancement (NOE) were combined with selected proton cross-relaxation measurements for sucrose in a viscous cryosolvent, D2O–DMSO, at several magnetic fields and two temperatures. The results, which were outside the extreme narrowing regime, were interpreted using the Lipari–Szabo formalism. All the carbon relaxation data and the proton cross-relaxation rates give a consistent description, demonstrating that the two sugar residues display a similar and highly limited internal mobility and that the hydroxymethyl groups are more mobile. Our combined carbon and proton data do not give evidence for flexibility of the glycosidic linkage in sucrose. Copyright © 2000 John Wiley & Sons, Ltd.

NMR relaxation studies of oligosaccharides in solution: Reorientational dynamics and internal motion

Some recent studies of nuclear spin relaxation in small oligosaccharides are presented. The emphasis is on the carbon-13 work, but some data on proton cross-relaxation are also reported.

A note on proton cross-relaxation in polymer dispersed liquid crystals

Measurements of the proton cross-relaxation rate in the polymer dispersed 4-pentyl4-cyanobiphenyl (5CB) droplets were performed by the selective magnetization inversion NMR technique. This method makes possible direct determination of the magnitude of the fast cross-relaxation rate in theMHz regime where the standard spin-lattice relaxation measurements only indicate its presence. In the isotropic phase, the cross-relaxation rate is found to be more than ten times larger in the droplets of pure 5CB than that reported earlier for the liquid crystal mixture E7 in the same polymer. The difference is discussed in terms of dynamic processes in the surface layer.

NMR analysis of carbohydrates with model-free spectral densities: the dispersion range revisited.

Over the past decade molecular mechanics and molecular dynamics studies have demonstrated considerable flexibility for carbohydrates. In order to interpret the corresponding NMR parameters, which correspond to a time-averaged or 'virtual' conformer, it is necessary to simulate the experimental data using the averaged geometrical representation obtained with molecular modelling methods. This structural information can be transformed into theoretical NMR data using empirical Karplus-type equations for the scalar coupling constants and the appropriate formalism for the relaxation parameters. In the case of relaxation data, the 'model-free' spectral densities have been widely used in order to account for the internal motions in sugars. Several studies have been conducted with truncated model-free spectral densities based on the assumption that internal motion is very fast with respect to overall tumbling. In this report we present experimental and theoretical evidence that suggests that this approach is not justified. Indeed, recent results show that even in the case of moderate-sized carbohydrates internal motions are occurring on the same timescale as molecular reorientation. Simulations of relaxation parameters (NOESY volumes, proton cross-relaxation rates, carbon T1 and nOe values) in the dispersion range (0.1 < tau(c) < 5 ns) show that rates of internal motion can be fairly precisely defined with respect to overall tumbling. Experimental data for a variety of oligosaccharides clearly indicate similar timescales for internal and overall motion.

A study of protein-water exchange through the off-resonance ROESY experiment: application to the DNA-binding domain of AlcR.

In this communication a new NMR experiment for the safe observation and quantification of water-protein exchange phenomena is presented. It combines a water-selective pulse, offering chemical shift-based separation, and the off-resonance ROESY dynamic filter, which permits the elimination of the unwanted intramolecular dipolar cross relaxation of protein protons. Moreover, pulsed field gradients are used for the suppression of radiation damping and the solvent signal. The straightforward incorporation of this sequence in heteronuclear experiments is demonstrated for the case of the DNA-binding domain of the alcohol regulator protein.

Dynamical Behavior of Carbohydrates As Studied by Carbon-13 and Proton Nuclear Spin Relaxation

Variable-field carbon-13 and proton relaxation data are reported for two saccharides: a monosaccharide, 1,6-anhydro-β-d-galactopyranoside; and a disaccharide, methyl 3-O-α-d-mannopyranosyl-β-d-glucopyranoside. Carbon-13 measurements were perfomed at two fields, 4.7 and 9.4 T, and at 268, 288, and 303 K for the monosaccharide and at 268, 288, 303, and 323 K for the disaccharide. Proton cross-relaxation measurements were performed at three magnetic field strengths, 7.05, 9.4, and 11.75 T, and at several temperatures, 268, 288, and 303 K for the monosaccharide and 268, 282, 288, and 323 K for the disaccharide. The carbon-13 results were analyzed with the Lipari−Szabo “model-free” approach to obtain estimates of the global correlation times and order parameters. The monosaccharide was found to be very rigid, with S2 = 0.91, while the disaccharide showed some internal motions reflected in a lower order parameter, S2 around 0.8. The intra-ring proton cross-relaxation could be explained by the motional paramete...

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.

Interpretation of Magnetization Transfer and Proton Cross-Relaxation Spectra of Biological Tissues

Magnetization-tfansfer (MT) experiments have been performed at 300 MHz on agar gels, solutions of sodium alginate, bovine nasal cartilage, and postmortem porcine muscle, The experimental results elucidate MT mechanisms between mobile macromolecules (correlation time τC On the order of 10−8 s) and water, and demonstrate the need to incorporate their effects in the characterization of biological samples. In addition, the results obtained confirm a recently published three-spin-bath theoretical treatment for proton magnetization transfer.

Measurement of the cross relaxation rate for a polymer dispersed liquid crystal system

Proton cross relaxation between liquid crystal and polymer in a polymer dispersed liquid crystal (PDLC) system has been studied by the use of magic angle spinning and polarization transfer. The cross relaxation rates have been determined as functions of temperature, irradiation power, and off-resonance frequency setting. The data at each temperature are treated by a new set of relaxation equations which are not limited by the assumption of complete saturation of the polymer protons. The cross relaxation rates for the aromatic and aliphatic protons are similar over the temperature range studied, indicating that the liquid crystal molecules anchor parallel to the polymer surface. Before the glass transition, the cross relaxation rates increase with temperature due to a reduction in the contact time. After the glass transition, at about 37 °C, the cross relaxation rates decrease rapidly with temperature due to an increase in the motions of the polymer molecules which cause a reduction in the efficiency of spin energy exchange.

Novel measurements of nuclear spin cross-relaxation in metal hydrides

Recent NMR measurements of proton relaxation have shown an unexpected frequency dependence in several metal-hydrogen systems at low temperatures. An explanation proposed by the Ames group involves cross-relaxation of protons to quadrupolar metal nuclei. We test this hypothesis with relaxation experiments involving large amplitude field modulation. The field modulation sweeps the proton resonance through the distribution of metal frequencies. Thus the protons come into contact with more metal nuclei, increasing the proton relaxation rate. Relaxation measurements have been performed on several samples and the proton resonance frequency, the modulation frequency and the modulation amplitude have been varied. Also, proton relaxation rates T 1 −1 have been measured on slowly spinning samples where the rotation produces periodic variations of the metal quadrupolar frequencies.

Frequency-dependent proton spin relaxation in Zr 2PdH x

The proton nuclear spin-lattice relaxation rates T 1 −1 of amorphous Zr 2PdH 2.9 and crystalline Zr 2PdH 1.9 were examined from 4 to 400 K at several frequencies. The observed temperature dependence is nearly T 1 −1 ∝ T, but the relaxation rate depends on frequency, unlike the behavior of the expected Heitler- Teller-Korringa mechanism. Furthermore, the relaxation rates in the crystalline and amorphous samples are surprisingly similar. The frequency dependence can be explained by two models: proton cross-relaxation to metal nuclei and low frequency tunneling motions.

Proton and tritium NMR relaxation studies of peptide inhibitor binding to bacterial collagenase: conformation and dynamics.

The interaction of succinyl-Pro-Ala, a competitive inhibitor of Achromobacter iophagus collagenase, with the enzyme was studied by longitudinal proton and tritium relaxation. Specific deuterium and tritium labeling of the succinyl part at vicinal positions allowed the measurement of the cross-relaxation rates of individual proton or tritium spin pairs in the inhibitor-enzyme complex as well as in the free inhibitor. Overall correlation times, internuclear distances, and qualitative information on the internal mobility in Suc1 (as provided by the generalized order parameter S2) could be deduced by the comparison of proton and tritium cross-relaxation of spin pairs at complementary positions in the -CH2- CH2- moiety as analyzed in terms of the model-free approach by Lipari and Szabo. The conformational and motional parameters of the inhibitor in the free and enzyme-bound state were directly compared by this method. The measurement of proton cross-relaxation in the Ala residue provided additional information on the inhibitor binding. The determination of the order parameter in different parts of the inhibitor molecule in the bound state indicates that the succinyl and alanyl residues are primarily involved in the interaction with the enzyme activity site. The succinyl moiety, characterized in solution by the conformational equilibrium among the three staggered rotamers--i.e., trans: 50%; g+: 20%; g-: 30%--adopted in the bound state the unique trans conformation.