Jean-Pierre Korb

Relative role of surface interactions and topological effects in nuclear magnetic resonance of confined liquids

The relative roles of surface and topological effects on the nuclear relaxation rates T−11, T−12, and T−11ρ of polar or nonpolar liquids in porous sol‐gel silica glasses are identified via their very different pore size and frequency dependences. On the basis of theory, experimental relaxation rates, and molecular dynamics simulations for the modeled porous systems, the 1/Ti’s are interpreted in terms of a linear combination of bulk, confinement, and surface effects: 1/Ti = 1/Tibulk + ai/R2+ bi/R, where R is the average pore size and ai and bi are given in terms of the usual relaxation parameters of the studied molecular species. This simple expression which allows the determination of the relative roles of surface and topological effects has been used to fit the observed 1H NMR relaxation rates as a function of pore size and frequency for methylcyclohexane, nitrobenzene, pyridine, and toluene both for nonmodified and surface modified porous silica glasses. Using this method, the surface (∝1/R) and pure g...

The physical basis for the magnetic field dependence of proton spin-lattice relaxation rates in proteins

The magnetic field dependence of the proton spin-lattice relaxation rate in polymeric materials and biological macromolecules may report important dynamical information. In the case where the system is dynamically heterogeneous as in plasticized polymeric systems or hydrated biopolymers, the spin-lattice relaxation of the liquid-proton population is generally coupled to the spin-relaxation behavior of the solid spins that often dominate the observable response of the liquid. In many of these systems the magnetic field dependence of the proton spin-lattice relaxation rate may be represented as a power law: 1/T1(ω)=Aω−b where a is a constant and b is usually found to be in the range of 0.5 to 0.8. We have shown that this power law may arise naturally from localized structural fluctuations along the backbone of chain molecules that modulate the proton dipole–dipole couplings, which form a network described by a fractal dimension that may be less than the Euclidean dimension. When the model for the solid spin...

Magnetic Field Dependence of Proton Spin-Lattice Relaxation Times

The magnetic field dependence of the water‐proton spin‐lattice relaxation rate (1/T1) in tissues results from magnetic coupling to the protons of the rotationally immobilized components of the tissue. As a consequence, the magnetic field dependence of the water‐proton (1/T1) is a scaled report of the field dependence of the (1/T1) rate of the solid components of the tissue. The proton spin‐lattice relaxation rate may be represented generally as a power law: 1/T1ω = Aω−b, where b is usually found to be in the range of 0.5–0.8. We have shown that this power law may arise naturally from localized structural fluctuations along the backbone in biopolymers that modulate the proton dipole‐dipole couplings. The protons in a protein form a spin communication network described by a fractal dimension that is less than the Euclidean dimension. The model proposed accounts quantitatively for the proton spin‐lattice relaxation rates measured in immobilized protein systems at different water contents, and provides a fundamental basis for understanding the parametric dependence of proton spin‐lattice relaxation rates in dynamically heterogeneous systems, such as tissues. Magn Reson Med 48:21–26, 2002.

Probing Structure and Dynamics of Bulk and Confined Crude Oils by Multiscale NMR Spectroscopy, Diffusometry, and Relaxometry

We propose using a set of noninvasive multiscale NMR techniques for probing the structure and dynamics of bulk and confined crude oils with and without asphaltene. High-field 1D (1)H and (13)C NMR spectroscopies evidence the proton species and the amount of asphaltene and give an average chain length for the hydrocarbon aliphatic chains. Two-dimensional (1)H diffusion-ordered NMR spectroscopy (DOSY) spectra allow us to identify two populations of hydrocarbons characterized by two distributions of translational diffusion coefficients in the presence of asphaltene and a single one without asphaltene. A detailed analysis of the distributions of longitudinal, T1, relaxation times measured at different magnetic fields is proposed in terms of highly skewed bimodal (or monomodal) log-normal distributions, confirming the two environments in the presence of asphaltene and a single one without asphaltene. We show that these distributions are similar to the gas and gel permeation chromatography distributions, thus showing a connection of the hydrocarbon dynamics with their chain lengths. The remarkable observed features of the nuclear magnetic relaxation dispersion (NMRD) profiles of <1/T1> for bulk and confined crude oils with and without asphaltene are interpreted with an original relaxation model of intermittent surface dynamics of proton species at the proximity of asphaltene nanoaggregates and bulk dynamics in between clusters of these nanoaggregates. This allows us to probe the 2D translational diffusion correlation time and the time of residence of hydrocarbons in the proximity of the asphaltene nanoaggregates. Provided that the diffusion of the hydrocarbons close to the asphaltene nanoaggregates is three times smaller than the bulk diffusion, as the DOSY experiments show, this time of residence gives an average radius of exploration for the 2D hydrocarbon diffusion, r2D ≈ 3.9 nm, of the same order of magnitude as the aggregate sizes found by J. Eyssautier with SAXS and SANS in asphaltene solutions and by O. C. Mullins with the observation of gravitational gradients of asphaltenes in oilfield reservoirs.

Dimensionality of Diffusive Exploration at the Protein Interface in Solution

The dynamics of water are critically important to the energies of interaction between proteins and substrates and determine the efficiency of transport at the interface. The magnetic field dependence of the nuclear spin-lattice relaxation rate constant 1/T(1) of water protons provides a direct characterization of water diffusional dynamics at the protein interface. We find that the surface-average translational correlation time is 30-40 ps and the magnetic field dependence of the water proton 1/T(1) is characteristic of two-dimensional diffusion of water in the protein interfacial region. The reduced dimensionality substantially increases the intermolecular re-encounter probability and the efficiency of the surface exploration by the small molecule, water in this case. We propose a comprehensive theory of the translational effects of a small diffusing particle confined in the vicinity of a spherical macromolecule as a function of the relative size of the two particles. We show that the change in the apparent dimensionality of the diffusive exploration is a general result of the small diffusing particle encountering a much larger particle that presents a diffusion barrier. Examination of the effects of the size of the confinement relative to the macromolecule size reveals that the reduced dimensionality characterizing the small-molecule diffusion persists to remarkably small radius ratios. The experimental results on several different proteins in solution support the proposed theoretical model, which may be generalized to other small-particle-large-body systems like vesicles and micelles.

Surface nuclear magnetic relaxation and dynamics of water and oil in granular packings and rocks.

Low field proton nuclear spin-relaxation at variable magnetic field strength and temperature provides surface dynamical parameters such as surface diffusion coefficients, activation energies, time of residence and coefficient of surface affinity. These parameters were extracted from measurements on grain packs and natural oil-bearing rocks. On grain packs, we show first that changing the amount of surface paramagnetic impurities leads to striking different relationships between the pore-size and the relaxation times T1 and T2. These relationships are well supported by fast-diffusion (surface-limited) or slow-diffusion relaxation models. Surface relaxivity parameters rho1 and rho2 are deduced from the pore size dependence in the fast-diffusion regime. Then, we evidence the frequency and temperature dependence of the surface relaxivity rho1 by field cycling NMR relaxation and relevant theoretical models. The typical frequency dependence found allows an experimental separation of the surface and bulk microdynamics in granular packings and petroleum rocks and the determination of the above mentioned surface dynamical parameters. Finally, we present the first field cycling nuclear spin relaxation experiments performed in water/oil saturated petroleum rocks. We believe that these experiments give new information about the surface localization of these two saturating liquids in pores.

Water and backbone dynamics in a hydrated protein.

Rotational immobilization of proteins permits characterization of the internal peptide and water molecule dynamics by magnetic relaxation dispersion spectroscopy. Using different experimental approaches, we have extended measurements of the magnetic field dependence of the proton-spin-lattice-relaxation rate by one decade from 0.01 to 300 MHz for (1)H and showed that the underlying dynamics driving the protein (1)H spin-lattice relaxation is preserved over 4.5 decades in frequency. This extension is critical to understanding the role of (1)H(2)O in the total proton-spin-relaxation process. The fact that the protein-proton-relaxation-dispersion profile is a power law in frequency with constant coefficient and exponent over nearly 5 decades indicates that the characteristics of the native protein structural fluctuations that cause proton nuclear spin-lattice relaxation are remarkably constant over this wide frequency and length-scale interval. Comparison of protein-proton-spin-lattice-relaxation rate constants in protein gels equilibrated with (2)H(2)O rather than (1)H(2)O shows that water protons make an important contribution to the total spin-lattice relaxation in the middle of this frequency range for hydrated proteins because of water molecule dynamics in the time range of tens of ns. This water contribution is with the motion of relatively rare, long-lived, and perhaps buried water molecules constrained by the confinement. The presence of water molecule reorientational dynamics in the tens of ns range that are sufficient to affect the spin-lattice relaxation driven by (1)H dipole-dipole fluctuations should make the local dielectric properties in the protein frequency dependent in a regime relevant to catalytically important kinetic barriers to conformational rearrangements.

Structure–texture correlation in ultra-high-performance concrete: A nuclear magnetic resonance study

Abstract The pore size distribution in three reactive powder concrete formulations has been studied by nuclear magnetic relaxation of protons. Confirming the discrete and fractal features of the distribution for this kind of concrete, each formulation is assessed a surface fractal dimension, which reveals the hierarchy of pores. The experimental results evidence a dependence between this dimension and both the filling ratio of cement grains and the reactivity of silica fume. 29 Si nuclear magnetic resonance (NMR) allows us to draw a relationship between the amount of calcium silicate hydrates (C-S-H) and this surface fractal dimension.

Nuclear magnetic resonance characterization of high- and ultrahigh-performance concrete: Application to the study of water leaching

Abstract In the present study, we show that high-resolution 29 Si and 27 Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) can be a powerful tool for analyzing actual concrete mixes. The influence of the amount of silica fume and of the type of cement in high-performance concrete (HPC), as well as the influence of the type of silica fume and of the granular packing in ultrahigh-performance concrete (UHPC) were investigated. Significant effects on the amount and shape of C-S-H, on the incorporation of aluminum in the C-S-H structure, and on the distribution of aluminum-containing hydrates were observed. Nuclear magnetic relaxation of protons was also performed and it showed the fractal feature of the pore size distribution in UHPC and the higher amount of larger pores in HPC. The microstructure of the surface of these same formulations leached by mineral water for up to 1 year exhibits slight modifications.

Surface dynamics of liquids in porous media

We report remarkable differences in the 1H nuclear magnetic relaxation dispersion data (NMRD) between water and other common aprotic solvents such as acetone when in contact with high surface area calibrated microporous chromatographic silica glasses that contain trace paramagnetic impurities located at or close to the pore surface. All these differences have been related to the particular chemical behaviors and dynamics of these liquids at the pore surface. We apply this technique to probe the structure and dynamics of water and oil at the surface of calibrated macroporous systems, where similar surface dynamics effects have been observed. This technique is also applied to follow the first hydration stage of a white cement-paste. Last, we present an analysis of the magnetic field dependence of 1H nuclear relaxation data to exhibit the microporosity of ultra high performance concretes.