NMR relaxation

This is a progress report on elucidating the behaviour of liquids,
in particular water, in confined geometry on the nano- to mesoscale, and at interfaces. There are important measurements still to make, conclusions still to be drawn, and above all leaps of understanding still to be made. However, a number of important
features in the behaviour of these systems have recently become
clearer.
Nano-structuring of liquids and their crystals changes their Gibbs free energy, and hence their dynamics. This may most readily be probed by monitoring the alteration of phase changes as a function of temperature, together with changes in other parameters, particularly the confinement diameter. Such studies may be performed by monitoring the change in the pressure (at constant temperature) of the liquid in its own vapour (Kelvin equation), or by monitoring the change in the freezing/melting temperature (at constant pressure) of a crystal in its own liquid (Gibbs–Thomson equation).
In the latter case the melting and freezing temperatures of liquids
are modified by the changes in the volumetric Gibbs free energy
due to nanostructuring; this is related to the surface energy of
the curved interface between the crystal and its own liquid. This is thus dependent on the geometry of the interface between the crystal and its liquid. There is still discussion on this point as to the exact geometric constants and functional forms that are applicable for different confining geometries. Experimental evidence is presented for the cases of cylindrical pores (SBA-15), and for pores that on average are spherical (sol–gel). However, reconciling this comparative data with melting/freezing temperatures in each of these systems still pose a number of questions.
It is well known that bulk brittle ice has a hexagonal structure,
while brittle ice that forms in pores may be cubic in structure [1,2], Figs. 10 and 11. Adjacent surfaces appear to further alter the dynamics and structure of confined liquids and their crystals, leading in the case of a water/ice system to a state of enhanced rotational motion (plastic ice) just below the confined freezing/
melting transitions. This plastic ice layer appears to form at both
the ice–silica interface and the ice–vapour surface, and reversibly
transforms to brittle ice at lower temperatures. There is good evidence to suggest that the plastic ice at a silica interface transforms to cubic ice, while the plastic ice at vapour surfaces transforms to hexagonal ice. That this plastic ice may correspond to a layer at the crystal surface is suggested by the presence of only amorphous ice in confined systems with small dimensions (<3 nm diameter), whereas systems with larger dimensions (10 nm) contain brittle cubic ice and also some hexagonal ice (if a vapour interface is present); even larger systems (>30 nm) contain predominately hexagonal ice. It is conjectured that this layer of plastic ice at vapour surfaces may be present at the myriad of such interfaces in macroscopic systems, such as snow-packs, glaciers and icebergs, and may be an explanation for the need for plastic terms in the macroscopic dynamical models of these systems [3].
These results also point the way forward for a wide-range of
cryoporometric metrology studies of systems that are ‘difficult’
for NMR, such as high iron content clays and rocks, as well as age concrete. Results are presented for cryoporometric measurements on meteorite samples with a significant metallic content, exhibiting T2 relaxation times down to 2.5 us.

With traditional sandstone oil reservoirs coming to the end of their useful lives, there is interest in extracting oil and gas from shale and carbonate rocks. Recovered samples often contain hydrocarbon material, sometimes in a fairly mobile form, sometimes in a tarry form. There is also an interest in studying forms of porous carbon, such as biochar, both for their soil-remedial properties, and for carbon sequestration. Biochars, depending on heat-treatment temperature and duration, also frequently contain residual hydrocarbon matter. There are two techniques that will be discussed: Proton NMR Relaxation (NMRR) and NMR Cryoporometry (NMRC) [10.1016/j.physrep.2008.02.001]. This study applies proton NMR Relaxation to characterise the quantity and mobility of hydrocarbon matter in dried shale and carbonate rock and biochar pores. Curve-fitting is applied to the Free Induction Decays (FIDs) and Carr–Purcell–Meiboom–Gill (CPMG) echo trains to quantify the measurements. This study also a...

Purpose To develop a robust T 1ρ magnetic resonance imaging (MRI) sequence for assessment of myocardial disease in humans. Materials and Methods We developed a breath-held T 1ρ mapping method using a single-shot, T 1ρ-prepared balanced steady-state free-precession (bSSFP) sequence. The magnetization trajectory was simulated to identify sources of T 1ρ error. To limit motion artifacts, an optical flow-based image registration method was used to align T 1ρ images. The reproducibility and accuracy of these methods was assessed in phantoms and 10 healthy subjects. Results are shown in 1 patient with pre-ventricular contractions (PVCs), 1 patient with chronic myocardial infarc-tion (MI) and 2 patients with hypertrophic cardiomyopathy (HCM). Results In phantoms, the mean bias was 1.0 ± 2.7 msec (100 msec phantom) and 0.9 ± 0.9 msec (60 msec phantom) at 60 bpm and 2.2 ± 3.2 msec (100 msec) and 1.4 ± 0.9 msec (60 msec) at 80 bpm. The coefficient of variation (COV) was 2.2 (100 msec) and 1.3 (60 msec) at 60 bpm and 2.6 (100 msec) and 1.4 (60 msec) at 80 bpm. Motion correction improved the alignment of T 1ρ images in subjects, as determined by the increase in Dice Score Coefficient (DSC) from 0.76 to 0.88. T 1ρ reproducibility was high (COV < 0.05, intra-class correlation coefficient (ICC) = 0.85–0.97). Mean myocardial T 1ρ value in healthy subjects was 63.5 ± 4.6 msec. There was good correspondence between late-gadolinium enhanced (LGE) MRI and increased T 1ρ relaxation times in patients.

The interactions of three alcohols, namely, 2-butanol (BuOH), 3-methyl-2-butanol (MeBuOH), and 3,3-dimethyl-2-butanol (Me2BuOH) with propylene oxide octamer (PO8) and the copolymers (EO)8(PO)13(EO)8(L35) and (EO)13(PO)30(EO)13(L64) in D2O were studied using (13)C NMR spectra and relaxations and (1)H PFG NMR diffusion measurements. For L64, it was shown that the temperature at which the PO chain starts to change its conformation under dehydration decreases by 6 K for each additional methyl group in the alcohol molecule (i.e. with increasing its hydrophobicity), and the analogous conformation states are attained at temperatures approximately 10 K lower compared using ketonic analogs of the alcohols under the same conditions. Also, the first signs of L64 aggregation, according to the normalized diffusion coefficients, are at temperatures 7, 10, and 13 K lower for BuOH, MeBuOH, and Me2BuOH, respectively. These effects are much weaker for (PO)13 in L35 or nonexistent for (PO)8 in PO8, thus showing the role of cooperativity in dehydration and aggregation processes. According to diffusion measurements, the molar fraction of the alcohol hydrogen bonded to L64 increases with its hydrophobicity and, in an apparent conflict with thermodynamics, with increasing temperature at which also higher NOE can be observed. Strong hydrogen bond interaction, which is in cooperation with hydrophobic interaction, does not preclude the exchange between bound and free states of the alcohol, however. Using (13)C transverse relaxation, its correlation time is shown to be of the order of 10 ms.

Variable-temperature 13C NMR spin-lattice relaxation times (T1) and Nuclear Overhauser Enhancements (NOE) at two magnetic fields have been used to study the dynamics of the amorphous part of a semicrystalline sample (33% of crystallinity) of poly(β-hydroxyoctanoate) (PHO). The interpretation of the relaxation data of the backbone carbons was made by employing a number of motional models. Among these, the DLM model offered the best interpretation of the relaxation data in terms of conformational transitions and librational motions of the backbone CH vectors, and proved to be superior to unimodal distribution functions. The interpretation of temperature- and frequency-dependent T1 and NOE data of the carbon nuclei in the n-pentyl side chain was made by employing a newly developed composite spectral density function for multiple internal CC bond rotations of restricted amplitude and chain segmental motion. The temperature dependence of the linewidths of the various protonated carbon resonances of PHO has been discussed in terms of the semicrystalline character of this polymer. © 1995 John Wiley & Sons, Inc.

Despite much progress in understanding the folding and the aggregation processes of proteins, the rules defining their interplay have yet to be fully defined. This problem is of particular importance since many diseases are initiated by protein unfolding and hence the propensity to aggregate competes with intramolecular collapse and other folding events. Here, we describe the roles of intramolecular and intermolecular interactions in defining the length of the lag time and the apparent rate of elongation of the 100-residue protein human beta(2)-microglobulin at pH 2.5, commencing from an acid-denatured state that lacks persistent structure but contains significant non-random hydrophobic interactions. Using a combination of site-directed mutagenesis, quantitative kinetic analysis and computational methods, we show that only a single region of about 10 residues in length, determines the rate of fibril formation, despite the fact that other regions exhibit a significant intrinsic prope...

Recent studies by Nuclear Magnetic Resonance and Neutron Scattering of the dynamics and phase-fractions of water/ice systems in templated porous silicas (SBA-15) indicate that what was believed to be a non-frozen surface water layer is actually plastic ice, the quantity varying (continuously and reversibly) with temperature, and converting to a brittle (mainly cubic) ice at lower temperatures.
Current research relates to the study the dynamics of polar water/ice and a-polar organics at both solid and vapour interfaces. The polar results are significant for water/ice systems in the environment, where snow-packs, glaciers and icebergs are common examples of water/ice systems with extensive air/vapour interfaces.
This research also points the way forward for wide-range cryoporometric metrology in 'difficult' systems such as high iron content clays and rocks, as well as aged concrete. Results are presented for cryoporometric measurements on meteorite samples with a significant metallic content, exhibiting 7^* relaxation times down to 2.5us.
Keywords: confined geometry, phase-change, Gibbs-Thomson, neutron scattering, neutron diffraction, plastic ice, NMR, NMR relaxation,
cryoporometry, DSC, thermoporosimetry, porous silica, meteorite, porosity
PACS: 64.60.-i, 81.07.-b, 61.12.Ld, 61.18.Fs, 03.75.Hh, 05.70.Fh, 64.60.Qb, 64.70.Dv, 68.03.Cd, 68.08.-p, 82.56.Na, 82.56.Ub, 61.43.Gt