H. Peemoeller

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 (T2, T1ρ, and T1) 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 (∼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. Magn Reson Med 44:840–851, 2000.

Two-dimensional nmr time evolution correlation spectroscopy in wet lysozyme

Abstract A two-dimensional time evolution approach with which the free-induction decay of a heterogeneous system can be resolved partially was applied to natural and deuterated wet hen egg-white lysozyme (HEWL). The study was performed in the laboratory and rotating reference frames. The two-dimensional approach made possible a resolution of the heterogeneous spin distribution into four groups, which are briefly discussed. It is shown that in HEWL the strongly coupled nonexchangeable protein protons and water protons are relaxed either by the intramolecular water relaxation mechanism or by an intermolecular protein-water mechanism.

Proton rotating frame spin-lattice relaxation study of slow motion of pore water

Proton rotating frame spin-lattice relaxation times of water in hydrated porous silica glass, with pore diameters of 7.4, 23.7, 49.1, and 54.8 nm, are reported. Experiments were limited to hydrations corresponding to more than one-third hydrated pore volumes. The frequency dependence of the relaxation rates reveals a slow motion of pore water with a characteristic correlation time of ∼10−5 s. Within the limits given above, this correlation time depends on pore dimension and hydration only slightly. This indicates that the surface water molecules, which reorient with a characteristic time of ∼10−8 s, are changing their orientational axis with the slower correlation time ∼10−5 s. This process, which disrupts the nearby water molecules, depends primarily on the environment in the vicinity of the molecule’s original binding site. The analysis, based on the two-site fast exchange model, indicates that in small pores all the water may be affected by these slow jumps.

Magnetic resonance microimaging of pore freezing in cement: Effect of corrosion inhibitor

Single-point magnetic resonance imaging is applied to study the freezing behavior of white cement paste with and without a Ca(NO2)2 based corrosion inhibitor. Pore size distributions are determined from consideration of the evaporable water content. This represents a unique study into the effect of a corrosion inhibitor on the final cement product. It is found that with the addition of a Ca(NO2)2 based corrosion inhibitor a significant reduction of pores between 3 and 10 nm results, producing a considerably coarser pore structure. A dramatic increase in capillary pores of radii larger than 30 nm is also observed in the cement with the inhibitor and is expected to lead to an increased movement of corrosive agents into the concrete when compared to concrete without the corrosion inhibitor.

Temperature and hydration dependence of proton MAS NMR spectra in MCM-41: Model based on motion induced chemical shift averaging

The proton MAS NMR spectra in MCM-41 at low hydration levels (less than hydration amounting to one water molecule per surface hydroxyl group) show complex proton resonance peak structures, with hydroxyl proton resonances seen in dry MCM-41 disappearing as water is introduced into the pores and new peaks appearing, representing water and hydrated silanol groups. Surface hydroxyl group-water molecule chemical exchange and chemical shift averaging brought about by a water molecule visiting different surface hydrogen bonding sites have been proposed as possible causes for the observed spectral changes. In this report a simple model based on chemical shift averaging, due to the making and breaking of hydrogen bonds as water molecules move on the MCM-41 surface, is shown to fully reproduce the NMR spectra, both as a function of hydration and temperature. Surface proton-water proton chemical exchange is not required in this model at low hydration levels.

Characterization of proteoglycan depletion in articular cartilage using two-dimensional time domain nuclear magnetic resonance.

In vitro proteoglycan (PG) depletion in the 20–40% range (enzymatic PG depletion of normal cartilage in the early osteoarthritis (OA) PG depletion range) was investigated in articular cartilage using 2D time domain NMR relaxation techniques. Spin–lattice relaxation times were measured at low fields (T1ρ) and at high fields (T1) using nonselective and selective excitation pulse sequences. The short relaxation time magnetization components in T1ρ (∼8% signal) and nonselective T1 (∼5% signal) experiments were significantly altered with PG degradation. In addition, a magnetization component (∼5% signal) with a “fast ” T1 ∼ 7 ms was observed in the T1 experiment involving selective excitation. This fast T1 was at least 10 times shorter than the short T1 in the nonselective experiment and was associated with a strong magnetization exchange mechanism between collagen and PG. The results suggest that T1ρ and T1 (nonselective and selective) relaxation based MRI techniques, which focus on the short relaxation time magnetization components, have the potential of detecting molecular abnormalities associated with early OA earlier than single, long relaxation time component approaches. Magn Reson Med, 2005.

Measurement of rapid magnetization transfer across a polymer-water interface

The characterization of the magnetization exchange is crucial for the understanding of the molecular dynamics in these systems. With the aim of obtaining more direct information about the above intermolecular spin-spin coupling, a less complex system was studied. Here we report on the measurement of an intermolecular interfacial spin-spin coupling rate of ∼3000 s −1 in hydrated polyproline

1H Nuclear Magnetic Resonance of Lodgepole Pine Wood Chips Affected by the Mountain Pine Beetle

In this study, wood-water interactions of mountain pine beetle affected lodgepole pine were found to vary with time since death. Based on an analysis of magnetization components and spin-spin relaxation times from 1H NMR, it was determined that the mountain pine beetle attack does not affect the crystalline structure of the wood. Both the amorphous structure and the water components vary with time since death, which could be due to the fungi present after a mountain pine beetle attack, as well as the fact that wood from the grey-stage of attack cycles seasonally through adsorption and desorption in the stand.

Nmr high-resolution magic angle spinning rotor design for quantification of metabolic concentrations

A new high-resolution magic angle spinning nuclear magnetic resonance technique is presented to obtain absolute metabolite concentrations of solutions. The magnetic resonance spectrum of the sample under investigation and an internal reference are acquired simultaneously, ensuring both spectra are obtained under the same experimental conditions. The robustness of the technique is demonstrated using a solution of creatine, and it is shown that the technique can obtain solution concentrations to within 7% or better.

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 Woessners 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.