Water Proton Transverse Relaxation Times Research Articles

Effect of ultrasound on mill starch and protein in ultrasound-assisted laboratory-scale corn wet-milling

Ultrasound was applied to facilitate starch-protein separation during ultrasound-assisted laboratory-scale corn wet-milling. The effects of ultrasound on the properties of mill starch and protein were investigated to explore the possible mechanisms in this study. A higher starch yield was obtained with sonication treatment in starch-protein separation (15 min, 200 W) and the results showed that ultrasound did not induce damage to the product starch. The differences in the distribution of water proton transverse relaxation time for mill starch suggested that the interaction between starch granules and protein in mill starch was destroyed. The free sulfhydryl content increased by 37.21% and the disulfide bond content decreased by 43.66% of the separated proteins indicated that ultrasound destroyed the disulfide bonds effectively (p < 0.05). Sonication treatment for longer time or at higher power decreased α-helix and β-turn while increased β-sheet and random coil (p < 0.05). Ultrasound increased surface hydrophobicity and decreased the thermal stability of the protein (p < 0.05). The higher intensity of ultraviolet–visible spectroscopy and ultraviolet-difference absorption spectroscopy indicated the unfolding of protein by sonication treatments. Ultrasound may break down the disulfide bonds and hydrogen bonds of protein molecules, effectively releasing starch from the disintegrated protein agglomerates.

Novel mineral contrast agent for magnetic resonance studies of bone implants grown on a chick chorioallantoic membrane

Magnetic resonance imaging (MRI) studies of tissue engineered constructs prior to implantation clearly demonstrate the utility of the MRI technique for studying the bone formation process. To test the utility of our MRI protocols for explant studies, we present a novel test platform in which osteoblast-seeded scaffolds were implanted on the chorioallantoic membrane of a chick embryo. Scaffolds from the following experimental groups were examined by high-resolution MRI: (a) cell-seeded implanted scaffolds (CIM), (b) unseeded implanted scaffolds (UCIM), (c) cell-seeded scaffolds in static culture (CIV) and (d) unseeded scaffolds in static culture (UCIV). The reduction in water proton transverse relaxation times and the concomitant increase in water proton magnetization transfer ratios for CIM and CIV scaffolds, compared to UCIV scaffolds, were consistent with the formation of a bone-like tissue within the polymer scaffold, which was confirmed by immunohistochemistry and fluorescence microscopy. However, the presence of angiogenic vessels and fibrotic adhesions around UCIM scaffolds can confound MRI findings of bone deposition. Consequently, to improve the specificity of the MRI technique for detecting mineralized deposits within explanted tissue engineered bone constructs, we introduce a novel contrast agent that uses alendronate to target a Food and Drug Administration-approved MRI contrast agent (Gd-DOTA) to bone mineral. Our contrast agent termed GdALN was used to uniquely identify mineralized deposits in representative samples from our four experimental groups. After GdALN treatment, both CIM and CIV scaffolds, containing mineralized deposits, showed marked signal enhancement on longitudinal relaxation time-weighted (T1W) images compared to UCIV scaffolds. Relative to UCIV scaffolds, some enhancement was observed in T1W images of GdALN-treated UCIM scaffolds, subjacent to the dark adhesions at the scaffold surface, possibly from dystrophic mineral formed in the fibrotic adhesions. Notably, residual dark areas on T1W images of CIM and UCIM scaffolds were attributable to blood inside infiltrating vessels. In summary, we present the efficacy of GdALN for sensitizing the MRI technique to the deposition of mineralized deposits in explanted polymeric scaffolds.

Investigation of alginate beads for gastro-intestinal functionality, Part 2: In vivo characterisation

This paper summarises work undertaken to visualise and characterise alginate gel beads, in vivo, in the human gastro-intestinal tract using magnetic resonance imaging (MRI). Two types of alginate beads were investigated: “strong” (strongly gelled) and “weak” (weakly gelled) beads, each prepared by long and short exposures to a calcium chloride gelling bath, respectively. Ten volunteers attended the study centre, on two different occasions, and consumed a different bead type on each visit. Before consuming the bead meal, the volunteers consumed 50 ml of Calogen ® (a fatty preload) which converted gastric motility to a fed pattern and delayed the emptying of the non-nutrient model bead meal from the stomach. Gastric emptying of the bead meal was dominated by the fatty preload, with the median half-emptying time 48 min for both bead types. Gastric sieving of the strong beads occurred with the percentage of the meal remaining at 60 min significantly higher for the strong bead meal compared to the weak bead meal. Both types of gelled beads were clearly visualised by MRI in both the stomach and the small intestine, with beads being more visible in the ileum compared to the jejunum and duodenum. The water proton transverse relaxation time, T 2, of the beads was measured in the stomach. After an initial increase, T 2 decreased slightly over time from the initial in vivo measurement. In the first paper of this series, we correlate in vitro T 2 shortening with formation of a more dense gel network. These in vivo investigations suggest that changes in the gel beads, within the GI tract, could be monitored using T 2.

Noncovalent Functionalization of Carbon Nanotubes with Amphiphilic Gd3+ Chelates: Toward Powerful T1 and T2 MRI Contrast Agents

An amphiphilic gadolinium (III) chelate (GdL) was synthesized from commercially available stearic acid. Aqueous solutions of the complex at different concentrations (from 1 mM to 1 microM) were prepared and adsorbed on multiwalled carbon nanotubes. The resulting suspensions were stable for several days and have been characterized with regard to magnetic resonance imaging (MRI) contrast agent applications. Longitudinal water proton relaxivities, r1, have been measured at 20, 300, and 500 MHz. The r1 values show a strong dependence on the GdL concentration, particularly at low field. The relaxivities decrease with increasing field as it is predicted by the Solomon-Bloembergen-Morgan theory. Transverse water proton relaxation times, T2, have also been measured and are practically independent of both the frequency and the GdL concentration. An in vivo feasibility MRI study has been performed at 300 MHz in mice. A negative contrast could be well observed after injection of a suspension of functionalized nanotubes into the muscle of the leg of the mouse.

Prospects for the rapid detection of mealiness in apples by nondestructive NMR relaxometry

The potential of nuclear magnetic resonance (NMR) relaxometry for quantitative evaluation of apple mealiness has been investigated. The degree of “mealiness” was defined by several mechanical techniques, including penetration, compression and shear rupture as well as by the BRIX (soluble solids) and juiciness levels. These data were correlated with both magnetic resonance imaging (MRI) and NMR water proton transverse relaxation time measurements on a fruit-by-fruit basis. It was found that increasing mealiness caused a systematic increase in the transverse relaxation rate. The potential for rapid, on-line NMR/MRI detection of apple mealiness is discussed.

Sequential changes in MR water proton relaxation time detect the process of rat brain myelination during maturation

For better understanding of the behavior of water molecules in the animal brain, changes in magnetic resonance water proton relaxation processes were studied in the rat during maturation. Midbrains of male Wistar rats were removed at various time points ranging from 2 to 70 days after birth. Changes in relaxation time (water proton longitudinal relaxation time by the inversion recovery, and water proton transverse relaxation time by the spin echo and the Carr–Purcell–Meiboom–Gill pulse sequence (CPMG)) and water content were then determined for various stages of brain development. During maturation both water proton longitudinal relaxation time and water proton transverse relaxation time values decreased and this finding paralleled the decline in water content. Using the CPMG pulse sequence, the transverse relaxation time values were observed to separate into two components after 21 days. Morphologically, the most prominent change at the matured stage of midbrain development in the rat is myelination. Water proton relaxation time, which can be estimated using the CPMG pulse sequence, showed a close correlation with myelination in the central nervous system.

Histomorphometry of the embryonic avian growth plate by proton nuclear magnetic resonance microscopy.

Quantitative nuclear magnetic resonance (NMR) microscopy was used to characterize the biochemical and morphological properties of the different zones within the growth plate of an embryonic chick femur. For precalcified tissue, water proton transverse relaxation times (T2) and magnetization transfer values (MT) were directly and inversely dependent, respectively, on tissue cellularity, defined as the intracellular area per unit area on histological sections. T2 values extrapolated for intra- and extracellular water were 96 ms and 46 ms, respectively. The extracellular T2 was comparable with that measured for mature cartilage. The MT values extrapolated for intra- and extracellular compartments were 0.32 and 0.85, respectively. These values were comparable with those values reported in the literature for cell pellets and for mature cartilage tissue. Thus, cellularity dominated the NMR properties of this immature cartilage tissue. Mineral deposits within calcified cartilage and periosteal bone invoked NMR relaxation processes that were dependent on the inorganic mineral phase. Additionally, collagen molecules present in mineralized zones gave rise to a significant MT effect. These results show the utility of water proton NMR microscopy for assessing both the organic and inorganic phases within mineralized tissues.

1H-nmr study of water dynamics in hydrated collagen: transverse relaxation-time and diffusion analysis.

Water proton transverse relaxation times (T2) and self-diffusion coefficients (D) were measured in randomly oriented hydrated collagen fibers. Three T2 relaxation times were discerned indicating the presence of at least three water fractions in the collagen sample. The D values associated with each water fraction were determined. The diffusion time dependence of D suggests water motion is restricted by macromolecular structure. The experimental results are discussed with reference to the structural properties of hydrated collagen fibers.

NMR studies of water compartmentation in carrot parenchyma tissue during drying and freezing

An analysis is presented of the effect of drying and freezing on the distribution and pulse spacing dependence of water proton transverse relaxation times in carrot parenchyma tissue. The relaxation behaviour can be interpreted by treating the effects of changing subcellular morphology with a numerical cell model and combining this with a two-site proton exchange model to take account of solutes dissolved in the vacuolar fluid. In this way it is shown that drying removes water primarily from the vacuolar compartment, causing cell shrinkage and concentration of dissolved solutes, with little change in the volume of intercellular air spaces. Freezing causes initial ice crystal formation in the vacuolar compartment which concentrates the dissolved solutes. However, even at 248 K substantial quantities of nonfreezing water are associated with the cell walls and dissolved biopolymers. Comparison is made with previous studies on apple tissue.

NMR studies of changes in subcellular water compartmentation in parenchyma apple tissue during drying and freezing

The potential of Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) for non‐invasively monitoring the subcellular and intercellular redistribution of water in cellular tissue during drying and freezing processes is assessed and it is concluded that despite exciting advances in NMR micro‐imaging and NMR microscopy, nonspatially resolved NMR relaxation and diffusion techniques still provide the best probes of subcellular water compartmentation in tissue. The power of the NMR relaxation technique is illustrated by using the changes in the distribution of NMR water proton transverse relaxation times to monitor the subcellular compartmentation of water and ice during the drying and freezing of parenchyma apple tissue. The NMR drying data are analysed with a numerical model of the cell and show that mild air‐drying in a fluidized bed results in loss of water from the vacuolar compartment, but not from the cytoplasm or cell wall regions. The loss of vacuolar water is associated with overall shrinkage of the cell and only a slight increase in air space. During freezing the vacuolar compartment is found to be the first to freeze, with the cytoplasmic and cell wall compartments only freezing at much lower temperatures. Freeze‐drying apple tissue gives much lower water contents than fluidized bed drying, but the NMR data confirms that it destroys membrane integrity and causes cell wall collapse.

Dynamic NMR q-space studies of microstructure with the multigrade CPMG sequence

A new approach to q-space studies of microstructure is proposed, which exploits the combined information contained in the water proton transverse relaxation time distribution and the frequency dependence of the apparent water diffusivity in heterogeneous systems. Using an automated two-dimensional multigrade CPMG sequence, both the pulse spacing and the amplitude of the applied field gradient are varied systematically and used to measure the frequency and wave vector dependence of the multiple exponential echo decay constants and amplitudes. Undesirable crossterms in the applied and background field gradients are eliminated by a simple procedure involving a sign reversal in the applied gradient. Nonlinear, local susceptibility-induced field gradients are shown to lead to enhanced, frequency-dependent apparent water diffusivities that are sensitive to the local microstructure.

Combined relaxation and diffusion studies of porous media using the multigrade CPMG sequence

A new approach to q-space NMR studies of microstructure is proposed that exploits the combined information contained in the water proton transverse relaxation time distribution and the frequency dependence of the apparent water diffusivity. A simple protocol is used to eliminate undesirable crossterms in background susceptibility gradients. Local, microscopic nonlinearity in the applied field gradients is shown to lead to enhancement of the apparent water diffusivity in small pores at high frequencies. The relationships between NMR relaxation studies of pore emptying with sorption isotherms, electrical conductivity, and microbiological survival are indicated.

NMR studies of non-freezing water in randomly packed beds of porous particles

NMR water proton transverse relaxation time distributions are shown to provide valuable information about the distribution of ice and nonfreezing water in complex heterogeneous systems. In a model system consisting of randomly packed Sephadex beads the NMR data confirm that ice inside the porous Sephadex beads coexists as a two phase system with unfrozen dextran gel. The NMR relaxation technique is shown to provide complementary information to both differential scanning calorimetry and cryomicroscopy.

NMR studies of non-freezing water in cellular plant tissue

The distribution of water proton transverse relaxation times is used to monitor the amount and subcellular distribution of non-freezing water and ice in potato tissue. At subzero temperatures most of the non-freezing water is found to be associated with starch granules and cell wall material, and the amount of unfrozen water at each temperature has been determined. The potential of NMR relaxation techniques in food cryopreservation is discussed.

The effects of proteins on the proton N.M.R. transverse relaxation time of water

The changes in water proton transverse relaxation behaviour induced by aggregation of Bovine serum albumin are explained in terms of the simple molecular processes of diffusion and chemical exchange without recourse to invoking changes in ‘bound’ water or the ‘state’ of water in the system. It is proposed that the main effect of aggregation is to reduce the protein proton transverse relaxation time because dipole-dipole interactions between protein protons are no longer as efficiently averaged by rotational motions, this in turn causes a reduction in water proton transverse relaxation time since water protons are in fast chemical exchange with protein protons. Diffusive exchange between water molecules then spatially averages the water proton signal to an extent that depends on the morphology of the aggregate-water system. The diffusive averaging process can give rise to multi-exponential relaxation.

N.M.R. studies of water proton relaxation in Sephadex bead suspensions

The effects of morphology and diffusive exchange on N.M.R. water proton transverse relaxation times in a model heterogeneous system consisting of packed Sephadex beads are interpreted within a unified theoretical framework based on the Bloch-Torrey equations. The relaxation depends on the radii of the Sephadex beads, the cross-linking density of the dextran and varies with the C.P.M.G. interpulse spacing. The larger beads show multiexponential relaxation with up to three components. Without recourse to concepts such as ‘bound-water’ or ‘multiple site occupancy’ we show how the data can be simply understood as arising from diffusive exchange between regions having different relaxation times and resonance frequencies.

Acceleration of the rate of deoxyhemoglobin S polymerization by the erythrocyte membrane

1. Introduction One rationale for the difference between the frequently severe clinical course observed in indi- viduals with sickle cell anemia and the benign clinical course observed in individuals with sickle cell trait may be found in the profound difference in the rate of deoxyhemoglobin S polymerization between the two states [ 11. The kinetic properties of this polym- erization process have been shown to be altered by both pH and the degree of oxygenation of hemo- globin S (HbS) [2]. However, the influence of the erythrocyte membrane on the kinetics of polym- erization has not been investigated. It might be clinically significant if polymerization could be delayed during the time period required for an ery- throcyte to traverse the circulation back to the lungs where reoxygenation of the hemoglobin would occur [3]. For this reason the effect of the erythrocyte membrane on the kinetics of deoxy HbS has been studied by measurement of transverse water proton relaxation times (T,) [4-61. The rate of polymeri- zation in erythrocytes having a normal hemoglobin concentration is too fast to be measured by available techniques. However, in studies with S/S erythrocytes containing a reduced hemoglobin concentration, the rate of polymerization is much more rapid than in solutions of hemoglobin S at the same hemoglobin concentration. Addition of erythrocyte membrane fragments to hemoglobin S solutions also results in a decreased delay time and a more rapid rate of polym- erization. These results show that the erythrocyte membrane accelerates the rate of deoxyhemoglobin S * Present

Inhibitory effect of deoxyhemoglobin A 2 on the rate of deoxyhemoglobin S polymerization

From a consideration of the primary sequence of hemoglobin A 2 and the reported 5 å molecular contacts between deoxyhemoglobin S molecules in a crystal, it is predicted that hemoglobin A 2 might act as an inhibitor of the polymerization of deoxyhemoglobin S in a manner similar to hemoglobin. F. This has been tested experimentally by measuring the rate of change of the transverse water proton relaxation times ( T 2) in equimolar mixtures of hemoglobin S and one of the non-gelling hemoglobins A, F or A 2. Hemoglobins A 2 and F have far more pronounced inhibitory effects on the rate of polymerization than does hemoglobin A. These molecules contain several amino acid differences from hemoglobin A beta chains which are located in the 5 Å molecular crystal contacts and these altered crystal contacts result in a much stronger inhibition of the rate of polymerization. Since hemoglobin A 2 is a normal hemoglobin found in small amounts in all adult red cells, increased delta chain synthesis may have potential importance in therapy for sickle cell disease.

Kinetics of polymerization of deoxyhemoglobin S and mixtures of hemoglobin A and hemoglobin S at high hemoglobin concentrations

Transverse water proton relaxation times ( T 2) have been measured as a function of time after deoxygenation of solutions containing hemoglobin S. The shortened T 2 values observed upon deoxygenation of hemoglobin S result from an increase in the correlation time ( τ c) of the water fraction irrotationally bound to deoxyhemoglobin S as it polymerizes. Therefore, the change in τ c as a function of time after deoxygenation can be used to measure the rate of polymer formation. The change in τ c observed is reasonably fit by the first-order equation τ = τ 0 (1 − e − kt ) + τ oxy . At a total hemoglobin concentration of approximately 300 mg/ml, the pseudo-first-order rate constant in a heterozygous AS sample is 25 times slower than in a homozygous S sample, k = 0.019 and 0.47 s −1, respectively. Since the transit time for an erythrocyte in vivo is approximately 15 s, these results suggest that the heterozygous A/S erythrocyte would traverse the circulation and become reoxygenated before extensive polymerization and, therefore, cell sickling could occur. For the homozygous S/S erythrocyte, there is ample time for polymerization and for cell sickling during circulation.

Kinetics of the polymerization of hemoglobin S: Studies below normal erythrocyte hemoglobin concentration

The kinetics of polymerization of deoxyhemoglobin S have been studied by measuring transverse water proton relaxation times (T 2) in hemoglobin solutions. As seen by other techniques, the kinetic profile consists of a delay time followed by a decrease in T 2 during polymerization. The length of the delay time can be decreased and the rate of change of T 2 can be increased by increasing the concentration of hemoglobin S or non-gelling hemoglobin or ovalbumin. At a total protein concentration of about 210 mg/ml the kinetic profiles in all three cases are indistinguishable suggesting that a non-specific protein-protein interaction may be involved in the kinetics of polymerization. In addition, it is suggested that no polymer formation occurs during the delay period.