Observed Water Proton Research Articles

Comparison of Overhauser DNP at 0.34 and 3.4 T with Frémy’s Salt

Dynamic nuclear polarization (DNP) is investigated in the liquid state using a model system of Frémy’s salt dissolved in water. Nuclear magnetic resonance signal enhancements at 0.34 and 3.4 T of the bulk water protons are recorded as a function of the irradiation time and the polarizer concentration. The build-up rates are consistent with the T 1n of the observed water protons at room temperature (for 9 GHz/0.34 T) and for about 50 ± 10 °C at 94 GHz/3.4 T. At 94 GHz/3.4 T, we observe in our setup a maximal enhancement of −50 at 25 mM polarizer concentration. The use of Frémy’s salt allows the determination of the saturation factors at 94 GHz by pulsed ELDOR experiments. The results are well consistent with the Overhauser DNP mechanism and indicate that higher enhancements at this intermediate frequency require higher sample temperatures.

On the inherent precision of mcDESPOT

A statistical analysis of the mcDESPOT protocol for characterizing two exchanging water proton pools--a seven-dimensional problem that fits to multiple flip angle measurements of both spoiled and refocused gradient echoes--is presented. Theoretical calculations of the Cramér-Rao lower bounds of the variance of fitted model parameters were made using a variety of model system parameters, meant to mimic those expected in human white matter. The results, validated by Monte Carlo simulations, indicated that mcDESPOT signals acquired at feasibly attainable signal-to-noise ratios cannot provide parameter estimates with useful levels of precision. Precision can be greatly improved by constraining solutions with a priori model information, although this will generally lead to biased parameter estimates with less specificity. These results indicate that previous, apparently successful applications of mcDESPOT to human white matter may have used data fitting methods that implicitly constrained parameter solutions, or that the two-pool model of white matter may not be sufficient to describe the observed water proton signal in mcDESPOT acquisitions. In either case, mcDESPOT-derived estimates of two-pool model parameters cannot yet be unambiguously related to specific tissue characteristics.

Theoretical analysis of water 1H T2 based on chemical exchange and polysaccharide mobility during gelation

It was demonstrated that macroscopic structural changes of polysaccharide chains, such as random coil–helix transition and aggregation of helices, accompanied with the sol–gel and the gel–sol transition can be monitored by numerically analyzing the temperature dependence of the observed water proton spin–spin relaxation time ( T 2obs) modified by the chemical exchange between water proton and labile proton on the chain. According to the numerical analysis of T 2obs, typical profiles of T 2obs against the temperature were simulated with various parameters of the relaxation time ( T 2 i ) and the mean residence time ( τ i ) of water and the labile protons on the random coil and the ordered chain as well as the activation energy ( E i , E ex, i ) for the motion and the chemical exchange of the respective proton. The difference of structural change of kappa- , iota- , and lambda-carrageenan aqueous systems in the cooling and the heating process was analyzed. In conclusion, (1) the characteristic profile of the temperature dependence of T 2obs, commonly observed in the temperature-induced gelling process, is attributable to the variation of fraction of the ordered chain and the relative rate of chemical exchange to the relaxation rate of labile protons on polysaccharide (1/ T 2p); (2) the loose aggregated or associated structure is detected for iota-carrageenan system; and (3) the thermally stable junction zones formed by well aggregated helices of kappa-carrageenan in the gel state provokes a thermal hysteresis in the temperature-induced structural change (experimentally, in T 2obs). It is clarified by the numerical simulation that the aggregated helices formed during further cooling down to the temperature below T sg results in the T 2obs shifts to a longer value in the heating process as compared with that in the cooling process.

Thermodynamic Stability and Physicochemical Characterization of Ligand (4S)-4-Benzyl-3,6,10-tris(carboxymethyl)-3,6,10-triazadodecanedioic Acid (H5[(S)-4-Bz-ttda]) and Its Complexes Formed with Lanthanides, Calcium(II), Zinc(II), and Copper(II) Ions

A derivative of H5ttda (=3,6,10-tris(carboxymethyl)-3,6,10-triazadodecanedioic acid=N-{2-[bis(carboxymethyl)amino]ethyl}-N-{3-[bis(carboxymethyl)amino]propyl}glycine), H5[(S)-4-Bz-ttda] (=(4S)-4-benzyl-3,6,10-tris(carboxymethyl)-3,6,10-triazadodecanedioic acid=N-{(2S)-2-[bis(carboxymethyl)amino]-3-phenylpropyl}-N-{3-[bis(carboxymethyl)amino]propyl}glycine; 1) carrying a benzyl group was synthesized and characterized. The stability constants of the complexes formed with Ca2+, Zn2+, Cu2+, and Gd3+ were determined by potentiometric methods at 25.0±0.1° and 0.1M ionic strength in Me4NNO3. The observed water proton relaxivity value of [Gd{(S)-4-Bz-ttda}]2− was constant with respect to pH changes over the range pH 4.5–12.0. From the 17O-NMR chemical shift of H2O induced by [Dy{(S)-4-Bz-ttda}]2− at pH 6.80, the presence of 0.9 inner-sphere water molecules was deduced. The water proton spin-lattice relaxation rate for [Gd{(S)-4-Bz-ttda}]2− at 37.0±0.1° and 20 MHz was 4.90±0.05 mM−1 s−1. The EPR transverse electronic relaxation rate and 17O-NMR transverse-relaxation time for the exchange lifetime of the coordinated H2O molecule (τM), and 2H-NMR longitudinal-relaxation rate of the deuterated diamagnetic lanthanum complex for the rotational correlation time (τR) were thoroughly investigated, and the results were compared with those previously reported for the other lanthanide(III) complexes. The exchange lifetime (τM) for [Gd{(S)-4-Bz-ttda}]2− (2.3±1.3 ns) was significantly shorter than that of the [Gd(dtpa)(H2O)]2− complex (dtpa=diethylenetriaminepentaacetic acid). The rotational correlation time τR for [Gd{(S)-4-Bz-ttda}]2− (70±6 ps) was slightly longer than that of the [Gd(dtpa)(H2O)]2− complex. The marked increase of relaxivity of [Gd{(S)-4-Bz-ttda}]2− mainly resulted from its longer rotational time rather than from its fast water-exchange rate. The noncovalent interaction between human serum albumin (HSA) and the [Gd{(S)-4-Bz-ttda}]2− complex containing the hydrophobic substituent was investigated by measuring the solvent proton relaxation rate of the aqueous solutions. The association constant (KA) was less than 100 M−1, indicating a weaker interaction of [Gd{(S)-4-Bz-ttda}]2− with HSA.

Synthesis of four derivatives of 3,6,10-tri(carboxymethyl)-3,6,10-triazadodecanedioic acid, the stabilities of their complexes with Ca(ii), Cu(ii), Zn(ii) and lanthanide(iii) and water-exchange investigations of Gd(iii) chelatesElectronic supplementary information (ESI) available: tables of pM values and relaxivities; potentiometric titration curves for TTDA-PY, TTDA-HP, TTDA-H1P and TTDA-H2P; species distribution curves, plots of temperature dependence of transverse electronic relaxation rates and plots of pH dependence

The protonation constants of four poly(aminocarboxylates), N′-pyridylmethyl (TTDA-PY), N′-2-hydroxypropyl (TTDA-HP), N′-2-hydroxy-1-phenylethyl (TTDA-H1P) and N′-2-hydroxy-2-phenylethyl (TTDA-H2P) derivatives of TTDA (3,6,10-tri(carboxymethyl)-3,6,10-triazadodecanedioic acid), and the stability constants of their complexes formed with Ca2+, Zn2+, Cu2+, La3+, Ce3+, Nd3+, Sm3+, Gd3+, Dy3+, Ho3+, Yb3+ and Lu3+ were determined by potentiometric methods at 25.0 ± 0.1 °C and 0.10 mol dm−3 ionic strength in Me4NNO3. The stability of the Gd(III) complexes follows the order TTDA-PY > TTDA-H2P ≊ TTDA-HP ≊ TTDA-H1P. The thermodynamic resistance of the gadolinium(III) complexes, at the plasma concentration used in clinical applications, towards demetallation in the presence of important components of blood plasma, such as Ca(II), Zn(II) and Cu(II), has been evaluated. The observed water proton relaxivity values of [Gd(TTDA-PY)]−, [Gd(TTDA-HP)]−, [Gd(TTDA-H1P)]− and [Gd(TTDA-H2P)]− became constant with respect to pH changes over the range of 4–10, 6–10, 6–10 and 6–10, respectively. 17O NMR shifts showed that the [Dy(TTDA-PY)]−, [Dy(TTDA-HP)]−, [Dy(TTDA-H1P)]− and [Dy(TTDA-H2P)]− complexes at pH 6.30 and 4.30 had 0.9 and 0.9; 2.2 and 3.4; 2.0 and 3.5; 1.8 and 3.0 inner-sphere water molecules, respectively. Water proton spin–lattice relaxation rates for gadolinium(III) complexes were also consistent with the number of inner-sphere water molecules. The EPR transverse electronic relaxation rate and 17O NMR transverse relaxation time were thoroughly investigated and the results obtained were compared with that previously reported for the other gadolinium(III) complex, [Gd(DTPA)(H2O)]2−. Short exchange lifetime values were obtained for the [Gd(TTDA)(H2O)]2−, [Gd(TTDA-PY)(H2O)]−, [Gd(TTDA-HP)(H2O)2]−, [Gd(TTDA-H1P)(H2O)2]− and [Gd(TTDA-H2P)(H2O)2]− complexes. Their water-exchange rates are about 24–45 times faster than that for the [Gd(DTPA)(H2O)]2− complex, which suggested that the longer backbone of the multidentate ligand may be pulled tightly into the first coordination sphere, resulting in high steric constraints at the water binding site.

Synthesis of Two Derivatives of 3,6,9‐tri(carboxymethyl)‐3,6,9‐triazaundecanedioic Acid and the Stabilities of Their Complexes with Ca2+, Cu2+, Zn2+, Dy3+ and Gd3+

AbstractTwo N‐2‐hydroxy‐1‐phenylethyl and N‐2‐hydroxy‐2‐phenylethyl derivatives of DTPA (3,6,9‐tri(carboxymethyl)‐3,6,9‐triazaundecanedioic acid), DTPA‐H1P = 3,9‐di(carboxymethyl)‐6‐2‐hydroxy‐1‐phenylethyl‐3,6,9‐triazaundecanedioic acid, and DTPA‐H2P = 3,9‐di(carboxymethyl)‐6‐2‐hydroxy‐2‐phenylethyl‐3,6,9‐triazaundecanedioic acid were synthesized. Their protonation constants were determined by Potentiometric titration in 0.10 M Me4NNO3 and by NMR pH titration at 25.0 ± 0.1°C. The formations of lanthanide(III), copper(II), zinc(II) and calcium(II) complexes were investigated quantitatively by potentiometry. The stability constant for Gd(III) complex is larger than those for Ca(II), Zn(II) and Cu(II) complexes with these two ligands. The selectivity constants and modified selectivity constants of the DTPA‐H1P and DTPA‐H2P for Gd(III) over endogenously available metal ions were calculated. Comparing pM values at physiological pH 7.4 assesses effectiveness of these two ligands in binding divalent and trivalent metal ions in biological media. The observed water proton relaxivity values of [Gd(DTPA‐H1P)]− and [Gd(DTPA‐H2P)]− became constant with respect to pH changes over the range of 4‐10. 17O NMR shifts showed that the [Dy(DTPA‐H1P)]− and [Dy(DTPA‐H2P)]− complexes at pH 6.30 had 1.91 and 2.28 inner‐sphere water molecules, respectively. Water proton spin‐lattice relaxation rates of [Gd(DTPA‐H1P)]− and [Gd(DTPA‐H2P)]− complexes were also consistent with the inner‐sphere Gd(III) coordination.

Cross-relaxation times of normal and biochemically induced osteoarthritic rabbit knee cartilages.

We measured the spin-lattice relaxation times (T1) of water protons and intermolecular cross-relaxation times (T(IS)) from irradiated protein protons (f2-irradiation at 1.95 or -4.00 ppm) of rabbit normal and monoiodoacetate-induced degenerated knee articular cartilages to observed water protons. The mean values of T1 (T1) for control and degenerated rabbit knee cartilages were 1.87+/-0.15 (mean+/-SD, n=29) and 1.82+/-0.13 s (n=34), respectively. The mean values of water content (W(H2O)) for control and degenerated rabbit knee cartilages were 82.9+/-2.09 (n=26) and 83.1+/-2.57% (n=28), respectively. These values were not statistically different from each other. However, the mean values of T(IS) (T(IS)) for normal knee articular cartilage were significantly different from those for degenerated cartilage: (normal), T(IS) (f2=1.95 ppm)=2.46+/-0.62 s (n=28), T(IS) (f2=-4.00 ppm)=4.25+/-1.26 s (n=26); (degenerated), T(IS) (f2=1.95 ppm)=1.99+/-0.76s (n=34), T(IS) (f2=-4.00 ppm)=3.33+/-0.76 s (n=31). Obtained results may be attributed to the reported switchover from type II to type I collagen syntheses in osteoarthritic cartilage, resulting in broad collagen fibers. This specificity of cross-relaxation effect may prove useful in the noninvasive and pathophysiological evaluation of cartilage tissues in vivo.

High-affinity Ca(2+)- and substrate-binding sites on protein kinase C alpha as determined by nuclear magnetic resonance spectroscopy.

Water proton nuclear magnetic resonance (NMR) relaxation rates were used to identify metal sites on protein kinase C (PKC) isozymes alpha and beta using paramagnetic Gd3+ as a probe. The paramagnetic effect of Gd3+ on water proton relaxation was enhanced with PKC isozymes alpha and beta in the presence of diheptanoylphosphatidylcholine/1,2-dioleoyl-sn-glycerol (PC7/DO). The data are consistent with a single class of metal-binding sites on PKC beta and two classes of sites on PKC alpha: a single high-affinity site with a KD for Gd3+ of 0.2 microM and a larger class of sites with a lower affinity for Gd3+. Titration with Ca2+ abolished the observed enhancement of water proton relaxation by the PKC alpha.Gd3+ complex, consistent with displacement of Gd3+ by Ca2+. Titrations of the PKC alpha.Gd3+ complex with Co(NH3)4ATP, a substitution-inert analogue of ATP, caused a substantial decrease in the observed water proton relaxation enhancement, consistent with formation of a ternary enzyme.metal.substrate complex with a KPKC alpha.Gd.[CoATP] of 30-100 nM. Titration of the metal enzyme complex with a model peptide substrate derived from the pseudosubstrate sequence of PKC alpha caused a similar decrease in enhancement at stoichiometric concentrations consistent with the formation of a PKC alpha.Gd3+.peptide complex with a KPKC alpha.Gd.[peptide] of less than or equal to 13 nM. Titrations of the fully formed PKC alpha.Gd3+.peptide complex with Co(NH3)4ATP caused a further decrease in enhancement consistent with formation of a quaternary complex.(ABSTRACT TRUNCATED AT 250 WORDS)

Proton NMR studies on ischemic rat brain tissue.

The spin-lattice relaxation time (T1) of water protons and the cross-relaxation time (TIS) between irradiated protein protons and observed water protons were measured in order to study water-macromolecular interactions in ischemic rat brain tissues. Tissues were obtained by bilateral common carotid artery occlusion from stroke-prone spontaneously hypertensive rats. Water, Na, and K contents were measured in ischemic brain tissue at the same time. Water and Na content increased while the TIS value and K content decreased following ischemic insults. The T1 value did not change until 180 min after ischemia had been induced. Changes in the TIS value occurred earlier than changes observed for the T1 value, water, and electrolyte contents. Results indicate that the value of TIS may be useful for detecting cerebral ischemia and that the physical structure of water-macromolecular interaction may be altered soon after ischemic onset in brain tissue.

Nature of lysozyme–water interactions by proton NMR

Proton spin-lattice relaxation measurements were performed in 10 mM lysozyme solution as a function of temperature and degree of substitution of solvent H2O with D2O. The results show that in the temperature range from 274 to 323 K, the intermolecular lysozyme proton water proton coupling contributes appreciably to the observed water proton relaxation rate. In this system exchange between water protons and labile protein protons does not dominate the behaviour with temperature of the water-lysozyme intermolecular contribution to the spin-lattice relaxation.

Thermally denatured proteins. Nuclear magnetic resonance, binding isotherm and chemical modification studies of thermally denatured bovine serum albumin

The properties of thermally denatured bovine serum albumin have been investigated by n.m.r., binding isotherm and chemical modification studies. The marked reduction observed in the protein spin-spin relaxation times on thermal denaturation indicates that the protein chains become rigid. There was no change in the bulk water properties on thermal denaturation but a slight reduction in the amount of water bound to the protein was observed. The increase in the average water proton spin-spin relaxation rate on thermal denaturation results from a decrease in the bound water spin-spin relaxation time due to a reduction in the mobility of protein chains to which water molecules are bound. At temperatures higher than about 285 K, there is a contribution to the observed water proton relaxation times from exchange between labile protein protons and water protons, which results in a minimum in the spin-spin relaxation time at 328 K. The native structure of bovine serum albumin is not extensively disrupted on thermal denaturation. The results are consistent with a two step mechanism for thermal denaturation, involving aggregation of initially unfolded protein molecules. The initial unfolding involves mainly changes in the tertiary structure rather than in the secondary structure and aggregation results in the formation of a rigid network. The molecules are held together by co-operative forces involving many amino acid residues and, although intermolecular disulphide bonds do form on thermal denaturation of bovine serum albumin, chemical modification studies show that aggregation does not depend upon formation of chemical cross-links, as is often supposed.