Water Proton Spin-lattice Relaxation Rate Research Articles

A proton T1-nuclear magnetic resonance dispersion study of water motion in snowflakes and hexagonal ice

ABSTRACTSnowflakes and ordinary hexagonal ice were studied measuring water proton spin–lattice relaxation rate -nuclear magnetic resonance dispersion (NMRD) profiles at proton Larmor frequencies ranging from 1 to 30 MHz and at different temperatures ranging from C to C. The spin–spin relaxation rate 1/ was determined at a single Larmor frequency of MHz. The high-field wing of the proton -NMRD profile was characterised by two parameters: a correlation time which described the dipole–dipole spectral density, and the relaxation rate at low fields which was determined from . The correlation time depended on the dynamic model used. A rotation diffusion model yield approximatively s at C to about s at C, whereas for a more realistic six-site discrete exchange model, the correlation times decreased slightly to about 80% for the same temperature interval. Proton dipole–dipole interactions were divided into intramolecular and intermolecular contributions where the intermolecular contribution was about 0.4–0.8 × the intramolecular contribution. It was not possible to discriminate between the dynamic models or to detect ice/water interface effects by comparing the NMRD data from snowflakes with ordinary hexagonal ice data.

The Dispersion of Water Proton Spin-Lattice Relaxation Rates in Aqueous Human Protein HC (α 1-Microglobulin) Solutions

The (1)H NMR Fast Field Cycling relaxometry was applied to study the molecular dynamics of the human protein HC (alpha (1)-microglobulin), its hydration and aggregation in solution state. The (1)H NMRD data have revealed the complex nature of the water/protein HC system resulting from the co-existence of monomer and dimer forms of the protein in solution as well as the presence of oligosaccharides linked to the polypeptide chain. A comparison of the average correlation time values <tau (c)> obtained from the model-free fits with the values predicted on the basis of hydrodynamic tau (r) theory, suggests that the dynamics in solution state is governed mainly by the dimer form of the protein HC (the dominant contribution to the water proton-spin lattice relaxation comes from exchanging protons from the surface of the dimer). The existence of small number of oligomeric forms of the protein HC in solutions is postulated because of the two-step shape of water proton spin-lattice relaxation rate dispersion profiles.

Estimation of free copper ion concentrations in blood serum using T1 relaxation rates

The water proton relaxation rate constant R 1 = 1/ T 1 (at 60 MHz) of blood serum is substantially increased by the presence of free Cu 2+ ions at concentrations above normal physiological levels. Addition of chelating agents to serum containing paramagnetic Cu 2+ nulls this effect. This was demonstrated by looking at the effect of adding a chelating agent—D-penicillamine (D-PEN) to CuSO 4 and CuCl 2 aqueous solutions as well as to rabbit blood serum. We propose that the measurement of water proton spin–lattice relaxation rate constants before and after chelation may be used as an alternative approach for monitoring the presence of free copper ions in blood serum. This method may be used in the diagnosis of some diseases (leukaemia, liver diseases and particularly Wilson’s disease) because, in contrast to conventional methods like spectrophotometry which records the total number of both bound and free ions, the proton relaxation technique is sensitive solely to free paramagnetic ions dissolved in blood serum. The change in R 1 upon chelation was found to be less than 0.06 s −1 for serum from healthy subjects but greater than 0.06 s −1 for serum from untreated Wilson’s patients.

Picosecond water dynamics adjacent to charged paramagnetic ions measured by magnetic relaxation dispersion

Measurements of water-proton spin-lattice relaxation rate constants as a function of magnetic field strength [magnetic relaxation dispersion (MRD)] in aqueous solutions of paramagnetic solutes reveal a peak in the MRD profile. These previously unobserved peaks require that the time correlation functions describing the water-proton-electron dipolar coupling have a periodic contribution. In aqueous solutions of iron(III) ion the peak corresponds to a frequency of 8.7 cm-1, which the authors ascribe to the motion of water participating in the second coordination sphere of the triply charged solute ion. Similar peaks of weaker intensity in the same time range are observed for aqueous solutions of chromium(III) chloride as well as for ion pairs formed by ammonium ion with trioxalatochromate(III) ion. The widths of the dispersion peaks are consistent with a lifetime for the periodic motion in the range of 5 ps or longer.

Physicochemical characterization of the dimeric lanthanide complexes [en{Ln(DO3A)(H2O)}2] and [pi{Ln(DTTA)(H2O)}2]2-: a variable-temperature 17O NMR study.

The Gd(III) complexes of the two dimeric ligands [en(DO3A)2] {N,N'-bis[1,4,7-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecan-10-yl-methylcarbonyl]-N,N'-ethylenediamine} and [pi(DTTA)2]8- [bisdiethylenetriaminepentaacetic acid (trans-1,2-cyclohexanediamine)] were synthesized and characterized. The 17O NMR chemical shift of H2O induced by [en{Dy(DO3A)}2] and [pi{Dy(DTTA)}2]2- at pH 6.80 proved the presence of 2.1 and 2.2 inner-sphere water molecules, respectively. Water proton spin-lattice relaxation rates for [en{Gd(DO3A)(H2O)}2] and [pi{Gd(DTTA)(H2O)}2]2- at 37.0 +/- 0.1 degrees C and 20 MHz are 3.60 +/- 0.05 and 5.25 +/- 0.05 mM(-1) s(-1) per Gd, respectively. The EPR transverse electronic relaxation rate and 17O NMR transverse relaxation time for the exchange lifetime of the coordinated H2O molecule and the 2H NMR longitudinal relaxation rate of the deuterated diamagnetic lanthanum complex for the rotational correlation time were thoroughly investigated, and the results were compared with those reported previously for other lanthanide(III) complexes. The exchange lifetimes for [en{Gd(DO3A)(H2O)}2] (769 +/- 10 ns) and [pi{Gd(DTTA)(H2O)}2]2- (910 +/- 10 ns) are significantly higher than those of [Gd(DOTA)(H2O)]- (243 ns) and [Gd(DTPA)(H2O)]2- (303 ns) complexes. The rotational correlation times for [en{Gd(DO3A)(H2O)}2] (150 +/- 11 ps) and [pi{Gd(DTTA)(H2O)}2]2- (130 +/- 12 ps) are slightly greater than those of [Gd(DOTA)(H2O)]- (77 ps) and [Gd(DTPA)(H2O)]2- (58 ps) complexes. The marked increase in relaxivity (r1) of [en{Gd(DO3A)(H2O)}2] and [pi{Gd(DTTA)(H2O)}2]2- result mainly from their longer rotational correlation time and higher molecular weight.

On the philosophy of optimizing contrast agents. An analysis of 1H NMRD profiles and ESR lineshapes of the Gd(III)complex MS-325 + HSA

A generalization of the modified SBM theory is developed in closed analytical form. The theory is applied to describe the paramagnetically enhanced water proton spin–lattice relaxation rates of the aqueous-systems containing a gadolinium( S=7/2) complex(MS-325) in the presence or absence of human serum albumin (HSA). MS-325 binds to HSA: in the absence of the protein the reorientational time, τ R, is short, but when HSA is added τ R becomes much longer. In this way, the effect of reorientational motion, static ( Δ s), and transient ( Δ t) zero-field splitting (ZFS) interactions on both the water proton relaxivity and the Gd ESR lineshapes are investigated. Two dynamic models of electron spin relaxation are presented, characterized by transient and static ZFS-interactions. X-, Q-, and W-bands ESR spectra of MS-325+HSA are analyzed in order to describe the effect on the electron spin system upon binding to a macromolecule. A computer program based on this theory is developed which calculates solvent water proton T 1 NMRD profiles and the corresponding X-, Q-, U-, and W-bands ESR lineshapes.

Protein Reorientation and Bound Water Molecules Measured by 1H Magnetic Spin-Lattice Relaxation

The water-proton spin-lattice relaxation rate constant, 1 /T 1, was measured as a function of magnetic field strength for several dilute protein solutions. By separating the intermolecular contributions from the intramolecular contributions to the water-proton spin-lattice relaxation, the number of water molecules that bind to the protein for a time long compared with the rotational correlation time may be measured. We find a good correlation between the number of long-lived water molecules and the predictions based on available free volume in the proteins studied. The rotational correlation times of these proteins are larger than predicted by the Stokes-Einstein-Debye (SED) model for a sphere reorienting in a viscous liquid. The discrepancy between experiment and theory is usually attributed to hydration effects increasing the effective radius of the particle. However, the average lifetime of water molecules at the protein interface is far too short to justify such a picture. We suggest that surface roughness may be responsible for the retardation of rotational mobility and find that the SED model provides a reasonable representation of experiment if the radius assumed for the reorienting particle is the arithmetic mean of the crystallographic packing radius and the radius deduced from the effective surface area of the protein.

Magnetic field dependence of proton spin-lattice relaxation times.

The magnetic field dependence of the water-proton spin-lattice relaxation rate (1/T(1)) 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/T(1)) is a scaled report of the field dependence of the (1/T(1)) rate of the solid components of the tissue. The proton spin-lattice relaxation rate may be represented generally as a power law: 1/T(1)omega = A omega(-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.

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 N′ -2 -pyridylmethyl and N′ -2-hydroxypropyl derivatives of diethylenetriaminepentaacetic acid and the stabilities of their complexes with Ln 3+, Ca 2+, Cu 2+ and Zn 2+

Two N′-2-pyridylmethyl and N′-2-hydroxypropyl derivatives of H 5dtpa (diethylene- N,N′ ,N′′-triamine- N, N, N′, N′′, N′′-pentaacetic acid), H 4L 1= N′-(2-pyridylmethyl)- N, N, N′′ N′′-diethylenetriaminetetraacetic acid and H 4L 2= N′-(2-hydroxypropyl)- N, N, N′′ N′′diethylenetriaminetetraacetic acid were synthesized. Their protonation constants were determined by potentiometric titration in 0.10 mol dm −3 Me 4NNO 3 and by NMR pH titration at 25.0±0.1°C. Stability and selectivity constants were determined to evaluate the possibility of using the corresponding gadolinium(III) complexes as magnetic resonance imaging contrast agents. Low stability or selectivity constants indicate higher possibility for releasing free Gd 3+ ion and free ligand as well from gadolinium(III) complexes. The formations of lanthanide(III), copper(II), zinc(II) and calcium(II) complexes were investigated quantitatively by potentiometry. The stability constants of lanthanides(III) complexes with H 4L 1 and H 4L 2 increase from La(III) to Nd(III) and then plateau at Sm(III) and Gd(III), before increasing again to Yb(III). The stability constant of the gadolinium(III) complex is larger than those of Ca(II), Zn(II) and Cu(II) complexes for these two ligands. The selectivity constants and modified selectivity constants of H 4L 1 and H 4L 2 for Gd 3+ over endogenously available metal ions were calculated. Effectiveness of these two ligands in binding divalent and trivalent metal ions in biological media is assessed by comparing p M values at physiological pH 7.4. Spin-lattice relaxivity R 1 for the Gd(III) complex was also determined. The observed relaxivity values of [GdL 1] − and [GdL 2] − became invariant with respect to pH changes over the range of 2–10 and 3–10, respectively. 17O NMR shifts showed that the [DyL 1] − and [DyL 2] − complexes have 1.50 and 2.51 inner-sphere water molecules, respectively. Water proton spin-lattice relaxation rates for the [GdL 1] − and [GdL 2] − complexes were also consistent with inner-sphere gadolinium(III) coordination.

Proton and Deuteron Relaxation Study of Molecular Dynamics in Lysozyme Solutions

A nuclear magnetic resonance spin—lattice relaxation dispersion study of the relaxation of several magnetization components in both natural and deuterated lysozyme solutions was undertaken at 20°C. Proton and deuteron resonances were employed. The two-dimensional time evolution of the magnetization and the spin—spin relaxation were analyzed. In addition, an isotopic dilution study was performed at 5 and 30.6 MHz. The results indicate that the water proton spin—lattice relaxation rate which arises from intermolecular relaxation between the water protons and the lysozyme protons represents a relatively strong relaxation mechanism. A model for the dynamics of the water molecules, consistent with the proton and deuteron dispersions as well as with the isotopic dilution results, is presented. PACS numbers: 87.15.—v, 76.60.—k,

Synthesis, stability and nuclear magnetic resonance studies for the complexation of trivalent lanthanides, Ca 2, Cu 2 and Zn 2 by N,N′-bis (amide) derivatives of ethylenedinitrilotetraacetic acid

Two N, N′- bis (amide) derivatives of H 4edta (ethylenedinitrilo- N, N′-diacetic acid), H 2L 1=bis ( iso-propylamide) and H 2L 2=bis ( tert-butylamide), were synthesized. Their protonation constants were determined by potentiometric titration in 0.10 mol dm −3 KCl and by NMR pH titration at 25.0±0.1°C. The stability constants of the complexes of calcium (II), copper (II), zinc (II), and gadolinium (III) with H 2L 1 and H 2L 2 were also investigated quantitatively by the potentiometric technique. The following stability constant sequence has been obtained: Gd 3>Cu 2>Zn 2>Ca 2 for the ligands H 2L 1 and H 2L 2. The proton NMR shift was measured for the complexes of Lu 3, Y 3 and Zn 2 with H 2L 1. These complexes are hexadentate, possibly of octahedral geometry and form various structural isomers. 17 O NMR shifts showed that the [DyL 1] + and [DyL 2] + complex had two to three inner-sphere water molecules. Water proton spin-lattice relaxation rates for the [GdL 1] + and [GdL 2] + complexes were also consistent with two inner-sphere gadolinium (III) coordination positions.

Synthesis and complexation of Gd3+, Ca2+, Cu2+ and Zn2+ by 3,6,10-tri(carboxymethyl)-3,6,10-triazadodecanedioic acid

3,6,10-Tri(carboxymethyl)-3,6,10-triazadodecanedioic acid (H5L), was synthesized and its protonation constants were determined by potentiometric titration in 0.10 mol dm–3 Me4NNO3 and by NMR pH titration at 25.0 ± 0.1 °C. Stability and selectivity constants have been measured to evaluate the possibility of using the corresponding gadolinium(III) complex as a magnetic resonance imaging contrast agent. The formations of gadolinium(III), copper(II), zinc(II) and calcium(II) complexes were investigated quantitatively by potentiometry. The stability constant for the gadolinium(III) complex is larger than those of CaII, ZnII and CuII for this octadentate ligand. The selectivity constants and modified selectivity constants of the ligand for Gd3+ over endogenously available metal ions were calculated. The spin–lattice relaxivity R1 for the gadolinium(III) complex was also determined. It was found to decrease with increasing pH below 4 and became invariant with respect to pH over the range 4–10. Oxygen-17 NMR shifts showed that the [DyL]2– complex had one inner-sphere water molecule. The water proton spin–lattice relaxation rate for the [GdL]2– complex was also consistent with one inner-sphere co-ordination position.

Impact of chemical stimuli and temperature on water transport and mobility in germinating rape seeds by pulsed 1H NMR spectroscopy

Pulsed 1H NMR in vivo difference spectroscopy and germination were combined to elucidate the effect of exogenously applied estriol or ethanol on water retention in fully hydrated rape seeds. The presence of estriol or ethanol in the imbibition medium resulted in a reduction of the photoreversible phytochrome. An approach to the assessment of cell membrane permeability related to the intracellular water exchange rate, using the bi-exponential feature in the water proton spin–lattice relaxation rate R1 and spin–spin relaxation rate R2, is presented. The intracellular water exchange rate increases approximately two- and three-fold in seeds pre-treated with estriol or ethanol solution in comparison with water imbibed seeds. The activation energy for the germination rate was 61±6, 42±4 and 37±4 kJ mol-1 and the transition temperature was 281±2, 286±2 and 284±2 K for seeds imbibed with water, estriol and ethanol solution, respectively. The temperature dependence of the intracellular water exchange rate showed comparable values of activation energy and transition temperatures. All the results support the hypothesis that the two effects, thermal activation and increase in the seed cell membrane permeability, combine during water transport into the cell and result in the germination of rape seeds imbibed with estriol or ethanol solution. © 1997 John Wiley & Sons, Ltd.

Impact of chemical stimuli and temperature on water transport and mobility in germinating rape seeds by pulsed1H NMR spectroscopy

Pulsed 1H NMR in vivo difference spectroscopy and germination were combined to elucidate the effect of exogenously applied estriol or ethanol on water retention in fully hydrated rape seeds. The presence of estriol or ethanol in the imbibition medium resulted in a reduction of the photoreversible phytochrome. An approach to the assessment of cell membrane permeability related to the intracellular water exchange rate, using the bi-exponential feature in the water proton spin–lattice relaxation rate R1 and spin–spin relaxation rate R2, is presented. The intracellular water exchange rate increases approximately two- and three-fold in seeds pre-treated with estriol or ethanol solution in comparison with water imbibed seeds. The activation energy for the germination rate was 61±6, 42±4 and 37±4 kJ mol-1 and the transition temperature was 281±2, 286±2 and 284±2 K for seeds imbibed with water, estriol and ethanol solution, respectively. The temperature dependence of the intracellular water exchange rate showed comparable values of activation energy and transition temperatures. All the results support the hypothesis that the two effects, thermal activation and increase in the seed cell membrane permeability, combine during water transport into the cell and result in the germination of rape seeds imbibed with estriol or ethanol solution. © 1997 John Wiley & Sons, Ltd.

Alkaline Earth Metal and Lanthanide(III) Complexes of Ligands Based upon 1,4,7,10-Tetraazacyclododecane-1,7-bis(acetic acid).

The macrocyclic ligand DO2A (1,4,7,10-tetraazacyclododecane-1,7-bis(acetic acid)) was prepared and used as a building block for four new macrocyclic ligands having mixed side-chain chelating groups. These ligands and their complexes with Mg(II), Ca(II), and Ln(III) were studied extensively by potentiometry, high-resolution NMR, and water proton relaxivity measurements. The protonation constants of all compounds compared well with those of other cyclen-based macrocyclic ligands. All Ca(II) complexes were found to be more stable than the corresponding Mg(II) complexes. Trends for the stabilities of the Ln(III) complexes are discussed and compared with literature data, incorporating the effects of water coordination numbers, Ln(III) contraction, and the nature of the side chains and the steric hindrance between them. (1)H NMR titrations of DO2A revealed that the first and second protonations take place preferentially at the secondary ring nitrogens, while the third and fourth involved protonation of the acetates. (17)O NMR shifts showed that the DyDO2A(+) complex had two inner-sphere water molecules. Water proton spin-lattice relaxation rates for the GdDO2A(+) complex were also consistent with water exchange between bulk water and two inner-sphere Gd(III) coordination positions. Upon formation of the diamagnetic complexes of DO2A (Ca(II), Mg(II), La(III), and Lu(III)), all of the macrocyclic ring protons became nonequivalent due to slow conformational rearrangements, while the signals for the acetate CH(2) protons remained a singlet.

Water molecule binding and lifetimes on the DNA duplex d(CGCGAATTCGCG)2.

Measurements of the water proton spin-lattice relaxation rate for aqueous solutions of the palindromic dodecamer, d(CGCGAATTCGCG)2, are reported as a function of the magnetic field strength. The magnitude of the relaxation rates at low magnetic field strengths and the shape of the relaxation dispersion curve permit assessment of the number of water molecules which may be considered bound to the DNA for a time equal to or longer than the rotational correlation time of the duplex. The data are examined using limiting models that arbitrarily use the measured rotational correlation time of the polynucleotide complex as a reference point for the water molecule lifetime. If it is assumed that water molecules are bound at DNA sites for times as long as or longer than the rotational correlation time of the duplex, then the magnitude of the relaxation rates at low field require that there may be only two or three such water sites. However, if the lifetime constraint is relaxed, and we assume that the number of water molecules bound to the DNA is more nearly the number identified in the X-ray structures, then the average water molecule lifetime is on the order of 1 ns. Measurements of 1H NOESY spectra demonstrate that some water molecules must have lifetimes sufficiently long that negative Overhauser effects are observed. Taken together, these results suggest a distribution of water molecule lifetimes in which most of the DNA-bound water molecule lifetimes are shorter than the rotational correlation time of the duplex, but where some have lifetimes of at least 1 ns under these concentrated conditions.

Noninvasive measurement of protein concentration

At selected magnetic field strengths, protein and water proton spin-lattice relaxation rates are sensitive to the concentration of rotationally immobilized peptide nitrogen because of field dependent heteronuclear cross relaxation coupling between protein proton and nitrogen-14 spins that is carried to the water by proton homonuclear cross-relaxation. Measurement of the water proton spin-lattice relaxation time, or a signal amplitude proportional to it, may provide a noninvasive measure of peptide bond concentration, which provides a direct measure of immobilized protein content in most tissues. The approach using protein gels in two magnetic field strengths is demonstrated. At 66.7 mT; the proton Zeeman energy matches one of the peptide nitrogen transitions dominated by the unaveraged nuclear electric quadrupole interaction; cross-relaxation between the protons and nitrogen-14 is efficient. At 77.5 mT, the proton Zeeman energy is not matched with the nitrogen energy and proton-nitrogen cross-relaxation is not efficient. It is shown that the difference in the water proton spin-lattice relaxation rates on and off the energy level match condition is a linear function of the rotationally immobilized protein concentration.

Field-Cycling Proton Nuclear Magnetic Relaxation-Dispersion Study of Aqueous Colloidal Silica Sols

The magnetic-field dependence of the water-proton spin-lattice relaxation rate 1/T1 is reported for aqueous colloidal silica suspensions as a function of temperature, particle size, silica concentration, and isotopical proton dilution. At low concentrations, it is found that T1 is essentially determined by a coupling of solvent protons with nonexchangeable protons situated near the colloid surface. Comparison of NMRD and photon correlation spectroscopy measurements indicates that interparticle interactions increase the NMR relaxation rates at low frequencies. Finally, it is also shown that, in contrast to protein solutions, there is no evident link between the NMRD inflection frequency and the correlation time of the rotational Brownian motion of the colloidal particles.