W-Band<sup>17</sup>O Pulsed Electron Nuclear Double Resonance Study of Gadolinium Complexes with Water

Raitsimring, Arnold M.; Astashkin, Andrei V.; Baute, Debbie; Goldfarb, D.; Caravan, Peter

doi:10.1021/jp040306i

Cited by 63 publications

(120 citation statements)

References 35 publications

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“…This is analogous to Gd-L 2, which was shown to be nine-coordinate in solution [6] as are other gadolinium(iii)-DTPA derivatives. [28][29][30][31][32] It was recently shown that gadolinium ENDOR spectroscopy is a useful method to determine the distance between the Gd III ion and the coordinated water oxygen atom [24] or protons. [23,25] Figure 2 shows the frozen solution D-band proton ENDOR spectrum corresponding to the À1/2$ + 1/2 electronic transition.…”

Section: Resultsmentioning

confidence: 99%

When are Two Waters Worse Than One? Doubling the Hydration Number of a Gd–DTPA Derivative Decreases Relaxivity

Caravan

Amedio

Dunham

et al. 2005

Chemistry A European J

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The synthesis of a novel ligand, based on N-methyl-diethylenetriaminetetraacetate and containing a diphenylcyclohexyl serum albumin binding group (L1) is described and the coordination chemistry and biophysical properties of its Gd(III) complex Gd-L1 are reported. The Gd(III) complex of the diethylenetriaminepentaacetate analogue of the ligand described here (L2) is the MRI contrast agent MS-325. The effect of converting an acetate to a methyl group on metal-ligand stability, hydration number, water-exchange rate, relaxivity, and binding to the protein human serum albumin (HSA) is explored. The complex Gd-L1 has two coordinated water molecules in solution, that is, [Gd(L1)(H2O)2]2- as shown by D-band proton ENDOR spectroscopy and implied by 1H and 17O NMR relaxation rate measurements. The Gd-H(water) distance of the coordinated waters was found to be identical to that found for Gd-L2, 3.08 A. Loss of the acetate group destabilizes the Gd(III) complex by 1.7 log units (log K(ML) = 20.34) relative to the complex with L2. The affinity of Gd-L1 for HSA is essentially the same as that of Gd-L2. The water-exchange rate of the two coordinated waters on Gd-L1 (k(ex) = 4.4x10(5) s(-1)) is slowed by an order of magnitude relative to Gd-L2. As a result of this slow water-exchange rate, the observed proton relaxivity of Gd-L1 is much lower in a solution of HSA under physiological conditions (r1(obs) = 22.0 mM(-1) s(-1) for 0.1 mM Gd-L1 in 0.67 mM HSA, HEPES buffer, pH 7.4, 35 degrees C at 20 MHz) than that of Gd-L2 (r1(obs) = 41.5 mM(-1) s(-1)) measured under the same conditions. Despite having two exchangeable water molecules, slow water exchange limits the potential efficacy of Gd-L1 as an MRI contrast agent.

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Section: Resultsmentioning

confidence: 99%

When are Two Waters Worse Than One? Doubling the Hydration Number of a Gd–DTPA Derivative Decreases Relaxivity

Caravan

Amedio

Dunham

et al. 2005

Chemistry A European J

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“…[47][48][49] Quadrupole coupling constants of oxygen-17 have been determined for neat water, but only few, sometimes contradictory estimations are available for H 2 O molecules in the first coordination sphere of the cation. [44,[50][51][52][53] Model calculations on Gd-H 2 O clusters have been used to assess the dependence of 17 O quadrupole coupling parameters on the Gd-O distance and on the orientation of the water dipole vector of the first-sphere water molecules (tilt angle). [54] Only slight changes of χ and η with the Gd-O distance have been found.…”

Section: Quadrupolar Relaxation -Electric Field Gradientsmentioning

confidence: 99%

“…[32] This is probably a consequence of the very similar Gd-O distance in both systems (2.4 Å for the model cluster and an average distance of 2.37 Å for the CPMD simulation). Most recent experimental values of A iso = A/h are 0.83 MHz [75] and 0.84 MHz [15] from NMR shift measurements and 0.75 MHz [53] from ENDOR experiments. The inner-sphere 1 H hyperfine coupling constant shows a similar negative correlation with distance (Figure 8, right).…”

Section: Scalar Hyperfine Interactionmentioning

confidence: 99%

Nuclear Spin Relaxation Parameters of MRI Contrast Agents – Insight from Quantum Mechanical Calculations

Yazyev

Helm

2007

Eur J Inorg Chem

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Keywords: Relaxivity / Hyperfine interactions / Quantum chemistry / Gadolinium / MRI contrast agent Nuclear magnetic relaxation in the presence of paramagnetic centres has gained increasing interest in recent years partly due to its importance for contrast agents in magnetic resonance imaging. Rational design of new more efficient agents is possible as a result of a better understanding of the underlying relaxation mechanisms. Quantum chemical calculations together with molecular dynamics simulations allow obtaining fundamental parameters such as quadrupole coupling constants and hyperfine interaction tensors directly at a molecular level. Recent results are presented on gadolinium(III) ions in aqueous solution and on [Gd(DOTA)(H 2 O)] -, a commercial MRI contrast agent. Isotropic hyperfine coupling

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“…The EPR spectra of highspin transition-metal ions with half-filled valence orbitals, such as Gd 3+ (S = 7/2) and Mn 2+ (S = 5/2), become much simpler at high fields, displaying an intense and relatively narrow central |−1/2⟩ → |1/2⟩ transition. 10,11 The width of this transition is proportional to D 2 /ν 0 , where D is the zero-field splitting (ZFS) parameter and ν 0 is the spectrometer frequency, leading to increased sensitivity with increased frequency. Capitalizing on this property, along with the short spin−lattice (T 1 ) relaxation times of metal ions and the efficient mw power utilization associated with high transition probabilities, a new type of spin label based on Gd 3+ chelates has been introduced.…”

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Nanometer-Range Distance Measurement in a Protein Using Mn²⁺ Tags

Banerjee

Yagi

Huber

et al. 2012

J. Phys. Chem. Lett.

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Pulse electron paramagnetic resonance measurements of long-range (nm scale) distances between spin labels site-specifically attached to biomacromolecules have proven highly effective in structural studies. The most commonly used spin labels are stable nitroxide radicals, and measurements are usually carried out at X-band frequencies (∼9.5 GHz, 0.35 T). Higher magnetic fields open new possibilities for distance measurements with increased sensitivity using alternative spin labels containing half-integer high-spin metal ions. Here we demonstrate W-band (95 GHz) pulse double electron−electron resonance (DEER) distance measurements in a protein labeled with two Mn 2+ -EDTA tags. The distance distribution obtained is in excellent agreement with model calculations based on the known solution NMR structure. Thus, sitespecific labeling with Mn 2+ tags opens a highly promising approach to nanometer distance measurements in biological macromolecules. SECTION: Biophysical Chemistry L ong-range (nm scale) distance measurements between specific sites in biological macromolecules offer important insight into their structure and interactions. In the past decade, such distance measurements by pulse electron paramagnetic resonance (EPR) techniques, often referred to as pulse dipolar spectroscopy (PDS), have proven highly efficient for nitroxidelabeled proteins and nucleic acids.1−3 Distances in the range of 2−5 nm can be routinely accessed, and distances up to 8 nm can be determined under favorable conditions. 4,5 In proteins, site-directed spin labeling is usually achieved by covalent attachment of nitroxide compounds to cysteine residues that are either native or, more commonly, have been introduced at strategically chosen positions by site-directed mutagenesis. where r is the electron−electron distance and θ is the angle between the interelectron vector r and the external magnetic field. The measurements are carried out at low temperatures on frozen solutions. The most popular PDS experiment is the four-pulse double electron−electron resonance (DEER) sequence, 7 often also referred to as PELDOR (pulse electron double resonance). DEER carried out at standard X-band frequencies (∼9.5 GHz, 0.35 T) has become well-established. An order of magnitude increase in sensitivity can be gained by high-frequency/highfield DEER, provided that the microwave (mw) power is sufficient to generate short enough microwave pulses, as recently demonstrated at the W-band (95 GHz, ∼3.5 T). 8,9 In addition, high-field measurements open new opportunities for the use of metal ions as spin labels. The EPR spectra of highspin transition-metal ions with half-filled valence orbitals, such as Gd 3+ (S = 7/2) and Mn 2+ (S = 5/2), become much simpler at high fields, displaying an intense and relatively narrow central |−1/2⟩ → |1/2⟩ transition. 10,11 The width of this transition is proportional to D 2 /ν 0 , where D is the zero-field splitting (ZFS) parameter and ν 0 is the spectrometer frequency, leading to increased sensitivity with increased freque...

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W-Band¹⁷O Pulsed Electron Nuclear Double Resonance Study of Gadolinium Complexes with Water

Cited by 63 publications

References 35 publications

When are Two Waters Worse Than One? Doubling the Hydration Number of a Gd–DTPA Derivative Decreases Relaxivity

When are Two Waters Worse Than One? Doubling the Hydration Number of a Gd–DTPA Derivative Decreases Relaxivity

Nuclear Spin Relaxation Parameters of MRI Contrast Agents – Insight from Quantum Mechanical Calculations

Nanometer-Range Distance Measurement in a Protein Using Mn²⁺ Tags

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W-Band17O Pulsed Electron Nuclear Double Resonance Study of Gadolinium Complexes with Water

Cited by 63 publications

References 35 publications

When are Two Waters Worse Than One? Doubling the Hydration Number of a Gd–DTPA Derivative Decreases Relaxivity

When are Two Waters Worse Than One? Doubling the Hydration Number of a Gd–DTPA Derivative Decreases Relaxivity

Nuclear Spin Relaxation Parameters of MRI Contrast Agents – Insight from Quantum Mechanical Calculations

Nanometer-Range Distance Measurement in a Protein Using Mn2+ Tags

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W-Band¹⁷O Pulsed Electron Nuclear Double Resonance Study of Gadolinium Complexes with Water

Nanometer-Range Distance Measurement in a Protein Using Mn²⁺ Tags