Category Archives: gadolinium

Hyperpolarized [15N]nitrate as a potential long lived hyperpolarized contrast agent for MRI

Gamliel, Ayelet, Sivaranjan Uppala, Gal Sapir, Talia Harris, Atara Nardi-Schreiber, David Shaul, Jacob Sosna, J. Moshe Gomori, and Rachel Katz-Brull. “Hyperpolarized [15N]Nitrate as a Potential Long Lived Hyperpolarized Contrast Agent for MRI.” Journal of Magnetic Resonance 299 (February 2019): 188–95.

https://doi.org/10.1016/j.jmr.2019.01.001.

Reports on Gadolinium deposits in the body and brains of adults and children who underwent contrast-enhanced MRI examinations warrant development of new, metal free, contrast agents for MRI. Nitrate is an abundant ion in mammalian biochemistry and sodium nitrate can be safely injected intravenously. We show that hyperpolarized [15N]nitrate can potentially be used as an MR tracer. The 15N site of hyperpolarized [15N]nitrate showed a T1 of more than 100 s in aqueous solutions, which was prolonged to more than 170 s below 20 C. Capitalizing on this effect for polarization storage we obtained a visibility window of 9 min in blood. Conversion to [15N]nitrite, the bioactive reduced form of nitrate, was not observed in human blood and human saliva in this time frame. Thus, [15N]nitrate may serve as a long-lived hyperpolarized tracer for MR. Due to its ionic nature, the immediate applications appear to be perfusion and tissue retention imaging.

Bis-Gadolinium Complexes for Solid Effect and Cross Effect Dynamic Nuclear Polarization #DNPNMR

Kaushik, M., et al., Bis-Gadolinium Complexes for Solid Effect and Cross Effect Dynamic Nuclear Polarization. Angew Chem Int Ed Engl, 2017. 56(15): p. 4295-4299.

https://www.ncbi.nlm.nih.gov/pubmed/28319293

High-spin complexes act as polarizing agents (PAs) for dynamic nuclear polarization (DNP) in solid-state NMR spectroscopy and feature promising aspects towards biomolecular DNP. We present a study on bis(Gd-chelate)s which enable cross effect (CE) DNP owing to spatial confinement of two dipolar-coupled electron spins. Their well-defined GdGd distances in the range of 1.2-3.4 nm allowed us to elucidate the GdGd distance dependence of the DNP mechanism and NMR signal enhancement. We found that GdGd distances above 2.1 nm result in solid effect DNP while distances between 1.2 and 2.1 nm enable CE for 1 H, 13 C, and 15 N nuclear spins. We compare 263 GHz electron paramagnetic resonance (EPR) spectra with the obtained DNP field profiles and discuss possible CE matching conditions within the high-spin system and the influence of dipolar broadening of the EPR signal. Our findings foster the understanding of the CE mechanism and the design of high-spin PAs for specific applications of DNP.

The effect of Gd on trityl-based dynamic nuclear polarisation in solids

Ravera, E., et al., The effect of Gd on trityl-based dynamic nuclear polarisation in solids. Phys Chem Chem Phys, 2015. 17(40): p. 26969-78.

http://www.ncbi.nlm.nih.gov/pubmed/26403358

In dynamic nuclear polarisation (DNP) experiments performed under static conditions at 1.4 K we show that the presence of 1 mM Gd(iii)-DOTAREM increases the (13)C polarisation and decreases the (13)C polarisation buildup time of (13)C-urea dissolved in samples containing water/DMSO mixtures with trityl radical (OX063) concentrations of 10 mM or higher. To account for these observations further measurements were carried out at 6.5 K, using a combined EPR and NMR spectrometer. At this temperature, frequency swept DNP spectra of samples with 5 or 10 mM OX063 were measured, with and without 1 mM Gd-DOTA, and again a (13)C enhancement gain was observed due to the presence of Gd-DOTA. These measurements were complemented by electron-electron double resonance (ELDOR) measurements to quantitate the effect of electron spectral diffusion (eSD) on the DNP enhancements and lineshapes. Simulations of the ELDOR spectra were done using the following parameters: (i) a parameter defining the rate of the eSD process, (ii) an “effective electron-proton anisotropic hyperfine interaction parameter”, and (iii) the transverse electron spin relaxation time of OX063. These parameters, together with the longitudinal electron spin relaxation time, measured by EPR, were used to calculate the frequency profile of electron polarisation. This, in turn, was used to calculate two basic solid effect (SE) and indirect cross effect (iCE) DNP spectra. A properly weighted combination of these two normalized DNP spectra provided a very good fit of the experimental DNP spectra. The best fit simulation parameters reveal that the addition of Gd(iii)-DOTA causes an increase in both the SE and the iCE contributions by similar amounts, and that the increase in the overall DNP enhancements is a result of narrowing of the ELDOR spectra (increased electron polarisation gradient across the EPR line). These changes in the electron depolarisation profile are a combined result of shortening of the longitudinal and transverse electron spin relaxation times, as well as an increase in the eSD rate and in the effective electron-proton anisotropic hyperfine interaction parameter.

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