Friday, March 16, 2018

Quantitative biosensor detection by chemically exchanging hyperpolarized 129Xe

Korchak, S., et al., Quantitative biosensor detection by chemically exchanging hyperpolarized 129Xe. PCCP, 2018. 20(3): p. 1800-1808.

Chemical sensors informing about their local environment are of widespread use for chemical analysis. A thorough understanding of the sensor signaling is fundamental to data analysis and interpretation, and a requirement for technological applications. Here, sensors explored for the recognition and display of biomolecular and cellular markers by magnetic resonance and composed of host molecules for xenon atoms are considered. These host-guest systems are analytically powerful and also function as contrast agents in imaging applications. Using nuclear spin hyperpolarization of 129Xe and chemical exchange saturation transfer the detection sensitivity is orders of magnitude enhanced in comparison to conventional 1H NMR. The sensor signaling reflects this rather complex genesis, furthering the mere qualitative interpretation of biosensing data; to harvest the potential of the approach, however, a detailed numerical account is desired. To this end, we introduce a comprehensive expression that maps the sensor detection quantitatively by integration of the hyperpolarization generation and relaxation with the host-xenon exchange dynamics. As demonstrated for the host molecule and well-established biosensor cryptophane-A, this model reveals a distinguished maximum in sensor signaling and exerts control over experimentation by dedicated adjustments of both the amount of xenon and the duration of the saturation transfer applied in a measurement, for example to capitalize on investigations at the detection limit. Furthermore, usage of the model for data analysis makes the quantification of the sensor concentration in the nanomolar range possible. The approach is readily applicable in investigations using cryptophane-A and is straightaway adaptable to other sensor designs for extension of the field of xenon based biosensing.

Wednesday, March 14, 2018

Re-polarization of nuclear spins using selective SABRE-INEPT

Knecht, S., et al., Re-polarization of nuclear spins using selective SABRE-INEPT. Journal of Magnetic Resonance, 2018. 287: p. 10-14.

A method is proposed for significant improvement of NMR pulse sequences used in high-field SABRE (Signal Amplification By Reversible Exchange) experiments. SABRE makes use of spin order transfer from parahydrogen (pH2, the H2 molecule in its singlet spin state) to a substrate in a transient organometallic Ir-based complex. The technique proposed here utilizes “re-polarization”, i.e., multiple application of an NMR pulse sequence used for spin order transfer. During re-polarization only the form of the substrate, which is bound to the complex, is excited by selective NMR pulses and the resulting polarization is transferred to the free substrate via chemical exchange. Owing to the fact that (i) only a small fraction of the substrate molecules is in the bound form and (ii) spin relaxation of the free substrate is slow, the re-polarization scheme provides greatly improved NMR signal enhancement, ε. For instance, when pyridine is used as a substrate, single use of the SABRE-INEPT sequence provides ε≈260 for 15N nuclei, whereas SABRE-INEPT with re-polarization yields ε>2000. We anticipate that the proposed method is useful for achieving maximal NMR enhancement with spin hyperpolarization techniques.

Monday, March 12, 2018

Testing signal enhancement mechanisms in the dissolution NMR of acetone

Alonso-Valdesueiro, J., et al., Testing signal enhancement mechanisms in the dissolution NMR of acetone. Journal of Magnetic Resonance, 2018. 286: p. 158-162.

In cryogenic dissolution NMR experiments, a substance of interest is allowed to rest in a strong magnetic field at cryogenic temperature, before dissolving the substance in a warm solvent, transferring it to a high-resolution NMR spectrometer, and observing the solution-state NMR spectrum. In some cases, negative enhancements of the 13C NMR signals are observed, which have been attributed to quantum-rotor-induced polarization. We show that in the case of acetone (propan-2-one) the negative signal enhancements of the methyl 13C sites may be understood by invoking conventional cross-relaxation within the methyl groups. The 1H nuclei acquire a relative large net polarization through thermal equilibration in a magnetic field at low temperature, facilitated by the methyl rotation which acts as a relaxation sink; after dissolution, the 1H magnetization slowly returns to thermal equilibrium at high temperature, in part by cross-relaxation processes, which induce a transient negative polarization of nearby 13C nuclei. We provide evidence for this mechanism experimentally and theoretically by saturating the 1H magnetization using a radiofrequency field pulse sequence before dissolution and comparing the 13C magnetization evolution after dissolution with the results obtained from a conventional 1H-13C cross relaxation model of the CH3 moieties in acetone.

Friday, March 9, 2018

The effect of Ho3+ doping on 13C dynamic nuclear polarization at 5 T

Sirusi, A.A., et al., The effect of Ho3+ doping on 13C dynamic nuclear polarization at 5 T. PCCP, 2018. 20(2): p. 728-731.

Dissolution dynamic nuclear polarization was introduced in 2003 as a method for producing hyperpolarized 13C solutions suitable for metabolic imaging. The signal to noise ratio for the imaging experiment depends on the maximum polarization achieved in the solid state. Hence, optimization of the DNP conditions is essential. To acquire maximum polarization many parameters related to sample preparation can be modulated. Recently, it was demonstrated that Ho3+, Dy3+, Tb3+, and Gd3+ complexes enhance the polarization at 1.2 K and 3.35 T when using the trityl radical as the primary paramagnetic center. Here, we have investigated the influence of Ho-DOTA on 13C solid state DNP at 1.2 K and 5 T. We have performed 13C DNP on [1-13C] sodium acetate in 1 : 1 (v/v) water/glycerol with 15 mM trityl OX063 radicals in the presence of a series of Ho-DOTA concentrations (0, 0.5, 1, 2, 3, 5 mM). We have found that adding a small amount of Ho-DOTA in the sample preparation not only enhances the 13C polarization but also decreases the buildup time. The optimum Ho-DOTA concentration was 2 mM. In addition, the microwave sweep spectrum changes character in a manner that suggests both the cross effect and thermal mixing are active mechanisms for trityl radical at 5 T and 1.2 K.

Thursday, March 8, 2018

[NMR] HYP18 conference Sep 2-5 2018, Southampton UK #DNPNMR

The HYP18 conference on hyperpolarization in Southampton is now open for registration and abstract submission at

This conference will cover the main areas of nuclear hyperpolarization and some other methods for sensitivity enhancement in NMR and MRI, including:
  • dynamic nuclear polarization (DNP), both in solids and in solution
  • optical pumping 
  • quantum-rotor-induced polarization 
  • parahydrogen-induced polarization 
  • diamond magnetometry 
and key applications such as clinical imaging, materials science, and molecular structure determination. As far as we know, a meeting of this kind has not taken place before. It is a unique opportunity to hear the latest news from this exciting frontier. 
The confirmed plenary speakers are:
The confirmed invited speakers are:
Welcome to Southampton in September!
Malcolm and Peppe

Hyperpolarized Magnetic Resonance
Southampton UK, Sep 2-5 2018
Prof Malcolm Levitt
School of Chemistry
Room 27:2026
University of Southampton
Southampton SO17 1BJ
tel. +44 23 8059 6753
fax: +44 23 8059 3781
iPhone: +44 77 7078 2024

This is the AMPERE MAGNETIC RESONANCE mailing list:

NMR web database:

Wednesday, March 7, 2018

High-resolution hyperpolarized metabolic imaging of the rat heart using k-t PCA and k-t SPARSE

Wespi, P., et al., High-resolution hyperpolarized metabolic imaging of the rat heart using k-t PCA and k-t SPARSE. NMR Biomed., 2018. 31(2): p. e3876-n/a.

The purpose of this work was to increase the resolution of hyperpolarized metabolic imaging of the rat heart with accelerated imaging using k–t principal component analysis (k–t PCA) and k–t compressed sensing (k–t SPARSE). Fully sampled in vivo datasets were acquired from six healthy rats after the injection of hyperpolarized [1-13C]pyruvate. Data were retrospectively undersampled and reconstructed with either k–t PCA or k–t SPARSE. Errors of signal–time curves of pyruvate, lactate and bicarbonate were determined to compare the two reconstruction algorithms for different undersampling factors R. Prospectively undersampled imaging at 1 × 1 × 3.5-mm3 resolution was performed with both methods in the same animals and compared with the fully sampled acquisition. k–t SPARSE was found to perform better at R < 3, but was outperformed by k–t PCA at R ≥ 4. Prospectively undersampled data were successfully reconstructed with both k–t PCA and k–t SPARSE in all subjects. No significant difference between the undersampled and fully sampled data was found in terms of signal-to-noise ratio (SNR) performance and metabolic quantification. Accelerated imaging with both k–t PCA and k–t SPARSE allows an increase in resolution, thereby reducing the intravoxel dephasing of hyperpolarized metabolic imaging of the rat heart.

Monday, March 5, 2018

Mechanism of spontaneous polarization transfer in high-field SABRE experiments

Knecht, S., et al., Mechanism of spontaneous polarization transfer in high-field SABRE experiments. Journal of Magnetic Resonance, 2018. 287: p. 74-81.

We propose an explanation of the previously reported SABRE (Signal Amplification By Reversible Exchange) effect at high magnetic fields, observed in the absence of RF-excitation and relying only on “spontaneous” polarization transfer from parahydrogen (pH2, the H2 molecule in its nuclear singlet spin state) to a SABRE substrate. We propose a detailed mechanism for spontaneous polarization transfer and show that it is comprised of three steps: (i) Generation of the anti-phase Î1zÎ2z spin order of catalyst-bound H2; (ii) spin order conversion Î1zÎ2z→(Î1z+Î2z) due to cross-correlated relaxation, leading to net polarization of H2; (iii) polarization transfer to the SABRE substrate, occurring due to NOE. Formation of anti-phase polarization is due to singlet-to-T0 mixing in the catalyst-bound form of H2, while cross-correlated relaxation originates from fluctuations of dipole–dipole interactions and chemical shift anisotropy. The proposed mechanism is supported by a theoretical treatment, magnetic field-dependent studies and high-field NMR measurements with both pH2 and thermally polarized H2.