Category Archives: Singlet State

Long live the singlet state! #DNPNMR

Levitt, Malcolm H. “Long Live the Singlet State!” Journal of Magnetic Resonance 306 (September 2019): 69–74.

https://doi.org/10.1016/j.jmr.2019.07.029

The field of long-lived states in NMR is reviewed. The relationship of long-lived-state phenomena to those associated with spin isomerism is discussed. A brief overview is given of key developments in the field of long-lived states, including chemical symmetry-switching, the role of magnetic equivalence and magnetic inequivalence, long-lived coherences, hyperpolarized NMR involving long-lived states, quantumrotor-induced polarization, and parahydrogen-induced hyperpolarization. Current application areas of long-lived states are reviewed, and a peer into the crystal ball reveals future developments in the field. Ó 2019 Published by Elsevier Inc.

Unlocking a diazirine long-lived nuclear singlet state via photochemistry: NMR detection and lifetime of an unstabilized diazo-compound

Procacci, Barbara, Soumya S Roy, Philip Norcott, Norman Turner, and Simon B Duckett. “Unlocking a Diazirine Long-Lived Nuclear Singlet State via Photochemistry: NMR Detection and Lifetime of an Unstabilized Diazo-Compound.” Journal of the American Chemical Society, 2018, 19.

https://doi.org/10.1021/jacs.8b10923.

Diazirines are important for photoaffinity labeling, and their photoisomerization is relatively well-known. This work shows how hyperpolarized NMR spectroscopy can be used to characterize an unstable diazo-compound formed via photoisomerization of a 15N2-labeled silyl-ether-substituted diazirine. This diazirine is prepared in a nuclear spin singlet state via catalytic transfer of spin order from para-hydrogen. The active hyperpolarization catalyst is characterized to provide insight into the mechanism. The photochemical isomerization of the diazirine into the diazo-analogue allows the NMR invisible nuclear singlet state of the parent compound to be probed. The identity of the diazo-species is confirmed by trapping with N-phenyl maleimide via a cycloaddition reaction to afford bicyclic pyrazolines that also show singlet state character. The presence of singlet states in the diazirine and the diazo-compound is validated by comparison of experimental nutation behavior with theoretical simulation. The magnetic state lifetime of the diazo-compound is determined as 12 ± 1 s in CD3OD solution at room temperature, whereas its chemical lifetime is measured as 100 ± 5 s by related hyperpolarized NMR studies. Indirect evidence for the generation of the photoproduct para-N2 is presented.

[NMR] POSTDOCTORAL POSITION: Nuclear Spin Singlet States and PHIP, New York University

POSTDOCTORAL POSITION: Nuclear Spin Singlet States and PHIP

New York University

DESCRIPTION:

A postdoctoral position is available immediately for the study of nuclear spin singlet state life times and singlet relaxation mechanisms, the development of efficient singlet/triplet conversion pulse sequences and methodology, as well as para-hydrogen induced polarization (PHIP) in the laboratory of Alexej Jerschow at New York University (NYU). The lab is located in newly renovated facilities of the Molecular Nanoscience Center at NYU’s Washington Square Campus in the heart of Manhattan.

Applicants should have an advanced degree (Ph.D) in Physics, Chemistry, or a related field, and should have experience with NMR/MRI theory and experiment. Knowledge of relaxation theory and computer programming and simulation skills would be a plus, as well as prior experience any of the specific research areas. Remuneration is competitive and commensurate with experience and will be based on New York University guidelines. Women and minorities are encouraged to apply.

CONTACT: 

To be considered, the application has to be submitted via the following link: https://apply.interfolio.com/49106.

Preliminary inquiries can be sent to

E-mail: alexej.jerschow@nyu.edu

Alexej Jerschow

Department of Chemistry

100 Washington Square East

New York University

New York, NY 10003.

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Two Research Fellow positions and one PhD studentship at University of Southampton #DNPNMR

From the Ampere Magnetic Resonance List

Dear Colleagues,

I have two open Reserach Fellow Positions and a fully funded PhD studentship in my group (http://www.southampton.ac.uk/chemistry/about/staff/pileio.page) at the University of Southampton.

* Post-Doctoral Research Fellowship in nuclear magnetic resonance in the research group of Dr Giuseppe Pileio, in collaboration with Prof Malcolm H Levitt. The project, funded by EPSRC(UK), concerns the development of NMR hardware and methodology that combines supercritical fluids with long-lived states NMR and dissolution-DNP to prolong the storage of hyperpolarised spin order and allow it to be transported remotely from the production site. The position is tenable from 1 December 2016 or as soon as possible thereafter with initial appointment for 2 years but with the possibility of a further extension of 1 more years, subject to project requirements. For further details and how to apply please follow this link: https://jobs.soton.ac.uk/Vacancy.aspx?id=14426&forced=1

* A 3 years PhD studentship is also available on the same project with application deadline 31 October 2016 and a salary of £14,296 per annum. For further details and how to apply please follow this link: https://jobs.soton.ac.uk/Vacancy.aspx?ref=782416EB . Please note that: due to funding restrictions this position is only open to UK/EU applicants

* Post-Doctoral Research Fellowship in nuclear magnetic resonance in the research group of Dr Giuseppe Pileio. The project, funded by EPSRC under the First Grant scheme, concerns the development of NMR methodology to probe translational dynamics in porous media by singlet-state NMR spectroscopy. The position is tenable from 1 November 2016 or as soon as possible thereafter with appointment for 1 year but with the possibility of a further extension of 1 more year, subject to funding and project requirements. For further details and how to apply please follow this link: https://jobs.soton.ac.uk/Vacancy.aspx?id=14420&forced=1

University of Southampton is a UK Russell Group university positioned in the top 1% of world universities according to QS World University Rankings. We have an international reputation for research, teaching and enterprise activities. Southampton is particularly well known for its magnetic resonance and computational chemistry research.

Many Thanks,

Dr. Giuseppe Pileio, PhD

Lecturer in Physical Chemistry,

Department of Chemistry,

Building 27 – Room 2059,

University of Southampton,

University Road, SO17 1BJ,

Internal Post Code: M16,

Southampton, Hampshire, UK.

Tel.: +44 (023) 80 59 4160

E-mail: G.Pileio@soton.ac.uk<mailto:G.Pileio@soton.ac.uk>

ORCID: 0000-0001-9223-3896

Web page: http://www.southampton.ac.uk/~pileio

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Singlet lifetime measurements in an all-proton chemically equivalent spin system by hyperpolarization and weak spin lock transfers

Zhang, Y., et al., Singlet lifetime measurements in an all-proton chemically equivalent spin system by hyperpolarization and weak spin lock transfers. Phys. Chem. Chem. Phys., 2015. 17(37): p. 24370-24375.

http://dx.doi.org/10.1039/C5CP03716F

Hyperpolarized singlet states provide the opportunity for polarization storage over periods significantly longer than T1. Here, we show how the singlet state in a chemically equivalent proton spin system can be revealed by a weak power spin-lock. This procedure allowed the measurement of the lifetimes of the singlet state in protic solvents. The contributions of different intra- and intermolecular relaxation mechanisms to singlet lifetimes are investigated with this procedure.

Long-lived localization in magnetic resonance imaging

Dumez, J.-N., et al., Long-lived localization in magnetic resonance imaging. J. Magn. Reson., 2014. 246(0): p. 27-30.

http://dx.doi.org/10.1016/j.jmr.2014.06.008

The longitudinal nuclear relaxation time, T1, sets a stringent limit on the range of information that can be obtained from magnetic resonance imaging (MRI) experiments. Long-lived nuclear spin states provide a possibility to extend the timescale over which information can be encoded in magnetic resonance. We introduce a strategy to localize an ensemble of molecules for a significantly extended duration (∼30 times longer than T1 in this example), using a spatially selective conversion between magnetization and long-lived singlet order. An application to tagging and transport is proposed.

Storage of nuclear magnetization as long-lived singlet order in low magnetic field

This week I will catch up with some articles that were published in the Proceedings of the National Academy of Sciences that slipped through the crack.

Pileio, G., M. Carravetta, and M.H. Levitt, Storage of nuclear magnetization as long-lived singlet order in low magnetic field. Proc. Nat. Aca. Sci. USA, 2010. 107(40): p. 17135-17139.

http://www.pnas.org/content/107/40/17135.abstract

Hyperpolarized nuclear states provide NMR signals enhanced by many orders of magnitude, with numerous potential applications to analytical NMR, in vivo NMR, and NMR imaging. However, the lifetime of hyperpolarized magnetization is normally limited by the relaxation time constant T1, which lies in the range of milliseconds to minutes, apart from in exceptional cases. In many cases, the lifetime of the hyperpolarized state may be enhanced by converting the magnetization into nuclear singlet order, where it is protected against many common relaxation mechanisms. However, all current methods for converting magnetization into singlet order require the use of a high-field, high-homogeneity NMR magnet, which is incompatible with most hyperpolarization procedures. We demonstrate a new method for converting magnetization into singlet order and back again. The new technique is suitable for magnetically inequivalent spin-pair systems in weak and inhomogeneous magnetic fields, and is compatible with known hyperpolarization technology. The method involves audio-frequency pulsed irradiation at the low-field nuclear Larmor frequency, employing coupling-synchronized trains of 180° pulses to induce singlet–triplet transitions. The echo trains are used as building blocks for a pulse sequence called M2S that transforms longitudinal magnetization into long-lived singlet order. The time-reverse of the pulse sequence, called S2M, converts singlet order back into longitudinal magnetization. The method is demonstrated on a solution of 15N-labeled nitrous oxide. The magnetization is stored in low magnetic field for over 30 min, even though the T1 is less than 3 min under the same conditions.

Hyperpolarized singlet lifetimes of pyruvate in human blood and in the mouse

Marco-Rius, I., et al., Hyperpolarized singlet lifetimes of pyruvate in human blood and in the mouse. NMR Biomed, 2013. 26(12): p. 1696-704.

http://www.ncbi.nlm.nih.gov/pubmed/23946252

Hyperpolarized NMR is a promising technique for non-invasive imaging of tissue metabolism in vivo. However, the pathways that can be studied are limited by the fast T1 decay of the nuclear spin order. In metabolites containing pairs of coupled nuclear spins-1/2, the spin order may be maintained by exploiting the non-magnetic singlet (spin-0) state of the pair. This may allow preservation of the hyperpolarization in vivo during transport to tissues of interest, such as tumors, or to detect slower metabolic reactions. We show here that in human blood and in a mouse in vivo at millitesla fields the (13)C singlet lifetime of [1,2-(13)C2]pyruvate was significantly longer than the (13)C T1, although it was shorter than the T1 at field strengths of several tesla. We also examine the singlet-derived NMR spectrum observed for hyperpolarized [1,2-(13)C2]lactate, originating from the metabolism of [1,2-(13)C2]pyruvate.

Direct Enhancement of Nuclear Singlet Order by Dynamic Nuclear Polarization

I don’t think I posted this one already.

Tayler, M.C.D., et al., Direct Enhancement of Nuclear Singlet Order by Dynamic Nuclear Polarization. J. Am. Chem. Soc., 2012. 134(18): p. 7668-7671.

http://dx.doi.org/10.1021/ja302814e

Hyperpolarized singlet order is available immediately after dissolution DNP, avoiding need for additional preparation steps. We demonstrate this procedure on a sample of [1,2?13C2]pyruvic acid.

Sensitivity enhancement and low-field spin relaxation in singlet NMR

This article does not describe any DNP experiments. However, singlet states can be useful for dissolution DNP experiments.

Bocan, J., G. Pileio, and M.H. Levitt, Sensitivity enhancement and low-field spin relaxation in singlet NMR. Phys. Chem. Chem. Phys., 2012. 14(46): p. 16032-16040.

http://dx.doi.org/10.1039/C2CP42553J

The singlet states of nuclear spin-1/2 pairs often display extended lifetimes that can be an order of magnitude longer than conventional relaxation times. We show that, in favourable circumstances, acquisition of the NMR signal during an extended multiple spin-echo train, followed by suitable data processing, enhances the signal-to-noise ratio of singlet NMR by up to an order of magnitude. The achievable enhancement depends on the transverse relaxation time constant, the magnetic field inhomogeneity, and the acceptable degradation in digital spectral resolution. We use the combination of singlet NMR and multiple spin-echo data acquisition to study the low-field nuclear relaxation processes of 15N-labelled nitrous oxide (15N2O) in solution. A general relaxation theory for coupled 2-spin-1/2 systems in low magnetic field is developed. Experimental trajectories of the nuclear spin observables are compared with theoretical expressions, including dipole-dipole and spin-rotation relaxation mechanisms. The estimated values of the spin-rotation tensors are compared with previous estimations from NMR and molecular beam electric resonance.

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