Long-Lived 1 H Singlet Spin States Originating from Para-Hydrogen in Cs-Symmetric Molecules Stored for Minutes in High Magnetic Fields (original) (raw)
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The Journal of Chemical Physics, 2006
Recently, Levitt and co-workers demonstrated that conserving the population of long-lasting nuclear singlet states in weak magnetic fields can lead to a preservation of nuclear spin information over times substantially longer than governed by the ͑high-field͒ spin-lattice relaxation time T 1 . Potential benefits of the prolonged spin information for magnetic resonance imaging and spectroscopy were pointed out, particularly when combined with the parahydrogen induced polarization ͑PHIP͒ methodology. In this contribution, we demonstrate that an increase of the effective relaxation time by a factor up to three is achieved experimentally, when molecules hyperpolarized by PHIP are kept in a weak magnetic field instead of the strong field of a typical NMR magnet. This increased lifetime of spin information makes the known PHIP phenomena more compatible with the time scales of biological processes and, thus, more attractive for future investigations.
Chemical Physics Letters, 2011
This communication describes a three-field experiment where inequivalent scalar coupled spin pairs are hyperpolarized at 3.35 T and 1.2 K by dynamic nuclear polarization (DNP), rapidly transferred to high field (7 T) to prepare a suitable initial condition that is converted adiabatically into a long-lived state (LLS) by shuttling to a 'low' magnetic field (2 mT-7 T). Even without applying any rf irradiation to sustain the LLS, it has a lifetime T LLS ) T 1 in low fields. Finally, the sample is shuttled back to high field for observation under high-resolution conditions.
Efficient Transformation of Parahydrogen Spin Order into Heteronuclear Magnetization
The Journal of Physical Chemistry B, 2013
Spin order obtained in the strong coupling regime of protons from parahydrogen-induced hyperpolarization (PHIP) is initially captured as an ensemble of singlet states. For biomedical applications of PHIP, locking this spin order on long-lived heteronuclear storage nuclei increases spectral dispersion, reduces background interference from water protons, and eliminates the need to synchronize subsequent detection pulse sequences to accrued singlet-state evolution. A variety of traditional sequences such as INEPT or HMQC are available to interconvert heteronuclear single quantum coherences at high field, but new approaches are required for converting singlet states into heteronuclear single quantum coherences at low field in the strong coupling regime of protons. Described here is a consolidated pulse sequence that achieves this transformation of singlet-state spin order into heteronuclear magnetization across a wide range of scalar couplings in AA′X spin systems. Analytic solutions to the spin evolution are presented, and performance was validated experimentally in the parahydrogen addition product, 2-hydroxyethyl 1-13 C-propionated 3. Hyperpolarized carbon-13 signals were enhanced by a factor of several million relative to Boltzmann polarization in a static magnetic field of 47.5 mT (~13% polarization). We anticipate that this pulse sequence will provide efficient conversion of parahydrogen spin order over a broad range of emerging PHIP agents that feature AA′X spin systems.
Journal of the American Chemical Society, 2013
Hyperpolarized magnetic resonance imaging is a powerful technique enabling real time monitoring of metabolites at concentration levels not accessible by standard MRI techniques. A considerable challenge this technique faces is the T 1 decay of the hyperpolarization upon injection into the system under study. Here we show that A n A' n XX' spin systems such as 13 C 2-1,2diphenylacetylene (13 C 2-DPA) sustain long-lived polarization for both 13 C and 1 H spins with decay constants of almost 4.5 min at high magnetic fields of up to 16.44 T without spin-locking; the T 1 of proton polarization is only 3.8 s. Therefore, storage of the proton polarization in a 13 C 2singlet state causes a 69 fold extension of the spin lifetime. Notably, this extension is demonstrated with proton-only pulse sequences, which can be readily implemented on standard clinical scanners.
Para-hydrogen induced polarization in multi-spin systems studied at variable magnetic field
Physical Chemistry Chemical Physics, 2009
A theoretical description of para-hydrogen-induced polarization (PHIP) is developed, applicable to coupled multi-spin systems that are polarized at an arbitrary magnetic field. Scalar spin-spin interaction is considered to be the leading factor governing PHIP formation and transfer. At low magnetic fields, these interactions make the spins strongly coupled and cause efficient, coherent redistribution of spin polarization. We describe the effects of strong coupling and field cycling for a three-spin system and compare calculated spectra with the experimental examples available. By using a fast field-cycling device, which shuttles the whole NMR probe, and thereby makes high-resolution NMR detection at high field possible, we studied PHIP patterns for a set of different fields between 0.1 mT and 7 T. PHIP spectra were measured for ethylbenzene as the product of a catalytic reaction between para-hydrogen and styrene. Additionally, the polarizations of ethylbenzene bound to the catalyst, and of the starting styrene molecule were analyzed. This is the first time that the full field dependence of PHIP has been determined experimentally. The spectra obtained are in perfect agreement with the simulations for the CH 2 and CH 3 protons of ethylbenzene and even for its weakly-polarized aromatic protons. Analysis of styrene polarization shows that the time profile of the field variation has pronounced effects on the PHIP pattern. Our study gives evidence that scalar spin-spin interactions determine the PHIP patterns. Possible applications of the theory are discussed.
The journal of physical chemistry letters, 2017
Parahydrogen is an inexpensive and readily available source of hyperpolarization used to enhance magnetic resonance signals by up to 4 orders of magnitude above thermal signals obtained at ~10 T. A significant challenge for applications is fast signal decay after hyperpolarization. Here, we use parahydrogen based polarization transfer catalysis at micro-Tesla fields (first introduced as SABRE-SHEATH) to hyperpolarize (13)C2 spin pairs and find decay time constants of 12 s for magnetization at 0.3 mT, which are extended to 2 minutes at that same field, when long lived singlet states are hyperpolarized instead. Enhancements over thermal at 8.5 T are between 30 and 170 fold. We control the spin dynamics of polarization transfer by choice of μT field allowing for deliberate hyperpolarization of either magnetization or long-lived singlet states. Density functional theory (DFT) calculations and experimental evidence identify two energetically close mechanisms for polarization transfer: Fi...
Symmetry Constraints on Spin Order Transfer in Parahydrogen-Induced Polarization (PHIP)
Symmetry, 2022
It is well known that the association of parahydrogen (pH2) with an unsaturated molecule or a transient metalorganic complex can enhance the intensity of NMR signals; the effect is known as parahydrogen-induced polarization (PHIP). During recent decades, numerous methods were proposed for converting pH2-derived nuclear spin order to the observable magnetization of protons or other nuclei of interest, usually 13C or 15N. Here, we analyze the constraints imposed by the topological symmetry of the spin systems on the amplitude of transferred polarization. We find that in asymmetric systems, heteronuclei can be polarized to 100%. However, the amplitude drops to 75% in A2BX systems and further to 50% in A3B2X systems. The latter case is of primary importance for biological applications of PHIP using sidearm hydrogenation (PHIP-SAH). If the polarization is transferred to the same type of nuclei, i.e., 1H, symmetry constraints impose significant boundaries on the spin-order distribution. F...
Reversible Interactions with para-Hydrogen Enhance NMR Sensitivity by Polarization Transfer
Science, 2009
The sensitivity of both nuclear magnetic resonance spectroscopy and magnetic resonance imaging is very low because the detected signal strength depends on the small population difference between spin states even in high magnetic fields. Hyperpolarization methods can be used to increase this difference and thereby enhance signal strength. This has been achieved previously by incorporating the molecular spin singlet para-hydrogen into hydrogenation reaction products. We show here that a metal complex can facilitate the reversible interaction of para-hydrogen with a suitable organic substrate such that up to an 800-fold increase in proton, carbon, and nitrogen signal strengths are seen for the substrate without its hydrogenation. These polarized signals can be selectively detected when combined with methods that suppress background signals.