Theory of long-lived nuclear spin states in solution nuclear magnetic resonance. I. Singlet states in low magnetic field

Carravetta, Marina; Levitt, Malcolm H.

doi:10.1063/1.1893983

Cited by 189 publications

(185 citation statements)

References 31 publications

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“…In low magnetic field, the chemical shift anisotropy mechanism is absent, and the intramolecular dipole-dipole coupling does not cause singlet relaxation. [1][2][3][4][5][6][7] In a forthcoming publication we show that for pure spin-rotation relaxation, 12 the ratio of T S and T 1 is given by (6) where C j and C k are the spin-rotation tensors for the two 15 N sites. This equation takes into account the strong cross-correlation of the spin-rotation interactions in this linear molecule.…”

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confidence: 82%

The Long-Lived Nuclear Singlet State of ¹⁵N-Nitrous Oxide in Solution

et al. 2008

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Nuclear singlet states may have lifetimes T S that exceed the conventional magnetization relaxation time T 1 by an order of magnitude. [1][2][3][4][5][6][7][8][9][10][11] Applications of these states to the NMR measurements of slow molecular diffusion, chemical exchange, and the transportofhyperpolarizednuclearspinorderhavebeendemonstrated. [8][9][10][11] So far, long-lived nuclear singlet states have only been observed for proton pairs. We now demonstrate an extraordinarily long lifetime (T S ) of ∼26 min for the nuclear spin singlet of 15 N 2 -nitrous oxide (dinitrogen monoxide, N 2 O) in solution. This result has high potential importance since nitrous oxide is soluble in many important fluids such as water, oil, and blood. It is used routinely as a food additive, a gas propellant, and an anesthetic.Doubly labeled 15 N 2 O gas, purchased from CK-gas (UK), was dissolved in a degassed solution of DMSO-d 6 at a pressure of ∼3. Figure 1a.The slow relaxation of singlet states is revealed by suppressing their interconversion with the triplet states, either by using a resonant radiofrequency field [3][4][5][6] or by reducing the static magnetic field to a very low value. 1,2 The radiofrequency method is not feasible for The spin system is allowed to reach thermal equilibrium, and two strong 90°pulses with a relative phase of 90°are applied at the mean chemical shift frequency of the two 15 N sites. The delay between the pulses, τ 1 ) 0.198 ms, was chosen so that the transverse magnetization vectors of the two 15 N sites precess through 180°r elative to each other. The two pulses act as a selective 180°pulse on one of the 15 N sites and lead to a spin density operator 10 of the formwhere the two sites are denoted j and k and the selective inversion is assumed to act on site j. In this and the following equations, the subscript refers to a time point in Figure 2. The sample is transported out of the magnetic field by activating a stepper motor to wind up a string attached to the sample holder. The transport process takes τ tr ) 40 s and transports the sample into a region of low magnetic field, B low ≈ 2 mT, estimated by a Hall effect device. As shown in ref 2, slow adiabatic transport converts the population of each high-field state into that of the corresponding low-field state, leading to a density operator of the formwhere the low-field eigenstates areThe sample is left in the low-field region for a variable time τ LF . During the first few minutes, the three triplet populations equilibrate with each other on a time scale set by the relaxation constant T 1 . The density operator after several minutes in low magnetic field is therefore given approximately byThe sample is transported back into the high-field region by running the stepper motor in the opposite direction. Adiabatic transport from the density operator in eq 3 leads to

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The Long-Lived Nuclear Singlet State of ¹⁵N-Nitrous Oxide in Solution

et al. 2008

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“…The evolution of the singlet-triplet population difference is described in ref. [12][13][14]. After equilibration of the triplet populations, the difference between the singlet population and the average of the three triplet populations decays with the time constant T S .…”

Section: Preparation Of Long-lived Statesmentioning

confidence: 99%

“…The long singlet lifetime is manifested during stage (ii). This requires that singlet-to-triplet interconversion is suppressed, by either transporting the sample into a region of low magnetic field, 1,12 keeping the sample in high magnetic field while applying resonant radiofrequency irradiation, 2,13 or switching the symmetry of the molecule using a chemical reaction. 10 In this article we explore the situation in which the difference of nuclear resonance frequencies is very small, i.e.…”

Section: Introductionmentioning

confidence: 99%

Singlet nuclear magnetic resonance of nearly-equivalent spins

Tayler

Levitt

2011

Phys. Chem. Chem. Phys.

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Nuclear singlet states may display lifetimes that are an order of magnitude greater than conventional relaxation times. Existing methods for accessing these long-lived states require a resolved chemical shift difference between the nuclei involved. Here, we demonstrate a new method for accessing singlet states that works even when the nuclei are almost magnetically equivalent, such that the chemical shift difference is unresolved. The method involves trains of 1801 pulses that are synchronized with the spin-spin coupling between the nuclei. We demonstrate experiments on the terminal glycine resonances of the tripeptide alanylglycylglycine (AGG) in aqueous solution, showing that the nuclear singlet order of this system is long-lived even when no resonant locking field is applied. Variation of the pulse sequence parameters allows the estimation of small chemical shift differences that are normally obscured by larger J-couplings.

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“…However, it remains that hyperpolarized magnetization is limited to the timescale of the spin-lattice relaxation (T 1 ), which is usually less than 1 min. In this article, we explore the use of pairs of magnetic nuclei to extend the lifetime of hyperpolarization by exploiting the properties of nuclear singlet states (3,4). Molecules containing two spin-1/2 nuclei may exist as singlet and triplet nuclear spin isomers; namely molecules that have identical molecular structure but differ in their nuclear magnetism.…”

Section: Introductionmentioning

confidence: 99%

Hyperpolarized singlet NMR on a small animal imaging system

Laustsen

Pileio

Tayler

et al. 2012

Magnetic Resonance in Med

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Nuclear spin hyperpolarization makes a significant advance toward overcoming the sensitivity limitations of in vivo magnetic resonance imaging, particularly in the case of low-gamma nuclei. The sensitivity may be improved further by storing the hyperpolarization in slowly relaxing singlet populations of spin-1/2 pairs. Here, we report hyperpolarized 13 C spin order transferred into and retrieved from singlet spin order using a small animal magnetic resonance imaging scanner. For spins in sites with very similar chemical shifts, singlet spin order is sustained in high magnetic field without requiring strong radiofrequency irradiation. The demonstration of robust singlet-to-magnetization conversion, and vice versa, on a small animal scanner, is promising for future in vivo and clinical deployments. Magn Reson Med 000:000-000, 2012. V C 2012 Wiley Periodicals, Inc.

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Theory of long-lived nuclear spin states in solution nuclear magnetic resonance. I. Singlet states in low magnetic field

Cited by 189 publications

References 31 publications

The Long-Lived Nuclear Singlet State of ¹⁵N-Nitrous Oxide in Solution

The Long-Lived Nuclear Singlet State of ¹⁵N-Nitrous Oxide in Solution

Singlet nuclear magnetic resonance of nearly-equivalent spins

Hyperpolarized singlet NMR on a small animal imaging system

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Theory of long-lived nuclear spin states in solution nuclear magnetic resonance. I. Singlet states in low magnetic field

Cited by 189 publications

References 31 publications

The Long-Lived Nuclear Singlet State of 15N-Nitrous Oxide in Solution

The Long-Lived Nuclear Singlet State of 15N-Nitrous Oxide in Solution

Singlet nuclear magnetic resonance of nearly-equivalent spins

Hyperpolarized singlet NMR on a small animal imaging system

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The Long-Lived Nuclear Singlet State of ¹⁵N-Nitrous Oxide in Solution

The Long-Lived Nuclear Singlet State of ¹⁵N-Nitrous Oxide in Solution