Long-Lived States of Methylene Protons in Achiral Molecules

Sonnefeld, Anna; Razanahoera, Aiky; Bodenhausen, Geoffrey; Sheberstov, Kirill F.

doi:10.48550/arxiv.2207.08608

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“…The results support simulations that show that different LLS are excited depending on the number of adjacent methylene units in the molecule and the SLIC sequence used. SLIC methods have also been shown to be efficient for other achiral molecules containing neighboring CH2 groups, such as dopamine, taurine and γ-aminobutyric acid (GABA), ethanolamine, and β-alanine (Sonnefeld, 2022a). All of these molecules contain aliphatic chains, so that the effects of paramagnetic polarizing agents like TEMPOL should be similar to what is reported in this work.…”

Section: Discussionsupporting

confidence: 63%

“…The coefficients of the first two bilinear terms are always equal, i.e., 𝜆 𝐴𝐴 ′= 𝜆 𝑋𝑋′ while the 4-spin term is always proportional to these bilinear terms, with a weight 𝜆 𝐴𝐴 ′ 𝑋𝑋 ′ = 8 3 ⁄ 𝜆 𝐴𝐴 ′ (Sonnefeld et al, 2022a). This state corresponds to the imbalance between the singlet-singlet state and the triplet-triplet manifold and is therefore expected to decay monoexponentially.…”

Section: Experiments and Simulations For Molecules With Three Ch2 Groupsmentioning

confidence: 99%

“…Therefore, one can transfer hyperpolarized samples to an NMR spectrometer for detection without significant losses of polarization. For small molecules, the ratios TLLS/T1 range typically from 2 to 6 for LLSs in CH2 groups in non-degassed samples (Sonnefeld et al, 2022a). In this work, we carried out a systematic analysis of relaxivities, i.e., of the dependence of the relaxation rates of LLS and longitudinal magnetization on the concentration of the paramagnetic species 4-hydroxy-2,2,6,6tetramethylpiperidin-1-oxyl (TEMPOL).…”

Section: Introductionmentioning

confidence: 99%

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Paramagnetic relaxivity of delocalized long-lived states of protons in chains of CH₂ groups

Razanahoera¹,

Sonnefeld²,

Bodenhausen³

et al. 2022

Preprint

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Abstract. Long-lived states (LLS) have lifetimes TLLS that can be much longer than longitudinal relaxation times T1. In molecules containing several geminal pairs of protons in neighbouring CH2 groups, it has been shown that delocalized long-lived states can be excited by converting magnetization into imbalances between the populations of singlet and triplet states of each pair. Since the yield of conversion of observable magnetization into LLS and back are on the order of 10 % or less if one uses spin-locked induced crossing (SLIC), it would be desirable to boost the sensitivity by dissolution dynamic nuclear polarization (d-DNP). To enhance the magnetization of nuclear spins by d-DNP, the analytes must be mixed with radicals such as 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPOL) prior to freezing at low temperatures in the vicinity of 1 K. After dissolution, these radicals lead to an undesirable paramagnetic relaxation enhancement (PRE) which shortens not only the longitudinal relaxation times T1 but also the lifetimes TLLS of long-lived states. It is confirmed in this work that PRE by TEMPOL is less deleterious for LLS than for longitudinal magnetization for four different molecules: 2,2-dimethyl-2-silapentane-5-sulfonate (DSS), homotaurine, taurine, and acetylcholine. The relaxivities (i.e., the slopes of relaxation rates as a function of the radical concentration) of LLS rLLS are 3 to 5 times smaller than the relaxivities of longitudinal magnetization r1. Partial delocalization of the LLS across neighbouring CH2 groups may decrease this advantage, but in practice, this effect was observed to be minor when comparing taurine containing two CH2 groups and homotaurine with three CH2 groups. Regardless of whether the LLS are delocalized or not, it is shown that PRE should not be a major problem for experiments combining d DNP and LLS, provided the concentration of paramagnetic species after dissolution does not exceed 1 mM, a condition that is readily fulfilled in typical d-DNP experiments. In bullet d-DNP experiments, however, it may be necessary to reduce TEMPOL by adding ascorbate or using lower concentrations of TEMPOL.

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Section: Discussionsupporting

confidence: 63%

Section: Experiments and Simulations For Molecules With Three Ch2 Groupsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Paramagnetic relaxivity of delocalized long-lived states of protons in chains of CH₂ groups

Razanahoera¹,

Sonnefeld²,

Bodenhausen³

et al. 2022

Preprint

View full text Add to dashboard Cite

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Long-Lived States of Methylene Protons in Achiral Molecules

Cited by 1 publication

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Paramagnetic relaxivity of delocalized long-lived states of protons in chains of CH₂ groups

Paramagnetic relaxivity of delocalized long-lived states of protons in chains of CH₂ groups

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Long-Lived States of Methylene Protons in Achiral Molecules

Cited by 1 publication

References 0 publications

Paramagnetic relaxivity of delocalized long-lived states of protons in chains of CH2 groups

Paramagnetic relaxivity of delocalized long-lived states of protons in chains of CH2 groups

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Paramagnetic relaxivity of delocalized long-lived states of protons in chains of CH₂ groups

Paramagnetic relaxivity of delocalized long-lived states of protons in chains of CH₂ groups