CH基团链中质子离域长寿命态的顺磁弛豫率
Paramagnetic relaxivity of delocalized long-lived states of protons in chains of CH groups.
作者信息
Razanahoera Aiky, Sonnefeld Anna, Bodenhausen Geoffrey, Sheberstov Kirill
机构信息
Department of Chemistry, École Normale Supérieure, PSL University, 75005 Paris, France.
出版信息
Magn Reson (Gott). 2023 Feb 16;4(1):47-56. doi: 10.5194/mr-4-47-2023. eCollection 2023.
Long-lived states (LLSs) have lifetimes that can be much longer than longitudinal relaxation times . In molecules containing several geminal pairs of protons in neighboring CH groups, it has been shown that LLSs can be excited by converting magnetization into imbalances between the populations of singlet and triplet states of each pair. Since the empirical yield of the conversion and reconversion of observable magnetization into LLSs and back is on the order of 10 % if one uses spin-lock 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). After dissolution, these radicals lead to an undesirable paramagnetic relaxation enhancement (PRE) which shortens not only the longitudinal relaxation times but also the lifetimes of LLSs. It is shown in this work that PRE by TEMPOL is less deleterious for LLSs 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 the relaxation rate constants as a function of the radical concentration) are 3 to 5 times smaller than the relaxivities of longitudinal magnetization. Partial delocalization of the LLSs across neighboring CH groups may decrease this advantage, but in practice, this effect was observed to be small, for example, when comparing taurine containing two CH groups and homotaurine with three CH groups. Regardless of whether the LLSs are delocalized or not, it is shown that PRE should not be a major problem for experiments combining d-DNP and LLSs, 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 decrease the concentration of TEMPOL or to add ascorbate for chemical reduction.
长寿命态(LLSs)的寿命可能比纵向弛豫时间长得多。在相邻CH基团中含有几对偕质子的分子中,研究表明,可以通过将磁化强度转化为每对单重态和三重态的粒子数失衡来激发LLSs。由于如果使用自旋锁定诱导交叉(SLIC),可观测磁化强度转化为LLS以及再转化回LLS的经验产率约为10%,因此希望通过溶解动态核极化(d-DNP)来提高灵敏度。为了通过d-DNP增强核自旋的磁化强度,分析物必须与诸如4-羟基-2,2,6,6-四甲基哌啶-1-氧基(TEMPOL)之类的自由基混合。溶解后,这些自由基会导致不良的顺磁弛豫增强(PRE),这不仅会缩短纵向弛豫时间,还会缩短LLSs的寿命。这项工作表明,对于四种不同的分子:2,2-二甲基-2-硅戊烷-5-磺酸盐(DSS)、高牛磺酸、牛磺酸和乙酰胆碱,TEMPOL引起的PRE对LLSs的有害性比对纵向磁化强度的有害性小。弛豫率(即弛豫速率常数随自由基浓度变化的斜率)比纵向磁化强度的弛豫率小3至5倍。LLSs在相邻CH基团间的部分离域可能会降低这种优势,但在实际中,例如比较含有两个CH基团的牛磺酸和含有三个CH基团的高牛磺酸时,观察到这种效应很小。无论LLSs是否离域,研究表明,只要溶解后顺磁物质的浓度不超过1 mM(这在典型的d-DNP实验中很容易满足),PRE对于结合d-DNP和LLSs的实验来说不应是一个主要问题。然而,在子弹d-DNP实验中,可能有必要降低TEMPOL的浓度或添加抗坏血酸进行化学还原。
相似文献
Magn Reson (Gott). 2023-2-16
Phys Chem Chem Phys. 2014-4-28
Sci Adv. 2022-12-2
J Chem Phys. 2024-4-14
Sci Rep. 2019-12-27
引用本文的文献
本文引用的文献
Sci Adv. 2022-12-2
Phys Rev Lett. 2022-10-28
Phys Chem Chem Phys. 2022-3-23
Sci Rep. 2019-12-27
Phys Chem Chem Phys. 2019-7-7