Department of Physics, University of Pavia, Via Bassi 6, Pavia (PV) 27100, Italy.
Department of Chemistry, University of Florence, Sesto Fiorentino (FI) 50019, Italy.
J Chem Phys. 2021 Dec 7;155(21):214201. doi: 10.1063/5.0072185.
Longitudinal and transverse H nuclear magnetic resonance relaxivities of Ln(III)-DOTA complexes (with Ln = Gd, Tb, Dy, Er; DOTA = 1,4,7,10-tetraazacyclododecane-N,N',N,N‴-tetraacetic acid) and Mn(II) aqueous solutions were measured in a wide range of frequencies, 10 kHz to 700 MHz. The experimental data were interpreted by means of models derived from the Solomon-Bloembergen-Morgan theory. The data analysis was performed assuming the orbital angular momentum L = 0 for Gd-DOTA and the aqua ion [Mn(HO)] and L ≠ 0 for Dy-, Tb-, and Er-DOTA. A refined estimation of the zero-field-splitting barrier Δ and of the modulation correlation time τ was obtained for [Mn(HO)] by extending the fitting of nuclear magnetic relaxation dispersion profiles to the low-field regime. The Gd-DOTA fitting parameters resulted in good agreement with the literature, and the fit of transverse relaxivity data confirmed the negligibility of the scalar interaction in the nuclear relaxation mechanism. Larger transverse relaxivities of Dy-DOTA and Tb-DOTA (∼10 mM s) with respect to Er-DOTA (∼1 mM s) were observed at 16 T. Such higher values are suggested to be due to a shorter residence time τ that is possibly linked to the fluctuations of the hyperfine interaction and the different shape of the magnetic anisotropy. The possible employment of Dy-DOTA, Tb-DOTA, and Er-DOTA as negative magnetic resonance imaging contrast agents for high-field applications was envisaged by collecting spin-echo images at 7 T. Particularly in Dy- and Tb-derivatives, the transverse relaxivity at 16 T is of the order of the Gd-one at 1.5 T.
在 10 kHz 至 700 MHz 的宽频率范围内，测量了 Ln(III)-DOTA 配合物（其中 Ln = Gd、Tb、Dy、Er；DOTA = 1,4,7,10-四氮杂环十二烷-N,N',N,N″-四乙酸）和 Mn(II)水溶液的纵向和横向 H 核磁共振弛豫率。通过源自 Solomon-Bloembergen-Morgan 理论的模型对实验数据进行了解释。数据分析是在假设 Gd-DOTA 的轨道角动量 L = 0 和水合离子 [Mn(HO)]的 L ≠ 0 以及 Dy-、Tb-和 Er-DOTA 的情况下进行的。通过将核磁共振弛豫色散曲线的拟合扩展到低场范围，对 [Mn(HO)]进行了零场分裂势垒 Δ 和调制相关时间 τ 的精细估计。Gd-DOTA 的拟合参数与文献值非常吻合，并且横向弛豫率数据的拟合证实了核弛豫机制中标量相互作用可以忽略不计。在 16 T 下，Dy-DOTA 和 Tb-DOTA（约 10 mM s）的横向弛豫率大于 Er-DOTA（约 1 mM s）。这些更高的值可能是由于停留时间 τ 较短所致，这可能与超精细相互作用的波动和不同的磁各向异性形状有关。通过在 7 T 下收集自旋回波图像，设想将 Dy-DOTA、Tb-DOTA 和 Er-DOTA 用作高场应用的负磁共振成像造影剂。特别是在 Dy-和 Tb-衍生物中，在 16 T 下的横向弛豫率与在 1.5 T 下的 Gd 相似。
