Spin–lattice relaxation times, T1s, for 13C nuclei in two cations Hn1n+ (n = 1, 5) of N-(2-aminoethyl)-cyclam (1, scorpiand) were determined by means of 13C{1H} NMR experiments in aqueous solution at pH 11.5 and 0.2. The theoretical study [modeling with OPLS-AA, B3LYP/6-31G(d) geometry optimizations, dispersion-corrected energies (DFT-D3), and DFT-GIAO predictions of the NMR chemical shifts (including an IEF-PCM simulation of hydration)] was also done for several conformers of the tautomer iso-H414+ not investigated before. The binding directions in protonated polyamino receptors necessary for efficient complexation of the nitrate anion(s) were briefly outlined, as well. All these results were discussed in terms of ‘abnormal’ 13C chemical shift changes found previously for the side-chain carbons of amine 1 in strongly acidic solution (HNO3). In conclusion, an earlier proposal of its association with NO3− at pH <1 was rejected. Instead, the participation of small amounts of a micro-species iso-H414+Dhydr under such conditions can be proposed.Graphical AbstractA small contribution of iso-H414+Dhydr (see figure) to an ionic mixture of pentamine 1 was proposed to explain the ‘abnormal’ 13C NMR shifts observed for atoms C11 and C12 in its side-chain arm, at pH <1.

中文翻译：

---

四氮杂大环蝎子系统的两个铵离子的 13C 纵向弛豫时间测量和 DFT-GIAO 核磁共振计算

通过 13C{1H} NMR 实验在水溶液中测定 N-(2-氨基乙基)-环己基酰胺 (1, 蝎子) 的两个阳离子 Hn1n+ (n = 1, 5) 中的 13C 核的自旋晶格弛豫时间 T1s pH 值 11.5 和 0.2 的溶液。理论研究 [使用 OPLS-AA 建模、B3LYP/6-31G(d) 几何优化、色散校正能量 (DFT-D3) 和 NMR 化学位移的 DFT-GIAO 预测（包括 IEF-PCM 水合模拟)] 还对之前未研究过的互变异构体 iso-H414+ 的几个构象异构体进行了研究。还简要概述了硝酸根阴离子有效络合所必需的质子化聚氨基受体中的结合方向。所有这些结果都根据先前在强酸性溶液 (HNO3) 中胺 1 的侧链碳发现的“异常”13C 化学位移变化进行了讨论。总之，早先提出的在 pH < 1 时与 NO3− 相关的提议被拒绝了。相反，可以提出在这种条件下少量的微物种 iso-H414+Dhydr 的参与。图形摘要提出了 iso-H414+Dhydr（见图）对五胺 1 离子混合物的少量贡献来解释在 pH < 1 时，观察到其侧链臂中原子 C11 和 C12 的“异常”13C NMR 位移。