Five Ni^II macrocyclic complexes are studied as water proton shift agents and as paraCEST agents (paraCEST = paramagnetic chemical exchange saturation transfer) for MRI applications. The five macrocycles have amide and/or alcohol pendent groups with either tetraaza‐ or triazamacrocycles including 1,1′,1′′‐(1,4,7‐triazonane‐1,4,7‐triyl)tris(propan‐2‐ol) (L1), 1,1′,1′′,1′′′‐(1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetra)tetrakis(propan‐2‐ol) (L2), 1,1′,1′′,1′′′‐(1,4,8,11‐tetraazacyclotetradecane‐1,4,8,11‐tetrayl)tetrakis(propan‐2‐ol) (L3), 2,2′,2′′‐(1,4,7‐triazonane‐1,4,7‐triyl)triacetamide (L4), or 2,2′‐(7‐benzyl‐1,4,7‐triazonane‐1,4‐diyl) diacetamide (L5). Solution magnetic moments are consistent with paramagnetic Ni^II complexes. The complexes are characterized by pH‐potentiometric titrations to determine the pK_a values of the bound amide or alcohol pendents or water ligand. Variable temperature ¹⁷O NMR studies are consistent with a water ligand in [Ni(L5)]²⁺ with an exchange rate constant of 4 × 10⁴ s^–1. All Ni^II complexes produce a substantial hyperfine shift of bulk water proton resonances. The smallest shifts are observed for [Ni(L4)]²⁺, which lacks alcohol pendents or bound water and the largest are observed for [Ni(L5)]²⁺ which contains a bound water molecule. The alcohol‐appended complexes, [Ni(L2)]²⁺ and [Ni(L3)]²⁺ produce CEST spectra with far‐shifted peaks of low intensity at 94 and 104 ppm versus bulk water, whereas [Ni(L5)]²⁺ shows a CEST peak at δ = 72 ppm.

中文翻译：

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镍（II）配合物作为顺磁性位移和paraCEST剂

研究了五个Ni ^II大环配合物作为水质子转移剂和paraCEST剂（paraCEST =顺磁性化学交换饱和转移），用于MRI应用。五个大环具有酰胺和/或醇侧基，具有四氮杂或三氮杂大环，包括1,1'，1''-（1,4,7-三氮杂烷-1,4,7-三基）三（丙烷-2- ol）（L1），1,1′，1′′，1′′′-（1,4,7,10-四氮杂环十二烷-1,4,7,10-tetra）四（丙烷-2-醇）（L2），1,1'，1''，1'''-（1,4,8,11-四氮杂环十四烷-1,4,8,11-四基）四（丙烷-2-醇）（L3）， 2,2'，2''-（1,4,7-三唑烷-1,4,7-三基）三乙酰胺（L4）或2,2'-（7-苄基-1,4,7-三唑烷- 1,4-二基）二乙酰胺（L5）。溶液磁矩与顺磁性Ni ^II络合物一致。通过pH电位滴定法表征复合物，以确定结合的酰胺或醇类或水配体的p K _a值。可变温度¹⁷ O NMR研究与[Ni（L5）] ^2+中的水配体相符，交换常数为4×10 ⁴ s ^–1。所有的Ni ^II络合物都会产生大量水质子共振的超精细位移。对于[Ni（L4）] ^2+，观察到最小的位移，它缺乏酒精悬垂物或结合水，并且对于含有结合水分子的[Ni（L5）] ²⁺观察到最大的。醇-所附络合物，[镍（L2）] ²⁺和[镍（L3）] ²⁺产生CEST谱与在94和低强度的远移峰104 ppm的对大体积的水，而[镍（L5）] ²⁺显示δ = 72 ppm时的CEST峰。