Paris Jérôme, Gameiro Cristiana, Humblet Valérie, Mohapatra Prasanta K, Jacques Vincent, Desreux Jean F
Coordination and Radiochemistry, University of Liège, Sart Tilman B16, B-4000 Liège, Belgium.
Inorg Chem. 2006 Jun 26;45(13):5092-102. doi: 10.1021/ic0603050.
PhenHDO3A is a ditopic ligand featuring a tetraazacyclododecane unit substituted by three acetate arms and one 6-hydroxy-5,6-dihydro-1,10-phenanthroline group (PhenHDO3A = rel-10-[(5R,6R)-5,6-dihydro-6-hydroxy-1,10-phenantholin-5-yl)-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid). This ligand was specially designed so as to obtain highly stable heteropolymetallic assemblies. PhenHDO3A has been prepared starting from phenanthroline epoxide and either a triprotected tetraazacyclododecane or tert-butyl triester of N,N',N' '-tetraazacyclododecane-triacetic acid. The latter yields PhenHDO3A in a single step. PhenHDO3A forms kinetically stable lanthanide complexes (acid-catalyzed kinetic constant kH = (1.2 +/- 0.2) x 10(-3) s(-1) M(-1)) whose solution structure has been deduced from a quantitative analysis of the paramagnetic shifts and the longitudinal relaxation times of the proton nuclei of YbPhenHDO3A. The alcohol group of the dihydro-phenanthroline unit remains coordinated to the encapsulated metal ion despite the steric crowding brought about by this group. Furthermore, the complexes are monohydrated, as shown by luminescence lifetime measurements on EuPhenHDO3A solutions. Relaxivity titrations at 20 MHz clearly indicate that the phenanthroline unit of GdPhenHDO3A is available for the spontaneous formation of highly stable tris complexes with the Fe2+ and Ni2+ ions. The water-exchange times and the rotational correlation times of GdPhenHDO3A and Fe(GdPhenHDO3A)32+ have been deduced from variable temperature 17O NMR studies and from nuclear relaxation dispersion curves. Despite rather slow water-exchange rates (taum0 = 1.0-1.2 x 10(-6) s), relaxivity gains of 90% have been observed upon the formation of the heterometallic tris complexes. The latter rotate about four times more slowly (taur0= 398 ps) than the monomeric unit (taur0 = 105 ps) and their relaxivity is, accordingly, twice as high. The relaxivity of the tris complexes between 10 and 50 MHz is comparable to relaxivities reported for Gd3+-containing dendrimers of much higher molecular weights. The high relaxivity of the tris-PhenHDO3A lanthanide complexes is attributed to their internal rigidity.
PhenHDO3A是一种双齿配体，具有一个四氮杂环十二烷单元，该单元被三个乙酸酯臂和一个6-羟基-5,6-二氢-1,10-菲咯啉基团取代（PhenHDO3A = rel-10-[(5R,6R)-5,6-二氢-6-羟基-1,10-菲咯啉-5-基]-1,4,7,10-四氮杂环十二烷-1,4,7-三乙酸）。设计该配体是为了获得高度稳定的异多金属组装体。PhenHDO3A是从菲咯啉环氧化物和三保护的四氮杂环十二烷或N,N',N''-四氮杂环十二烷-三乙酸叔丁酯开始制备的。后者可一步生成PhenHDO3A。PhenHDO3A形成动力学稳定的镧系配合物（酸催化动力学常数kH = (1.2±0.2)×10⁻³ s⁻¹ M⁻¹），其溶液结构已通过对YbPhenHDO3A质子核的顺磁位移和纵向弛豫时间的定量分析推导得出。尽管二氢菲咯啉单元的醇基由于该基团带来的空间拥挤而保持与包封的金属离子配位。此外，通过对EuPhenHDO3A溶液的发光寿命测量表明，这些配合物是一水合物。在20 MHz下的弛豫率滴定清楚地表明，GdPhenHDO3A的菲咯啉单元可用于与Fe²⁺和Ni²⁺离子自发形成高度稳定的三配合物。GdPhenHDO3A和Fe(GdPhenHDO3A)₃²⁺的水交换时间和旋转相关时间已从变温¹⁷O NMR研究和核弛豫色散曲线推导得出。尽管水交换速率相当慢（τm0 = 1.0 - 1.2×10⁻⁶ s），但在形成异多金属三配合物时观察到弛豫率提高了90%。后者的旋转速度比单体单元（τr0 = 105 ps）慢约四倍（τr0 = 398 ps），因此其弛豫率是单体单元的两倍。在10至50 MHz之间，三配合物的弛豫率与报道的分子量高得多的含Gd³⁺树枝状大分子的弛豫率相当。三-PhenHDO3A镧系配合物的高弛豫率归因于其内部刚性。
