新型金属轮烷自组装体系的表征及配位平衡研究

Characterization and Coordination Equlibrium Study on theSelf Assembly System of a New Metallo Rotaxane

由cucurbituril和精胺盐酸盐生成的类轮烷,与水合烷基钴肟发生自组装反应后,在水溶液中形成了一种新型的金属轮烷。本文通过1HNMR,ESI-MS,UV-vis方法进行了表征并对该金属轮烷生成的配位反应进行了热力学研究。

Rotaxane is a kind of interesting supramolecular assemblies that consists ofa macrocyclic wheel, a threading molecular axle and two attached stoppers. Mostly, the stoppers are organic groups with big hindrance to prevent the componentsof a rotaxane from disassembly.In this study, we report a new metallo rotaxane(s) at which spermine tetrahydrochloride (Sp) threaded the cucurbituril, which is a highly symmetrical cage compound with an exceptional capacity to encapsulate alkylammonium ions , anddifferent kinds of aqua(alkyl)cobaloximes (RCo(Hdmg)2H2O) as the two stoppers. The rotaxanes were characterized by 1H NMR and ESI MS analyses. It is interesting to note that chemical shifts of Sp and cobaloxime are mostly moving to upfield after forming rotaxane. The assignment of Sp in rotaxane was based on the 2D COSY study. The ESI MS spectrum for R=methyl showed that the peak m/e=904 is the whole matello rotaxane with two positive charges.Furthermore, we determined the equilibrium constants K(T) and thermodynamic parameters in aqueous solution between the pseudorotaxane and aqua(methyl)cobaloxime by UV/Vis spectroscopy. The K(T), at different temperatures are: 1.88×103(278K); 1.68×103(283K); 1.36×103(288K); 1.16×103(293K); 1.02×103(298K); 8.78×102(303K), respectively. And from the plot of RlnK against 1/T, we can calculate the changes of the enthalpy (ΔH=-21.6kJ·mol-1) and the entropy (ΔS=-14.8J·mol·K-1) for the coordinative reaction.In short, we have shown a new self assemble metallo rotaxane in aqueous solution whose most remarkable character is using coordinative compounds as stoppers that includes metal carbon bond. Such rotaxanes might have interesting optical, electrical or catalytic properties and further investigations are in progress.