Department of Chemistry and Biochemistry, University Station-A5300, University of Texas, Austin, TX 78712-0165, USA.
Science. 2010 Sep 10;329(5997):1324-7. doi: 10.1126/science.1192044.
Ion binding often mediates electron transfer in biological systems as a cofactor strategy, either as a promoter or as an inhibitor. However, it has rarely, if ever, been exploited for that purpose in synthetic host-guest assemblies. We report here that strong binding of specific anions (chloride, bromide, and methylsulfate but not tetrafluoroborate or hexafluorophosphate) to a tetrathiafulvalene calix[4]pyrrole (TTF-C4P) donor enforces a host conformation that favors electron transfer to a bisimidazolium quinone (BIQ2+) guest acceptor. In contrast, the addition of a tetraethylammonium cation, which binds more effectively than the BIQ2+ guest in the TTF-C4P cavity, leads to back electron transfer, restoring the initial oxidation states of the donor and acceptor pair. The products of these processes were characterized via spectroscopy and x-ray crystallography.
离子键合通常作为辅因子策略在生物系统中介导电子转移，无论是作为促进剂还是抑制剂。然而，在合成主体-客体组装中，很少（如果有的话）将其用于此目的。我们在这里报告，特定阴离子（氯离子、溴离子和甲基硫酸盐，但不是四氟硼酸盐或六氟磷酸盐）与四硫富瓦烯杯[4]吡咯（TTF-C4P）给体的强结合强制主体构象有利于电子转移到双咪唑并醌（BIQ2+）客体接受体。相比之下，添加四乙基铵阳离子，其在 TTF-C4P 腔中比 BIQ2+客体更有效地结合，导致电子回传，恢复供体和受体对的初始氧化态。这些过程的产物通过光谱和 X 射线晶体学进行了表征。
