Walmsley J A, Schneider M L, Farmer P J, Cave J R, Toth C R, Wilson R M
Division of Earth and Physical Sciences, University of Texas, San Antonio 78249.
J Biomol Struct Dyn. 1992 Dec;10(3):619-38. doi: 10.1080/07391102.1992.10508672.
The aggregation behavior of guanylyl-(3'-5')-guanosine, GpG, in the form of the tetramethylammonium (TMA), Li, Na, and K salts in aqueous solution has been investigated by NMR and FTIR techniques. The salts were prepared by a cation-exchange method. The ability of the cations to induce aggregate formation is TMA+ < Li+ < Na+ < K+, where TMA+ has only a weakly promoting action and K+ has a very strong effect. Three types of aggregates have been observed: (a) small aggregates which are in rapid exchange with respect to the NMR time scale; (b) intermediate-sized aggregates which are slow to exchange; (c) very large aggregates which can only be observed by FTIR. In all cases the aggregated species are held together by base stacking and guanine-guanine hydrogen bonding. A stoichiometry of 2 GpG per K+ has been determined by a 1H NMR titration of TMAGpG with KCl. Models have been proposed for the various-sized species. These include stacked dimers, stacked tetramers (similar to G-tetrads), and species in which K+ ion bridges between phosphates in separate tetramers.
通过核磁共振（NMR）和傅里叶变换红外光谱（FTIR）技术，研究了鸟苷酰 -（3'-5'）- 鸟苷（GpG）以四甲基铵（TMA）盐、锂盐、钠盐和钾盐形式在水溶液中的聚集行为。这些盐是通过阳离子交换法制备的。阳离子诱导聚集体形成的能力为TMA⁺ < Li⁺ < Na⁺ < K⁺，其中TMA⁺只有微弱的促进作用，而K⁺有非常强的作用。观察到了三种类型的聚集体：（a）在NMR时间尺度上快速交换的小聚集体；（b）交换缓慢的中等大小聚集体；（c）只能通过FTIR观察到的非常大的聚集体。在所有情况下，聚集的物种通过碱基堆积和鸟嘌呤 - 鸟嘌呤氢键结合在一起。通过用KCl对TMAGpG进行¹H NMR滴定，确定了每个K⁺对应2个GpG的化学计量比。已经为各种大小的物种提出了模型。这些模型包括堆叠二聚体、堆叠四聚体（类似于G - 四联体），以及K⁺离子在单独四聚体的磷酸盐之间形成桥连的物种。
