Induction of helicity in polyuridylic acid and polyinosinic acid by silver ions
Induction of helicity in polyuridylic acid and polyinosinic acid by silver ions
复制标题
银离子诱导聚尿苷酸和聚肌苷酸的螺旋性
DOI：
10.1002/bip.1980.360190308
复制
发表时间：
1980
期刊：
影响因子：
2.9
通讯作者：
G. Eichhorn
中科院分区：
文献类型：
--
作者：
Y. Shin;G. Eichhorn
与聚（U）和聚（I）结合的银离子在会导致无规卷曲的条件下产生高度有序的多链螺旋。螺旋性的证据来自于 Ag+ 结合在聚合物中产生的低色度和高椭圆度，以及 X 射线研究和 Ag+ 络合反应的协同性。连续变化研究表明，两种聚合物形成 1:1 和 2:1 聚合物-Ag+ 复合物。低pH值有利于与聚(U)的1:1复合物和与聚(I)的2:1复合物；高 pH 值时则相反。 Ag+ 结合和质子释放实验清楚地表明，在低 pH 条件下，未质子化的电子供体基团优先络合，但在高 pH 条件下，Ag+ 很容易取代质子化基团中的 H+。在聚(I)中，非质子化供体是N(7)，在低pH下形成含有N(7)-Ag-N(7)键的2:1复合物；在高 pH 值下，N(1) 释放质子，形成含有 N(1)-Ag-O 键的 1:1 复合物。在聚（U）中没有未质子化的供体；低pH 1:1复合物涉及每个结合Ag+仅一个N(3)的去质子化，导致N3-Ag-O键合，而高pH导致每个Ag+两个N(3)去质子化和2:1 N(3)-Ag-N(3)复合物。因此，银离子以化学可预测的方式与核苷酸碱基反应，不同的银-核苷酸键的形成导致不同的多螺旋结构。
Silver ions binding to poly(U) and poly(I) produce highly ordered multistranded helices under conditions which would otherwise lead to random coils. Evidence for helicity comes from the hypochromicity and high ellipticity generated in the polymers by Ag+ binding, as well as from x‐ray studies and from the cooperativity of the Ag+ complexing reaction. Continuous variation studies show that both polymers form 1:1 and 2:1 polymer–Ag+ complexes. Low pH favors the 1:1 complex with poly(U) and the 2:1 complex with poly(I); the reverse is true at high pH. Ag+ binding and proton‐release experiments make it clear that at low pH, unprotonated electron‐donor groups are complexed preferentially, but that at high pH, Ag+ readily displaces H+ from protonated groups. In poly(I) the unprotonated donor is N(7), leading at low pH to a 2:1 complex containing N(7)‐Ag‐N(7) bonds; at high pH, proton release from N(1) leads to a 1:1 complex containing N(1)‐Ag‐O bonds. In poly(U) there is no unprotonated donor; the low‐pH 1:1 complex involves deprotonation of only one N(3) per bound Ag+, leading to N3‐Ag‐O bonding, while high pH causes deprotonation of two N(3) per Ag+ and a 2:1 N(3)‐Ag‐N(3) complex. Thus silver ions react with the nucleotide bases in chemically predictable ways, and the formation of different Ag–nucleotide bonds leads to different multiple‐helix structures.