The effect of divalent ions on the thermal stability of the double-stranded polynucleotide polyinosinic:polycytidylic acid (poly(I:C)) in a buffer solution (pH 7) was studied by UV absorption spectroscopy and thermal denaturation by measuring the absorbance at 260 nm. The concentration dependence of the polynucleotide melting temperature (T_m) in the presence of metal ions (2.5 × 10⁻⁶–10⁻² M) was obtained. It was found that the duplex thermal stability grew gradually upon an increase of Ca²⁺ and Mn²⁺ concentration. The thermal stability of the duplex in the presence of Cd²⁺, Ni²⁺, and Zn²⁺ rises up to an ion concentration of about 10⁻⁴ M and further falls. In contrast to these ions, the addition of Cu²⁺ to the solution leads to a sharp decline in Т_m of the duplex at a concentration above 10⁻⁵ M. The observed difference in the influence of metal ions on the poly(I:C) thermal stability is explained by the different affinity of these ions to both the phosphate groups and the nitrogenous bases of the polynucleotides. Based on the analysis of the T_m concentration dependence, the dominant binding of each ion to the specific polynucleotide components was proposed.

中文翻译：

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二价金属离子对聚（I：C）双相金属温度稳定性的影响

通过紫外吸收光谱和通过测量260的吸光度进行热变性研究了二价离子对缓冲溶液（pH 7）中双链多聚肌苷酸：聚胞苷酸（poly（I：C））的热稳定性的影响纳米 获得了在金属离子（2.5×10 ^-6 -10 ^-2  M）存在下多核苷酸解链温度（T _m）的浓度依赖性。发现随着Ca ²⁺和Mn ²⁺浓度的增加，双相热稳定性逐渐增加。在Cd 2 ⁺，Ni ²⁺和Zn ²⁺存在下双链体的热稳定性上升至约10 ^-4  M的离子浓度，然后进一步下降。相对于这些离子，Cu的添加²⁺到该溶液中，因而在急剧下降Т_米的双链体在高于10的浓度^-5  M的该聚观察到的金属离子的影响的差异（I： C）热稳定性由这些离子对多核苷酸的磷酸根基团和含氮碱基的不同亲和力解释。基于对T _m浓度依赖性的分析，提出了每个离子与特定多核苷酸组分的显性结合。