i-Motifs, also known as i-tetraplexes, are secondary structures of DNA occurring in cytosine-rich oligonucleotides (CROs) that recall increasing interest in the scientific community for their relevance in various biological processes and DNA nanotechnology. This study reports the design of new structurally modified CROs, named Double-Ended-Linker-CROs (DEL-CROs), capable of forming stable i-motif structures. Here, two C-rich strands having sequences d(AC₄A) and d(C₆) have been attached, in a parallel fashion, to the two linker's edges by their 3′ or 5′ ends. The resulting DEL-CROs have been investigated for their capability to form i-motif structures by circular dichroism, poly-acrylamide gel electrophoresis, HPLC–size-exclusion chromatography, and NMR studies. This investigation established that DEL-CROs could form more stable i-motif structures than the corresponding unmodified CROs. In particular, the i-motif formed by DEL-5′-d(C₆)₂ resulted stable enough to be detected even at near physiological conditions (37 °C, pH 7.0). The results open the way to developing pH-switchable nanocarriers and aptamers based on suitably functionalized DEL-CROs.

i-Motifs，也称为 i-四链体，是 DNA 的二级结构，出现在富含胞嘧啶的寡核苷酸 (CRO) 中，这让人想起科学界对它们在各种生物过程和 DNA 纳米技术中的相关性越来越感兴趣。本研究报告了新的结构修饰 CRO 的设计，称为双端接头-CRO (DEL-CRO)，能够形成稳定的 i-motif 结构。这里，两条富含 C 的链具有序列 d(AC ₄ A) 和 d(C ₆) 以平行方式通过它们的 3' 或 5' 末端连接到两个连接器的边缘。已经通过圆二色性、聚丙烯酰胺凝胶电泳、HPLC-尺寸排阻色谱和 NMR 研究研究了所得 DEL-CRO 形成 i-motif 结构的能力。该调查确定 DEL-CRO 可以形成比相应的未修饰 CRO 更稳定的 i-motif 结构。特别是，由 DEL-5'-d(C ₆ ) ₂形成的 i-motif足够稳定，即使在接近生理条件（37 °C，pH 7.0）下也能被检测到。该结果为开发基于适当功能化的 DEL-CRO 的 pH 可切换纳米载体和适体开辟了道路。