No abstract

Hexapyrrole‐α,ω‐dialdehyde, which has eight donor atoms, afforded a dipalladium(II) single helicate (see picture; Pd pink, O red, N blue). A rapid interchange of the helical screw was slowed down by imine formation at the terminal aldehyde units with (R)‐(−)‐1‐cyclohexylethylamine, leading to an overwhelming excess of a P‐helical screw. This stable dinuclear single helicate has a redox‐driven reversible change in chiroptical properties.

The hexapyrrole‐α,ω‐dicarbaldehydes 1 a and 1 b were metallated with CuII, NiII, and PdII to give bimetallic complexes where a pair of 3 N+O four‐coordinate metal planes are helically distorted and the central 2,2′‐bipyrrole subunit adopts a cis or trans conformation. X‐ray crystallographic analysis of the bisCu complex revealed a closed form with a cis‐2,2′‐bipyrrole subunit and an open form with a trans‐2,2′‐bipyrrole subunit. The bisPd complexes took a closed form both in the solid state and in solution. They are regarded as single helicates of two turns and the energy barrier for the interchange between an M helix and a P helix was remarkably influenced by the bulky 3,3′‐substituent of the central 2,2′‐bipyrrole subunit. Although the bisNi complexes adopt a closed form in the solid state, they exist as a homohelical open C2‐symmetric form or a heterohelical open Ci‐symmetric form in solution. A theoretical study suggested that the closed form of 1 aPd was stabilized by the Pd–Pd interaction. Compound 1 aPd was reversibly oxidized by one electron at 0.14 V versus ferrocene/ferrocenium (Fc/Fc+) and this oxidized species showed Vis/NIR absorption bands at λ=767 and 1408 nm.

Based on the reactions of different sequences with single ions K+, Na, NH4 +, double ions high + low, low + high, and triple ions with different addition orders, the best stable ion combinations of 12 quadruplexes with different DNA sequences were reported. From the fluorescence spectrum, except for HT-V15 and PW17 and AS1411 and HT-V18, the structural stability of G-quadrangle formed basically follows a certain rule. In terms of this experiment, according to circular dichroism, the antiparallel quadrupole structure has the largest proportion among quadrupole structures, and 12 optimal DNA addition schemes and sequences have been obtained through exploration. It is worth mentioning that, on the whole, the best addition scheme of AS1411 and HT-V18 is a three-ion scheme, which provides an effective reference for similar experiments in the future.