School of Chemistry and Chemical Engineering, Shandong University, Jinan, 250100, People's Republic of China.
Phys Chem Chem Phys. 2019 Sep 18;21(36):20095-20106. doi: 10.1039/c9cp03234g.
Rational modification of biomolecules especially DNA base pairs for the theoretical design of molecular magnets has attracted extensive interest. In this work, we report a modification strategy for adenine/thymine-based magnets through introducing a N,N-dioxidized pyrazine ring to either adenine or thymine to form ring-expanded bases (noA/noT) based on their experimentally synthesized derivatives. Further functionalization is conducted by double protonation and pairing with a normal complementary base (nohA-T/nohT-A), respectively. The diversity of protonation sites in noA generates totally six nohA-Ts, together with nohT-A forming seven two-step modified topic base pairs. DFT calculations are performed to characterize the magnetic properties and the diradical character, which indicate three diamagnetic (DM) nohA-Ts and three antiferromagnetic (AFM) nohA-Ts with extremely large magnetic coupling constants J ranging from -1279.7 to -2807.4 cm-1, while a relatively mild AFM nohT-A with a J of -194.6 cm-1. The electron separation effect induced by attraction of positive charges originating from protonation is proposed to explain the diradicalization, which is different from the traditional radical-coupler-radical coupling mode. In addition, atomic natural charges and spin densities, and H-bond and molecular orbital analyses are further discussed for verification and deep understanding of the observed unique phenomena. It should be noted that our designed seven topic base pairs have excellent characters including a good synthetic basis, a large scope of the |J| values, and the AFM-DM magnetic conversion or AFM strength modulation controlled by protonation/deprotonation, prototropic tautomerization, base pairing/dissociation, single proton transfer, and even the applied electric field. All these indicate the promising applications in the field of magnetic information storage or switch control. This work highlights the magnetic modification schemes and possible modulation methods of double positive charge doped DNA base pairs by utilizing their potential spin coupling modes.
理性地修饰生物分子，特别是 DNA 碱基对，以进行分子磁体的理论设计，这引起了广泛的关注。在这项工作中，我们报道了一种通过向腺嘌呤或胸腺嘧啶中引入 N,N-二氧化吡嗪环来修饰腺嘌呤/胸腺嘧啶基磁体的策略，该策略基于其已合成的衍生物。进一步通过双重质子化和与正常互补碱基配对（nohA-T/nohT-A）进行功能化。nohA 中的质子化位点的多样性产生了总共六个 nohA-T，与 nohT-A 一起形成了七个两步修饰的主题碱基对。通过 DFT 计算来表征磁性和自由基特性，表明有三个抗磁性（DM）nohA-T 和三个反铁磁（AFM）nohA-T 具有非常大的磁耦合常数 J，范围从-1279.7 到-2807.4 cm-1，而相对温和的 AFM nohT-A 的 J 为-194.6 cm-1。提出了由质子化引起的正电荷吸引产生的电子分离效应来解释自由基化，这与传统的自由基偶联体-自由基偶联模式不同。此外，还进一步讨论了原子自然电荷和自旋密度、氢键和分子轨道分析，以验证和深入理解所观察到的独特现象。值得注意的是，我们设计的七个主题碱基对具有出色的特性，包括良好的合成基础、|J|值的范围大、质子化/去质子化、质子转移甚至外加电场控制的 AFM-DM 磁转换或 AFM 强度调制、互变异构、碱基配对/解离。所有这些都表明它们在磁信息存储或开关控制领域具有广阔的应用前景。这项工作突出了通过利用其潜在的自旋偶联模式对双正电荷掺杂 DNA 碱基对进行磁性修饰的方案和可能的调制方法。
