标题：Remarkable Differences in Spin Couplings for Various Self-Paired Dimers of Ring-Expansion-Radicalized Uracil: A Basis for the Design of Magnetically Anisotropic Assemblies
作者：Zhao, Peiwen; Bu, Yuxiang
作者机构：[Zhao, Peiwen; Bu, Yuxiang] Shandong Univ, Sch Chem & Chem Engn, Jinan 250100, Shandong, Peoples R China.; [Bu, Yuxiang] Qufu Normal Univ, Sch Chem 更多
通讯作者：Bu, YX;Bu, YX
通讯作者地址：[Bu, YX]Shandong Univ, Sch Chem & Chem Engn, Jinan 250100, Shandong, Peoples R China;[Bu, YX]Qufu Normal Univ, Sch Chem & Chem Engn, Qufu 273165, Peop 更多
关键词：density functional calculations; hydrogen bonds; magnetic properties;; nucleobases; radicals
摘要：The spin-coupling properties of a series of radicalized uracil (rU) dimer diradicals with different H-bonding modes is examined. Each rU has four double H-bonding sites [the amide units: two at the Watson-Crick face (upper site WC1 and lower site WC2), a Hoogsteen site (HO), and a minor-groove site (MI)], and ten homogeneous dimers (rU-rU) can self-pair with well-defined diradical characters and comparable stability to the native U dimers. More interestingly, all these dimers exhibit distinctly different spin-coupling characters (ferromagnetic (FM) versus antiferromagnetic (AFM) and large- versus small-magnitude spin couplings), indicative of remarkable magnetic-coupling anisotropy of rU. This observation originates from the fusion of a cyclopentadienyl radical to U, which leads to uneven spin-density distribution. In rU, the fused five-membered radical ring can spin-polarize to the edge in the minor groove, and thus dimerization of rU leads to different H-bonded structures with remarkably different magnetic couplings. The calculated larger magnetic coupling constants J are 1003.7 and 540.2 cm(-1) for the WC2-HO and MI-HO H-bonding modes between rU, which exhibit considerably large FM couplings, the MI-MI, WC1-WC2 and WC2-WC2 modes show moderate FM couplings (J = 0.4-77 cm(-1)), and the other modes exhibit moderate or weak AFM couplings. These observations indicate that the HO and MI sites are favorable spin-coupling sites. In addition, the H-bond lengths and electronic structures of the H-bonding sites, proton transfer, and extra H-bonding interaction with the surroundings can also affect the magnetic couplings of the base pairs. Clearly, the unique magnetic coupling anisotropy of rU provides a promising application basis for the design and assembly of bio-inspired anisotropically magnetic membranes and even magnetism-tunable building blocks for novel magnetic nanoscale devices.