Guanine-rich nucleic acid sequences are known to form G-quadruplex - four-stranded DNA or RNA structures stabilized by an array of Hoogsteen hydrogen bonds. G-quadruplex structures are involved in the modulation of gene expression at the transcription and translation levels. Accordingly, G-quadruplexes are considered as novel therapeutic targets for anticancer drug development. In this review, the authors provide a brief, up-to-date summary of G-quadruplex binding ligands, including naturally occurring molecules, synthetic compounds, and molecules identified by computational database screening. The key structural motifs of G-quadruplex binding ligands, that is, an aromatic core and basic side chains, are addressed in the context of how these molecules interact with G-quadruplex. A better understanding of these interactions would facilitate the rational design of ligands selective for DNA or RNA G-quadruplex.
Low-field magnetic studies on [Mn(4,4‘-bipyridine)(N3)2]
n
reveal a spontaneous magnetization below ordering temperatures of 42.5 K, due to a transition to a weak ferromagnetic ground state.
Heterobimetallic hexanuclear cyano-bridged complexes, [{Fe(Tp)(CN)3}4{M(MeCN)(H2O)2}(2)].10H2O.2MeCN [M = Ni (1), Co (2), Mn (3); Tp = hydrotris(1-pyrazolyl)borate], have been synthesized in H2O-MeCN solution. Complexes 1-3 are isostructural and hexanuclear with [{Fe(Tp)(CN)3}4{M(MeCN)(H2O)2}2] units linked by hydrogen bonds to form a 2D-structure in the solid state. Complex 1 is a canted antiferromagnet that undergoes a field-induced spin-flop-like transition at approximately 1 T and 2 K. At 4.45 K 1 has a transition to paramagnetic state of noninteracting S = 4 magnetic clusters. However, 2 and 3 show antiferromagnetic intracluster coupling. Facile loss of solvent from 2 alters the local symmetry resulting in changing the intracluster interaction from antiferro- to ferromagnetic.
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