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CCTG repeat expansion in intron 1 of the cellular nucleic acid-binding protein (CNBP) gene has been identified to be the genetic cause of myotonic dystrophy type 2 (DM2). Yet the underlying reasons for the genetic instability in CCTG repeats remain elusive. In recent years, CCTG repeats have been found to form various types of unusual secondary structures including mini-dumbbell (MDB), hairpin and dumbbell, revealing that there is a high structural diversity in CCTG repeats intrinsically. Upon strand slippage, the formation of unusual structures in the nascent strand during DNA replication has been proposed to be the culprit of CCTG repeat expansions. On the one hand, the thermodynamic stability, size, and conformational dynamics of these unusual structures affect the propensity of strand slippage. On the other hand, these structural properties determine whether the unusual structure can successfully escape from DNA repair. In this short overview, we first summarize the recent advances in elucidating the solution structures of CCTG repeats. We then discuss the potential pathways by which these unusual structures bring about variable sizes of repeat expansion, high strand slippage propensity and efficient repair escape.

Ferrocene-based diphosphine complexes are subjected to NMR conformational analysis to illustrate their fluxionalities. The phenyl rotations and the ferrocenyl mobilities allow the dppf ligand to have a suitable conformation between two metal centers. The metal environment has no influence in the conformation. The ligand adaptability stabilizes the dppf ligand with respect to dissociation.

Here we report that incorporation of an abasic site to DNA minidumbbells formed by natural sequences can lead to significant enhancements in their thermodynamic stability. Based on these stable minidumbbells, the first metal ion-controlled molecular switch which can regulate instant and reversible DNA duplex formation and dissociation has been constructed. [ABSTRACT FROM AUTHOR]

A series of cobalt(ii) complexes of a highly electron-withdrawing amido ligand, [N(C6F5)(C6H3Pri2-2,6)]− (L), were synthesized and structurally characterized. Mononuclear [CoL(Cl)(TMEDA)] (3) and heterobimetallic [CoL2(μ-Cl)Li(THF)3] (4) were obtained by direct metathetical reactions of anhydrous CoCl2 with one molar equivalent of [LiL(TMEDA)] (1) (TMEDA = Me2NCH2CH2NMe2) and [LiL(THF)3] (2), respectively. Complex 3 underwent facile ligand substitution reactions with LiMe and NaN3, yielding the corresponding mixed-ligand complexes [CoL(X)(TMEDA)] (X = Me 5, N36). Treatment of 3 with NaOMe led to the heterobimetallic complex [CoL2(μ-OMe)Na(TMEDA)] (7). The solid-state structures of complexes 1–7 were established by X-ray diffraction analysis. [ABSTRACT FROM AUTHOR]