Expansion of the GAA/TTC repeats in the first intron of the FXN gene causes Friedreich’s ataxia. Non-canonical structures are linked to this expansion. DNA triplexes and R-loops are believed to arrest transcription, which results in frataxin deficiency and eventual neurodegeneration. We present a systematic in silico characterization of the possible DNA triplexes that could be assembled with GAA and TTC strands; the two hybrid duplexes [r(GAA):d(TTC) and d(GAA):r(UUC)] in an R-loop; and three hybrid triplexes that could form during bidirectional transcription when the non-template DNA strand bonds with the hybrid duplex (collapsed R-loops, where the two DNA strands remain antiparallel). For both Y·R:Y and R·R:Y DNA triplexes, the parallel third strand orientation is more stable; both parallel and antiparallel protonated d(GA+A)·d(GAA):d(TTC) triplexes are stable. Apparent contradictions in the literature about the R·R:Y triplex stability is probably due to lack of molecular resolution, since shifting the third strand by a single nucleotide alters the stability ranking. In the collapsed R-loops, antiparallel d(TTC+)·d(GAA):r(UUC) is unstable, while parallel d(GAA)·r(GAA):d(TTC) and d(GA+A)·r(GAA):d(TTC) are stable. In addition to providing new structural perspectives for specific therapeutic aims, our results contribute to a systematic structural basis for the emerging field of quantitative R-loop biology.

Nowadays, functional ceramics have been largely explored for application in various fields. However, magnetic functional ceramics for spintronics remain little studied. Here, we propose a nano-functional ceramic of sphalerite SiN-SiC nanofilm with intrinsic ferromagnetic order. Based on first principles calculations, the SiN-SiC nanofilm is found to be a ferromagnetic semiconductor with an indirect band gap of 1.71 eV. By mean field theory, the Curie temperature is estimated to be 304 K, close to room temperature. Furthermore, the valence band and conduction band states of the nanofilm exhibit inverse spin-polarization around the Fermi level. Thus, the SiN-SiC nanofilm is a typical bipolar magnetic semiconductor in which completely spin-polarized currents with reversible spin polarization can be created and controlled by applying a gate voltage. Such a nano-functional ceramic provides a possible route for electrical manipulation of carrier's spin orientation.

The direct control of carrier's spin by electric field under room temperature is one of the most important challenges in the field of spintronics. For this purpose, we here