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Human chromosomes terminate in long, single-stranded, DNA overhangs of the repetitive sequence (TTAGGG)n. Sets of four adjacent TTAGGG repeats can fold into guanine quadruplexes (GQ), four-stranded structures that are implicated in telomere maintenance and cell immortalization and are targets in cancer therapy. Isolated GQs have been studied in detail, however much less is known about folding in long repeat sequences. Such chains adopt an enormous number of configurations containing various arrangements of GQs and unfolded gaps, leading to a highly frustrated energy landscape. To better understand this phenomenon, we used mutagenesis, thermal melting, and global analysis to determine stability, kinetic, and cooperativity parameters for GQ folding within chains containing 8-12 TTAGGG repeats. We then used these parameters to simulate the folding of 32-repeat chains, more representative of intact telomeres. We found that a combination of folding frustration and negative cooperativity between adjacent GQs increases TTAGGG unfolding by up to 40-fold, providing an abundance of unfolded gaps that are potential binding sites for telomeric proteins. This effect was most pronounced at the chain termini, which could promote telomere extension by telomerase. We conclude that folding frustration is an important and largely overlooked factor controlling the structure of telomeric DNA., (© The Author(s) 2021. Published by Oxford University Press on behalf of Nucleic Acids Research.)

In this study, all Zn 1 - x Cu 0.05 Mn x O QUOTE Zn 1 - x Cu 0.05 Mn x O QUOTE polycrystalline nanoparticles were produced with various compositions (0.01 < x < 0.05) QUOTE (0.01 < x < 0.05) QUOTE by using sol–gel techniques. Zinc acetate dihydrate, manganese(II), and Cu(II) acetates were used as the precursors for the solutions. Methanol and acetylacetone were used as solvents while preparing the homogenous solutions. Halder–Wagner method (H–W), Williamson–Hall (W–H), and size–strain plot (SSP) were utilized in order to examine the crystal size and intrinsic strain by X-ray diffraction peak expansion analysis. In addition, different models were developed for the definition of microstructural and physical values including stress, strain, and energy density, in the W–H method. The average crystal sizes determined using W–H, SSP, and H–W methods were compared. The magnetic properties of Cu/Mn-doped zinc oxide nanoparticles were analyzed at room temperature. The highest saturation magnetization (Ms) value was found in the 5% wt Mn doping of ZnO and Ms increased with increasing the Mn doping due to the magnetic (paramagnetic) nature of manganese. In this study, XRD peak broadening analysis has been carried out by different models and X-ray peak profile analysis were used to estimate the physical parameters; different models are modified such as W–H plot, SSP method, and H–W method. D–S method, W–H plot, H–W plot, and SSP technique results were highly intercorrelated. [ABSTRACT FROM AUTHOR]

The present study investigates the concentration dependence of physical properties and structural parameters of YbMn1−хFeхO3 (YbMF) compositions, which were nanostructured using the mechanical activation method at a pressure of 1 GPa. Using X-ray diffraction, the dependence of the unit cell parameters of the H-hexagonal (P63cm) and O-orthorhombic (Pnma) phases on the Fe3+ dopant concentration was studied. It was found for the first time that a morphotropic region (MR) was formed in YbMF in the concentration range x = 0.6–0.8, characterized by the coexistence of H and O-phases. At the point х = 0.5, the minimum values of all bond lengths of the H-phase were observed, while at х = 0.8, the bond length minimum of the YbO8 dodecahedra of the O-phase was observed. The tilt θ° and rotation φ° angles of oxygen octahedra MnO6/FeO6 of the O-phase also vary with the Fe3+ concentration in the range of (19.354–19.754)° and (12.648–12.677)°, respectively. Using the complex impedance method Z* = Z′(ω) − j·Z″ (ω), the study showed that the relaxation character was non-Debye. Theoretical and experimental curves were obtained for each YbMF composition at different temperatures, along with the corresponding equivalent circuits. The study also investigated the parameters of the stochastic magnetic domain structure using the random magnetic anisotropy model. It was found that in the region of solid solutions of YbMF, the values of Hc and Mr have maxima at x = 0.5, and the highest value of Hc, equal to 452 Oe, is inside the MR. [ABSTRACT FROM AUTHOR]

In this work, the structural phase state and physical properties of YbMn1-xFexO3 (hereinafter YbMF) ceramics in the range of x = 0.0–1.0 with a concentration step Δx = 0.1 were studied by complex methods. X-ray diffraction revealed that the YbMF compositions in the range of x = 0.1–0.5 were hexagonal (H) phase solid solutions. In the concentration range of x = 0.6–0.8, the hexagonal and orthorhombic (O) systems coexist, and the unit cell parameters of these phases rise with increasing x. The study of the lattice parameters, bond lengths, bond angles and the main parameters of the magnetic hysteresis loop of the H-phase revealed the presence of a singular point x = 0.5 in the concentration range, where extrema of the corresponding parameters were observed. By analyzing the Cole–Cole plots for the electric modulus M*(ω), a conclusion was drawn about the thermally activated nature of the dielectric relaxation for each composition with a single relaxation time τ. The magnetodielectric MD(ω) and magnetoresistive MR(ω) coefficients measured in crossed and parallel fields E and H show high values, which reach 1.6% and 50%, respectively, depending on the frequency of the measuring field. [ABSTRACT FROM AUTHOR]