Selective Formation of Stable Triplexes Including a TA or a CG Interrupting Site with New Bicyclic Nucleoside Analogues (WNA)

Triplex-forming oligonucleotides (TFOs) are potential DNA-targeting molecules and would become powerful tools for genomic research. As the stabilization of the TFO is partially provided by hydrogen bonds to purine bases, the most stable triplexes form with homopurine/homopyrimidine sequences, and a pyrimidine base in the purine strand of the duplex interrupts triplex formation. If a TFO can recognize sequences including such an interrupting site, the target regions in the genome would be expanded to a greater extent. However, this problem has not been generally solved despite extensive studies. We have previously reported a new base analogue (WNA) constructed of three parts, a benzene ring, a heterocyclic ring, and a bicyclic skeleton to hold these two parts. In this study, we have further investigated modification of WNA systematically and determined two useful WNA analogues, WNA-βT and WNA-βC, for selective stabilization of triplexes at a TA and a CG interrupting site, respectively. The triplexes with WNA analogues have exhibited an interesting property in that they are more stable than natural-type triplexes even at low Mg2+ concentration. From comparison of the results with H-WNA-βT lacking benzene and those with WNA-H without thymine, it has been suggested that benzene is a major contributor for triplex stability and thymine provides selectivity. Thus, it has been successfully demonstrated that WNA-βT/TA and WNA-βC/CG combinations may expand triplex recognition codes in addition to the natural A/AT and G/GC base triplet codes. The results of this study will provide useful information for the design of new WNA analogues to overcome inherent problems for further expansion of triplex recognition codes

Hybridization-Promoted and Cytidine-Selective Activation for Cross-Linking with the Use of 2-Amino-6-vinylpurine Derivatives

Recently, we have proposed a new concept for cross-linking agents with inducible reactivity, in which the highly reactive cross-linking agent, the 2-amino-6-vinylpurine nucleoside analogue (1), can be regenerated in situ from its stable precursors, the phenylsulfide (4) and the phenylsulfoxide (3) derivatives, by a hybridization-promoted activation process with selectivity to cytidine. The phenylsulfide precursor (4) exhibited cross-linking ability despite its high stability toward strong nucleophiles such as amines and thiols. In this study, we investigated the substituent effects of the phenylsulfide group on the cross-linking reaction, and determined the 2-carboxy substituent of the phenylsulfide derivative (11k) as an efficient cross-linking agent with inducible reactivity. Detailed investigations have shown that the phenylsulfoxide (3) and phenylsulfide (4) precursors produce the 2-amino-6-vinylpurine nucleoside (1) as the common reactive species. It has been concluded that the nature of the inducible reactivity of the precursors (3 and 4) is acceleration of their elimination to the 2-amino-6-vinylpurine nucleoside (1) through the selective process in the duplex with the ODN having cytidine at the target site

Fundamental insight in the design of multifilament MgB2 joint for boosting the persistent-mode operation

Persistent-mode operation is a key feature of magnetic resonance image systems to improve the required field stability. The superconducting joint is known to be beneficial for reducing all the resistant components in an electrically closed-circuit. The joint technique of magnesium diboride (MgB2) multifilamentary wire, however, is the main obstacle to the use of magnet in practical applications. In response, herein, we designed and developed a unique configuration of superconducting joint to further enhance the interconnection of exposed cores between two 18-multifilamentary wires. It was confirmed that developed joint samples achieved high critical current similar to a non-jointed wire. The proposed joint technique was directly applied to the MgB2 single-turn coil and MgB2 magnet for estimating a joint property through persistent-mode operation. This work provides fundamental insights into the design of persistent-mode MgB2 magnets to boost magnetic resonance image systems

Performance of MgB2 superconducting wire fabricated with non-identical Mg particles

Core densification in superconducting wire is highly desirable for obtaining high performance superconducting wires. Since voids hinder current flow in the superconducting core and they directly affect electrical property. In this study, we proposed a magnesium powder blending to regulate the porous properties. Our study delved deeper into the relationship between various particle parameters (such as particle size and distribution), impurities (MgO and Mg(OH)2), superconducting transition temperature, and current carrying capacity for MgB2 superconducting wires. We found a significant correlation between these factors and the porous properties. In particular, the blending of raw powders having spherical shape enables tuning of morphological structures and crystallinities inside cores of the power-in-tube processed MgB2 wires, resulting in superior superconducting properties. Our finding provides in-depth insights of methodological approaches towards more widespread use of superconducting materials and their applications

Disorder anisotropy of layered structure in multi-band MgB2 superconducting materials with high critical current performance

Layered crystal structures of various materials form through strong in-plane covalent and weaker out-of-plane bonding. The different bonding states can lead to the appearance of anisotropies not only of electronic/electrical and magnetic properties but also of structural disorder. A deeper understanding of the disorder anisotropy is essential to carry out structural modification and to enhance the material properties. However, in the case of multi-band MgB2 superconducting materials that have layered structures, including graphene-like and six-membered rings, the nature and extent of the disorder anisotropy are not well understood. Also unknown is the influence on the transport critical current performance under magnetic fields in terms of charge-carrier scattering and vortex pinning. Herein, we have investigated the disorder anisotropy to reveal the relation with the in-field superconductivity. The MgB2 phase formed by appropriate sintering conditions with carbon doping for high transport critical current performance exhibited a small anisotropy in the strain distribution and a large anisotropy in the crystallite size. The anisotropic behavior reflects small out-of-plane domains of crystallites with the strain distribution. The disordered formation may be the reason why the π band is usually dirtier than the σ band. In contrast, although the strain distribution in the in-plane structural state can be selectively tuned by carbon doping, the in-plane crystal growth is still considerably large. Such in-plane crystallization has shortcomings in terms of scattering and pinning. We therefore argue that further selective modification of the disordered structure, especially for the in-plane size properties, is a practical approach to achieve enhancement beyond the currently attainable transport performance

Evaluation of in-plane and out-of-plane crystallinities with residual amorphous phases for MgB2 superconductor

We focus on in-plane and out-of-plane crystallinities of the MgB2 superconductor. These two structural properties were evaluated in terms of peak broadening at lower angles in the X-ray diffraction. The angular behavior of the in-plane and out-of-plane peaks was used to compare it with the corresponding behavior estimated in the case of several crystallite sizes (that affect the in-field superconductivity of MgB2). We propose that this comparison allows a simple evaluation to provide insight into the individual influences of in-plane and out-of-plane crystallinities on the in-field critical current density (without needing to calculate numerical values of crystallite sizes and lattice strains of fabricated MgB2 materials). For this study, we used MgB2 samples sintered at different temperatures. The sintering conditions affected not only the crystallinities but also the phase compositions. The behavior of the compositions, including amorphous phases, was also evaluated by using a quantitative analysis for X-ray diffraction results

Interfacial reaction and side effect of MgB2 superconducting material through low-rotation mechanical milling

Powder processing by ball milling is an effective approach for materials engineering. Although various methods for material processing are available, only high-energy shaker/vibratory or planetary mills have been intensively utilized to develop mechanical milling or alloying routes for structural control of MgB2 superconducting materials. Herein, we have attempted structural modification by using a low-rotation shaker, which is categorized as a low-energy and economical mill in terms of industrial applications. The operation speed was kept constant at 40 rpm, which is much lower than typical conditions employed for planetary mills. Instead of adjusting the low rotational speed, the other processing parameters were controlled to enhance the energy transfer from the balls to powders. The applied milling conditions were ultimately found to cause severe plastic deformation of the raw powders. The shape and size changed drastically, depending on the processing time. The morphological variation of the processed powders as precursors for the MgB2 materials influenced the void structure and the composition including amorphous phases. By considering these results, we also elucidated the mechanism underlying the structural changes upon ball milling and their effects on the transport critical current performance. The present approach for powder processing offers potential as an effective milling route for structural modification of superconducting materials

Evaluation and control of residual amorphous phases in carbon-doped MgB₂ superconductors

Evaluation and control of amorphous phases in materials are very important for optimizing their properties. Herein, we focus on polycrystalline MgB materials prepared with hydrocarbon doping and study the effects of residual amorphous impurities on the superconducting performance. Carbon is known to be an effective element for enhancing the transport critical current under an external magnetic field. The doped samples were prepared under two different nominal conditions, MgB (C H ) and MgB (C H ) , which respectively correspond to additional and substitutional type doping of the MgB composition. Regardless of the doping type, both fabrication methods retarded the formation of the MgB phase due to the dopant, leading to an increase in amorphous impurities. However, the apparent phenomena that arise from the additional and substitutional types are still elusive. Ultimately, the structural differences due to the impurity effects caused significant changes in the transport critical current performance. The present quantitative analysis of the amorphous impurities thus paves the way to further optimize the doping methodology for MgB superconducting materials. 2 2 16 10 x/16 2−x 16 10 x/16 2 2

MgB₂ Superconducting Joint Architecture with the Functionality to Screen External Magnetic Fields for MRI Magnet Applications

A superconducting joint architecture to join unreacted carbon-doped multifilament magnesium diboride (MgB2) wires with the functionality to screen external magnetic fields for magnetic resonance imaging (MRI) magnet applications is proposed. The intrinsic diamagnetic property of a superconducting MgB2 bulk was exploited to produce a magnetic field screening effect around the current transfer path within the joint. Unprecedentedly, the joint fabricated using this novel architecture was able to screen magnetic fields up to 1.5 T at 20 K and up to 2 T at 15 K and thereby almost nullified the effect of the applied magnetic field by maintaining a constant critical current (Ic). The joint showed an Ic of 30.8 A in 1.5 T at 20 K and an ultralow resistance of about 3.32 × 10–14 Ω at 20 K in a self-field. The magnetic field screening effect shown by the MgB2 joint is expected to be extremely valuable for MRI magnet applications, where the Ic of the joints is lower than the Ic of the connected MgB2 wires in a given magnetic field and temperature

MgB2 Superconducting Joint Architecture with the Functionality to Screen External Magnetic Fields for MRI Magnet Applications

A superconducting joint architecture to join unreacted carbon-doped multifilament magnesium diboride (MgB2) wires with the functionality to screen external magnetic fields for magnetic resonance imaging (MRI) magnet applications is proposed. The intrinsic diamagnetic property of a superconducting MgB2 bulk was exploited to produce a magnetic field screening effect around the current transfer path within the joint. Unprecedentedly, the joint fabricated using this novel architecture was able to screen magnetic fields up to 1.5 T at 20 K and up to 2 T at 15 K and thereby almost nullified the effect of the applied magnetic field by maintaining a constant critical current (Ic). The joint showed an Ic of 30.8 A in 1.5 T at 20 K and an ultralow resistance of about 3.32 × 10–14 Ω at 20 K in a self-field. The magnetic field screening effect shown by the MgB2 joint is expected to be extremely valuable for MRI magnet applications, where the Ic of the joints is lower than the Ic of the connected MgB2 wires in a given magnetic field and temperature