An Activatable T1-Weighted MR Contrast Agent: A Noninvasive Tool for Tracking the Vicinal Thiol Motif of Thioredoxin in Live Cells

We have synthesized new magnetic resonance imaging (MRI) T₁ contrast agents (CA1 and CA2) that permit the activatable recognition of the cellular vicinal thiol motifs of the protein thioredoxin. The contrast agents showed MR relaxivities typical of gadolinium complexes with a single water molecule coordinated to a Gd³⁺ center (i.e., ~4.54 mM⁻¹s⁻¹) for both CA1 and CA2 at 60 MHz. The contrast agent CA1 showed a ~140% relaxivity enhancement in the presence of thioredoxin, a finding attributed to a reduction in the flexibility of the molecule after binding to thioredoxin. Support for this rationale, as opposed to one based on preferential binding, came from ¹H-¹⁵N-HSQC NMR spectral studies; these revealed that the binding affinities toward thioredoxin were almost the same for both CA1 and CA2. In the case of CA1, T₁-weighted phantom images of cancer cells (MCF-7, A549) could be generated based on the expression of thioredoxin. We further confirmed thioredoxin expression-dependent changes in the T₁-weighted contrast via knockdown of the expression of the thioredoxin using siRNA-transfected MCF-7 cells. The nontoxic nature of CA1, coupled with its relaxivity features, leads us to suggest that it constitutes a first-in-class MRI T₁ contrast agent that allows for the facile and noninvasive monitoring of vicinal thiol protein motif expression in live cells.     

A New Concept for Obtaining SnO2 Fiber‐in‐Tube Nanostructures with Superior Electrochemical Properties

Tin oxide (SnO₂) nanotubes with a fiber‐in‐tube structure have been prepared by electrospinning and the mechanism of their formation has been investigated. Tin oxide‐carbon composite nanofibers with a filled structure were formed as an intermediate product, which were then transformed into SnO₂ nanotubes with a fiber‐in‐tube structure during heat treatment at 500 °C. Nanofibers with a diameter of 85 nm were found to be located inside hollow nanotubes with an outer diameter of 260 nm. The prepared SnO₂ nanotubes had well‐developed mesopores. The discharge capacities of the SnO₂ nanotubes at the 2nd and 300th cycles at a current density of 1 A g^?1 were measured as 720 and 640 mA h g^?1, respectively, and the corresponding capacity retention measured from the 2nd cycle was 88 %. The discharge capacities of the SnO₂ nanotubes at incrementally increased current densities of 0.5, 1.5, 3, and 5 A g^?1 were 774, 711, 652, and 591 mA h g^?1, respectively. The SnO₂ nanotubes with a fiber‐in‐tube structure showed superior cycling and rate performances compared to those of SnO₂ nanopowder. The unique structure of the SnO₂ nanotubes with a fiber@void@tube configuration improves their electrochemical properties by reducing the diffusion length of the lithium ions, and also imparts greater stability during electrochemical cycling.     

Mass spectrometry imaging of latent fingerprints using titanium oxide development powder as an existing matrix

Recent research has focused on increasing the evidentiary value of latent fingerprints through chemical analysis. Although researchers have optimized the use of organic and metal matrices for matrix‐assisted laser desorption/ionization‐mass spectrometry imaging (MALDI‐MSI) of latent fingerprints, the use of development powders as matrices has not been fully investigated. Carbon forensic powder (CFP), a common nonporous development technique, was shown to be an efficient one‐step matrix; however, a high‐resolution mass spectrometer was required in the low mass range due to carbon clusters. Titanium oxide (TiO₂) is another commonly used development powder, especially for dark nonporous surfaces. Here, forensic TiO₂ powder is utilized as a single‐step development and matrix technique for chemical imaging of latent fingerprints without the requirement of a high‐resolution mass spectrometer. All studied compounds were successfully detected when TiO₂ was used as the matrix in positive mode, although, generally, the overall ion signals were lower than the previously studied CFP. TiO₂ provided quality mass spectrometry (MS) images of endogenous and exogenous latent fingerprint compounds. The subsequent addition of traditional matrices on top of the TiO₂ powder was ineffective for universal detection of latent fingerprint compounds. Forensic TiO₂ development powder works as an efficient single‐step development and matrix technique for MALDI‐MSI analysis of latent fingerprints in positive mode and does not require a high‐resolution mass spectrometer for analysis.     

Multifaceted Influences of Melanin‐Like Particles on Amyloid‐beta Aggregation

The properties of eumelanin‐like particles (EMPs) and pheomelanin‐like particles (PMPs) in regulating the process of amyloid formation of amyloid‐beta 42 (Aβ42) were examined. EMPs and PMPs are effective both in interfering with amyloid aggregation of Aβ42 and in remodeling matured Αβ42 fibers. The results suggest that some (but not all) molecular species consisting of melanin‐like particles (MPs) are responsible for their inhibiting property toward amyloid formation, and the influence is likely manifested by long‐range interactions. Incubating preformed Aβ42 fibers with catechols or MPs leads to the formation of mesh‐like, interconnected Aβ42 fibers encapsulated with melanin‐like material. MPs are kinetically more effective than catechol monomers in this process, and a detailed investigation reveals that 4,5‐dihydroxyindole, a major intermediate in the formation of melanin‐like species, and its derivatives are mainly responsible for remodeling amyloid fibers.     

Magnetoelectric multiferroicity and quantum paraelectricity in hexaferrites

Multiferroic materials with coexisting ferroelectric and magnetic orders have attracted tremendous research interests because of their intriguing fundamental physics as well as potential applications in the next-generation multifunctional devices. Hexaferrites with conical magnetic structures are among the most promising single-phase multiferroics because strong magnetoelectric effects can be achieved in them from low temperatures up to room temperature in low magnetic fields. In this review, after briefly introducing the background on multiferroics and classification of hexaferrites, we summarize recent progress in multiferroic hexaferrites, including the mechanisms of spin-induced ferroelectricity, the magnetoelectric phase diagram, giant direct and converse magnetoelectric effects. Furthermore, we present a new mechanism of magnetic-ion-induced displacive polarization in hexaferrites, which leads to quantum paraelectricity and quantum electric-dipole liquid in M-type hexaferrites.     

The Synergistic Effect of a Bimetallic Catalyst for the Synthesis of Carbon Nanotube Aerogels and their Predominant Chirality

Synthesis of continuous spinnable carbon nanotube (CNT) fibers is the most promising method for producing CNT fibers for commercial applications. The floating-catalyst chemical vapor deposition (FC-CVD) method is a rapid process that achieves catalyst formation, CNT nucleation and growth, and aerogel-like sock formation within a few seconds. However, the formation mechanism is unknown. Herein, the progress of CNT fiber formation with bimetallic catalysts was studied, and the effect of catalyst composition to CNT fiber synthesis and their structural properties was investigated. In the case of bimetallic catalysts, the carbon source rapidly decomposes and generates various secondary hydrocarbon species, such as CH₄, C₂H₄, C₂H₂, C₃H₆, and C₄H₁₀ whereas monometallic catalysts generate only CH₄ and C₂H₄ on decomposition. CNT fiber formation with Fe₁Ni₀ begins about 400 mm from the reactor entrance, whereas CNT formation with Fe_0.8Ni_0.2 and Fe_0.5Ni_0.5 begins at about 500 and 300 mm, respectively. The formed CNT bundles and individual CNTs are oriented along the gas flow at these locations. The enhanced rate of fiber formation and lowering of growth temperature associated with bimetallic catalysts is explained by the synergistic effects between the two metals. The synthesized CNTs become predominantly semiconducting with increasing Ni contents.