Artificially Linked Ubiquitin Dimers Characterised Structurally and Dynamically by NMR Spectroscopy

As one of the most prevalent post-translational modifications in eukaryotic cells, ubiquitylation plays vital roles in many cellular processes, such as protein degradation, DNA metabolism, and cell differentiation. Substrate proteins can be tagged by distinct types of polymeric ubiquitin (Ub) chains, which determine the eventual fate of the modified protein. A facile, click chemistry based approach for the efficient generation of linkage-defined Ub chains, including Ub dimers, was recently established. Within these chains, individual Ub moieties are connected through a triazole linkage, rather than the natural isopeptide bond. Herein, it is reported that the conformation of an artificially K48-linked Ub dimer resembles that of the natively linked dimer, with respect to structural and dynamic characteristics, as demonstrated by means of high-resolution NMR spectroscopy. Thus, it is proposed that artificially linked Ub dimers, as generated by this approach, represent potent tools for studying the inherently different properties and functions of distinct Ub chains.     

Resistance Degradation of Iron-Doped Strontium Titanate Investigated by Spatially Resolved Conductivity Measurements

Resistance degradation in perovskites generally is assumed to be caused by stoichiometry variations that occur during high field stress. According to this assumption, distinct conductivity profiles should develop during degradation. In this study, microcontact impedance spectroscopy is used to determine the conductivity profiles in iron-doped strontium titanate after dc stress with a spatial resolution of ∼20 μm. All the features of the characteristic conductivity distributions experimentally observed in single crystals agree with the theoretically predicted distributions and confirm the validity of the stoichiometry polarization model. The degraded samples are concluded to exhibit an oxygen-vacancy enhancement at the cathode and a vacancy depletion at the anode, which leads to a hole–ionic–electron conduction ( p – v – n ) transition of the conduction mechanism. Conductivity measurements at polycrystals revealed subprofiles within single grains, which can be explained by the blocking character of grain boundaries and the resulting accumulation of vacancies on one side of the grain boundaries and a depletion of vacancies on the other side.     

Characterization of Nanoscale Titanium Nitride Dispersions by Small-Angle Neutron Scattering

Suspensions of nanoscale titanium nitride (TiN) with a high solids content can be prepared by using guanidino propionic acid (GPA) as a stabilizing agent. The steric effect of an organic shell with polar groups on the surface of TiN spheres has been suggested in the literature as being a reason for the colloidal stability. To verify this hypothesis experimentally, we have performed small-angle neutron scattering (SANS) on this system; there is no evidence of an organic shell. Even at higher concentrations, in accordance with the Percus-Yevick theory, we could not observe any significant interparticular ordering. A plausible explanation for the stabilization of TiN suspensions is the buffer action of the amino acid GPA.     

Mechanical properties of silicone methacrylate microparticles determined by AFM Colloidal Probe Technique

The mechanical properties of seven types of silicone methacrylate microparticles prepared by solution polymerization with a Pickering emulsifier were investigated by Atomic Force Microscope force–displacement curves acquired in air with the Colloidal Probe Technique, i.e., with spherical SiO₂ particles of known radius glued on tipless cantilevers. The deformation curves derived from the force–displacement curves were fitted with Hertz equation for the contact between two spherical particles, which lead to the determination of the elastic modulus of the samples.