Domains In Solid State Research Articles

Recent developments in deuterium solid-state NMR for the detection of slow motions in proteins

Slow timescale dynamics in proteins are essential for a variety of biological functions spanning ligand binding, enzymatic catalysis, protein folding and misfolding regulations, as well as protein–protein and protein–nucleic acid interactions. In this review, we focus on the experimental and theoretical developments of 2H static NMR methods applicable for studies of microsecond to millisecond motional modes in proteins, particularly rotating frame relaxation dispersion (R1ρ), quadrupolar Carr–Purcell–Meiboom–Gill (QCPMG) relaxation dispersion, and quadrupolar chemical exchange saturation transfer NMR experiments (Q-CEST). With applications chosen from amyloid-β fibrils, we show the complementarity of these approaches for elucidating the complexities of conformational ensembles in disordered domains in the non-crystalline solid state, with the employment of selective deuterium labels. Combined with recent advances in relaxation dispersion backbone measurements for 15N/13C/1H nuclei, these techniques provide powerful tools for studies of biologically relevant timescale dynamics in disordered domains in the solid state.

A computational investigation on the electronic and optical properties of Coronene and its Boron-Nitride and perfluorinated counterparts

We present a computational study on the electronic and optical properties of a representative C-made and Boron-Nitride-made (BN) planar molecule of interest for potential applications in the solid state domain. In particular, we analyzed the case of Coronene (C24H12) in its BN and perfluorinated analogues. We performed all electrons Density Functional Theory (DFT) and Time Dependent-DFT (TD-DFT) calculations using a localized Gaussian basis-set in combination with a hybrid exchange-correlation functional. For all the systems we have calculated different electronic properties and the optical absorption spectra. A discussion on the possible implications of the general trends, observed for the BN-made clusters properties as compared to their C-based parents, will be given.

Quinoxaline-Based Semiconducting Polymers: Effect of Fluorination on the Photophysical, Thermal, and Charge Transport Properties

A novel fluorinated quinoxaline-based acceptor has been synthesized and then copolymerized with an electron-rich benzodithiophene derivative to yield a low band gap polymer (PBDT-QxF). A non-fluorinated analogue of the same polymer (PBDT-Qx) has also been synthesized in order to disclose the effect of fluorination on polymer properties. PBDT-QxF exhibits better thermal and oxidative stability compared to non-fluorinated analogue. Fluorine atoms induce crystalline domains in solid state—possibly as a result of favorable C–F···H interactions—whereas such ordering is absent in PBDT-Qx. Principal component analysis on variable temperature absorption data collected in solution revealed a stabilization energy of ∼0.5 kcal mol–1 per repeat unit upon fluorination. Theoretical calculations predict higher oxidation potential for PBDT-QxF, which is confirmed by experimental data. Theoretical calculations also suggest inductive effect of fluorine atoms on electronic structure. The hole mobility of PBDT-QxF is also hi...

Biophysical characterisation of thermal-induced precipitates of recombinant anthrax protective antigen: Evidence for kinetically trapped unfolding domains in solid-state

Insoluble aggregation or precipitation is one of the most common degradation pathways observed for biotherapeutics; despite this, the structural mechanisms by which this occurs remain poorly understood due to difficulties associated with biophysical characterisation of protein particulates. To address this knowledge gap, we developed a solid-state circular dichroism (CD) technique, which allows in situ measurements of the secondary and tertiary structural changes associated with the formation of visible therapeutic protein aggregates. We demonstrate how solid-state CD, in conjunction with other biophysical and computational methods can aid in gaining valuable insights into the mechanisms and pathways of thermal-induced precipitation of Bacillus anthracis recombinant protective antigen (rPA), the primary immunogen of anthrax subunit vaccine. Using these methods, we show the domains d3 and d4 are the most labile of the four structurally distinct domains of rPA and play the critical role in nucleating the cascade of unfolding and aggregation. During the assembly process, the domains d1 and d2 become kinetically trapped within the insoluble aggregate and reveal previously intractable distinct tertiary structural elements of the rPA native structure. These findings reveal a uniquely detailed insight into the role of rPA domains on protein stability and provide a mechanistic framework for thermal-induced unfolding and precipitation. It also shows that solid-state CD provides a novel approach in characterising protein precipitation that may facilitate rational improvements to the stability of biopharmaceuticals.

A Study of Texture Evolution during Deformation and Annealing in Fe 3 wt.-% Si by Orientation Contrast Microscopy

Electrical steels, in particular Fe-Si alloys, are used as magnetic flux carrier in transformers and motors because of their excellent magnetic properties. They owe these magnetic properties in part to the presence of specific texture components such as the Goss ({110} <001>) or the cube components ({001} <010>), but also to the chemical composition which is optimum with 6.5 wt. % Si. This high silicon content provides a stable BCC lattice structure to the alloy over the entire solid state domain, but also renders the material more brittle. This embrittlement, which is induced by ordering phenomena, makes it impossible to produce the alloy in a conventional rolling process unless a specific thermomechanical route at high temperature is applied. In order to examine the working behaviour of high Si electrical steels, a series of room temperature plane strain compression tests was carried out on a Fe-3%Si alloy in hot band condition. The samples were compressed with a constant strain rate of 20 s-1 to a reduction of 10, 35 and 70% and subsequently annealed for different times at 800 and 900°C in an electrical furnace without protecting atmosphere. The hot rolled microstructure displayed an average grain size of 195 7m and the texture showed on the cube component ({001} <010>) of maximum 5x random levels. After plane strain compression the samples developed the conventional α (<110> // RD) / γ (<111> // ND) fibre texture by plastic shear which was also accommodated, in part, by mechanical twinning. With regard to the annealed material, it was observed that the recrystallisation started in grains with the higher stored energy and within the shear bands. After a reduction of 70% the samples that were annealed at 800°C for 4 hours displayed an average grain size of 27 7m and a relative maximum of 4x random on the cube component. Also other less intense components such as the rotated cube ({001} <110>) and the Goss ({110} <001>) were present in the annealing texture. The samples that were annealed at 900°C, after a reduction of 70%, were characterized by an average grain size of 36 7m and by the appearance of the {111} <121> γ fibre component with an intensity of 4.7.