Thermostability of lysozyme amyloid fibrils

Ordered protein aggregates, amyloid fibrils, are a marker of many serious diseases, such as Alzheimer’s, Parkinson’s, prion diseases, etc. At present, special attention is paid to the study of external influences that can affect the structure and stability of mature amyloid fibrils, which may be in demand in the development of approaches to the therapy of amyloidosis, as well as in the creation of new high-strength materials on the basis of these protein aggregates. An external factor, the influence of which on fibrils was studied in this work, was temperature denaturation. It was shown that heating lysozyme amyloid fibrils to 60 °C does not lead to their degradation, but leads only to a reversible increase in the intramolecular mobility of amyloid-forming proteins, but does not change their morphology. At the same time, boiling of lysozyme amyloids leads to their irreversible degradation, which occurs at least 5 days after exposure: fibrils that form larger clusters change their secondary structure, and fibrils with a lesser degree of clustering are divided into separate fibers. Obtained data about the factors that change the stability and structure of amyloids can be applied in biotechnology for creating new high-strength nanomaterials on their basis.

Intramolecular Mobility in Nitroxide Biradicals with Flexible Linkers

Intramolecular electron spin exchange has been studied by X-band electron paramagnetic resonance (EPR) spectroscopy in two long-chain flexible nitroxide biradicals existing in fluid solutions in three spectroscopy-different spatial conformations as a function of temperature, solvent viscosity and polarity. Certain thermodynamic parameters of the conformational transitions were calculated from the EPR spectra. The process of spin-exchange in these biradicals dissolved in five different alcohols was compared with that in the non-polar solvents (toluene) and aprotic (acetonitrile), as well as with two other biradicals studied earlier, and with thermodynamic characteristics of the solvents. A distinct correlation was found between macroscopic (solvent viscosity) characteristics of solvents and thermodynamic parameters of the intramolecular conformational transitions.

Intramolecular mobility affects the energy migration from quantum dots to reaction centers of photosynthesizing bacterium rb. Sphaeroides

The temperature dependence of the efficiency of energy migration from the CdSe/CdS/ZnS quantum dots (QDs, a fluorescence maximum at 580 nm) to the reaction centers (RCs) of the bacteria Rb.sphaeroides is practically constant over the temperature range from 100 to ~230–240 K but then decreases 2,5–3 times as temperature further increases to 310 K. The analysis of this dependence on the basis of Forster’s theory showed that the major changes in the energy transfer efficiency are associated with the temperature change in the quantum yield of QD fluorescence, which is due to the activation of intramolecular mobility in the RC structure.

Development of solid-state emissive o-carboranes and theoretical investigation of the mechanism of the aggregation-induced emission behaviors of organoboron “element-blocks”

This paper presents the aggregation-induced emission (AIE) properties of o-carborane derivatives and proposes a potential strategy for constructing AIE-active organoboron complexes via the enhancement of freedom of intramolecular mobility. Initially, the optical properties of o-carborane derivatives with or without the fused ring structure at the C–C bond in o-carborane in which elongation should be induced by photo-excitation according to theoretical calculations were compared. Accordingly, it was shown that large mobility at the C–C bond in o-carborane should be responsible for the annihilation of emission in solution, leading to the AIE property. From this result, it was presumed that by enhancing the freedom of intramolecular mobility in conventional luminescent organoboron complexes, the deactivation of the excited state in solution and emission recovery in the aggregate can be induced. Based on this idea, we have performed several studies and introduce two representative results. Firstly, the decrease in luminescent properties of boron dipyrromethene (BODIPY) in solution by introducing a movable functional group is explained. Next, the AIE behaviors of boron ketoiminates and the potential mechanism concerning conformational changes for the deactivation of the excited state in the solution state are illustrated. It is proposed that enhancement of the freedom of mobility in the excited state of luminescent organoboron complexes could be a potential strategy for realizing AIE behaviors.

Intramolecular mobility of η5-ligands in chiral zirconocene complexes and the enantioselectivity of alkene functionalization by organoaluminum compounds

Conformational behavior of chiral zirconocenes affects their activity and enantioselectivity.