High Temperature Creep of Metal Oxides

This chapter presents a comprehensive review of the creep technique used for the study of defect structure and diffusion in metal oxides, both single crystals and ceramics. At high temperatures, the creep rate is proportional to the diffusion coefficient of the slowest species in solid compounds, whatever deformation mechanisms are present (Nabarro viscous creep, recovery creep or pure climb creep). The creep rate dependence on deviation from stoichiometry can be determined from this diffusion. In the case of metal oxides, the departure from stoichiometry is controlled by the oxygen activity which usually is identified with oxygen partial pressure, pO2. The pO2 dependence of the creep rate provides direct information about the nature of minority point defects. On the other hand, studies of the temperature dependency of the creep rate inform us about the activation energy of the diffusion coefficient.This review focuses primarily on the creep behavior of transition metal oxides such as Ni1−yO, Co1−yO, Fe1−yO exhibiting disorder in metal sublattice, as well as ZrO2−x with majority defects in oxygen sublattice. The advantage of these studies is determination of both defect structure and diffusion coefficients of minority defects namely in oxygen sublattice in iron-triad oxides and in zirconium ZrO2 sublattice

Structure/function studies of dogfish α-crystallin, comparison with bovine α-crystallin

Purpose: α-Crystallin is the major protein of the mammalian lens where it contributes to the refractive properties needed for vision and possibly to the stability of the tissue. The aim of this study was to determine whether the properties of α-crystallin have changed during the course of evolution. Methods: Dogfish α-crystallin, which appeared over 420 million years ago, has been contrasted with bovine α-crystallin, which emerged around 160 million years later, by comparing their sizes, the microenvironments of their cysteine and tryptophan residues, their chaperone-like activities and the flexibility of their COOH-terminal extensions. Results: Dogfish α-crystallin consists of α A- and α B-polypeptides, in a 1: 5 ratio, and has a molecular mass of around 400 kDa. By contrast, the bovine protein is around 600-800 kDa in mass and has a 3: 1 subunit ratio. Cysteine residues in the proteins were equally accessible to reaction with 5,5'-dithiobis-(2-nitrobenzoic acid). Quenching of fluorescence with acrylamide indicated tryptophan residues in the two proteins were in similar environments. The chaperone activity of dogfish α-crystallin was comparable to that of bovine α-crystallin in preventing the heat-induced precipitation of β(L)-crystallin but the dogfish protein was three times more effective at preventing insulin precipitation after reduction at 37 degrees C. H-1 nuclear magnetic resonance spectroscopic studies showed that the last 17 amino acids of the dogfish α B polypeptide (V162-K178) have great conformational flexibility, are highly exposed to solvent and adopt little ordered conformation. This is comparable to, but slightly longer in length, than the COOH-terminal extension observed in mammalian alpha-crystallins. Conclusions: The structure and properties of α-crystallin have changed relatively little during the evolutionary period from the emergence of sharks and mammals. © US National Library of Medicine National Institutes of Healt

Small heat-shock proteins and clusterin: intra- and extracellular molecular chaperones with a common mechanism of action and function

Small heat-shock proteins (sHsps) and clusterin are molecular chaperones that share many functional similarities despite their lack of significant sequence similarity. These functional similarities, and some differences, are discussed. sHsps are ubiquitous intracellular proteins whereas clusterin is generally found extracellularly. Both chaperones potently prevent the amorphous aggregation and precipitation of target proteins under stress conditions such as elevated temperature, reduction and oxidation. In doing so, they act on the slow off-folding protein pathway. The conformational dynamism and aggregated state of both proteins may be crucial for their chaperone function. Subunit exchange is likely to be important in regulating chaperone action; the dissociated form of the protein is probably the chaperone-active species rather than the aggregated state. They both exert their chaperone action without the need for hydrolysis of ATP and have little ability to refold target proteins. Increased expression of sHsp and clusterin accompanies a range of diseases, e.g. Alzheimer’s, Creutzfeldt-Jakob and Parkinson’s diseases, that arise from protein misfolding and deposition of highly structured protein aggregates known as amyloid fibrils. The interaction of sHsps and clusterin with fibril-forming species is discussed along with their ability to prevent fibril formation, probably via utilization of their chaperone ability

Ophthalmological and obstetric management in pregnant women with retinal disorders

Objectives: To analyze the clinical significance of ophthalmological assessment in pregnant women affected with degenerative retinal lesions, and the lesions’ clinical relevance in determining the obstetric management and delivery method.  Material and methods: 69 pregnant women affected with retinal degenerative lesions were included in our study. In each patient, the risk of ophthalmological complications during vaginal delivery was evaluated. After the woman’s delivery, alignment between the ophthalmological recommendations and the obstetric management were analyzed. Each case where the management plan differed from the clinical proceedings was thoroughly investigated to determine the cause.  Results: In 69 pregnant women the risk of ophthalmological complications was evaluated, and in 24 cases (35%) assessed as low, as medium in 37 cases (54%) and as high in 8 cases (11%). Among the 69 patients, 42 of women delivered vaginally and the remaining 27 underwent caesarean section. In the high-risk group, the rate of caesarean section was 87%, while in both the low- and medium-risk groups the rate of vaginal births was 75%. Two years of postnatal ophthalmological follow-up did not reveal any complications that could have been associated with the delivery.  Conclusions: Every pregnant woman should undergo ophtalmological examination to assess peripartum risk of complications and determine the method of delivery.

Effect of Nb doping on structural, optical and photocatalytic properties of flame-made TiO2 nanopowder

TiO2:Nb nanopowders within a dopant concentration in the range of 0.1-15at.% were prepared by one-step flame spray synthesis. Effect of niobium doping on structural, optical and photocatalytic properties of titanium dioxide nanopowders was studied. Morphology and structure were investigated by means of Brunauer-Emmett-Teller isotherm, X-ray diffraction and transmission electron microscopy. Diffuse reflectance and the resulting band gap energy were determined by diffuse reflectance spectroscopy. Photocatalytic activity of the investigated nanopowders was revised for the photodecomposition of methylene blue (MB), methyl orange (MO) and 4-chlorophenol under UVA and VIS light irradiation. Commercial TiO2-P25 nanopowder was used as a reference. The specific surface area of the powders was ranging from 42.9m2/g for TiO2:0.1at.% Nb to 90.0m2/g for TiO2:15at.% Nb. TiO2:Nb particles were nanosized, spherically shaped and polycrystalline. Anatase was the predominant phase in all samples. The anatase-related transition was at 3.31eV and rutile-related one at 3.14eV. TiO2:Nb nanopowders exhibited additional absorption in the visible range. In comparison to TiO2-P25, improved photocatalytic activity of TiO2:Nb was observed for the degradation of MB and MO under both UVA and VIS irradiation, where low doping level (Nb < 1at.%) was the most effective. Niobium doping affected structural, optical and photocatalytic properties of TiO2. Low dopant level enhanced photocatalytic performance under UVA and VIS irradiation. Therefore, TiO2:Nb (Nb < 1at.%) can be proposed as an efficient selective solar light photocatalys

Wrapping the alpha-crystallin domain fold in a chaperone assembly

Small heat shock proteins (sHsps) are oligomers that perform a protective function by binding denatured proteins. Although ubiquitous, they are of variable sequence except for a C-terminal similar to 90-residue "alpha-crystallin domain". Unlike larger stress response chaperones, sHsps are ATP-independent and generally form polydisperse assemblies. One proposed mechanism of action involves these assemblies breaking into smaller subunits in response to stress, before binding unfolding substrate and reforming into larger complexes. Two previously solved non-metazoan sHsp multimers are built from dimers formed by domain swapping between the alpha-crystallin domains,. adding to evidence that the smaller subunits are dimers. Here, the 2.5 angstrom resolution structure of an sHsp from the parasitic flatworm Taenia saginata Tsp36, the first metazoan crystal structure, shows a new mode of dimerization involving N-terminal regions, which differs from that seen for non-metazoan sHsps. Sequence differences in the a-crystallin domains between metazoans and nonmetazoans are critical to the different mechanism of dimerization, suggesting that some structural features seen for Tsp36 may be generalized to other metazoan sHsps. The structure also indicates scope for flexible assembly of subunits, supporting the proposed process of oligomer breakdown, substrate binding and reassembly as the chaperone mechanism. It further shows how sHsps can bind coil and secondary structural elements by wrapping them around the alpha-crystallin domain. The structure also illustrates possible roles for conserved residues associated with disease, and suggests a mechanism for the sHsp-related pathogenicity of some flatworm infections. Tsp36, like other flatworm sHsps, possesses two divergent sHsp repeats per monomer. Together with the two previously solved structures, a total of four alpha-crystallin domain structures are now available, giving a better definition of domain boundaries for sHsps

Evaluation of butyric acid as a potential supportive treatment in anterior uveitis

Background: The aim of the study was to evaluate the anti-inflammatory effect of topically administered aqueous sodium butyrate solution in an endotoxin-induced uveitis rat model and compare the results with corticosteroid treatment. Material and methods: Forty female Lewis rats were randomly divided into five groups. Uveitis was induced by a single lipopolysaccharide (LPS) injection into each footpad of each LPS+ rat. Group I (naive) received saline injected into the footpad of each rat at a dose of 0.1 mL/each footpad; Group II (LPS+) received saline solution topically. Group III (LPS+ Dex) — an aqueous dexamethasone sodium phosphate solution topically; Group IV (LPS+ But 0.5 mM) — 0.5 mM aqueous sodium butyrate solution topically, Group V (LPS+ But 1 mM) — 1.0 mM aqueous sodium butyrate solution topically. Clinical scoring of inflammation in rat eyes was evaluated before LPS injection and after 24 hours. The iris involvement, posterior synechiae presence, and insight into the eye fundus were clinicallyassessed. A histopathological examination was also performed. The rats were euthanatized 24 hours after LPS injection, and aqueous humor (AqH) was collected from the eyes by anterior chamber puncture. Levels of inflammatory cytokines and chemokines in the AqH were determined with commercially available Luminex assays. Results: Development of iris hyperemia associated with miosis and poor visibility of fundus details occurred 24 hours after LPS injection. Compared to the LPS+ group, the clinical scores were strongly suppressed in rats treated with Dexamethasone and moderately diminished in LPS+ But 0.5 mM. These clinical features were not observed in the controls (Group 1 — naive). Data from inflammatory cytokines evaluation indicates no significant differences between the LPS+ group (Group 2) and the LPS+ But groups (Groups 4 and 5). Histopathological examinations suggest that hyperemia, corneal stratification, and lesions were less common in the group of animals treated with BA in a lower concentration. Conclusion: Topical administration of sodium butyrate as a therapeutic agent might alleviate the severity of intraocular inflammation in eyes with uveitis. The effect of sodium butyrate was slight but clinically significant in 0.5 mM dose, so other doses of topically administered sodium butyrate should be considered and evaluated in further research

The Interaction of αB-Crystallin with Mature α-Synuclein Amyloid Fibrils Inhibits Their Elongation

αB-Crystallin is a small heat-shock protein (sHsp) that is colocalized with α-synuclein (αSyn) in Lewy bodies—the pathological hallmarks of Parkinson's disease—and is an inhibitor of αSyn amyloid fibril formation in an ATP-independent manner in vitro. We have investigated the mechanism underlying the inhibitory action of sHsps, and here we establish, by means of a variety of biophysical techniques including immunogold labeling and nuclear magnetic resonance spectroscopy, that αB-crystallin interacts with αSyn, binding along the length of mature amyloid fibrils. By measurement of seeded fibril elongation kinetics, both in solution and on a surface using a quartz crystal microbalance, this binding is shown to strongly inhibit further growth of the fibrils. The binding is also demonstrated to shift the monomer-fibril equilibrium in favor of dissociation. We believe that this mechanism, by which a sHsp interacts with mature amyloid fibrils, could represent an additional and potentially generic means by which at least some chaperones protect against amyloid aggregation and limit the onset of misfolding diseases