Thermostatic Cell Research Articles

Properties of Zinc Phosphate Coatings on Carbon Steel Using a Thermostatic Cell and a Mobile System

Properties of Zinc Phosphate Coatings on Carbon Steel Using a Thermostatic Cell and a Mobile System

Influence of hydrogen on the localization of plastic strain in low-carbon steel during electrolytic saturation

Attention focuses on the macroscopic localization of the plastic deformation and structure in polycrystals of low-carbon 08ps steel sheet after hot rolling as a result of electrolytic saturation by hydrogen in a thermostatic three-electrode cell at constant potential. The basic types of macroscopic localization of the plastic deformation and its parameters (the velocity and wavelength) at different stages of strain hardening are determined by two-position speckle photography. By optical and electronic microscopy, the influence of interstitial hydrogen atoms on the defect substructure and morphology of cementite is investigated. The formation of dislocational substructure is considered. Torsional flexure of the α-phase lattice is discovered, corresponding to flexural extinction contours. The basic sources of the stress fields are the boundaries of the grains and fragments.

HYDROGEN EFFECT ON MACROLOCALIZATION OF PLASTIC DEFORMATION OF LOW CARBON STEEL

The paper presents the localization of the plastic deformation features. The studies were performed for the test samples of low-carbon 08ps steel sheet after hot rolling as a result of electrolytic saturation by hydrogen in a thermostatic three-electrode cell at constant potential. Enhancement of the localization of plastic deformation was established. Analysis of the stages of the stress-strain curves revealed the yield line, linear work-hardening stage and (Taylor) parabolic work-hardening stage. Using the speckle-photography technique, the patterns of plastic deformation localization were exposed with subsequent determination of the displacement vector fi eld in the fl at sample and calculation of the components of the tensor plastic distortion (local elongation exx , exy shift and rotation ωz ). The main type and parameters of the localization of plastic fl ow for distinct work-hardening stages were determined

Structural Characterization of Heparin-induced Glyceraldehyde-3-phosphate Dehydrogenase Protofibrils Preventing α-Synuclein Oligomeric Species Toxicity

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a multifunctional enzyme that has been associated with neurodegenerative diseases. GAPDH colocalizes with α-synuclein in amyloid aggregates in post-mortem tissue of patients with sporadic Parkinson disease and promotes the formation of Lewy body-like inclusions in cell culture. In a previous work, we showed that glycosaminoglycan-induced GAPDH prefibrillar species accelerate the conversion of α-synuclein to fibrils. However, it remains to be determined whether the interplay among glycosaminoglycans, GAPDH, and α-synuclein has a role in pathological states. Here, we demonstrate that the toxic effect exerted by α-synuclein oligomers in dopaminergic cell culture is abolished in the presence of GAPDH prefibrillar species. Structural analysis of prefibrillar GAPDH performed by small angle x-ray scattering showed a particle compatible with a protofibril. This protofibril is shaped as a cylinder 22 nm long and a cross-section diameter of 12 nm. Using biocomputational techniques, we obtained the first all-atom model of the GAPDH protofibril, which was validated by cross-linking coupled to mass spectrometry experiments. Because GAPDH can be secreted outside the cell where glycosaminoglycans are present, it seems plausible that GAPDH protofibrils could be assembled in the extracellular space kidnapping α-synuclein toxic oligomers. Thus, the role of GAPDH protofibrils in neuronal proteostasis must be considered. The data reported here could open alternative ways in the development of therapeutic strategies against synucleinopathies like Parkinson disease.

Experimental Analysis of an Advanced Dynamic Glazing Prototype Integrating PCM and Thermotropic Layers

Glazing components are the most challenging element of the building envelope system. The insertion of a Phase Change Material coupled with a thermotropic layer is herewith proposed as an innovative solution aimed at improving the energy performance of the fenestration. The intention is to increase the dynamic features of glazing systems and to enhance their capability of exploiting solar energy – a crucial feature in nearly Zero Energy Buildings.The paper presents the experimental analysis of two prototypes of such a glazing concept and the assessment of their energy performance during the warm season. The samples are installed on an outdoor thermostatic cell facing south, together with a reference triple glazed unit, and continuous measurements of temperatures, irradiances and heat fluxes are performed. In the summer season, when the aim of the glazing system is to reduce the solar gain and to allow daylighting the energy performance is very promising. When compared to the reference technology, both the prototypes are able to reduce to a great extend the direct transmitted solar energy, as well as to smooth the peak indoor surface temperature of the glazing. In particular, one of the two configurations lowers down the solar energy gain under all boundary conditions, while the other configuration presents a slightly worse performance than the other prototype when high solar irradiation occurs. An attempt to measure the thermal transmittance was also carried out and it is shown that the insertion of PCM does not increase the U-value of the component.

The effect of organics on the structure and magnetization of electro-synthesised magnetite nanoparticles

An electro-oxidation method was used to produce magnetite (Fe3O4) nanoparticles in the presence of several different organic molecules. The synthesis was carried out in a thermostatic electrochemical cell at 60 °C with two iron electrodes, using an electrolyte which was an aqueous solution of sodium sulfate, and either thiourea, propylamine, sodium butanoate, hexamethylene-tetra-amine, β-cyclodextrine, or tetrabutylammonium bromide. All the nanoparticle samples were characterized by X-ray diffraction, electron microscopy, magnetometry, and Mossbauer spectrometry. Electron microscopy images confirmed that the mean magnetite particle size is in the range 20–90 nm, and depends critically on the type of organic additive. Room-temperature saturation magnetization of the samples ranges from 19 to 91 Am2 kg−1, again depending on the type of organic molecules. Mossbauer spectra, which were recorded at 18 and 290 K for all the samples using a Co57 source, are typical of non-stoichiometric Fe3-δO4, with a small excess of Fe3+, 0.05 ≤ δ ≤ 0.10. In most cases, there was relatively little organic material associated with the magnetite nanoparticles, but for molecules with carboxylic groups, the strong coulombic interaction led to an association between the negatively charged carboxylate and Fe3+, leading to the formation of a secondary paramagnetic phase.

Influence of Growth Conditions on Magnetite Nanoparticles Electro-Crystallized in the Presence of Organic Molecules

Magnetite nanoparticles were synthesized by electrocrystallization in the presence of thiourea or sodium butanoate as an organic stabilizer. The synthesis was performed in a thermostatic electrochemical cell containing two iron electrodes with an aqueous solution of sodium sulfate as electrolyte. The effects of organic concentration, applied potential and growth temperature on particle size, morphology, structure and magnetic properties were investigated. The magnetite nanoparticles were characterized by X-ray diffraction, electron microscopy, magnetometry and Mössbauer spectrometry. When the synthesis is performed in the presence of sodium butanoate at 60 °C, a paramagnetic ferric salt is obtained as a second phase; it is possible to avoid formation of this phase, increase the specific magnetization and improve the structure of the oxide particles by tuning the growth conditions. Room-temperature magnetization values range from 45 to 90 Am2kg−1, depending on the particle size, type of surfactant and synthesis conditions. Mössbauer spectra, which were recorded at 290 K for all the samples, are typical of nonstoichiometric Fe3−δO4, with a small excess of Fe3+, 0.05 ≤ δ ≤ 0.15.

Liquid–Liquid Equilibria for Dipropylene Glycol–Hydrocarbon Binary Systems: Experimental Data and Regression

Propylene glycols (mono- and di-) have an important potential as solvents in liquid–liquid extraction of aromatics and in azeotropic distillation. Literature and databases provide few accurate experimental data on liquid–liquid and vapor–liquid equilibria in systems consisting of propylene glycols and hydrocarbons (paraffinic, naphthenic, and aromatic hydrocarbons). However, an increasing interest in this field can be observed in recent years. This paper reports the results of an experimental study on the liquid–liquid equilibria in binary systems consisting of dipropylene glycol and paraffinic, naphthenic, and aromatic hydrocarbons with six, seven, and eight atoms of carbon. The experimental data were obtained in a high-precision thermostatic equilibrium cell. The first and most important result was that all normal paraffinic and naphthenic hydrocarbons are partially miscible with dipropylene glycol (4-oxa-2,6-heptanediol), whereas aromatics are completely dissolved. To obtain the binary interaction para...

Rapid Nondestructive Spectrometric Measurement of Temperature-Dependent Gas−Liquid Solubility Equilibria

Gas-liquid solubility equilibria (Henry's Law behavior) are of basic interest to many different areas. Temperature-dependent aqueous solubilities of various organic compounds are of fundamental importance in many branches of environmental science. In a number of situations, the gas/dissolved solute of interest has characteristic spectroscopic absorption that is distinct from that of the solvent. For such cases, we report facile nondestructive rapid measurement of the temperature-dependent Henry's law constant (K(H)) in a static sealed spectrometric cell. Combined with a special cell design, multiwavelength measurement permits a large range of K(H) to be spanned. It is possible to derive the K(H) values from the absorbance measured in the gas phase only, the liquid phase only (preferred), and both phases. Underlying principles are developed, and all three approaches are illustrated for a solute like acetone in water. A thermostatic spectrophotometer cell compartment, widely used and available, facilitates rapid temperature changes and allows rapid temperature-dependent equilibrium measurements. Applicability is shown for both acetone and methyl isobutyl ketone. Very little sample is required for the measurement; the K(H) for 4-hydroxynonenal, a marker for oxidative stress, is measured to be 56.9 ± 2.6 M/atm (n = 3) at 37.4 °C with 1 mg of the material available.

A thermostatic cell with gas diffusion electrode for oxygen reduction reaction under fuel cell relevant conditions

A thermostatic cell with gas diffusion electrode (GDE) as working electrode has been developed, where gas reactant is directly supplied to the catalysts surface through the porous GDE. The setup greatly eliminates the interferences of temperature-dependent change in mass transport (solubility, diffusion coefficient) of gaseous reactants on the kinetic analysis, as demonstrated by results from the cyclic voltammetric measurements of oxygen reduction reaction (ORR) on Pt-GDE at various temperatures. In contrast to the previous studies using rotating disk electrode or flow cell systems, a monotonically increase in the ORR current with decrease in potential from 1.0 to 0.3 V or with the increase in temperature from 5 to 70 °C is observed. The versatile applicability of such setup for the kinetic studies of reactions with gaseous reactants is discussed.

The Rough Endoplasmic Reticulum-resident FK506-binding Protein FKBP65 Is a Molecular Chaperone That Interacts with Collagens

The rough endoplasmic reticulum-resident FK-506-binding protein FKBP65 can be isolated from chick embryos on a gelatin-Sepharose column, indicating some involvement in the biosynthesis of procollagens. The peptidylprolyl cis-trans-isomerase activity of FKBP65 was previously shown to have only marginal effects on the rate of triple helix formation (Zeng, B., MacDonald, J. R., Bann, J. G., Beck, K., Gambee, J. E., Boswell, B. A., and Bächinger, H. P. (1998) Biochem. J. 330, 109-114). Here we show that FKBP65 is a monomer in solution and acts as a chaperone molecule when tested with two classic chaperone assays: FKBP65 inhibits the thermal aggregation of citrate synthase and is active in the denatured rhodanese refolding and aggregation assay. The chaperone activity is comparable to that of protein-disulfide isomerase, a well characterized chaperone. FKBP65 delays the in vitro fibril formation of type I collagen, indicating that FKBP65 is also able to interact with triple helical collagen, and acts as a collagen chaperone.

Copolymerization of two bromine containing methacrylate monomers with methylmethacrylate. Determination of reactivity ratios by in situ quantitative 1H NMR monitoring

AbstractAn important method used to make medical implants radiologically visible is based on introduction of radiopaque bromine or iodine containing methacrylic monomers. Thus, 2-(2-bromopropionyloxy) propyl methacrylate (BPPM) and 2-(2-bromoisobutyryloxy) propyl methacrylate (BIPM) were synthesized with the aim to use them as radiopaque agents. The free radical initiated copolymerization of BPPM and BIPM with methyl methacrylate (MMA) were performed directly in a thermostatic cell of the NMR spectrometer. The copolymer compositions obtained from 1H NMR spectra led to the determination of the reactivity ratios (rMMA = 1.08 ± 0.12; rBPPM = 1.01 ± 0.13 and rMMA = 0.95 ± 0.09; rBIPM = 0.95 ± 0.1). The reactivity ratios of these two monomers is similar to that of MMA suggesting that the length of the bromine containing monomers side chain does not affect significantly the reactivity of the methacrylic double bond. From the results we conclude the copolymers to have random structure.

New Radio-opaque Acrylic Bone Cements. I. The Synthesis of Bromine Containing Methacrylates

In this work, results are presented concerning the synthesis and characterization (FTIR, 1H-NMR, 13C-NMR) of two bromine containing monomers: 2-(2-bromoisobutyryloxy) ethyl methacrylate (BIEM) and 2-(2-bromopropionyloxy) ethyl methacrylate (BPEM). The synthesis of these monomers has been made with the aim to use them as radio-opaque agents in the composition of PMMA-based bone cements. Copolymers were synthesized by free radical polymerization, using methyl methacrylate (MMA) and one of the bromine containing monomers in different concentrations. Copolymerizations were carried out directly in the thermostatic cell of an NMR spectrometer using deuterated benzene as solvent. The reactivity ratios of the copolymerization systems were determined by 1H NMR analysis.

Characterization of low density lipoprotein receptor ligand interactions by fluorescence resonance energy transfer

The low density lipoprotein receptor (LDLR) is the prototype of a family of cell surface receptors involved in a wide range of biological processes. A soluble low density lipoprotein receptor (sLDLR) and a tryptophan (Trp)-deficient variant human apolipoprotein E3 (apoE3) N-terminal domain (NT) were used in binding studies. The sole cysteine in apoE3-NT was covalently modified with an extrinsic fluorescence probe, N-(iodoacetyl)-N'-(5-sulfo-1-napthyl)ethylenediamine (AEDANS), and the protein was complexed with lipid. Incubation of sLDLR with AEDANS-Trp-null apoE3-NT dimyristoylphosphatidylcholine (DMPC) disks, but not lipid-free AEDANS-apoE, induced an enhancement in AEDANS fluorescence emission intensity (excitation, 280 nm) consistent with intermolecular energy transfer from excited Trp in sLDLR to receptor-bound apoE. Ligand binding to sLDLR required calcium and was saturable. In competition binding assays, unlabeled apoE3-NT DMPC inhibited AEDANS-apoE DMPC binding to sLDLR more effectively than low density lipoprotein. Fluorescence changes in this system reflected pH-dependent ligand binding and release from sLDLR consistent with models derived from the X-ray crystal structure of the receptor at endosomal pH. Intermolecular energy transfer from excited Trp in LDLR family members to fluorescently tagged ligands represents a sensitive and convenient assay for the characterization of the myriad molecular interactions ascribed to this family of receptor.

Protofibril Formation of Amyloid β-Protein at Low pH via a Non-cooperative Elongation Mechanism

Deposition of the amyloid beta-protein (Abeta) in senile or diffuse plaques is a distinctive feature of Alzheimer's disease. The role of Abeta aggregates in the etiology of the disease is still controversial. The formation of linear aggregates, known as amyloid fibrils, has been proposed as the onset and the cause of pathological deposition. Yet, recent findings suggest that a more crucial role is played by prefibrillar oligomeric assemblies of Abeta that are highly toxic in the extracellular environment. In the present work, the mechanism of protofibril formation is studied at pH 3.1, starting from a solution of oligomeric precursors. By combining static light scattering and photon correlation spectroscopy, the growth of the mass and the size of aggregates are determined at different temperatures. Analysis and scaling of kinetic data reveal that under the studied conditions protofibrils are formed via a single non-cooperative elongation mechanism, not prompted by nucleation. This process is well described as a linear colloidal aggregation due to diffusion and coalescence of growing aggregates. The rate of elongation follows an Arrhenius law with an activation enthalpy of 15 kcal mol(-1). Such a value points to a conformational change of peptides or oligomers being involved in binding to protofibrils or in general to a local reorganization of each aggregate. These results contribute to establishing a clearer relation at the molecular level between the fibrillation mechanism and fibrillar precursors. The observation of a non-cooperative aggregation pathway supports the hypothesis that amyloid formation may represent an escape route from a dangerous condition, induced by the presence of toxic oligomeric species.

The molecular chaperone, Atp12p, from Homo sapiens. In vitro studies with purified wild type and mutant (E240K) proteins.

Work in Saccharomyces cerevisiae has shown that Atp12p binds to unassembled alpha subunits of F(1) and in so doing prevents the alpha subunit from associating with itself in non-productive complexes during assembly of the F(1) moiety of the mitochondrial ATP synthase. We have developed a method to prepare recombinant Atp12p after expression of its human cDNA in bacterial cells. The molecular chaperone activity of HuAtp12p was studied using citrate synthase as a model substrate. Wild type HuAtp12p suppresses the aggregation of thermally inactivated citrate synthase. In contrast, the mutant protein HuAtp12p(E240K), which harbors a lysine at the position of the highly conserved Glu-240, fails to prevent citrate synthase aggregation at 43 degrees C. No significant differences were observed between the wild type and the mutant proteins as judged by sedimentation analysis, cysteine titration, tryptophan emission spectra, or limited proteolysis, which suggests that the E240K mutation alters the activity of HuAtp12p with minimal effects on the physical integrity of the protein. An additional important finding of this work is that the equilibrium chemical denaturation curve of HuAtp12p shows two components, the first of which is associated with protein aggregation. This result is consistent with a model for Atp12p structure in which there is a hydrophobic chaperone domain that is buried within the protein interior.

A new microcalorimeter for measurements in 3.5-mm coaxial line

A new microcalorimeter has been realized for implementing the national power standard up to 26.5 GHz in a 3.5-mm coaxial line at the Istituto Elettrotecnico Nazionale (IEN) Galileo Ferraris, Turin, Italy. The system is based on a dry thermostatic cell controlled by Peltier elements. The thermal load consists of a twin sensor system that is alternately supplied with high frequency test power and low frequency or direct current (DC) reference power through adiabatic coaxial lines. This microcalorimeter was originally designed for calibrating bolometric mounts. Recently, it has been modified for thermocouple power sensors, which can operate from DC to 26.5 GHz in a 3.5-mm coaxial line.

Acyclovir permeation through rat skin: mathematical modelling and in vitro experiments

The aim of this work is to characterise the skin permeation properties of a male rat by means of a purely diffusive mathematical model based on Fick’s second law. Additionally, in the attempt of proposing a reliable tool allowing the skin permeability (or resistance) determination on the basis of experimental data, the model automatically accounts also for two typical experimental conditions. In particular, drug dissolution in the donor environment and receiver sampling technique (part of the receiver volume is withdrawn and immediately replaced by fresh solvent) are considered. The results of this characterisation are then compared with those coming from a common simplified approach. Acyclovir is chosen as model drug and a thermostatic (37 °C) Franz cell apparatus is used to perform permeation experiments. This study suggests that Acyclovir permeation through the rat skin can be well described by the proposed model and that some differences arise in the evaluation of the full-skin resistance performed by means of our model or the usual simpler approach.

The Folding and Stability of Human Alpha Class Glutathione Transferase A1-1 Depend on Distinct Roles of a Conserved N-capping Box and Hydrophobic Staple Motif

An N-capping box and a hydrophobic staple motif are strictly conserved in the core of all known glutathione S-transferases (GST). In the present work, mutations of hGSTA1-1 enzyme residues forming these motifs have been generated. The analysis of S154A, D157A, and S154A/D157A capping mutants indicate that the removal of this local signal destabilizes the protein. The fact that the third helical residue D157A mutation (N-3) was much more destabilizing than the first helical residue S154A mutation (N-cap) suggests that the appropriate conformation of the conserved substructure formed by the alpha 6-helix and preceding loop (GST motif II) is crucial for the overall protein stability. The refolding study of GSTA1-1 variants supports the prediction that this subdomain could represent a nucleation site of refolding. The analysis of L153A, I158A, L153G, and L153A/I158A hydrophobic staple mutants indicate that the removal of this motif destabilizes the GSTA1-1 structure as well as its refolding transition state. The hydrophobic staple interaction favors essential inter-domain contacts and, thereby, in contrast to capping interactions, accelerates the enzyme reactivation. Its strict conservation in the GST system supports the suggestion that this local signal could represent an evolutionarily conserved determinant for rapid folding.

Do Sequence Repeats Play an Equivalent Role in the Choline-binding Module of Pneumococcal LytA Amidase?

Do Sequence Repeats Play an Equivalent Role in the Choline-binding Module of Pneumococcal LytA Amidase?