Loss Of Thermal Stability Research Articles

Preparation and Characterization of Biocomposites Based on Fibrous Brucite and Poly (Butylene Succinate)

In our research described in this manuscript, fibrous brucite (FB) was modified with common silane coupling agent (KH-570) and the facile melt blending method was used to fabricate fibrous brucite/poly(butylene succinate) (FB/PBS) composites. To evaluate the influence of surface modification of the FB, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) showed that the KH-570 reacted with brucite and the treated FB (OFB) could be well dispersed in the polymer matrix. The mechanical properties and dynamic mechanical analysis (DMA) results showed the effect of the surface modification on the tensile strength, impact strength, storage modulus and glass transition temperature (Tg), which were enhanced with the incorporation of the treated FB in the composites. The flame retardancy of the FB/PBS composites was improved significantly, indicating that the FB could be used as an efficient flame retardant. The addition of FB deteriorated the thermal stability of the PBS. However, the loss in thermal stability was exchanged for a considerable increase in the mechanical and flame retardancy properties. The prepared composites demonstrated better mechanical and flame retardancy properties, compared to PP or PP composites, presenting the potential to be widely used in various industrial fields.

Combustion Behavior of Cellulose Ester Fibrous Bundles from Used Cigarette Filters: Kinetic Analysis Study.

This study is focused on the detailed examination of the combustion properties and kinetic analysis of a cellulose acetate fibrous bundle (CAFB), separated from used cigarette filters. It was shown that the faster rate of CAFB heating allows a large amount of heat to be supplied to a combustion system in the initial stages, where the increase in heating rate has a positive response to ignition behavior. The best combustion stability of CAFB is achieved at the lowest heating rate. Through the use of different kinetic methods, it was shown that combustion takes place through two series of consecutive reaction steps and one independent single-step reaction. By optimizing the kinetic parameters within the proposed reaction models, it was found that the steps related to the generation of levoglucosenone (LGO) (by catalytic dehydration of levoglucosan (LG)) and acrolein (by breakdown of glycerol during CAFB burning-which was carried out through glycerol adsorption on a TiO2 surface in a the developed dehydration mechanism) represent rate-controlling steps, which are strongly controlled by applied heating rate. Isothermal predictions have shown that CAFB manifests very good long-term stability at 60 °C (which corresponds to storage in a sea shipping container), while at 200 °C, it shows a sudden loss in thermal stability, which is related to the physical properties of the sample.

NanoLuc tandem repeats show misfolding during thermal denaturation which is reversible by E. coli chaperones (DnaK/DnaJ/GrpE).

Monomeric NanoLuc (Nluc) is a thermally robust bioluminescent protein with its thermal denaturation temperature at 58oC. In order to further examine this thermal behavior, we developed three protein constructs (monomeric, dyad, and triad Nluc). Interestingly, thermal denaturation experiments at 58oC showed sudden decrease in thermal stability when Nluc was linked to itself, dyad and triad Nluc constructs, while monomeric Nluc remained mostly folded under same conditions. Also, all three constructs maintained their activity (bioluminescence) when brought back to room temperature with no spontaneous recovery observed. However, when we examined the E. coli DnaK/DnaJ/GrpE chaperone system effect on this loss of thermal stability in refolding assays, we observed recovery in bioluminescence signal up to 70% for the poly-Nluc constructs. This observation strongly supports poly-Nluc is a strong chaperone substrate. Another interesting observation was that the refolding of these poly-Nluc constructs was possible at similar percentages even in the absence of GrpE showing a deviation from the canonical chaperone mechanism described up to now in literature. However, high GrpE concentrations were inhibitory to the protein refolding. Similarly, addition of disaggregase ClpB chaperone, showed no further assistance in refolding of the proteins and in some cases proved to be inhibiting the refolding. Lastly, we performed MD simulations of thermally unfolded and refolded monomeric and poly-Nluc constructs. These show that monomeric Nluc is able to correctly refold, while dyad Nluc misfolds with 78% and triad Nluc misfolds with 63%. Also, additional MD simulations suggest the reason of dyad and triad Nluc constructs misfolding is due to domain swapping preventing the correct refolding of these two constructs during thermal renaturation.

Lysine 101 in the CRAC Motif in Transmembrane Helix 2 Confers Cholesterol-Induced Thermal Stability to the Serotonin1A Receptor.

G protein-coupled receptors (GPCRs) constitute the largest class of membrane proteins that transduce signals across the plasma membrane and orchestrate a multitude of physiological processes within cells. The serotonin1A receptor is a crucial neurotransmitter receptor in the GPCR family involved in a multitude of neurological, behavioral and cognitive functions. We have previously shown, using a combination of experimental and simulation approaches, that membrane cholesterol acts as a key regulator of organization, dynamics, signaling and endocytosis of the serotonin1A receptor. In addition, we showed that membrane cholesterol stabilizes the serotonin1A receptor against thermal deactivation. In the present work, we explored the molecular basis of cholesterol-induced thermal stability of the serotonin1A receptor. For this, we explored the possible role of the K101 residue in a cholesterol recognition/interaction amino acid consensus (CRAC) motif in transmembrane helix 2 in conferring the thermal stability of the serotonin1A receptor. Our results show that a mutation in the K101 residue leads to loss in thermal stability of the serotonin1A receptor imparted by cholesterol, independent of membrane cholesterol content. We envision that our results could have potential implications in structural biological advancements of GPCRs and design of thermally stabilized receptors for drug development.

Co-stabilization of θ′-Al2Cu and Al3Sc precipitates in Sc-microalloyed Al–Cu alloy with enhanced creep resistance

As to the increasing demands for the light materials in weight-sensitive fields, scandium (Sc) is arguably known as one of the most attractive and effective microalloying elements to develop high-performance aluminum-based alloys applied at elevated temperature. This report exemplifies how the Sc microalloying effect can be fully utilized to seek for the synergetic stabilization between dual precipitates, more than simply forming the well-known Al3Sc nanoprecipitates. Two sets of precipitation protocols are introduced to create a coexistence of θ′-Al2Cu and Al3Sc precipitates in an Al–Cu–Sc alloy, and the thermal stabilization of the two precipitates is found to be closely correlated. In the case of θ′-Al2Cu precipitate decomposed because of an invalid protection from weak interfacial Sc segregation, the Al3Sc precipitates will coarsen much quickly, which induces a simultaneous loss in thermal stability and strengthening effect of the dual precipitates. In contrast, a sensible approach is proposed to induce a strong Sc segregation at the θ′-Al2Cu/matrix interface to greatly stabilizes the θ′-Al2Cu precipitates even crept at 300°C and concomitantly suppresses the coarsening of Al3Sc precipitates, leading to extremely high creep resistance. The acceleration effect of the Cu on the Al3Sc coarsening is illustrated and can be alternatively prohibited by modified Sc partitioning to stabilized θ′-Al2Cu precipitates as Cu storage and thus provides a much stronger coupling precipitate strengthening as well as creep resistance at elevated temperatures. This strategy is broadly applicable to other high-temperature alloy containing Sc together with primary elements such as Si, Mg, and Zn via the creation of precipitate co-stabilization.

Mechanism of Polyacrylamide Hydrogel Instability on High-Temperature Conditions.

A gel system composed of acrylamide (AM), N,N′-methylenebisAM (BIS), and ammonium persulfate ((NH4)2S2O8) was developed and applied extensively in reservoirs to reduce water cut and increase oil production in mature fields. However, this gel system suffers from thermal stability loss and syneresis at high temperatures that reduces its ability to control water flow. It has been widely accepted that the loss of gel thermal stability can be explained via three aspects: the rupture of polymer chains, the breakage of cross-linker chains, and hydrolysis of polymer. The mechanism of hydrogel syneresis through polymer hydrolysis has been investigated extensively in other publications. However, research on the other two mechanisms is quite limited. In this article, we conduct a series of experiments to demonstrate how the rupture of polymer and cross-linker chains leads to the hydrogel instability at high temperatures. Viscosity and energy-dispersive system measurements suggested that polyAM chains were disrupted by the oxidation reactions involving free radicals. The method to measure the cross-linking degree was established and in combination with X-ray photoelectron spectroscopy measurements, the results showed that cross-linker chains were broken as a result of weaker C–N bond resulting from positively charged mesomethylene carbon and hydrolysis of amide groups on the cross-linker. Because of the application of deionized water in the experiments, nuclear magnetic resonance and FTIR measurements showed that the hydrolysis degree of polymer was weak. Hence, our results verified that breakage of polymer and cross-linker chains led to the rupture of the gel network at high temperature. Besides, cross-linker chains may play a more important role in the thermal stability of the gel, which explains some work into high-temperature-resistant gels.

Mercury-induced aggregation of human lens γ-crystallins reveals a potential role in cataract disease.

Cataract disease results from non-amyloid aggregation of eye lens proteins and is the leading cause of blindness in the world. A variety of studies have implicated both essential and xenobiotic metals as potential etiological agents in cataract disease. Essential metal ions, such as copper and zinc, are known to induce the aggregation in vitro of human γD crystallin, one of the more abundant γ-crystallins in the core of the lens. In this study, we expand the investigation of metal-crystallin interactions to heavy metal ions, such as divalent lead, cadmium and mercury. The impact of these metal ions in the non-amyloid aggregation, protein folding and thermal stability of three homologous human lens γ-crystallins has been evaluated using turbidity assays, electron microscopy, electronic absorption and circular dichroism spectroscopies. Our results show that Hg(II) ions can induce the non-amyloid aggregation of human γC and γS crystallins, but not γD crystallin. The mechanism of Hg-induced aggregation involves direct metal-protein interactions, loss of thermal stability, partial unfolding of the N-terminal domain of these proteins, and formation of disulfide-bridged dimers. Putative Hg(II) binding sites in γ-crystallins involved in metal-induced aggregation are discussed. This study reveals that mercury ions can induce the aggregation of human lens proteins, uncovering a potential role of this heavy metal ion in the bioinorganic chemistry of cataract disease.

Promiscuous Protein Binding as a Function of Protein Stability

Proteins have evolved to balance efficient binding of desired partners with rejection of unwanted interactions. To investigate the evolution of protein-protein interactions, we selected a random library of pre-stabilized TEM1 β-lactamase against wild-type TEM1 using yeast surface display. Three mutations were sufficient to achieve micromolar affinity binding between the two. The X-ray structure emphasized that the main contribution of theselected mutations was to modify the protein fold, specifically removing the N'-terminal helix, which consequently allowed protein coupling via a β-sheet-mediated interaction resembling amyloid interaction mode. The only selected mutation located at the interaction interface (E58V) is reminiscent of the single mutation commonly causing sickle-cell anemia. Interestingly, the evolved mutations cannot be inserted into the wild-type protein due to reduced thermal stability of the resulting mutant protein. These results reveal a simple mechanism by which undesirable binding is purged by loss of thermal stability.

High switching efficiency in FePt exchange coupled composite media mediated by MgO exchange control layers

Satisfying the mutually conflicting requirements of easy switchability and high thermal stability still remains a hindrance to achieving ultra-high areal densities in hard disk drives. Exchange coupled composite media used with proper exchange control layers (ECLs) presents a potential solution to circumvent this hindrance. In this work, we have studied the role of MgO and Ta ECLs of different thicknesses in reducing the switching field of FePt media. MgO ECL was found to be more effective than a Ta ECL. For a 2 nm MgO ECL, the switching field could be reduced by 41% and at the cost of only a limited loss in thermal stability. Furthermore, a very high switching efficiency of 1.9 was obtained using 2 nm MgO ECL. So, with a proper choice of ECL material and thickness, the switching field of FePt media can be substantially reduced while ensuring high thermal stability and a better signal-to-noise ratio, thus potentially paving the way for very high areal density media.

Predicting Heat Propagation in Roebel-Cable-Based Accelerator Magnet Prototype: One-Dimensional Approach With Coupled Turns

When designing superconductor-based magnets, to be prepared for the loss of thermal stability under operation is of the utmost importance. In this paper, heat propagation during a quench in the Roebel-cable-based accelerator magnet prototype is predicted by using a one-dimensional approach. The heat diffusion equation is solved using the finite element method and thermal coupling between the turns is taken into account using the thermal network model. However, when reducing the dimensions of the problem, modeling decisions are often unavoidable. Here, we present the challenges of this approach and discuss the appropriateness of these decisions via simulations.

An extended loop in CE7 carbohydrate esterase family is dispensable for oligomerization but required for activity and thermostability.

The carbohydrate esterase family 7 (CE7) belonging to the α/β hydrolase superfamily contains a structurally conserved loop extension element relative to the canonical α/β hydrolase fold. This element called the β-interface loop contributes 20-30% of the total buried surface area at intersubunit interfaces of the functional hexameric state. To test whether this loop is an enabling region for the structure and function of the oligomeric assembly, we designed a truncation variant of the thermostable CE7 acetyl esterase from Thermotoga maritima (TmAcE). Although deletion of 26 out of 40 residues in the loop had little impact on the hexamer formation, the variant exhibited altered dynamics of the oligomeric assembly and a loss of thermal stability. Furthermore, the mutant lacked catalytic activity. Crystal structures of the variant and a new crystal form of the wild type protein determined at 2.75Å and 1.76Å, respectively, provide a rationale for the properties of the variant. The hexameric assembly in the variant is identical to that of the wild type and differed only in the lack of buried surface area interactions at the original intersubunit interfaces. This is accompanied by disorder in an extended region of the truncated loop that consequently induces disorder in the neighboring oxyanion hole loop. Overall, the results suggest that the β-interface loop in CE7 enzymes is dispensable for the oligomeric assembly. Rather, the loop extension event was evolutionarily selected to regulate activity, conformational flexibility and thermal stability.

PHB nanostructured: Production and characterization by NMR relaxometry

Nanostructured materials based on PHB and different types of nanoclay were prepared and characterized as regards changes in the thermal behavior and morphological/structural characteristics. With respect to the thermal degradation profile, the addition of nanoclays to the PHB matrix did not, in general, cause loss of thermal stability. Regarding morphology/structure, X-ray diffraction revealed that the addition of the nanonoclays altered the crystallinity profile of some samples and suggested that the materials containing 1 wt% nanoclay have a predominantly exfoliated structure. In turn, the information obtained by NMR relaxometry provided a more precise and detailed understanding of the nanomaterials' structure, including the systems with 1 wt% nanoclay. The T1H values provided details on the degree of intercalation/exfoliation attained by the different systems, and the domain distribution curves allowed insight into the homogeneity of the systems. According to the NMR relaxometry data, the system formed by PHB/S7 presented the best exfoliated/intercalated relation.

Influence of Duration of Mechanical Activation of Plant Material Pyrolysis Products on Thermal Stability of Moldable Multilayer Carbon Nanotubes

The influence of duration of mechanical activation of amorphous carbon produced by plant material pyrolysis on the morphology of moldable multilayer carbon nanotubes is studied. The maximum nanotube yield is observed when amorphous carbon is mechanically activated for 36 hours. The nanotube yield depends a great deal on the type of plant materials submitted to pyrolysis. It is demonstrated that prolonged mechanical activation of carbon composite in a vario-planetary mill leads to formation of aggregates consisting of multilayer nanotubes and amorphous carbon and to loss of thermal stability of nanotubes. This fact is responsible for the decrease in carbon nanotube content in products of vacuum annealing carried out for nanotube purification.

RF Sputtering Thermal Barrier Coating for Enhance Corrosion Efficiency of Aero-Engines Components

Nickel base superalloys have been widely used for manufacturing key structural materials for aircraft engine blades. These alloys are developed to withstand the most deleterious degradation mechanisms as creep damage, fatigue, loss of thermal stability and environmental attacks as oxidation and hot corrosion during service. The damages can compromise the structural integrity of the aircraft and in the next generation of advanced engines they will require even higher gas temperature. Consequently, much work has been done in order to develop protective approaches that will increase component lifetimes and meet the development of advanced gas turbine engines. One of such is the used of thermal barrier coatings (TBCs). Thus the aim of the present investigation is to study the electrochemical behavior of YSZ coatings deposited by physical vapor deposition (PVD) on an aeronautical nickel based superalloy to improve the oxidation resistance. The electrochemical techniques conducted on Incoloy 800HT substrates, show that the corrosion velocity decreased with the YSZ coating system.

Tripodal polyhedral oligomeric silsesquioxanes as a novel class of three-dimensional emulsifiers

Tripodal amphiphilic molecules toward organic–inorganic hybrid emulsions were successfully synthesized based on incompletely condensed polyhedral oligomeric silsesquioxanes (POSSs). The three silanol groups provide an excellent scaffold for the construction of three-dimensional amphiphilic molecules, thus well-defined tripodal amphiphilic POSS derivatives were readily synthesized. Thermal analyses revealed that an incompletely condensed POSS exhibited lower crystallinity without loss of thermal stability in comparison with a completely condensed POSS, whereas readily forms aggregates because of its high crystallinity. The newly synthesized tripodal amphiphilic POSSs possessed good solubility in water and effectively stabilized oil-in-water emulsions, while a conventional mono-substituted amphiphilic POSS did not work as an emulsifier because of its lack of water solubility. The prepared organic–inorganic hybrid emulsions were stable against coalescence, and no demulsification occurred over 1 month. Novel molecular design for organic–inorganic emulsifiers has been developed based on an incompletely condensed polyhedral oligomeric silsesquioxane (POSS). Hydrophilic poly(ethylene) glycol chains were introduced to the three silanol groups of heptaisobutyl trisilanol POSS. The obtained amphiphilic POSSs worked as good emulsifiers, and the emulsions were stable for at least 1 month without coalescence of the droplets. The simple synthetic procedure, the well-defined three-dimensional structure and the obtained stable emulsions are advantageous in developing organic–inorganic hybrid materials.

Montmorillonite–multiwalled carbon nanotube nanoarchitecture reinforced thermoplastic polyurethane

Montmorillonite (MMT)–multiwalled carbon nanotube (MWCNT) hybrids were prepared in different weight ratios by simple dry grinding method and characterized. Subsequently, MMT–MWCNT (1:1) hybrid was used as reinforcing filler in developing thermoplastic polyurethane (TPU) nanocomposites by solution blending method. Thermogravimetric analysis showed that 0.25 wt% hybrid‐loaded TPU nanocomposite exhibited maximum enhancement of 31°C corresponding to 50 wt% loss in thermal stability when compared with neat TPU. Differential scanning calorimetry of this composite also indicated that its crystallization and melting temperatures are enhanced by 37 and 13°C, respectively. Mechanical data showed that tensile strength and Young's modulus of 0.50 wt% filled TPU were maximum improved by 57 and 87.5%, respectively. Dynamic mechanical analysis (DMA) measurements indicated 174% (50°C) improvement in storage modulus of 0.50 wt% hybrid‐loaded TPU. Such improvements in thermal and mechanical properties have been attributed to homogeneous dispersion, strong interfacial interaction, and synergistic effect. POLYM. COMPOS., 37:1775–1785, 2016. © 2014 Society of Plastics Engineers

Physical Ionic Liquid/Polysiloxane Mixtures for Tuning the Polarity and the Selectivity of the Polysiloxane Stationary Phase for GC Analysis

Two novel room-temperature ionic liquids (RTILs), a mono-cationic (tetra-n-octylammonium) and a dicationic (bis-methylpiperidinium-butylidene) room-temperature ionic liquid with the bis[(trifluoromethyl)sulfonyl]imide anion, were individually mixed with OV-1701 polysiloxane to tune the selectivity and the polarity of stationary phases for GC. The interaction properties of the stationary phases were investigated on the basis of polarity calculations and the linear solvation energy relationship. The incorporation of the monocationic RTIL in the OV-1701 increased the dipolarity/polarizability capacities (s) and the hydrogen-bond basicity ability (a) allowing the separation of the m-chloroaniline/p-chloroaniline isomers and the m-xylene/p-xylene isomers which are not usually separated on polysiloxane stationary phase. The mixed stationary phases exhibited a greater selectivity than the OV-1701 phase for the majority of the aromatic compounds tested, demonstrating a kind of synergistic effect of the combination of polysiloxane and RTIL. The addition of RTIL proved to be an original method to modulate the polarity and the selectivity of the stationary phase of intermediate polarity in order to prepare stationary phases dedicated for specific separation with good durability (more than 20 months and more than 1,000 injections) and without any loss of thermal stability.

An Unusual Interstrand H-Bond Stabilizes the Heteroassembly of Helical αβγ-Chimeras with Natural Peptides

The substitution of α-amino acids by homologated amino acids has a strong impact on the overall structure and topology of peptides, usually leading to a loss in thermal stability. Here, we report on the identification of an ideal core packing between an α-helical peptide and an αβγ-chimera via phage display. Selected peptides assemble with the chimeric sequence with thermal stabilities that are comparable to that of the parent bundle consisting purely of α-amino acids. With the help of MD simulations and mutational analysis this stability could be explained by the formation of an interhelical H-bond between the selected cysteine and a backbone carbonyl of the β/γ-segment. Gained results can be directly applied in the design of biologically relevant peptides containing β- and γ-amino acids.

Introduction of additional thiol groups into glucoamylase in Aspergillus awamori and their effect on the thermal stability and catalytic activity of the enzyme

Five mutant forms of glucoamylase (GA) from the filamentous fungus Aspergillus awamori with artificial disulfide bonds (4D-G137A\A14C, 6D-A14C\Y419C\G137A, 10D-V13C\G396C, 11D-V13C\G396C\A14C\Y419C\G137A, and 20D-G137A\A246C\A14C) were constructed using computer simulation and experimentally tested for thermostability. The introduction of two additional disulfide bonds between its first and thirteenth alpha-helices and that of the loop located close to a catalytic residue--E400--made it possible to assess the effects of disulfide bridges on protein thermostability. The mutant proteins with combined amino acid substitutions G137A\A14C, V13C\G396C\A14C\Y419C\G137A, and G137A\A246C\A14C showed higher thermal stability as compared to the wild-type protein. At the same time, new disulfide bridges in the mutant A14C\Y419C\G137A and V13C\G396C proteins led to the destabilization of their structure and the loss of thermal stability.

Effect of the character of the (Ni, Pd) cluster/graphene interatomic bonds on the thermosize effects and structural-isomeric transitions

The thermal evolution of nanoclusters is studied by molecular dynamics simulation to analyze the nucleation and kinetics of the kinetic processes that determine the basic factors of the onset of premelting and the loss of thermal stability of a two-dimensional system of transition-metal (Pd, Ni) nanoclusters located on a graphene substrate. A comprehensive analysis reveals the effect of the initial structural characteristics of nanoclusters, the heating conditions, and the kinetic factors during thermally activated diffusion on the nanostructuring in the thermal evolution of the nanoclusters. This evolution includes the following stages: isomerization, quasi-melting, and the decomposition of a given regular structure; it is classified as an order-disorder transition and as an analog of phase transitions in macroscopic systems on the nanoscale.