Thermostability of Vane Absorber

Aim To improve the thermostability of vane absorbers while designing and manu- facturing. Methods Having considered the structural features of vane absorbers, measures that could reduce the force decay ratio of vane absorbers were discussed. A kind of practical auto temperature compensation apparatus, whose theoretical basis had been discussed, was designed. Results Compared to the prototype vane absorber, this kind of apparatus could decrease force decay ratio sharply. Thus, the thermostability of vane absorbers was improved greatly The accuracy of theoretical analysis and the effectiveness and feasibility of the apparatus was proved by actual testing Conclusion changing vane absorber's configuration, its performance is improved.

Thermostability,mechanical and tribological behaviors of polyimide matrix composites interpenetrated with foamed copper

Polyimide matrix composites interpenetrated with foamed copper were prepared via pressure impregnation and vacuum immersion to focus on their thermostability, mechanical and tribological behaviors as sliding electrical contact materials. The results show that the interpenetrating phase composites（IPC） are very heat-resistant and exhibit higher hardness as well as bending strength, when compared with homologous polyimide matrix composites without foamed copper. Sliding electrical contact property of the materials is also remarkably improved, from the point of contact voltage drops. Moreover, it is believed that fatigue wear is the main mechanism involved, along with slight abrasive wear and oxidation wear. The better abrasive resistance of the IPC under different testing conditions was detected, which was mainly attributed to the successful hybrid of foamed copper and polyimide.

Effects of the Composition of Electrodeposited Fe-Ni-P Alloy on the Thermostability and Magnetic Properties

The magnetic properties, structure defects of electrodeposited Fe-Ni-P alloys with various compositions and the thermostability at amorphous state have been studied by DSC, positron annihilation and electronic integrating instrument methods. The results show that the thermostability of amorphous Fe-Ni-P alloys increases with Fe content. Emergence and recrystallization of stable phases defer as the P content of the coating increases. The minimum H-c, B-r and P-h occur at 9.4 P (wt pet) content. Maximum H-c, B-r and P-h occur at the weight ratio of Fe to Ni equaling to 1/9.

Synthesis,characterization,and thermostability of bis(2,2,6,6-tetramethyl-3,5-heptanedionato)copper(Ⅱ)

Owing to the adaptability to large scale processing,excellent composition control and film uniformity,the metal-organic chemical vapor deposition（MOCVD） technique is a promising process for high-temperature superconductor YBa;Cu;O;（YBCO） preparation.In this technique,the evaporation characteristics and thermostability of adopted precursors in whole process will decide the quality and reproducible results of YBCO film.In the present report,bis（2,2,6,6-tetramethyl-3,5-heptanedionato）copper（II）(Cu（TMHD）;) was synthesized by the interaction of copper acetate hydrate with TMHD in methanol solution,and its structure was identified by FTIR,1 H NMR,and EI-MS spectroscopy.Subsequently,thermal property and the kinetics of decomposition were systematically investigated by nonisothermal thermogravimetric analysis methods（TGA） at different heating rates in streams of N;,and the average apparent activation energy of evaporation process was evaluated by the Ozawa,Kissinger,and Friedman methods.The possible conversion function was estimated through the Coats-Redfern method to characterize the evaporation patterns and followed a phase boundary reaction mechanism by the contracting area equation with average activation energy of 85.1 kJ·mol;.

Enhancement of the thermostability of β-1,3-1,4-glucanase by directed evolution

In order to improve the thermostability of β- 1,3-1,4-glucanase, evolutionary molecular engineering was used to evolve the β-1,3-1,4-glucanase from Bacillus subtilis ZJF-1A5. The process involves random mutation by error-prone PCR and DNA shuffling followed by screening on the filter-based assay. Two mutants, EGsl and EGs2, were found to have four and five amino acid substitutions, respectively. These substitutions resulted in an increase in melting temperature from Tm=62.5℃ for the wild-type enzyme to Tm=65.5℃ for the mutant EGsl and 67.5℃ for the mutant EGs2. However, the two mutated enzymes had opposite approaches to produce reducing sugar from lichenin with either much higher （28%） for the former or much lower （21.6%） for the latter in comparison with their parental enzymes. The results demonstrate that directed evolution is an effective approach to improve the thermostability of a mesophilic enzyme.

Synthesis, characterization, and thermostability of bis(2,2,6,6-tetramethyl-3,5-heptanedionato)barium(Ⅱ)

The metal-organic chemical vapor deposition （MOCVD） technique is a promising process for high-tem- perature superconductor YBa2Cu307_6（YBCO） preparation. In this technique, it is a challenge to obtain barium precursors with high volatility. In addition, the purity, evaporation characteristics, and thermostability of adopted precursors in whole process will decide the quality and reproducible results of YBCO film. In the present report, bis（2,2,6,6-tetramethyl- 3,5-heptanedionato）barium（II） （Ba（TMHD）2） was synthe- sized, and its structure was identified by PTIR, 1H NMR, 13C NMR, and ESI-MS spectroscopy. Subsequently, the thermal properties and the kinetics of decomposition were systemati- cally investigated by nonisothermal thermogravimetric anal- ysis methods. Based on the average apparent activation energy evaluated by the Ozawa, Kissinger, and Friedman methods, the volatilization process was discussed, and all results show that Ba（TMHD）2 is unstable and highly sensitive to the change of temperature during the whole evaporation process. There- fore, it is very important to choose suitable volatilization technology and conditions for avoiding Ba（TMHD）2 break- down （or thermal aging） during MOCVD process. Subse- quently, the possible conversion function is estimated through the Coats-Redfern method to characterize the evaporation patterns and follows a phase boundary reaction mechanism by the contracting surface equation with average activation energy of 118.7 kJ.mo1-1.

Substitution of His260 residue alters the thermostability of Pseudoalteromonas carrageenovora arylsulfatase

This study aimed to improve the thermostability of arylsulfatase from Pseudoalteromonas carrageenovora. A library of P. carrageenovora arylsulfatase mutants was constructed by introducing random mutagenesis using error-prone PCR. After screening, two mutants of H260L and D84A/H260L showed enhanced thermal stability than the wild-type predecessor (WT). Site-directed mutagenesis demonstrated that only amino acid residue at Position 260 plays an important role in the thermostability of P. carrageenovora arylsulfatase. Thermal inactivation analysis showed that the half-life (t1/2) values at 55°C for H260L, H260I, H260Q, H260F and H260R were 40.6, 48.4, 30.9, 29.1 and 34.5 min, respectively, while that of WT was 9.1 min. Structure modeling demonstrated that the additional hydrogen bonds and/or optimization of surface charge-charge interactions could be responsible for the increased thermostability imparted by H260L, H260I, H260Q, H260F and H260R.

Structural Basis for the Thermostability of Sulfur Oxygenase Reductases

The thermostability of three sulfur oxygenase reductases （SORs） was investigated from thermoacidophilic achaea Acidianus tengchongensis （SORAT） and Sulfolobus tokodaii （SORsT） as well as the moderately thermophilic bacterium Acidithiobacillus sp. SM-1 （SORsB）. The optimal temperatures for catalyzing sulfur oxidation were 80 ℃ （SORAT）, 85 ℃ （SORsT）, and 70 ℃ （SORsB）, respectively. The half-lives of the three SORs at their optimal catalytic conditions were 100 min （SORAT）, 58 min （SORsT）, and 37 min （SORsB）. In order to reveal the structural basis of the thermostability of these SORs, three-dimensional structural models of them were generated by homology modeling using the previously reported high-resolution X-ray structure of SORAA （from Acidianus ambivalens） as a template. The results suggest that thermostability was dependent on： （a） high number of the charged amino acid glutamic acid and the flexible amino acid proline, （b） low number of the therraolabile amino acid glutamine, （c） increased number of ion pairs, （d） decreased ratio of hydrophobie accessible solvent surface area （ASA） to charged ASA, and （e） increased volumes of the cavity. The number of cavities and the number of hydrogen bonds did not signifieantly affect the thermostability of SORs, whereas the cavity volumes increased as the thermal stability increased.

Thermostability and Application of the Copper-based SMA Engineering Component

The influence of thermo cycle times under variant loads and environment temperatures on the properties of Cu-16.4Zn-4Al (Re) SMA component was studied by thermostability experiments on Cu-16.4Zn-4Al SMA with the composition containing corium Re. Tangent rule was applied to determine the transformation temperature from displacement-temperature loop plot by computer in each thermal-cold cycle. The results is as follows the transformation temperature increases and shape memory property decrease with increasing load, which leads the action temperature of component to be abnormal, and the memory property decreases after overheating aging, and the memory property decreases with increasing cycle times, while the decreasing is not obvious and the recovery ratio is higher than 90% in one thousand times. It is due to the addition of corium Re which has the function of grain refinement. Therefore, it is necessary to avoid overloading and overheating in the application of such component. Thus, a kind of thermo valve that works at normal pressure and in the water as working substance was designed to replace complicate original electromechanical system.

Thermostability of montmorillonitic clays

Bentonite is one of the most widespread used clays connected with various applications. In the case of foundry technology, bentonite is primarily used as a binder for mold manufacture. Thermal stability of bentonites is a natural property of clay minerals and it depends on the genesis, source and chemical composition of the clay. This property is also closely connected to bentonite structure. According to DTA analysis if only one peak of dehydroxylation is observed(about 600 oC), the cis- isomerism of bentonite is expected, while two peaks of de-hydroxylation(about 550 and 850 oC) are expected in the trans- one. In this overview, the bentonite structure, the water – bentonite interaction and the swelling behavior of bentonite in connection with the general technological properties of bentonite molding mixture are summarized. Further, various types of methods for determination of bentonite thermostability are discussed, including instrumental analytical methods as well as methods that employ evaluation of various technological properties of bentonite binders and/or bentonite molding mixtures.

Effect of Ceria on Structure and Thermostability of Copper-Iron-Oxide Catalyst

The solid structures and thermostabilities of Cu-Fe-O and Cu-Fe-Ce-O supported on alumina were studied by XRD, ESR, Mossbauer and TPR techniques. The studies indicate that there are Fe2CuO4, CuO and alpha-Fe2O3 phases in Cu-Fe-O with the granula of less than 13 nm. With the catalyst pretreatment temperature rising, the crystallite of Fe2CuO4 in the catalysts grows up and that of CuO disappears gradually. The presence of Ce leads to the increase of Cu2+ concentration, inhibits the crystal growth of CuO and Fe2CuO4 in the catalyst except that of Fe2O3, and eliminates the difference for reductive reaction of oxygen in Fe-O and Cu-O. At 800 degrees C, the crystal growth of Fe2O3 in Cu-Fe-Ce-O is slower than that in Cu-Fe-O, i.e., CeO2 in Cu-Fe-Ce-O inhibits the growth of Fe2O3 phase effectively, and enhances the thermostability of catalysts so as to avoid the sintering of active elements in catalysts. CeO2 promotes the reducibility of catalysts at lower temperature.

Synthesis, characterization and thermostability of barium β-diketonate with tetraethylenepentamine ligand

The metal-organic chemical vapor deposition (MOCVD) technique is a promising process for high-temperature superconductor YBa2Cu3O7-δ(YBCO) preparation. In this technique, it is a challenge to obtain barium precursors with high volatility. In addition, the purity, evaporation characteristics and thermostability of adopted precursors in the whole process would decide the quality and reproducible results of YBCO film. In the present report, the barium precursor containing 2,2,6,6-tetramethylheptane-3,5-dionate and tetraethylenepentamine ligands (Ba(TMHD)-tetraen) was synthesized and identified by FTIR, 1H NMR, 13C NMR and ESI-MS spectroscopy. Subsequently the thermal property and the kinetics of decomposition were systematically investigated by combining non-isothermal thermogravimetric analysis methods (TGA), Ozawa, Kissinger and Friedman methods. On the basis of the apparent activation energy of the evaporation process, the thermostability and evaporation characteristics of the precursors were discussed. All results show that Ba(TMHD)-tetraen has higher volatility than Ba(TMHD)2, but it is unstable and highly sensitive to the change of temperature during the whole evaporation process. Therefore, it is very important to choose suitable volatilization technology and conditions for avoiding Ba(TMHD)-tetraen breakdown (or thermal aging) during the MOCVD process.

Fluorescence and Thermostability of Nanometer Porphyrin Trimer

A nanometer porphyrin trimer was firstly synthesized with 1 ,3-dibromopropane as a bridge-linked agent and the fluorescence property and thermostability were studied. The results show that the fluorescence property and thermostability of the trimer are different from those of monoporphyrin. The effects of the molecule structure on the optical property and the thermostability were also studied in detail.

INFLUENCE OF PURIFICATION ON GLASS FORMABILITY AND THERMOSTABILITY OF METALLIC GLASS Ni_(75)B_(17)Si_8

The glass formability of NiBSimelt and the thermostability of this metallic glass formedfrom the the melt can be enhanced by eliminating the heterogeneous catalystg. The purificationwas done by cyclical superheating melt in special glasses and subsequently cyclicallysuperheating it in an electromagnetic levitation apparatus. The purified NiBSiamorphoussample sized up to 20 ~ I0 x 0.5 mm was prepared as four times the thickness of unpurifiedones.

Synthesis,Characterization and Thermostability of a Novel Pb(Ⅱ) Coordination Polymer with Mixed Ligands

A novel mixed-ligand coordination polymer [Pb（phen）（NNDS）（H2O）]n·n H2O（1） was obtained from the reaction of 1,10-phenanthroine（phen）, Pb（OAc）2 and sodium 1-nitroso-2-naphthol-3,6-disulfonate（Na2NNDS） in a mixed solvent. The complex was characterized by elemental analysis, IR and X-ray single-crystal diffraction. Crystal data for 1： monoclinic, space group P21/c, a = 11.5835（9）, b = 14.6334（11）, c = 13.9030（11） A, β = 98.4180（10）o, V = 2331.3（3） A3, Z = 4, Mr = 754.70, Dc = 2.150 mg/m3, μ = 7.483 mm-1, F（000） = 1456, the final R = 0.0430 and w R = 0.0841 for 4221 observed reflections with I 〉 2σ（I）. The Pb（II） center is coordinated by six O and two N atoms showing a distorted dodecahedron configuration. The multidentate ligand of NNDS dianion exhibits peculiar coordination mode, and the two O atoms of two sulfonate anions bridge two Pb（II） cations into a dimer, and the O atom of nitroso group links the other dimer into 2D sheets extending in the [011] plane. There exist significant π-π stacking interactions between adjacent phen and NNDS. The 3D network is formed by 2D sheets interlinked by hydrogen bonds and π-π stacking interactions. The thermostability of 1 was investigated by TG and DSC.

Engineering the thermostability of D-lyxose isomerase from Caldanaerobius polysaccharolyticus via multiple computer-aided rational design for efficient synthesis of D-mannose

D-Mannose is an attractive functional sugar that exhibits many physiological benefits on human health.The demand for low-calorie sugars and sweeteners in foods are increasingly available on the market.Some sugar isomerases,such as D-lyxose isomerase(D-LIase),can achieve an isomerization reaction between D-mannose and D-fructose.However,the weak thermostability of D-LIase limits its efficient conversion from D-fructose to D-mannose.Nonetheless,few studies are available that have investigated the molecular modification of D-LIase to improve its thermal stability.In this study,computer-aided tools including FireProt,PROSS,and Consensus Finder were employed to jointly design D-LIase mutants with improved thermostability for the first time.Finally,the obtained five-point mutant M5(N21G/E78P/V58Y/C119Y/K170P)showed high thermal stability and cat-alytic activity.The half-life of M5 at 65◦C was 10.22 fold,and the catalytic efficiency towards 600 g/L of D-fructose was 2.6 times to that of the wild type enzyme,respectively.Molecular dynamics simulation and intramolecular forces analysis revealed a thermostability mechanism of highly rigidity conformation,newly formed hydrogen bonds andπ-cation interaction between and within protein domains,and redistributed surface electrostatic charges for the mutant M5.This research provided a promising D-LIase mutant for the industrial production of D-mannose from D-fructose.

Three amino acid substitutions contributing to thermostability of phosphoglucose isomerase in the Glanville fritillary butterfly

Temperature is one of the most important environmental factors that affect organisms,especially ectotherms,due to its effects on protein stability.Understanding the general rules that govern thermostability changes in proteins to adapt high-temperature environments is crucial.Here,we report the amino acid substitutions of phosphoglucose isomerase(PGI)related to thermostability in the Glanville fritillary butterfly(Melitaea cinxia,Lepidoptera:Nymphalidae).The PGI encoded by the most common allele in M.cinxia in the Chinese population(G3-PGI),which is more thermal tolerant,is more stable under heat stress than that in the Finnish population(D1-PGI).There are 5 amino acid substitutions between G3-PGI and D1-PGI.Site-directed mutagenesis revealed that the combination of amino acid substitutions of H35Q,M49T,and I64V may increase PGI thermostability.These substitutions alter the 3D structure to increase the interaction between 2 monomers of PGI.Through molecular dynamics simulations,it was found that the amino acid at site 421 is more stable in G3-PGI,confining the motion of theα-helix 420-441 and stabilizing the interaction between 2 PGI monomers.The strategy for hightemperature adaptation through these 3 amino acid substitutions is also adopted by other butterfly species(Boloria eunomia,Aglais urticae,Colias erate,and Polycaena lua)concurrent with M.cinxia in the Tianshan Mountains of China,i.e.,convergent evolution in butterflies.

Improvement of the activity and thermostability of l‑threonine aldolase from Pseudomonas putida via tailoring of the active sites lining the binding pocket

l-threonine aldolases catalyze the conversion of glycine and aldehydes to synthesizeβ-hydroxy-α-amino acids with unsatisfactory enzyme activity.Here,we expressed the l-threonine aldolase from Pseudomonas putida KT2440(l-PpTA)in Escherichia coli BL21(DE3)and improved the activity and thermostability by protein engineering.Five amino acid residues(Ser10,His89,Asp93,Arg177,and Arg321)located in the substrate-binding pocket were selected and for mutation.Eight mutants(D93A,D93G,D93M,D93F,D93S,D93Q,D93Y and D93H)with increased enzyme activity were identified and their k_(cat)/K_(M)values showed about 1-7-fold higher than wild-type.Among all the variants,D93H showed the highest catalytic efficiency with 2925 and 4515 s^(−1)mM^(−1)of k_(cat)/K_(M)values toward l-threonine and l-allo-threonine,respectively.In addition,circular dichroism spectrum exhibited that the melting temperature of D93H(54.2℃)was 5℃higher than wild-type(49.2℃).Molecular dynamics simulations illustrated that the D93H variant shortens the distance between the imidazole group of H93 and the hydroxyl group of substrate,which facilitated the proton extraction and promote the enzymatic reaction.This work affords a candidate for the synthesis ofβ-hydroxy-α-amino acids with improved catalytic efficiency and thermostability and provides structural insights into the l-TA family by protein engineering.

Effects of terminal modification on the catalytic efficiency and thermostability of Brucella melitensis 7α‑hydroxysteroid dehydrogenase

Brucella melitensis 7α-hydroxysteroid dehydrogenase(Bm7α-HSDH)catalyzes the oxidation of chenodeoxycholic acid to 7-oxolithocholic acid.In this work,we investigated the effects of terminal modification(His-tags location and terminal truncation)on its catalytic efficiency and thermostability.Compared with C-terminal His-tagged Bm7α-HSDH(C-Bm7α-HSDH),N-Bm7α-HSDH showed a 3.6-fold higher kcat and a 1.3-fold lower Km,resulting in a 7.0-fold higher kcat/Km value toward chenodeoxycholic acid.Circular dichroism spectroscopy indicated that the melting temperature of N-Bm7α-HSDH(46.13℃)was 3.0℃lower than that of C-Bm7α-HSDH(49.13℃).N-Bm7α-HSDH produced 7-oxolithocholic acid in the highest yield of 96.7%in 4 h,whereas the C-Bm7α-HSDH gave 96.4%in 10 h.Moreover,amino acids truncation and His-tag cleave experiments confirmed the C-terminal residues played key roles in catalytic functions.Molecular dynamics simulations further indicated C-terminal His-tagged modification could deform the substrate-binding region to disrupt the enzyme–substrate interactions and catalytic motion.However,the N-terminal His-tag hardly affected the catalytic efficiency due to its location far from the active site of the enzyme.This study provides structural insights into the terminus modifications of hydroxysteroid dehydrogenase on steroid substrate recognition and stabilization,thus affecting its catalytic functions.

Thermostability of photosynthesis in two new chlorophyll b-less rice mutants

Leaves of the two new chlorophyll b-less rice mutants VG28-1, VG30-5 and the wild type rice cv. Zhonghua 11 were subjected to temperatures 28, 36, 40, 44 and 48℃ in the dark for 30 min or gradually elevated temperature from 30℃ to 80℃ at 0.5℃/min. The thermostability of photosynthetic apparatus was estimated by the changes in chlorophyll fluorescence parameters, photosynthetic rate and pigment content, chloroplast ultrastructure and tissue location of H2O2 accumulation. There were different patterns of Fo-temperature curves between the Chl b-less mutants and the wild type plant, and the temperature of Fo rising threshold was shifted 3℃ lower in the Chl b-less mutants (48℃) than in the wild type (51℃). At temperature up to about 45℃, chloroplasts were swollen and thylakoid grana became misty accompanied with the complete loss of photosynthetic oxygen evolution in the two Chl b-less mutants, but chloroplast ultrastruc- ture in the wild type showed no obvious alteration. After 55℃ exposure, the disordered thylakoid and significant H2O2 accumulation in leaves were found in the two Chl b-less mutants, whereas in the wild type plant, less H2O2 was accumulated and the swollen thylakoid still maintained a cer- tain extent of stacking. A large extent of the changes in qP, NPQ and Fv/Fm was consistent with the Pn decreasing rate in the Chl b-less mutants during high temperature treatment as compared with the wild type. The results indicated that the Chl b-less mutants showed a tendency for higher thermosensitivity, and loss of Chl b in LHC II could lead to less thermostability of PSII structure and function. Heat damage to photosynthetic apparatus might be partially attributed to the in- ternal oxidative stress produced at severely high temperature.