Comparative stability of dihydrofolate reductase mutants in vitro and in vivo

Dihydrofolate reductase mutants with amino acid replacementsin the active center (Thr35 Asp mutant, Arg57 His mutant andthe mutant with triple replacement Thr35 Asp, Asn37 Ser, Arg57 His) were obtained by site-directed mutagenesis. The stabilizationeffect of trimethoprim and NADP·H on the protein tertiarystructure in vitro has been investigated. In the case of mutantswith a ‘weak’ tertiary structure (Thr35 Asp35 andthe triple mutant) the separate addition of ligands does notaffect their stability. The simultaneous addition of these ligandsto Thr35 Asp35 and the triple mutant leads to the large increasein their stability. A distinct correlation was found betweenthe in vitro studied stability of the mutant proteins to theurea- or heat-induced denaturation and the level of proteolyticdegradation of these mutants previously observed in vivo.     

硬脂酸盐热稳定剂对胶乳法氯化橡胶热稳定性的影响

用多种分析方法探讨硬脂酸盐热稳定剂对胶乳法氯化橡胶(CNRA)热稳定性的影响。结果表明．硬脂酸盐改善CNRA热空气老化变色性能的优劣顺序为：硬脂酸铅、硬脂酸钙、硬脂酸钡、硬脂酸镉、硬脂酸锌；在一定范围内．硬脂酸盐质量分数增大，CNRA的变色程度降低；硬脂酸铅盐并用体系抑制氯化氢生成能力的大小顺序为：硬脂酸铅／硬脂酸镉／硬脂酸钡(并用比l：0．5：1．5)并用体系、硬脂酸镉／硬脂酸钡(并用比l：3)并用体系、硬脂酸铅／硬脂酸锌／硬脂酸钙(并用比l：0．4：1．6)并用体系、硬脂酸锌/硬脂酸钙(并用比1：4)并用体系。     

硝酸铵的热稳定性研究

分析了硝酸铵热分解的机理及影响因素,介绍了测定硝酸铵热稳定性的方法及其优缺点。结果发现,加速度量热仪和C80微热量热法是目前最安全、简便、实用的反应性化学物质热危险性的评价方法。研究结论为解决硝酸铵生产、储存和运输过程中的安全问题提供了重要参考。     

PVC树脂热稳定性能评价方法

分析了评价PVC树脂热稳定性的6种方法,即老化白度法、刚果红法、氯化氢水吸收法、变色法、紫外光谱法以及转矩流变仪法的优缺点,并结合生产实际提出了评价过程中的要求。     

Excellent energy-storage property and thermal stability of PLZT-based antiferroelectric ceramics

(Pb, La)(Zr, Ti)O₃ antiferroelectric (AFE) materials are promising materials due to their energy-storage density higher than 10 J cm⁻³, but their low energy-storage efficiency and poor temperature stability limit their application. In this paper, the (1 − x)(Pb_0.9175La_0.055)(Zr_0.975Ti_0.025)O₃–xPb(Yb_1/2Nb_1/2)O₃ (PLZTYN100x) AFE ceramics were prepared via two-step sintering method and investigated thoroughly. With the doping of Yb³⁺ and Nb⁵⁺, the phase structure transforms from the orthorhombic phase (AFE_O) to the coexistence of the orthorhombic-and-tetragonal phases. This structure reduces the free energy difference between the AFE and ferroelectric phases and reduces the fluctuation of energy with temperature, improving the energy storage efficiency and temperature stability. When the x = 0.05 (PLZTYN5), the AFE ceramic exhibits excellent temperature stability and ultrahigh energy storage performance, whose recoverable energy density (W_rec) is 6.8–8.2 J cm⁻³ at 30 kV mm⁻¹ in the temperature range from −55 to 75°C, and efficiency (ƞ) is 78%–86.7%. In addition, the change of W_rec is less than 15%, exceeding the performance of most AFE ceramics. The results demonstrate that the PLZTYN5 ceramic has great potential in pulse power capacitors.     

聚氯乙烯热稳定性测试方法的研究

热稳定性是影响聚氯乙烯(PVC)加工和使用的重要性能之一,PVC热稳定测试方法的研究对PVC热稳定剂的研发起到至关重要的作用.从介绍PVC的降解机理入手,系统介绍和论述了白度法、变色法、刚果红法和电导法等聚氯乙烯稳定性能的测试方法,指出了不同测试方法的优缺点与适用范围.这些方法都以高温下聚氯乙烯降解释放HC l并生成共轭双键导致其颜色变化这一降解机理为依据来测试其稳定性.     

聚吡咯纳米线的合成及热稳定性研究

以阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)为软模板,磷酸(PA)、苯甲酸(BA)和乙酸(EA)为掺杂剂,通过化学氧化法合成了直径为40～90 nm的聚吡咯(PPy)纳米线,通过热重分析(TGA)系统地研究了有机酸(BA,EA)、无机酸(PA)、CTAB和PA的浓度以及反应温度对PPy纳米线热稳定性的影响,同时对形成机理进行了探讨。结果表明,刚性结构的有机酸和多元无机酸掺杂的PPy纳米线的热稳定性最好。     

添加剂对环丁砜热稳定性的影响研究

考察了加热温度和加热时间及添加剂对环丁砜热稳定性的影响,以SO2的释放量作为环丁砜热稳定性的最终评价指标。结果表明,在水气吸收、氮气保护2、30℃加热2 h的实验条件下,添加剂E的使用效果最好,加入量为环丁砜的0.04%时,环丁砜分解产生的硫酸钡沉淀量与SO2释放量最少,释放量为10.99 mg。     

提高PVC热稳定性因素探讨

讨论了影响PVC热稳定性的因素，提出了提高加工热稳定性的研究重点。采用链转移剂、降低聚合度、保持适当的PVC反应温度等是抑制羰基烯丙基生成的重要措施。     

影响PVC树脂热稳定性的原因及分析

对比分析了3批聚合度为1000的聚氯乙烯(PVC)树脂的热稳定性、相对分子质量及其分布、偏二氯乙烯链节含量、分子链双键的相对含量及重金属离子含量.结果发现,热稳定性差的树脂双键相对含量较高,重金属离子相对含量明显高出正常批次料;同时还检测出了偏二氯乙烯链节.研究认为,引起配混料和医用粒料颜色发暗、雾度升高、制品黄色指数高的主要原因首先是树脂重金属离子含量高,对树脂老化起到了催化作用;其次是原料单体中的杂质参与了聚合,形成了分子链缺陷,导致热稳定性下降.     

PVC树脂热稳定性的评价方法

介绍了刚果红法、老化白度法及双辊炼塑法3种评价PVC树脂热稳定性的方法,具体分析了在测试过程中的注意事项。     

PTT树脂热分解稳定性研究

研究了不同相对分子质量PTT树脂在氮气和空气 2种气氛中的热分解稳定性。结果表明 ,在氮气中 ,PTT树脂只有 1个热失重台阶 ,相对分子质量对于PTT热分解参数影响不大 ,相应的热分解温度分别为θdi为 3 82 .2～ 3 83℃ ,θmax为 3 99.3～40 3 .4℃ ,θdf为 418.1～ 419.0℃ ,总失重为 88.4%～ 88.7% ,这可以作为PTT热分解稳定性的表征。在空气中 ,PTT树脂存在2个热失重台阶 ,在第 1失重台阶中 ,θdi为 3 70 .9～ 3 75 .2℃ ,θmax为 40 3 .9～ 40 5 .5℃ ,θdf为 414 .7～ 416.0℃ ,样品的总失重为88.9%～ 89.8% ,可以作为PTT热氧化分解稳定性的表征 ;而在第 2失重台阶中 ,θdi为 461.8～ 472 .2℃ ,θmax为 473 .9～ 487.8℃ ,θdf为 480 .5～ 494.1℃ ,样品的总失重为 8.6%～ 9.7% ,第 2失重台阶是残留物进一步氧化燃烧过程的体现。在 2 60℃下 ,PTT在氮气和空气气氛中受热 60min后分别有 1.4%和 4.8%的热失重。说明PTT的热氧化分解稳定性较其热分解稳定性要差 ,但两者相差不大。     

Enhanced thermal stability of high yttria concentration YSZ aerogels

Aerogels are a promising class of materials for lightweight, high-performance insulation. However, their high specific surface area contributes to rapid densification of the structure at elevated temperatures. Upon densification, the favorable properties of low thermal conductivity and low density are lost. Investigation of doped metal oxide systems presents a route to stabilization of porous structures at high temperatures and a platform to study parameters conducive to thermal stability. Our work focuses on yttria-stabilized zirconia (YSZ) aerogels prepared via a sol-gel method and supercritically dried. Yttria concentrations were studied from 0 to 50 mol% YO_1.5 to stabilize porosity to temperatures of 1200°C and develop an understanding of properties contributing to improved stability. Increased yttria content improved the thermal stability of the pore structure by reducing densification and suppressing crystallite growth, resulting in retention of the mesoporous structure to 1200°C. The improvement in thermal stability is related to associated reductions in specific surface energy and cation diffusivity at higher yttria concentrations. This work demonstrates that tuning thermodynamic and kinetic factors is a viable route to improved thermal stability in highly porous structures for use as insulation in extreme environments.     

Syntheses of novel soluble carborane polyimides with ultrahigh thermal stability

Novel carborane polyimides were synthesized and studied. Aromatic meta‐carborane diamines of different structures were initially prepared. Polymerization of these new diamines with the commercially available 4,4′‐oxydiphthalic dianhydride led to meta‐carborane polyimides with various structures and thermal properties. The amorphous polymers obtained are of moderate molecular weight and show good solubility in organic solvents. Thermal analyses of these polyimides reveal that they have moderate to ultrahigh thermal stability depending on their specific structures, with 5% decomposition temperatures ranging from 382 to 786 °C in nitrogen. Different thermal properties of these polyimides are observed when the analyses are performed in dry air, with 5% decomposition temperatures shifting to temperatures ranging from 388 to 1128 °C. Due to the ever‐present requirement of higher performance polymers in fields like aerospace and defense, the methods developed here could be an impetus for the development of these industries. © 2015 Society of Chemical Industry     

酰胺基卟啉化合物的制备、表征及热分析

5-(4-氨基)苯基-10,15,20-三苯基卟啉(MATPP)与棕榈酸在CH2Cl2中直接反应,得到一种新型不对称酰胺基卟啉5-(4-棕榈酸酰亚胺基)苯基-10,15,20-三苯基卟啉(PITPPH2),利用紫外-可见光谱、红外光谱、核磁共振氢谱、元素分析等测试方法对化合物的结构加以确认。热分析表明,卟啉PITPPH2从200℃开始分解,具有较高的热稳定性。     

耐高温加成型硅橡胶灌封料耐热性研究

研究加成型硅橡胶灌封料耐热性。通过热老化前后物理机械性能测试，考察了影响加成型硅橡胶灌封料耐热性的因素，用热失重－差示热分析仪（ＴＧ－ＤＴＡ）考察了金属氧化物耐热添加剂对提高加成型硅橡胶灌封料耐热性的效果，分析了耐热添加剂的作用机制。     

Time and thermal stability improvement of polyethylene ferroelectrets

Ferroelectrets with good piezoelectric coefficients have been produced based on cellular polyethylene (PE) via extrusion film blowing. The quasi-static piezoelectric coefficient (d₃₃) value obtained (935 pC/N) was well above typical values for cellular polypropylene (PP) considered as the workhorse of piezoelectric polymers. Here, a focus was made on increasing the time and thermal stability of cellular PE piezoelectric activity. To do so, specific thermal treatments were applied on the films to improve their microstructure. First, films crystallinity was increased via thermal annealing at 80 °C for 5 min leading to a 32% increase of the initial d₃₃ value as well as its time stability. However, thermal treatment did not give a significant thermal stability improvement because the treated films almost completely lost their piezoelectric activity (96%) at 80 °C. Therefore, the films were treated with orthophosphoric acid resulting in substantial charge stability improvements, especially at higher temperature. Overall, it was possible to increase the continuous service temperature (CST) of PE ferroelectrets from 40 to 80 °C, which is similar to the typical CST of PP. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47646.     

不溶性硫磺的萃取和热稳定性研究

研究了用二硫化碳作萃取剂时萃取时间、萃取温度、萃取剂用量等因素对不溶性硫磺含量的影响,并考察多种稳定剂对不溶性硫磺热稳定性的影响。试验结果表明,在室温条件下萃取时间60 min、不溶性硫磺粗品与二硫化碳质量比1：5时,可获得不溶性硫磺质量分数90%以上的高品质不溶性硫磺产品。在105℃石蜡油恒温15 min条件下,采用橡胶促进剂类复合稳定剂和有机锡类复合稳定剂时试样的热稳定性较好,最高分别达到90.27%和94.77%。     

Influence of thermal treatments on the structure and stability of gelatin gels

The influence of thermal history on the structure of gelatin gels has been investigated by measuring the specific optical rotation [α]_λ at λ = 436 nm. The helix content χ in the gels was derived by reference to the native collagen. Two types of thermal treatments have been applied: (a) cooling and heating at constant rates, and (b) quenching and annealing for long periods. Our results support the idea that the gels are non-equilibrium systems and exhibit thermal hysteresis. The kinetics of helix formation were analysed by the Avrami theory and compared to other techniques. The stability of the structures formed suggests the existence of several mechanisms of hydrogen bonding of the helices: disordered aggregation or partial collagen renaturation.     

Thermal stability and thermal conductivity of stacked Cs intercalated layered niobate

Layered materials exhibit competitively low thermal conductivity along the out-of-plane direction. The solution process is a promising method for preparing stacked structures. However, the thermal stability of the layered materials is poor after processing in solution, thus hindering their applications at high temperatures. One of the solutions to improve the thermal stability of layered structures is to expand the interlayer distance by inserting large-size metal ions. In this work, we studied the thermal properties of Cs⁺ intercalated layered niobate obtained by the ion-exchanged process. The layered structure of the Cs⁺ intercalated layered niobate survives after thermal treatment even at 1200 °C. The room temperature thermal conductivity of as prepared stacked Cs–HCa₂Nb₃O₁₀ is as low as 0.11 W m⁻¹ k⁻¹. Upon thermal annealing, the thermal conductivity increases. After annealing at 1200 °C, the value is 0.90 W m⁻¹ k⁻¹. The finding suggests Cs⁺ intercalated layered niobate is a promising material for high-temperature insulation applications.