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1.
This study observed the activities of bromelain in the presence of various cationic surfactants at different temperatures and the conformational changes in bromelain by 1H NMR spectroscopy. We found that the bromelain activity was enhanced by tens to hundreds of micromoles per liter of the surfactant. In the presence of the surfactants, bromelain exhibited good tolerance to a range of substrate temperatures and its thermal stability was also increased. The 1H NMR experiments indicated that when the temperature was increased from 25.0 to 45.0 °C, the protons of bromelain having chemical shifts (δ) between 3.7 and 5.2 ppm moved upfield, while those having δ values between 3.2 and 3.7 ppm moved downfield. In the bromelain/cationic surfactant mixture, the values of δ for the protons in both bromelain and the cationic surfactants decreased, accompanied by the broadening of the half-peak width of the surfactant protons. These results indicated that both increasing temperature and adding a cationic surfactant made the bromelain chain more flexible and hence, increased the bromelain activity. To the best of our knowledge, this was the first time that the relationship between the protein activity and the 1H NMR data was expounded.  相似文献   
2.
腐蚀控制是石油天然气管输过程中的一个重要问题.CO2是石油天然气管道中最常见的腐蚀介质,研究CO2腐蚀机制和防护措施具有重要科学意义和经济价值.综述了CO2的腐蚀机理,包括化学反应、电化学反应和传质过程.对现有的腐蚀理论进行了深入讨论,发现阴极反应对CO2腐蚀具有重要影响,CO2对阳极过程的影响尚未明确.在腐蚀机理的基础上,考虑管道实际工况,结合电化学实验结果阐述了各影响因素对CO2腐蚀行为的影响,并结合CO2腐蚀的影响因素讨论了常用管道防护措施的缺陷:阴极保护系统受电位影响较大,应确立新的阴极保护电位,以保证在杂散电流作用下的阴极保护效果;防护涂层容易在杂散电流干扰下发生降解,失去保护性;多数缓蚀剂对环境有害.最后,展望了未来CO2腐蚀和防护的发展方向:为进一步了解CO2腐蚀机理,需要对CO2的电化学腐蚀行为进行系统地实验测试.研究不同缓蚀剂的协同效应,使用环境友好型绿色缓蚀剂,利用新材料开发智能涂层和新型阴极保护系统,也是未来的研究方向之一.  相似文献   
3.
Metal organic frameworks (MOFs) containing zirconium secondary building units (SBUs) in UiO-67 and related MOFs, are highly active for neutralizing both the chemical warfare agents and simulants, such as dimethyl methylphosphonate (DMMP). However, two recent publications gave conflicting reports of DMMP reaction with UiO-67 under ultra high vacuum (UHV) conditions, with one reporting chemisorption and reaction (Wang et al., J Phys Chem C, 2017, 121, 11261–11272) and the other reporting only physisorption and reversible desorption (Ruffley et al., J Phys Chem C, 2019, 123, 19748–19758) from very similar temperature programmed desorption experiments. We show that the discrepancy between these experiments may be explained by different levels of missing linker defects in the UiO-67 samples. We present density functional theory calculations showing that SBU sites having two-adjacent missing linkers exhibit reaction barriers that are about 30 kJ/mol lower than SBU sites having a single missing linker. We also show that topology of the undercoordinated sites plays an important role in the reaction barrier under UHV conditions.  相似文献   
4.
使用马来酸酐(MA)、乙酸乙烯酯(VA)、乙烯基磺酸钠(VS)和2-丙烯酰胺-2-甲基丙磺酸(AMPS)合成了一种四元共聚物阻垢剂MA-VA-VS-AMPS,并探究其在高Ca2+质量浓度和高矿化度环境中的阻垢机理。采用FT-IR分析阻垢剂结构,研究了阻垢剂质量浓度、Ca2+质量浓度、溶液温度和pH值等因素在静态条件下对阻垢剂阻垢性能的影响;利用动态流动测试方法评价阻垢剂在动态条件下的阻垢率;采用Materials studio(MS)中分子动力学模拟方法计算阻垢剂与CaCO3之间的结合能;采用扫描电镜(SEM)和X-射线衍射(XRD)仪分析CaCO3晶体的形貌和晶型。结果表明:在静态测试条件下,MA-VA-VS-AMPS的阻垢率是99.3%;在动态测试条件下,MA-VA-VS-AMPS的阻垢率为96.8%,且阻垢剂使CaCO3发生变形, Ca2+和阻垢剂中的O之间形成了化学键,阻垢剂与CaCO3发生吸附作用。  相似文献   
5.
High loadings of fillers are usually needed to achieve high-thermal conductivity (TC) of polymer-based composites, which inevitably sacrifices processability and meanwhile causes high-cost. Therefore, it is of great significance to achieve high-TC composites under low-filler loading. Here, a novel p-phenylenediamine (PPD) modified expanded graphite (EG-PPD)/epoxy (EP) composite with high TC and low-filler content was successfully prepared via pre-dispersion and vacuum assisted mixing strategy. With the improved interfacial compatibility between EG and EP by PPD, the prepared EG-PPD/EP composite exhibited excellent thermal management performance, resulting in the TC of which reached 4.00 W·m−1·K−1 with only 10 wt% (5.59 vol%) of EG-PPD, which is approximately 19 times higher than that of pure EP. Meantime, the interface thermal resistance of EG-PPD/EP composite between EG-PPD and EP is reduced by 33% compared with EG/EP composite. This composite with excellent TC property is expected to be used in thermal management field.  相似文献   
6.
Succinic acid is an important synthetic monomer but it is difficult to use it as a precursor for synthesizing high molecular weight polyamide, due to its tendency to perform intra-cyclization reaction at high temperature. In order to solve this problem, in this paper, the direct solid-state polymerization (DSSP) method with the initial reactant, nylon salt which was composed of 1, 5-diaminopentane, succinic acid, and terephthalic acid, was applied to synthesize the bio-based copolyamide PA 5T/54. In comparison with the conventional melting polymerization method, the DSSP method can prevent the cyclization reaction of succinic acid effectively due to the lower reacting temperature as well as the restriction effect of the nylon salt. As a result, the product fabricated by DSSP method has higher molecular weight and much lighter color from red to white. Therefore, the DSSP method is advantageous for the synthesis of the polymers or copolymers composed of the succinic acid as the monomer. Furthermore, the polymerization mechanism proposed in this work can serve as a guidance for the design of the molecular structure and control of the polymerization process.  相似文献   
7.
8.
Chemistry and Technology of Fuels and Oils - At present, the wellbore overflow in a fractured gas reservoir is mainly characterized by qualitative methods. The development of quantitative methods...  相似文献   
9.
实际工况下近钻头伽马成像仪在井筒中难以保持绝对居中,需要根据偏心程度对不同方向上的伽马扇区原始测量数值进行环境校正。依据伽马成像测量原理以及近钻头伽马成像仪的结构特点,分析了不同工况下近钻头伽马成像仪偏心程度对测量结果的影响,建立了近钻头伽马成像仪偏心情况下钻井液衰减、钾基钻井液补偿等主要因素的修正图版和校正方法。试验结果表明,偏心条件下,由于井筒和近钻头伽马成像仪之间环空内钻井液的影响,根据原始伽马成像图谱计算出的地层倾角存在较大误差。采用建立的校正方法对偏心情况下的近钻头伽马成像图谱进行测量环境校正后,利用其计算出的地层倾角与地层真实倾角基本一致。研究结果表明,采用建立的测量环境校正方法对近钻头伽马成像仪偏心情况下获得的伽马成像图谱进行环境校正后,可以真实反映地层情况,计算出的地层倾角更准确。   相似文献   
10.
为了解锥形齿在旋转冲击和扭转冲击载荷作用下的破岩过程和破岩效率,采用数值模拟和试验数据验证的方法,研究了2种破岩方式下不同冲击幅值和冲击频率对应的岩石内部应力变化、岩石损伤特征、岩石破碎体积和破碎深度、破岩比功。数值模拟分析结果表明,锥形齿在旋转冲击和扭转冲击破岩过程中均表现为切削齿侵入岩石、岩石损伤贯通裂纹萌生、岩石损伤贯通裂纹扩展、裂缝贯通岩屑崩落4个阶段,拉应力是引起岩石内部到表面贯通裂缝产生的主要原因,压剪应力是岩石内部出现损伤和形成微裂纹的主要原因。随着冲击幅值和冲击频率增大,旋转冲击和扭转冲击破岩方式下,锥形齿破碎岩石的体积都会增大,但当冲击幅值和冲击频率增加到一定值时,岩石破碎体积的增加趋势趋于平缓;锥形齿旋转冲击破岩方式下的最大破碎体积高于扭转冲击破岩方式。常规切削、旋转冲击和扭转冲击3种破岩方式下,锥形齿常规切削的破岩比功最大,不同冲击幅值和冲击频率条件下,锥形齿扭转冲击破岩方式下的破岩比功普遍比旋转冲击破岩方式低。   相似文献   
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