Cottonseed extraction with a new solvent system: Isohexane and alcohol mixtures

A solvent system, consisting of isohexane and 5 to 25% alcohol, either ethanol (EtOH) or isopropyl alcohol (IPA), was tested for extracting gossypol and oil from cottonseed. The test results indicate that this new solvent system not only is effective in removing free and total gossypol but also is as efficient as n-hexane when extracting oil. The amino acid analysis of cottonseed meal, produced by the new solvent system, is similar to that produced by commercial n-hexane. Present commercial cottonseed extraction and downstream processing of cottonseed oil refining may need little change to adopt this new solvent system. This new solvent system may lead to a solution to the gossypol problem of cottonseed extraction.     

pH和有机配体对Cu-Pb复合污染土壤中Cu的解吸行为的影响

以黄棕壤为供试土壤,研究了pH对Cu-Pb复合污染土壤中Cu的解吸行为的影响。实验结果表明,无论以EDTA还是以C IT为萃取剂,pH值都会对Cu的解吸情况产生重要影响。当解吸液pH值为4.0时,Cu的解吸量最小;Cu的解吸率在各个pH下的大小顺序大致为:pH 5.6的>pH 3.0的>pH 4.0的。     

体系pH值对利福霉素恶嗪环合反应的影响

基于利福平合成反应中间体利福霉素恶嗪的环合反应机制,考察反应体系的pH值对利福霉素恶嗪纯度的影响,以及调节反应体现的pH值对环合反应的温度、时间、合成利福霉素恶嗪和终产品利福平纯度和收率的影响,确定环合反应体系最佳pH值范围在5-7范围时,可以使环合反应的温度从60℃降低到55℃,反应时间由2 h缩短到1.5 h,并可以抑制副反应的发生,提高利福霉素恶嗪和终产品利福平的纯度和收率。     

Effect of pH on hydride transfer by Escherichia coli dihydrofolate reductase

The kinetic isotope effect (KIE) on hydride transfer in the reaction catalysed by dihydrofolate reductase from Escherichia coli (EcDHFR) is known to be temperature dependent at pH 7, but essentially independent of temperature at elevated pH. Here, we show that the transition from the temperature-dependent regime to the temperature-independent regime occurs sharply between pH 7.5 and 8. The activation energy for hydride transfer is independent of pH. The mechanism leading to the change in behaviour of the KIEs is not clear, but probably involves a conformational change in the enzyme brought about by deprotonation of a key residue (or residues) at high pH. The KIE on hydride transfer at low pH suggests that the rate constant for the reaction is not limited by a conformational change to the enzyme under these conditions. The effect of pH on the temperature dependence of the rate constants and KIEs for hydride transfer catalysed by EcDHFR suggests that enzyme motions and conformational changes do not directly influence the chemistry, but that the reaction conditions affect the conformational ensemble of the enzyme prior to reaction and control the reaction though this route.     

水杨醛缩胺类双席夫碱过渡金属配合物的合成与表征

以水杨醛与乙二胺为原料,通过席夫碱反应合成一类水杨醛缩胺类双席夫碱,并进一步与铜、锌、镍3种金属离子络合得到3种过渡金属配合物;采用元素分析、红外光谱和紫外光谱对席夫碱及其金属配合物的结构进行表征.结果表明,合成的水杨醛缩乙二胺配体分子结构与理论结构相符,且分别与铜、锌、镍离子络合形成了稳定的过渡金属配合物.     

Power law models as descriptors of the kinetics of complex systems: Temperature effects

The effects of temperature on power law models for the kinetics of parallel first order systems are studied. The variation of the empirical power law parameters with temperature provides information on the relationship between the rate constant and activation energy distributions; in particular. if the power law exponent increases with temperature, there is a positive correlation between the rate constants and the activation energies; if the power law exponent decreases with temperature, there is a negative correlation between the rate constants and the activation energies; Arrhenius plots will always be concave unless the activation energies for all the reactions are equal. Application of the techniques described here to data from the catalytic cracking of gas oil over LaY zeolite reveals a compensation effect among the reacting hydrocarbon species.     

Oxidation of cod phospholipids in liposomes: Effects of salts,pH and zeta potential

This work examines how different salts and pH influence both the zeta potential and the lipid oxidation rate of liposomes made from cod phospholipids. The rate of Fe²⁺‐induced lipid oxidation was measured by consumption of dissolved oxygen by liposomes in a closed vessel. Cations (Na⁺, K⁺, Ca⁺, Mg⁺) did not influence the rate of oxidation in the tested range [ionic strength (I) 0–0.14 M). Among the tested anions, sulphates and nitrates did not significantly change the oxygen uptake rate, but chlorides (KCl, NaCl, CaCl₂) reduced the oxidation rate down to approximately 45%, and dihydrogen phosphate down to 14%, when I = 0.14 M. The effect of Cl^? and H₂PO4₄^? was additive. Addition of salts increased the zeta potential of the liposomes, divalent cation salts even resulted in a positive zeta potential. When the liposomes contained different concentrations of chlorides, a linear relationship between oxygen uptake rate and zeta potential was observed. When phosphate was added, the oxygen uptake rate was not related to the changes in zeta potential. The decrease in pH was followed by an increase in zeta potential. The oxygen uptake rate did not change significantly at different positive zeta potentials (pH <3). When the zeta potential was negative, the oxygen uptake rate was influenced by the zeta potential and may also be influenced by iron solubility. Absolute values of the zeta potential alone cannot be used to predict oxidation rates.     

pH值变化对珍珠漂白的影响

研究了九种海水珍珠水系漂白液在使用过程中ｐＨ值的变化情况及影响因素，阐述了ｐＨ值变化原因及规律，探讨了ｐＨ值变化对珍珠漂白质量的影响。     

Electrodeposition of Zn in acid sulphate solutions: pH effects

The kinetics of zinc electrodeposition from acid sulphate solution on a platinum electrode was investigated by means of stationary polarization curves, interfacial pH measurement and electrochemical impedance spectroscopy. The effect of pH, namely pH 2, 3 and 4, was analyzed. A significant dependence of Zn electrodeposition with solution pH was verified. The results obtained cannot be predicted by the available models for Zn electrodeposition. A reaction model is then proposed based on the predominant steps as a function of the potential and the electrode surface nature.     

Effect of pH on the properties of protonated polyaniline-based films for pH sensing applications

The chemical and physical properties of protonated polyaniline (PANI)-based films, including PANI-emeraldine salt (ES) and PANI/polyvinyl acetate (PVAc) films, before and after pH treatments are characterized and compared. Protonated PANI-based films are prepared by spin coating. The effects of pH value and immersion time on the film properties are investigated to gain a better understanding of their performance in pH sensing. The films are characterized based on color, morphology, chemical structure, phase state, and protonation state. Protonated PANI-based films exhibit a color change from green to dark blue as deprotonation occurs in solutions with higher pH. The highly porous structure of PANI/PVAc films is slightly affected by the pH of the solution. However, the globular structure of the PANI-ES films forms cracks with increasing immersion time. PANI/PVAc films exhibit better stability in acidic and neutral solutions than in alkaline solutions because of the hydrolysis of PVAc. Compared with the negligible differences in the PANI/PVAc film in buffers with different pH, PANI-ES exhibits noticeable changes. Therefore, PVAc improves the stability and performance of PANI for pH-sensing applications.     

Rigid Schiff Base Complex Supermolecular Aggregates as a High-Performance pH Probe: Study on the Enhancement of the Aggregation-Caused Quenching (ACQ) Effect via the Substitution of Halogen Atoms

Optical signals of pH probes mainly driven from the formation or rupture of covalent bonds, whereas the changes in covalent bonds usually require higher chemical driving forces, resulting in limited sensitivity and reversibility of the probes. The exploration of high-performance pH probes has been a subject of intense investigation. Herein, a new pH probe has been developed, with optical property investigation suggesting the probe has excellent signal-to-noise ratio, and fluorescence intensity shows exponential growth, combined with a visible color change, as pH increased from 5.1 to 6.0; Moreover, the probe has outstanding stability and reversibility, with more than 90% of the initial signal intensity remaining after 30 cycles. In order to better understand the special fluorescence behavior of the reported probe, the non-halogenated isomer is introduced for comparison, combined with the results of structural analysis, quantitative calculation and optical experiments, and the possible mechanism of the special supramolecular aggregation-caused quenching effect induced by the halogen atom is discussed.     

Hydrothermal pretreatment for deconstruction of plant cell wall: Part I. Effect on lignin‐carbohydrate complex

Hydrothermal pretreatment with characteristic of green chemistry is considered as promising technology in the biorefineries. Using material balance and multiscale characterization techniques, the effects of process severity factor and pH on chemical behaviors of lignin‐carbohydrate complex (LCC) were systematically studied. During pretreatment, spatial relocation of lignin with covalently linked xylan facilitated local cell wall collapse. A kinetic model was established to describe the behaviors of LCC components changing with severity factor. It was found that cleavage of LCC linkage was strongly pH‐dependent. Low pH dominated cleavage of coumarate/ferulate esters which cross‐linking lignin with xylan and repolymerization of aromatics either from furfural or lignin into polymers such as pseudo lignin, while high pH which allowed the existence of soluble LCC dominated the aldol condensations from xylose to aromatics and depolymerizaton of lignin to phenols. Detailed reaction pathways concerned with LCC were finally established to elucidate the underlying mechanism. © 2018 American Institute of Chemical Engineers AIChE J, 64: 1938–1953, 2018     

Effect of FA chain length on normal- and reversed-phase HPLC of phospholipids

Forty-seven saturated synthetic diacyl PA, PC, PE, PG, and PS and five unsaturated diacyl phospholipids (PL) underwent normal- and reversed-phase (RP) HPLC with isocratic isopropanol/hexane/water (5∶4∶1) and methanol/chloroform/acetonitrile/water (79.5∶9∶8∶3.5) mobile phases, respectively. For normal-phase HPLC, capacity factors (k′ _i ) decrease with chain length (n) of the two identical PL FA residues, whereas the opposite occurs with RP (C₁₈)-HPLC. Plots of In k′ _i vs. n for individual PL classes are in general curved, violating the linear free-energy relationship. For PL of the same n but with different head groups, k′ _i with normal-phase HPLC varies as PE<PG<PA<PS<PC, except when n≥16, when the order is PE<PS≈PA≈PG<PC. For RP-HPLC, the order of k′ _i values is PG<_A≈PS≤PC≈PE until n≥16, when it is PA≈PG<PS≪PC≈PE. With normal-phase HPLC, k′ _i values of PL with unsaturated FA of n=18 are ordered as PE<PA<PC. Increasing degrees of unsaturation lead to increasing k′ _i .     

pH值对脱硫石膏晶须生长行为的影响

以脱硫石膏为原料,采用水热法制备CaSO4晶须. 借助电导率、SEM和XRD、高分辨显微镜等分析方法,研究了不同pH值下CaSO4晶须的生长规律. 结果表明,随着pH值增加,CaSO4晶须的长径比呈先升高后降低的趋势,初始pH值为5时,晶须的直径为1~4 mm,平均长度为218.67 mm,长径比达最大,为82.57. pH值直接影响杂质的存在状态,随pH值增加,杂质中的SiO2逐渐转变为CaSiO3,并使溶液中的离子平衡发生变化,从而影响晶须在某一方向的生长趋势.     

pH Effect on Ozonation of Ampicillin: Kinetic Study and Toxicity Assessment

Ampicillin (AP) is a penicillin-type antibiotic and one of the most widely used bacteriostatic antibiotics in human and veterinary medicine. A kinetic study was performed under different pH conditions (5, 7.2, and 9) to determine the degradation efficiency of AP by ozonation. The second-order rate constants for the direct reaction of AP with ozone were measured to be 2.2 ?5.4×10⁵ M^?1s^?1 under the pH conditions tested. The rate constants were greater at higher pH. The potential toxicity of the AP intermediates formed after ozonation under the various pH conditions were examined using a bioluminescence assay on Vibrio fischeri species. The biodegradability of the AP degraded products was also determined by measuring the BOD₅/COD of the ozonated samples under the different pH conditions. A lower biodegradability and acute toxicity was observed at the lowest pH (pH 5). These results suggest that higher pH conditions are needed for the removal of AP by ozonation in order to mitigate the residual toxicity that can remain even after complete removal of the parent compound by ozonation.     

Effect of pH on phase separation of globular protein

A molecular-thermodynamic framework is proposed to describe protein precipitation by inorganic salt. The equation of state consists of a hard-sphere reference contribution and a perturbation term. The reference term is derived based on the modified Chiew’s model to describe the pre-aggregation effect of protein at various solution pH. In this study, we discuss protein-protein effective two-body potentials. The distribution and magnitude of charges on the surface of a protein vary significantly with pH. It changes the magnitude of charge-charge repulsion, charge-dipole attraction, dipole-dipole attraction, and induced dipole-induced dipole attraction forces between protein pairs in solution. The distribution of the charge fluctuation is slightly effective in solution pH. To investigate the effect of pH, modified charge fluctuation distribution model is proposed. Using the proposed model, we successfully describe the pH dependence of the protein precipitation.     

pH值对Ni-Cr-Mo合金电沉积机制的影响

采用循环伏安曲线、电化学阻抗谱、扫描电镜、能谱仪等手段,研究了pH值对Ni-Cr-Mo合金电沉积机制的影响。结果表明:当pH值为3.0时,循环伏安曲线的共沉积还原峰最正,电化学阻抗谱的极化电阻最小,Ni-Cr-Mo合金的电沉积最容易发生。当pH值不大于3.0时,Ni-Cr-Mo合金的电沉积受动力学和扩散混合控制;当pH值大于3.0时,Ni-Cr-Mo合金的电沉积受动力学过程控制。随着pH值的增大,Ni-Cr-Mo合金的晶粒尺寸逐渐增大,Cr的质量分数先增大后减小,Ni、Mo的质量分数均先减小后增大。     

不同pH对焦磷酸铵水解的影响

以主成分为焦磷酸铵的水溶性聚磷酸铵为实验原料,设置8.2、6.0、4.0、3.5、3.0、2.5、2.0等7组pH梯度,系统研究了酸度对焦磷酸铵水解的影响。结合一级反应动力学方程与阿累尼乌斯方程进行焦磷酸铵的水解动力学计算,结果表明：经过310 d（第二批260 d）的放置,pH从8.2降低到2.0时焦磷酸铵质量分数从初始态的92.6%依次减少为85.4%、51.2%、50.6%、50.2%、24.3%、12.9%和6.0%。焦磷酸铵在自然温度下的水解速率随着pH的降低而不同程度地加快,服从一级反应机理。pH从8.2降低到2.0时焦磷酸铵的水解速率常数从2.92×10-4~3.43×10-4增加至3.41×10-3~1.47×10-2,二者相差10~40余倍,对应半衰期为50~2 000 d。秋冬与春夏两时段的水解速率差异很大,二者水解速率常数相差1.17~4.32倍,焦磷酸铵的水解活化能为7.5~68.5 kJ/mol。     

pH值对高锰酸钾作阴极的微生物燃料电池阴极电位的影响

构建了一个以葡萄糖水溶液为阳极原料,高锰酸钾为阴极氧化剂的双室微生物燃料电池。考察了MnO_4溶液的pH值对MFC产电性能的影响。结果表明,在pH值不同时,其对MFC的还原电位和MnO_4的还原产物有显著影响。当pH>3时,阴极E°=+1.51V,当pH>11时,E°=+0.56V。研究表明:(1)二氧化锰沉淀是导致阴极极化的主要原因,当阴极电解液流动时可有效抑制二氧化锰的沉淀。(2)根据电池电压曲线图判断,pH值对电池的阴极电位有较大影响,电池电压的变化与阴极电位变化具有很好的一致性,但不会对阳极电位造成影响。(3)pH值对阴极电势的影响符合Nernst方程。     

Effect of pH on microbial hydrogen fermentation

The influence of initial pH of the culture medium on hydrogen production was studied using sucrose solution and a mixed microbial flora from a soybean‐meal silo. Hydrogen production was not observed at pH values of 3.0, 11.0 and 12.0 but low production was observed at pH values 5.0 and 5.5. The pH of the experimental mixture decreased rapidly and produced hydrogen gas within 30 h. Methane was not detected at initial pH values between 6.0 and 10.0. The sucrose degradation efficiency increased as the initial pH value increased from 3.0 to 9.0. The maximum sucrose degradation efficiency of 95% was observed at pH 9.0. The maximum specific production yields of hydrogen, VFAs and alcohols were 126.9 cm³ g^?1 sucrose (pH of 9.0), 0.7 gCOD g^?1 sucrose (pH of 8.0) and 128.7 mgCOD g^?1 sucrose (pH of 9.0), respectively. The relationship between the hydrogen ion concentration and the specific hydrogen production rate has been mathematically described. The best kinetic parameters on the specific hydrogen production rate were K_OH = 1.0 × 10^?7 mol dm^?3 and K_H = 1.1 × 10^?4 mol dm^?3 (r² = 0.86). The maximum specific hydrogen production rate was 37.0 cm³ g^?1 VSS h^?1. © 2002 Society of Chemical Industry