叔丁醇水溶液臭氧氧化的降解过程及反应机理研究

在ＳｔｏｐｐｅｄＦｌｏｗ反应器研究了叔丁醇（ＴＢＡ）水溶液按Ｏ３的降解过程,结果表明,在酸性和中性条件下ＴＢＡ较难被Ｏ３氧化降解,随着ｐＨ增加,ＴＢＡ的臭氧化降解速率加快,探讨了ＴＢＡ的臭氧氧化过程的降解机理。     

Torsional braid analyzer measurements of polymer damping factors

Measurements were made in a torsional braid analyzer (TBA) and a torsional pendulum (TP) on a diglycidyl ether of bisphenol A cured with methaphenylenediamine over a broad temperature range that included the γ transition of this polymer. Based on a comparison of the results from the two instruments, we conclude that (1) the relative shear modulus measured in the TBA differs from the absolute modulus measured in the TP by a multiplicative constant that is independent of temperature in the glassy state; (2) the damping factor measured in the TBA is, at least approximately, equal to the damping factor measured in the TP, contrary to the usual assumption that only relative values are obtained from the TBA; and (3) as a result of (1) and (2), the TBA can be used to determine not only the temperature of a transition but also its activation energy.     

Development of an Efficient G‐Quadruplex‐Stabilised Thrombin‐Binding Aptamer Containing a Three‐Carbon Spacer Molecule

The thrombin‐binding aptamer (TBA), which shows anticoagulant properties, is one of the most studied G‐quadruplex‐forming aptamers. In this study, we investigated the impact of different chemical modifications such as a three‐carbon spacer (spacer‐C₃), unlocked nucleic acid (UNA) and 3′‐amino‐modified UNA (amino‐UNA) on the structural dynamics and stability of TBA. All three modifications were incorporated at three different loop positions (T3, T7, T12) of the TBA G‐quadruplex structure to result in a series of TBA variants and their stability was studied by thermal denaturation; folding was studied by circular dichroism spectroscopy and thrombin clotting time. The results showed that spacer‐C₃ introduction at the T7 loop position (TBA‐SP7) significantly improved stability and thrombin clotting time while maintaining a similar binding affinity as TBA to thrombin. Detailed molecular modelling experiments provided novel insights into the experimental observations, further supporting the efficacy of TBA‐SP7. The results of this study could provide valuable information for future designs of TBA analogues with superior thrombin inhibition properties.     

叔丁醇的复合氧化反应动力学及其降解的研究

在光谱反应器中研究了有机物叔丁醇（ＴＢＡ）在Ｈ２Ｏ２,Ｏ３和Ｏ３／Ｈ２Ｏ２及不同ｐＨ值时的氧化反应动力学及其降解过程。结果表明,ＴＢＡ几乎不被过氧化氢氧化;在酸性及中性条件下,ＴＢＡ较难在臭氧中降解,随着ｐＨ增加,ＴＢＡ的臭氧化速率加快,ＴＢＡ较容易在Ｏ３／Ｈ２Ｏ２中氧化降解。     

Comparison of Various Procedures Employed in the TBA Test of Spanish Edible Vegetable Oils

A comparison of the TBA single extraction procedure in relation to the TBA distillation and TBA heating reflux procedures on Spanish edible vegetable oils was carried out. V/e have emphasized taking up the TBA single extraction procedure to obtain more precise results on the vegetable oils samples. The better correlation (r=0.864) was shown between the single extraction and heating reflux procedures. Mean TBA values obtained by the distillation and heating reflux procedures (heating samples) were higher than those obtained through the single extraction procedure. Samples packed in “tetrabrik” showed TBA values higher than those packed in PVC containers (p<0.01).     

制取无水叔丁醇的精馏工艺优化和对比

无水叔丁醇是一种重要的化工原料,然而在工业生产过程中会与水形成最低共沸物,难以通过简单精馏的方式获得。基于此,本文提出双塔萃取精馏、隔壁塔萃取精馏和反应精馏三种精馏工艺来制取高纯度叔丁醇。在双塔和隔壁塔萃取精馏的优化中,利用Aspen Plus软件模拟该分离过程,以年度总费用（TAC）为目标进行过程优化,得到最佳操作参数。在反应精馏塔中,采用环氧乙烷多股进料的方式,环氧乙烷可与水反应并打破叔丁醇/水的共沸平衡最终制得无水叔丁醇。鉴于反应精馏塔的复杂性,对于反应精馏塔的操作参数进行详细的灵敏度分析以确定反应精馏塔在叔丁醇除水的可行性和潜力。模拟结果表明,与双塔萃取精馏相比,隔壁塔萃取精馏虽然能降低能耗但是也会增加6.51%的TAC,因此隔壁塔萃取精馏并不具有经济性;而反应精馏塔则能降低47.69%的能耗和35.36%的TAC,显现出巨大的应用潜力。     

Preparation of ultrahigh molecular weight syndiotactic poly(vinyl alcohol) microfibrillar fibers by low‐temperature solution polymerization of vinyl pivalate in tertiary butyl alcohol and saponification

Vinyl pivalate (VPi) was solution polymerized in tertiary butyl alcohol (TBA) and in dimethyl sulfoxide (DMSO) with a low chain transfer constant using a low temperature initiator, 2,2′‐azobis(2,4‐ dimethylvaleronitrile) (ADMVN). The effects of polymerization temperature and initiator concentration were investigated in terms of polymerization behavior and molecular structures of poly(vinyl pivalate) (PVPi) and its saponification product poly(vinyl alcohol) (PVA). TBA was absolutely superior to DMSO in increasing the syndiotacticity and molecular weight of PVA. In contrast, TBA was inferior to DMSO in causing conversion to polymer, indicating that the initiation rate of VPi production in TBA was lower than that in DMSO. These effects could be explained by a kinetic order of ADMVN concentration, calculated by the initial rate method. Low‐temperature solution polymerization of VPi in TBA or DMSO by adopting ADMVN proved to be successful in obtaining PVA of ultrahigh molecular weight [maximum number‐average degree of polymerization (P_n): 13,500–17,000] and of high yield (ultimate conversion of VPi into PVPi: 55–83%). In the case of bulk polymerization of VPi at the same conditions, maximum P_n and conversion were 14,500–17,500 and 22–36%, respectively. The P_n and syndiotactic diad content were much higher and the degree of branching was lower with PVA prepared from PVPi polymerized at lower temperatures in TBA. Moreover, PVA from the TBA system was fibrous, with a high degree of orientation of the crystallites, indicating the syndiotactic nature of TBA polymerization. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1992–2003, 2002     

Properties of ultrasonically irradiated human serum lipoproteins

Human serum low density lipoprotein (LDL) and human serum high density lipoprotein (HDL) were treated with ultrasonic irradiation. The immunochemical properties, spectrophotometrical analysis and thiobarbituric acid test (TBA) value of ultrasonically irradiated lipoproteins were examined. The agar gel precipitin reaction of sonicated LDL disappeared as the irradiation time increased. The effects of ultrasonic irradiation upon human serum lipoproteins resulted in a loss of lipids from the sonicated lipoproteins and are increased in TBA value. TBA value of LDL increased in two steps.     

Improving Structural Stability and Anticoagulant Activity of a Thrombin Binding Aptamer by Aromatic Modifications

The thrombin binding aptamer (TBA) is a 15-mer DNA oligonucleotide (5′-GGT TGG TGT GGT TGG-3′), that can form a stable intramolecular antiparallel chair-like G-quadruplex structure. This aptamer shows anticoagulant properties by interacting with one of the two anion binding sites of thrombin, namely the fibrinogen-recognition exosite. Here, we demonstrate that terminal modification of TBA with aromatic fragments such as coumarin, pyrene and perylene diimide (PDI), improves the G-quadruplex stability. The large aromatic surface of these dyes can π-π stack to the G-quadruplex or to each other, thereby stabilizing the aptamer. With respect to the original TBA, monoPDI-functionalized TBA exhibited the most remarkable improvement in melting temperature (ΔT_m≈+18 °C) and displayed enhanced anticoagulant activity.     

Charge-Transfer Interactions Stabilize G-Quadruplex-Forming Thrombin Binding Aptamers and Can Improve Their Anticoagulant Activity

In the search for optimized thrombin binding aptamers (TBAs), we herein describe the synthesis of a library of TBA analogues obtained by end-functionalization with the electron-rich 1,5-dialkoxy naphthalene (DAN) and the electron-deficient 1,8,4,5-naphthalenetetra-carboxylic diimide (NDI) moieties. Indeed, when these G-rich oligonucleotides were folded into the peculiar TBA G-quadruplex (G4) structure, effective donor–acceptor charge transfer interactions between the DAN and NDI residues attached to the extremities of the sequence were induced, providing pseudo-cyclic structures. Alternatively, insertion of NDI groups at both extremities produced TBA analogues stabilized by π–π stacking interactions. All the doubly-modified TBAs were characterized by different biophysical techniques and compared with the analogues carrying only the DAN or NDI residue and unmodified TBA. These modified TBAs exhibited higher nuclease resistance, and their G4 structures were markedly stabilized, as evidenced by increased T_m values compared to TBA. These favorable properties were also associated with improved anticoagulant activity for one DAN/NDI-modified TBA, and for one NDI/NDI-modified TBA. Our results indicated that TBA pseudo-cyclic structuring by ad hoc designed end-functionalization represents an efficient approach to improve the aptamer features, while pre-organizing and stabilizing the G4 structure but allowing sufficient flexibility to the aptamer folding, which is necessary for optimal thrombin recognition.     

Thiobarbituric acid reaction of methyl arachidonate monohydroperoxide isomers

Methyl ester of monohydroperoxy eicosatetraenoic acid (MeHPETE) was prepared from methylene blue sensitized photooxidation products of methyl arachidonate. The thiobarbituric acid (TBA) value of MeHPETE was increased by adding ferrous sulfate to the reaction mixture. A linear relationship existed betweent he TBA value and the concentration of MeHPETE when ferrous sulfate was added. By using high performance liquid chromatography, MeHPETE was separated into 5 fractions whose isomeric compositions were determined by gas chromatography-mass spectrometry. The results of the TBA test for each fraction suggest that all of the MeHPETE isomers are positive to the TBA test. It is concluded that each isomer of HPETE formed by peroxidation of arachidonic acid in a biological system can yield TBA-reacting materials during the test reaction.     

Isobutene hydration over Amberlyst-15 in a slurry reactor

The synthesis of tertiary butyl alcohol (TBA) via isobutene (iB) hydration was studied over Amberlyst-15 sulfonic acid catalyst particles using pure water and aqueous TBA solutions in a bubbling slurry reactor. Preliminary studies to investigate mass transfer effects showed that pore diffusion was present for catalyst particles greater than 165 μm in diameter. Therefore, intrinsic kinetic measurements were made using 90.5 μm catalyst particles and a catalyst loading of 10 kg m⁻³. The kinetic measurements revealed that iB hydration is a pseudo-first-order reaction with an activation energy of 69 kJ mol⁻¹. Isobutene hydration experiments using TBA concentrations in water revealed a hindering effect of TBA, which indicates that separation of TBA formed by iB hydration in three-phase reactors using catalytic distillation is promising from a process design perspective.     

叔丁醇对异丁烯二聚反应选择性的影响

以强酸性阳离子交换树脂为催化剂,在高压釜内考察了加入叔丁醇(TBA)前后异丁烯(IB)二聚反应工艺条件对二异丁烯(DIB)选择性的影响.结果表明.在加入TBA后.降低了IB二聚速率.但提高了DIB选择性.当反应温度为90℃、原料中IB质量分数为17%～20%、TBA质量分数为0.6%、搅拌速率750r/min、反应3.5h后,IB的转化率约为60%,DIB的选择性可达80%左右。     

Thrombin-Binding Aptamer with Inversion of Polarity Sites (IPS): Effect on DNAzyme Activity and Anticoagulant Properties

In this work we examined the properties of thrombin-binding aptamer (TBA) modified by the introduction of inversion of polarity sites (IPS) in order to assess the effect of modification on the activation of TBA to serve as DNAzyme with peroxidase-like activity. Two oligonucleotides were designed to possess one (IPS1) or three (IPS2) inversion sites. TBA typically forms antiparallel G-quadruplexes with two G-tetrads, which exhibits very low DNAzyme peroxidise activity. DNAzyme activity is generally attributed to parallel G-quadruplexes. Hence, inversion of polarity was introduced in the TBA molecule to force the change of G-quadruplex topology. All oligonucleotides were characterized using circular dichroism and UV-Vis melting profiles. Next, the activity of the DNAzymes formed by studied oligonucleotides and hemin was investigated. The enhancement of peroxidase activity was observed when inversion of polarity was introduced. DNAzyme based on IPS2 showed the highest peroxidase activity in the presence of K⁺ or NH₄⁺ ions. This proves that inversion of polarity can be used to convert a low-activity DNAzyme into a DNAzyme with high activity. Since TBA is known for its anticoagulant properties, the relevant experiments with IPS1 and IPS2 oligonucleotides were performed. Both IPS1 and IPS2 retain some anticoagulant activity in comparison to TBA in the reaction with fibrinogen. Additionally, the introduction of inversion of polarity makes these oligonucleotides more resistant to nucleases.     

An Assay Method for Determining the Total Lipid Content of Fish Meat Using a 2-Thiobarbituric Acid Reaction

A method for the determination of the total lipid content in fish meat was established using a 2-thiobarbituric acid (TBA) reaction, which had previously been used for the determination of lipid peroxides in animal tissues. In this method, an unspecific peroxidation of fish oils was created by omitting the addition of antioxidant to the reaction mixture during the TBA reaction, because fish meat is more sensitive to the TBA reaction due to its higher concentration of polyunsaturated fatty acids, especially docosahexaenoic acid and eicosapentaenoic acid, which can easily react artificially with TBA in the absence of an antioxidant in the assay system. As for a practical application of this method, we tried to optimize the assay procedures in the sampling, reaction, and detection steps of this method, and finally proposed a new standard procedure recommended for determining the total lipid content of fish using a TBA reaction. In order to confirm the accuracy of the new procedure, comparative evaluations for the lipid contents of commercially available fish, i.e., chub mackerel (Scomber japonicus) and saury (Cololabis saira) were made between the conventional procedure and the recommended TBA method. The lipid contents obtained by the two methods coincided well with high correlation. This method is relevant for total lipid content analysis of fish meat under restricted laboratory conditions.     

The torsion pendulum in the investigation of polymer

The early history of the use of the torsion pendulum in the investigation of polymers is described together with the development of dynamic mechanical testing at TNO. Examples are listed of studies of structure-property relationships by means of the torsion pendulum. Techniques using supported. Samples are compared with those using unsupported samples, particular attention being paid to the advantages and restrictions of torsional braid analysis (TBA). The comprehensive application of TBA by Professor Gillham is reviewed; a few TBA results are compared with our torsion pendulum measurements. A rheologist's view on the so-called liquid-liquid transition (T_n) in polymer melts, as observed by TBA, is presented.     

An improved 2-thiobarbituric acid (TBA) procedure for the measurement of autoxidation in fish oils

An improved 2-thiobarbituric acid (TBA) method suitable for routine testing of autoxidative changes of fish oil and other polyunsaturated lipids has been developed. Air oxidation of the lipid during the TBA reaction was found to produce misleading results. The air oxidation may be controlled by addition of antioxidants to the reaction system. Other factors causing inconsistent TBA results and methods of prevention are also described. A comparison of peroxide and TBA values in autoxidized menhaden oil is presented.     

Tuning the morphology of SrTiO3 nanocubes and their enhanced electrical conductivity

Strontium titanate (SrTiO₃) nanocubes were prepared via the solvothermal method in an isopropanol-water system, using cetyltrimethylammonium bromide (CTAB) as a capping agent and tert-butylamine (TBA) as a mineralizer. We found that the presence of TBA produced a synergistic effect in the nucleation and growth of SrTiO₃ in the solution, which enabled control over the formation of well-defined cubic particles. X-ray diffraction patterns of SrTiO₃, synthesized with the addition of 1 mol of TBA, showed a perovskite structure with high crystallinity. The presence of specific absorption peaks in the fourier-transform infrared (FTIR) spectrum confirmed the existence of CTAB and TBA on the surface of the particles. Transmission electron microscope (TEM) images showed that the sharp-edged cubic particles had narrow size distributions, and selected area electron diffraction (SAED) patterns indicated a high crystallinity. An increase in electrical conductivity values was found in the bulk samples with regular nanocube particles compared to those of non-regular nanocubes.     

Comparison of methods for determining fatty acid oxidation produced by ultraviolet irradiation

Summary The thiobarbituric acid (TBA) reaction for fatty acid oxidation has been compared with Lundberg and Chipault's method for peroxides, the Kreis test for aldehydes, and with the degree of conjugation, using fatty acid esters exposed to ultraviolet light for various periods. The TBA test paralleled the other methods for methyl linolenate and methyl linoleate but was essentially negative for methyl oleate oxidation. The sensitivity of the TBA test for linolenate was 30–80 times that for linoleate at the same peroxide values. The TBA test appears to be a reliable method of estimating the oxidation products of linolenic and linoleic acids in tissues and other biological material. Supported by a grant from the Atomic Energy Commission.