含氮杂环协助的醛胺缩合反应机理的研究

采用密度泛函理论（DFT）方法研究了在酸性条件下对带有氮杂原子的伯胺与醛的缩合反应机理.研究结果表明,在酸性条件下,碱性更强的杂环氮比羰基氧更容易被质子化,杂环氮作为氢质子桥使缩合反应能垒大大降低,计算得到的反应能量跨度为13.08 kcal/mol.同时,将伯胺上含氮杂环上的N原子调变为P,As原子及改变N原子的位置后缩合反应能垒升高,证实了杂环氮原子协助氢转移的重要性,此理论研究为揭示含氮杂环伯胺与醛的缩合反应机理提供了新的思路与理论依据.     

四氯化碳存在下大孔苯乙烯-二乙烯苯共聚物的后交联反应

对在四氯化碳存在下 ,大孔St DVB共聚物以三氯化铝为催化剂的后交联反应进行了研究 .结果表明 ,起始共聚物的合成条件 ,包括交联剂DVB的用量 ,致孔剂的性质及其与单体的配比 ,对后交联产物的孔结构有重要影响 .以良溶剂甲苯为致孔剂及采用较高的DVB用量 ,所合成的起始共聚物经后交联后 ,比表面积很容易达到或超过 10 0 0m2 /g .一般情况下 ,后交联产物的孔容增加 ,孔径减小 ,孔结构稳定性明显提高 .当起始共聚物的DVB含量较低时 ,后交联反应以四氯化碳的参与为主 ;当DVB含量较高时 ,后交联反应以起始共聚物中固有的悬挂双键的参与为主     

高温水中多产物反应模型的构建及机理研究

建立了高温水中的反应模型并采用密度泛函理论(DFT)对香叶醇在高温水中的反应路径进行了研究. 通过前线轨道分析确定了反应的可能性. 高温水中香叶醇的反应路径与常温水中不同, 从常态下的酸催化反应路径转变为高温水状态下的酸碱共催化路径, 计算所得反应能垒为205.8 kJ/mol. 分别计算分析了高温水环境和周围水分子对反应能垒的影响, 结果表明, 高温水对反应物零点能的影响最大为0.966 kJ/mol, 水分子个数的影响最大可达94.7 kJ/mol. 官能团周围水分子个数变化对反应所产生的的影响大于高温水环境的影响.     

亲水性二苯甲胺树脂制备及用于肽合成研究

通过反相悬浮共聚合成了含酯基的聚丙烯酰胺树脂, 再经乙二胺取代和两步缩合反应引入二苯甲胺功能基团。讨论了反应条件对各步反应的影响。测定了该载体与几种保护氨基酸的缩合率并合成了模型肽。缩合率和模型肽的纯度都令人满意。     

锰配合物催化CO2加氢生成甲酸的理论研究

采用密度泛函理论(DFT)对锰配合物催化二氧化碳加氢生成甲酸的反应进行了理论研究. 整个催化循环主要包括氢气活化和二氧化碳氢化2个阶段. 计算结果表明, 甲酸的参与明显降低了氢气活化的反应能垒; 二氧化碳的氢化过程遵循外层机理并且氢转移是分步进行的, 决速步骤为氢负离子的转移过程, 自由能垒为21.0 kJ/mol. 对配合物中硫原子上的取代基R进行了调变, 研究结果表明, 当R为吸电子基团时能降低氢气裂解和二氧化碳氢化过程中质子转移的能垒, 而当R为推电子基团时有利于氢负离子的转移,当R=CF₃时整个反应的能量跨度(80.4 kJ/mol)最小.     

交联聚内酯血管支架在动物兔模型中的应用

首先通过左旋丙交酯(L-Lactide)、乙交酯(Glycolide)等合成了可发生交联反应的PLG9010预聚体(crosslinkable PLG9010),使用光引发剂诱发交联反应制备交联型PLG9010(crosslinked PLG9010),研究了辐照时间对于交联聚内酯性能的影响。研究发现,随着辐照时间的增加,交联产物的凝胶含量、力学性能呈上升趋势,在光引发剂含量为1.0%(wt),辐照时间20min条件下,交联型PLG9010的凝胶含量达到97.5%。利用飞秒激光切割技术将交联型PLG9010管材制备成血管支架,考察其支撑力、静态降解行为以及动物实验有效性。25℃下存储6个月时,支架的径向支撑力为88.65k Pa。37℃静态降解系统中,交联型PLG9010的凝胶含量在6个月时仍能保持在88.9%。采用兔为动物实验模型植入支架,支架植入后,明显观察到支架扩张,血管开通,且未对植入部位的血管造成损伤。术后2h时间节点,通过解剖观察,支架在植入部位未发生移位,植入处血管保持畅通。     

聚氯乙烯的热可逆共价交联

利用环戊二烯 (CPD)在常温下自动二聚形成双环戊二烯 (DCPD)、在高温下DCPD又可解聚成CDD的热可逆Diels Alder反应 ,合成了DCPD二羧酸衍生物 ,并将其引作聚氯乙烯 (PVC)的共价交联 ,研究了交联剂种类和用量对交联程度、力学性能和流动特性的影响及交联产物的热可逆转化行为 ,制得了力学性能和耐热性均有所提高的热可逆共价交联PVC     

(NBR/PVC)/CuSO_4复合材料中配位交联反应的研究

采用差示扫描量热法(DSC)和傅立叶转换红外光谱(FT-IR)对丁腈橡胶/聚氯乙烯合金/无水硫酸铜((NBR/PVC)/CuSO4)混合物的配位交联反应进行了研究.结果表明,(NBR/PVC)/CuSO4共混物在升温过程中出现两个放热峰,分别归因于腈基(—CN)和CuSO4之间的配位交联反应和体系中NBR/PVC的自交联反应.通过对共混物配位交联反应动力学参数的计算发现,混合物中CuSO4含量的多少并未对体系配位交联反应的进行产生影响.同时共混物中PVC的存在促进了配位交联反应的进行,降低了铜离子(Cu2+)与—CN之间配位交联反应的表观活化能Ea.     

酸性分子筛催化乙烯二聚反应

应用密度泛函理论(DFT), 采用5T簇模型来模拟分子筛催化剂的酸性位, 在B3LYP/6-311+G(3df, 2p)的条件下通过理论计算研究了乙烯在酸性分子筛上的二聚反应. 对反应各驻点进行了全局优化, 经过零点能校正后, 计算得出乙烯二聚反应的活化能. 研究表明, 乙烯在分子筛上的二聚反应分三步进行: 单个乙烯分子化学吸附→第二个乙烯分子的物理吸附→两乙烯分子二聚反应. 乙烯化学吸附生成的烷氧化合物与物理吸附的乙烯分子发生二聚反应生成新的C—C键同时生成新的烷氧化合物. 计算得到的乙烯化学吸附和二聚反应的反应能垒分别为108和149 kJ·mol-1. 反应的逆过程也就是1-丁烯在酸性分子筛表面的1-丁基烷氧化合物发生β分裂反应, 计算所得相应的1-丁烯β分裂反应的能垒为217 kJ·mol-1, 远高于相应的乙烯二聚反应能垒. 此外还进一步研究了所用基组对计算结果的影响.     

聚对苯二甲酸丁二醇酯二聚体热降解机理的理论研究

采用密度泛函理论(DFT)方法 M06-2X/6-311G(d)研究了聚对苯二甲酸丁二醇酯(PBT)二聚体的热降解机理,对PBT二聚体热解过程设计了八条可能反应路径,计算了每条反应路径的各基元反应步的热力学及动力学参数。计算结果表明,在PBT初始热解过程中,主链发生协同反应的反应能垒明显低于自由基反应的能垒,因此,通过协同反应生成的对苯二甲酸、对苯二甲酸单丁烯酯、对苯二甲酸二丁烯酯和二对苯二甲酸-1,4-丁二酯是PBT初始热解主要产物。主链通过六元环过渡态进行的协同反应的反应能垒低于通过四元环过渡态的,PBT主链的断裂主要通过六元环过渡态的协同反应而进行。此外,还讨论了PBT主要产物的二次降解反应,研究发现,在二次降解反应过程中主要以协同反应为主,生成1,3-丁二烯、四氢呋喃、苯、CO₂、苯甲酸等主要产物。     

PROTOPORPHYRIN-SENSITIZED PHOTODYNAMIC MODIFICATION OF PROTEINS IN ISOLATED HUMAN RED BLOOD CELL MEMBRANES

Abstract— The photodynamic action of protoporphyrin on red cell ghosts is reflected by extensive cross-linking of membrane proteins to very high molecular weight protein aggregates. This process was studied with sepharose gel chromatography and sodium dodecyl sulphate polyacrylamide gel electrophoresis.
Most sensitive to this photodynamic effect are spectrin and band 2. 1, 2. 2, 2.3 and 4.1. polypeptides, which are cross-linked after very brief illumination periods, with a concomitant loss of spectrin-associated ATPase activity. Band 6 protein, representing the monomeric form of glyceraldehyde-3-phosphate dehydrogenase, is also very sensitive to protoporphyrin-induced cross-linking. The enzymatic activity decreased even faster than the amount of band 6 polypeptides, suggesting that modification(s) of the enzyme other than cross-linking, possibly by rapid photooxidation of a thiol group, may be responsible for inactivation.
Extracted and purified spectrin was cross-linked with about the same velocity as membrane-bound spectrin, reinforcing our previously drawn conclusion that membrane lipids are not involved in the cross-linking reaction. Eluted band 6 polypeptides on the other hand exhibited a relatively fast photo-oxidative modification but a much slower cross-linking to dimers and tetramers. This suggests that the membrane structure, e.g. the spectrin matrix may play an essential role in the incorporation of membrane-bound band 6 polypeptides in the high molecular weight cross-linked complex.     

Gamma radiation synthesis of rapid swelling superporous polyacrylamide hydrogels

In this report a simple route for gamma radiation induced synthesis of superporous hydrogel (SPH) is described. Conventional SPH synthesis requires foaming and cross-linking reactions to take place simultaneously. However, in radiation synthesis it is difficult to introduce foaming during the cross-linking reactions. In order to overcome this limitation, the foaming and radiation cross-linking reactions were decoupled and carried out in two stages. The polyacrylamide SPH synthesized by this approach has very fast swelling kinetics compared to the non-porous hydrogel.     

Gelation in aqueous solutions of carboxylated polyacrylamide in the presence of chromium(III) acetate,studied by oscillation rheometry

The time dependences of the elastic moduli and loss moduli of aqueous solutions of Alcoflood-254S carboxylated polyacrylamide, containing chromium(III) acetate as a cross-linking agent, were studied by oscillation rheometry in the temperature interval 50–80°?. The gel time increases with a decrease in the temperature, as well as in the concentration of the polymer and cross-linking agent. The elastic properties of hydrogels at the moment of the onset of their formation, characterizing the concentration of cross-links between the macromolecules, are due to the polymer concentration in the solution and are independent of the chromium(III) acetate concentration and temperature. Presumably, equal degree of conversion in the reaction between carboxylate groups of the polymer and chromium(III) ion, leading to cross-linking of macromolecules of carboxylated polyacrylamide, allows determination of the kinetic parameters of the gelation from data obtained by oscillation rheometry under nonisothermal conditions.     

Identification of opioid-binding materials of rat brain

Digitonin-solubilized opioid receptors from rat brain were purified with an affinity resin, AH-Sepharose coupled with [D-Ala2, D-Leu5]enkephalin (DADLE). Radioreceptor binding assay showed that the purified materials had specific opioid-binding activity of 310 pmol/mg protein on DADLE binding. Analyses by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS-PAGE) revealed that the materials were rich in two polypeptides; the major component had a molecular weight of 62000-64000. To establish the materials responsible for binding opiates, the purified materials were cross-linked with 125I-labeled beta-endorphin using bis[2-(succinimidooxycarbonyloxy)-ethyl]sulfone as a cross-linker. The molecular weight of 62000-64000, the major band of the purified materials on SDS-PAGE, agreed closely with that determined by the cross-linking experiment. The results suggest that the purified materials contained opioid-binding materials (opioid receptors).     

Separation system for fractionation of polyacrylamide by gel permeation chromatography

Samples of polyacrylamide were prepared by radical polymerisation of monomer in aqueous solution. Fractions of polyacrylamide were produced by a fractional precipitation technique with methanol as non-solvent. Molecular weights of the polyacrylamides were determined by solution viscometry. Analytical gel permeation chromatography (GPC) of the polyacrylamide samples and fractions was performed with porous silicas having a chemically bonded aminopropyl phase and with an eluent consisting of formamide-water (1:5). The GPC retention results indicated the successful separation of polyacrylamides having molecular weights in the range 10⁴–10⁶. GPC of polyacrylamide with this separation system appeared to be dominated by a steric exclusion mechanism.     

Retention Behaviors of Hydrophobically Associating Polyacrylamide Prepared via Inverse Microemulsion Polymerization Through Porous Media

The retention behavior of hydrophobically associative polyacrylamide (HAPAM) with homogeneous composition in porous media was investigated. The results showed that HAPAM could exhibit different retention behavior, compared to PAM due to the existence of hydrophobic association group in HAPAM molecular frame. The critical association concentration could also be reflected by the curves between HAPAM concentration and retention amount. The retention amount of HAPAM was higher than that of polyacrylamide (PAM) and was smaller than the absorption amount of HAPAM. The retention mechanism was mainly controlled by adsorption mechanism.     

STRUCTURE AND STABILITY OF γ-CRYSTALLINS-V. COVALENT AND NONCOVALENT PROTEIN-PROTEIN INTERACTIONS IN PHOTOSENSITIZED REACTIONS

Abstract— Irradiation of γ-crystallins with 300 nm light or with the photosensitizers riboflavin or methylene blue (MB) leads to intermolecular cross-linking and insolubilization. Sodium dodecyl sulfate polyacrylamide gel electrophoresis studies reveal that these cross-links are composed of nondisulfide covalent bonds. The water-insoluble phase is stabilized by noncovalent forces, as denaturants readily dissolve it. High-performance liquid chromatography and electrophoresis results further indicate that the higher multimers are part of this water-insoluble fraction only, with the exception of MB-sensitized reactions, which are also able to produce a water-soluble, high-molecular-weight protein of at least 1 million. Labeling the external sulfhydryl groups with iodoacetamide does not prevent the photoreac-tions; however, a reducing agent such as dithiothreitol does. A mechanism involving initial oxidation and interaction of sulfhydryl groups (forming an intramolecular disulfide) buried within the protein as a necessary precursor to polymerization and precipitation has been proposed in the preceding paper. The present study provides support for this mechanism.     

Crosslinked polyacrylamide-hydrazide (paah) as matrix for the gel entrapment of cells and enzymes - an overview

The development and use of a gel entrapment technique designed for the immobilization of viable, sensitive cells is described. The method is based on the controlled chemical cross-linking of prepolymerized, linear polyacrylamide partially substituted with acylhydrazide groups, by glyoxal. The methodology, applications and advantages of this technique for the immobilization of cells and enzymes by gel entrapment are reviewed.     

Caracterisation physico-chimique de polyacrylamides utilises comme agents floculants—I. Etude en solution

The physicochemical behaviour of flocculating agents (polyacrylamide and copolymers with acrylic acid) has been investigated. In aqueous solution after elimination of insoluble fractions by ultracentrifugation, light scattering shows the presence of molecular aggregates. The more important is the ionic character of macromolecules in solution, the more numerous are aggregates. By submitting polymer solutions to mechanical stress, the molecular weight decreases; the mechanism of chain-breaking is radical.     

正负离子和表面活性剂对水解聚丙烯酰胺分子线团尺寸的影响及其作用机理

采用动态光散射(DLS)方法,研究了无机电解质正离子与负离子对部分水解聚丙烯酰胺(HPAM)分子线团尺寸的影响,也研究了阴离子型表面活性剂与非离子型表面活性剂对HPAM分子线团尺寸的影响.结果表明,无机电解质负离子对HPAM分子尺寸(分子流体力学直径(Dh))影响较小,而无机电解质正离子对Dh的影响较大,且影响程度随正离子浓度增大而减小.Ca2+、Mg2+、K+和Na+对Dh的作用强弱顺序为Mg2+>Ca2+>Na+>K+.当向聚合物溶液中加入阴离子型表面活性剂时,随表面活性剂浓度增大,Dh先减小,后增大,再减小.此外,由于强烈的静电斥力作用,阴离子型表面活性剂分子在聚合物分子表面吸附较弱,难形成"表面活性剂-聚合物"络合物,而非离子型表面活性剂会以类似于胶束聚集体的形式吸附在聚合物分子链上,形成"表面活性剂-聚合物"络合物,结果造成Dh随表面活性剂浓度增加而逐渐增大.