β-环糊精黄原酸酯引发的RAFT聚合用于β-环糊精改性

碱性条件下β-环糊精(β-CyD)与二硫化碳反应生成黄原酸盐,随后与α-溴丁酸甲酯反应制得β-环糊精黄原酸酯,并以此为可逆加成-断裂链转移聚合(RAFT)的链转移剂,制备了3种不同接枝链长的共聚物β-环糊精-聚(N,N-二甲基丙烯酰胺)(β-CyD-PDMA).用核磁共振对β-环糊精黄原酸酯及其接枝共聚物进行了结构表征,考察了β-CyD-PDMA水溶液的黏度、表面张力随接枝链长的变化.通过圆二色谱研究了分子结构的不对称性.使用高分辨透射电镜(HRTEM)、动态光散射(DLS)研究了β-CyD-PDMA在水溶液中的自组装行为.结果表明:β-环糊精上3个6位羟基参与了黄原酸化反应,生成的共聚物为不对称的皇冠状结构;β-CyD-PDMA分子量分布较窄,表现出很好的可控活性聚合特征;接枝共聚物可以进行类胶束聚集,而含有较长PDMA链的共聚物在低浓度下自组装形成直径为280 nm的胶束结构,在高浓度下形成6 nm的新聚集结构.     

聚乙二醇-聚谷氨酸-聚丙氨酸三嵌段共聚物的合成及其胶束的pH-响应性药物控制释放

通过大分子引发剂ω-胺基-α-甲氧基聚乙二醇引发N-羧基-α-氨基环内酸酐开环聚合和酸性水解制备了一种具有pH-响应性的三嵌段共聚物聚乙二醇-聚谷氨酸-聚丙氨酸(mPEG-PLGA-PLAA).通过核磁共振、ζ-电势、动态光散射、电子显微镜等手段表征了此类三嵌段共聚物的自组装过程及所形成胶束的pH-响应性.使用圆二色谱和红外光谱,分析了胶束结构随环境pH值转变过程中聚氨基酸链段二级结构的变化.以阿霉素作为模型药物,研究了三嵌段共聚物的载药能力和在不同pH条件下的药物释放能力.在碱性条件下,PLGA链段去质子化,链段从疏水性变为亲水性,胶束中间层由于水合作用变得松散,药物释放速率增加;在酸性条件下,PLGA链段质子化,不带电荷,与阿霉素药物分子间的静电相互作用消失.同时,PLGA链段α-螺旋含量增加,形成由链内氢键维持的刚性棒状结构,将链段周围包埋的药物分子"挤出",加速了药物的释放.     

新颖光控Dex-H交联胶束药物释放体系的制备及协同抗肿瘤性能

合成了一种基于血红素中双键交联的葡聚糖(Dex)载药(5-氟尿嘧啶)胶束(Dex-H交联胶束).接枝在葡聚糖上的血红素不仅可以用作光控开关控制5-氟尿嘧啶在定点部位的快速释放,而且可以同时在光照下作为光动力学疗法的光敏剂产生单线态氧,实现协同抗肿瘤作用.交联后的胶束具有良好生物相容性,同时,稳定性也相应增强,高度稀释后仍能保持稳定,有望在体内安全运输.采用3-(4,5-二甲基噻唑-2)-2,5-二甲苯基四氨唑溴盐(MTT)和荧光显微镜观察发现,激光照射下载药交联胶束表现出高效的抗癌效果,具有协同抗肿瘤作用.     

交联聚天冬氨酸基聚离子胶束的制备与表征

通过胺端基聚乙二醇(CH3O-PEG-NH2)开环聚琥珀酰亚胺(PSI), 进一步碱解和胺解制备了聚乙二醇接枝聚天冬氨酸(PEG-g-PAsp)和聚乙二醇接枝聚乙二胺基天冬酰胺(PEG-g-PDEA)两种聚天冬氨酸衍生物. 利用它们之间的静电相互作用, 在磷酸缓冲液中形成了以PEG为壳、聚天冬氨酸复合物为核的聚离子胶束. 研究发现, 该聚离子胶束粒子呈球形, 粒径约为70 nm, 且粒径分布较窄. 然而, 体系的稳定性受溶液的pH和盐离子强度影响较大. 通过戊二醛交联PEG-g-PDEA中的伯胺可以有效提高该聚离子胶束对pH和盐离子强度的稳定性.     

双亲水性超支化接枝共聚物的pH响应性药物释放

首先利用阳离子开环聚合合成了超支化聚缩水甘油醚（HPG）,然后通过酯化反应制备了低接枝率的大分子引发剂HPG-Br,并进一步引发甲基丙烯酸-2-（N,N-二甲氨基）乙酯（DMAEMA）单体的原子转移自由基聚合,合成了低接枝率的双亲水性超支化接枝共聚物HPG-g-PDMAEMA,用1HNMR和GPC对聚合物结构进行了表征.并采用芘荧光探针法,HNMR和DLS研究了HPG-g-PDMAEMA在不同pH水溶液中的组装行为.以1香豆素102为模型药物研究了HPG-g-PDMAEMA聚合物在不同pH条件下的药物释放行为,发现在pH连续振荡刺激下HPG-g-PDMAEMA聚合物胶束对药物分子能实现部分＂可逆＂的释放和再包载.     

聚苯乙烯-丙烯酸嵌段共聚物在不同pH值和Ca2+浓度下的胶束行为

近年来, 对具有纳米尺寸的聚合物自组装结构的研究日益增多. 其中, 嵌段共聚物在选择性溶剂中的胶束行为研究得最为广泛和深入[1~5]. 纳米胶束表现出诸多常规尺寸材料所不具备的特殊性能, 在材料化学、生物医学以及环境科学等领域有广阔的应用前景. Webber等[6]对聚丙烯酸和聚苯乙烯接枝共聚物的研究发现, 聚合物的接枝率和聚合物浓度以及溶液离子强度对胶束结构有影响; Eisenberg等[1,7]对不同嵌段比例的苯乙烯-丙烯酸嵌段共聚物的自组装行为进行研究发现, 不同嵌段比例所对应的胶束结构不同. 胶束形成的环境对胶束的形成与稳定性的影响是人们研究的重点. 本文报道了聚苯乙烯-丙烯酸嵌段共聚物在水中的胶束行为, 着重讨论了溶液pH值和钙离子浓度对聚丙烯酸链段相互作用的影响.     

蠕虫状聚离子复合型胶束的合成、组装和胶体稳定性

采用开环聚合方法制备了嵌段共聚物聚乙二醇-聚乙烯亚胺(PEG-b-PEI), 通过静电组装方法使其与质粒DNA(pDNA)在溶液中自发构筑成蠕虫状聚离子复合型胶束(PICmicelle), 利用原子力显微镜、 动态光散射、 Zeta电势和凝胶电泳等方法研究了血液或细胞间质中各种因素对胶束稳定性的影响. 结果表明, 在蠕虫状聚离子复合型胶束中, PEI和pDNA通过静电吸引构成疏水性内核, 而亲水性的PEG分子作为保护型外壳包裹在内核的表面. 在保持PEG链段长度不变的前提下, 增加PEI链段长度可明显增强PEI与pDNA的静电结合力, 有效地防止了NaCl对胶体结构的破坏, 而且有助于抑制阴离子的取代. 但增加PEI链段长度会导致胶束表面PEG分子含量的降低, 不利于胶束抵抗蛋白质的吸附和DNA酶的降解. 因此合理地调整PEG-b-PEI分子的结构, 对于获得高效、 安全和稳定的蠕虫状聚离子胶束具有重要意义.     

离子液体作为功能单体制备溶菌酶分子印迹复合膜的研究

以1-乙烯基-3-乙酸乙酯咪唑氯离子液体为功能单体,以再生纤维素膜为基膜,采用温和的表面ATRP接枝聚合技术在水溶液中制备了溶菌酶分子印迹膜.通过紫外-可见光谱分析了离子液体与模板分子的作用力,讨论了功能单体1-乙烯基-3-乙酸乙酯咪唑氯用量对印迹复合膜性能的影响,研究了分子印迹复合膜对溶菌酶模板分子及其结构类似物的吸附行为和选择性识别特性.结果表明,以1-乙烯基-3-乙酸乙酯咪唑氯离子液体作为功能单体的溶菌酶分子印迹膜能够从结构类似物混合体系中选择性分离富集溶菌酶,且具有很好的稳定性和可再生性能.     

表面张力法研究温敏性接枝共聚物的微胶束化行为

用表面张力法研究了以水溶性可生物降解的葡聚糖为主链 ,具有温敏相变特性的聚 (N 异丙基丙烯酰胺 )为接枝链的葡聚糖 接枝 聚 (N 异丙基丙烯酰胺 ) (Dextran g PNIPAM)共聚物在水溶液中的胶束化行为 .研究结果表明Dextran g PNIPAM体系的微胶束化行为与共聚物结构和溶液体系的温度密切相关 ,接枝共聚物中PNIPAM含量越大 ,水溶液体系的温度越高 ,形成胶束的临界胶束浓度 (CMC)越小 .特别值得指出的是 ,无论水溶液的温度是否高于PNIPAM接枝链段的相变温度 (LCST) ,即PNIPAM链段由亲水性转变为疏水性的温度 ,Dextran g PNIPAM均呈现一个临界胶束浓度大 ,对该现象给予了解释 .     

单分子胶束的制备及应用研究进展

单分子胶束由单个分子构成且有核-壳结构的胶束,这种独特的结构,使其显示出优异的稳定性,在稀释的条件下,不会发生解离。单分子胶束因其在复杂多变的微环境中具有良好的热力学稳定性和尺寸分布均匀性,使得单分子胶束在药物运输、靶向释放、染料去除、荧光标记、无机纳米颗粒模板的制备、能量收集和储存等方面都有重要应用。本文从不同聚合物结构及功能方向,综述了单分子胶束制备及应用的研究进展。     

Unfolding and refolding details of lysozyme in the presence of β-casein micelles

In this work, we selected a small globular protein, lysozyme, to study how it unfolds and refolds in the presence of micelles composed of the unstructured β-casein proteins by using microcalorimetry and circular dichroism spectroscopy. It was found that a partially unfolded structure of lysozyme starts to form when the β-casein/lysozyme molar ratio is above 0.7, and the structure forms exclusively when the β-casein/lysozyme molar ratio is above 1.6. This partially unfolded state of lysozyme loses most of its tertiary structure and after heating, the denatured lysozyme molecules are trapped in the charged coatings of β-casein micelles and cannot refold upon cooling. The thus obtained protein complex can be viewed as a kind of special polyelectrolyte complex micelle. The net charge ratios of the two proteins and the ionic strength of the dispersions can significantly modulate the electrostatic and hydrophobic interactions between the two proteins. Our present work may have implications for the nanoparticle protein engineering therapy in the biomedicine field and may provide a better understanding of the principles governing the protein-protein interactions. Besides, the heating-cooling-reheating procedure employed in this work can also be used to study the unfolding and refolding details of the target protein in other protein-protein, protein-polymer and protein-small solute systems.     

DSB显著提高羧酸盐驱油体系抗钙镁离子能力的研究

测定了工业品级的天然混合长链烷基羧酸盐(SDC)以及与3-(N,N-二甲基十二烷基胺)-2-羟基-丙磺酸(DSB)复配驱油体系的界面张力(ITFmin), 分别得出其抗钙镁离子的能力为400和5000 mg/L. 选择试剂级十二烷基羧酸钠与DSB复配, 测定了不同配比溶液的表面张力值和临界胶束浓度cmc, 结合长链烷基脂肪酸与钙离子的溶度积Ksp, 分析了对不溶性长链烷基羧酸盐形成的影响. 根据现场驱油体系配方, 计算了两者在溶液中的摩尔配比为4:1时的十二烷基羧酸盐在胶束中的摩尔分数xm1为0.51, 相互作用参数βm值为-3.11, 反映了两者有较强的相互作用. 采用量子化学方法, 对由1个十二烷基羧酸分子、1个DSB分子及1个二价钙离子组成的模型复合物进行了能量计算和电荷分布计算, 得出在长链烷基羧酸盐和DSB两者混合胶束的界面层中存在负电荷空穴, 提出二价金属离子被络合的模型, 合理地解释了实验事实.     

Protonation of the acidic residues in the transmembrane cation-binding sites of the ca(2+) pump

The ionization states of the acidic residues around the Ca2+-binding sites of sarcoplasmic reticulum Ca2+ ATPase are studied by continuum electrostatic calculations and all-atom molecular dynamics simulations with explicit solvent and phospholipids. The two methods consistently indicate that Glu58 and Glu908 are protonated at neutral pH. The Ca2+ coordination and the H-bonds formed by the protonation of Glu58 and Glu908 are stable in an MD simulation, whereas the H-bonds are disrupted and the Ca2+ coordination geometry is severely altered in another simulation treating these residues unprotonated. The results clearly indicate that the H-bonds formed by protonation of Glu58 and Glu908 provide extra stability for the Ca2+-binding sites of Ca2+ ATPase.     

Mixed micellization between natural and synthetic block copolymers: β-casein and Lutrol F-127

Amphiphilic block copolymers and mixtures of amphiphiles find broad applications in numerous technologies, including pharma, food, cosmetic and detergency. Here we report on the interactions between a biological charged diblock copolymer, β-casein, and a synthetic uncharged triblock copolymer, Lutrol F-127 (EO(101)PO(56)EO(101)), on their mixed micellization characteristics and the micelles' structure and morphology. Isothermal titration calorimetry (ITC) experiments indicate that mixed micelles form when Lutrol is added to monomeric as well as to assembled β-casein. The main driving force for the mixed micellization is the hydrophobic interactions. Above β-casein CMC, strong perturbations caused by penetration of the hydrophobic oxypropylene sections of Lutrol into the protein micellar core lead to disintegration of the micelles and reformation of mixed Lutrol/β-casein micelles. The negative enthalpy of micelle formation (ΔH) and cooperativity increase with raising β-casein concentration in solution. ζ-potential measurements show that Lutrol interacts with the protein micelles to form mixed micelles even below its critical micellization temperature (CMT). They further indicate that Lutrol effectively masks the protein charges, probably by forming a coating layer of the ethyleneoxide rich chains. Small-angle X-ray scattering (SAXS) and cryogenic-transmission electron microscopy (cryo-TEM) indicate relatively small changes in the oblate micellar shape, but do show swelling along the small axis of β-casein micelles in the presence of Lutrol, thereby confirming the formation of mixed micelles.     

On the binding of calcium by micelles composed of carboxy-modified pluronics measured by means of differential potentiometric titration and modeled with a self-consistent-field theory

We perform differential potentiometric titration measurements for the binding of Ca2+ ions to micelles composed of the carboxylic acid end-standing Pluronic P85 block copolymer (i.e., CAE-85 (COOH-(EO)26-(PO)39-(EO)26-COOH)). Two different ion-selective electrodes (ISEs) are used to detect the free calcium concentration; the first ISE is an indicator electrode, and the second is a reference electrode. The titration is done by adding the block copolymers to a known solution of Ca2+ at neutral pH and high enough temperature (above the critical micellization temperature CMT) and various amount of added monovalent salt. By measuring the difference in the electromotive force between the two ISEs, the amount of Ca2+ that is bound by the micelles is calculated. This is then used to determine the binding constant of Ca2+ with the micelles, which is a missing parameter needed to perform molecular realistic self-consistent-field (SCF) calculations. It turns out that the micelles from block copolymer CAE-85 bind Ca2+ ions both electrostatically and specifically. The specific binding between Ca2+ and carboxylic groups in the corona of the micelles is modeled through the reaction equilibrium -COOCa+ <==> -COO- + Ca2+ with pKCa = 1.7 +/- 0.06.     

二元阴离子型丙烯酰胺共聚物在二价金属离子存在下相分离行为的研究

水溶性丙烯酰胺类共聚物 ,作为粘度改性剂 ,在工业上已得到广泛应用 .特别近年来 ,它们大量应用于石油工业强化采油技术 ,引起了人们很大的重视[1] .目前 ,这类用途的聚合物 ,主要在聚丙烯酰胺结构中 ,引入阴离子组分和不断增高产物分子量的方法 ,以提高聚合物溶液粘度和增粘效果 ,然而 ,在二价金属离子 (如Ｃａ2 + ,Ｍｇ2 + 等 )存在下 ,羧酸阴离子型丙烯酰胺类共聚物很容易络合发生沉淀 ,从而失去增粘作用[2 ] .同时这类聚合物中酰胺基不稳定 ,易发生水解反应转化为羧酸基 ,并随温度升高而加剧[3 ] ,因此在温度较高的应用条件下 ,二价金属…     

Structure of cationized glycine, gly.m (m = be, mg, ca, sr, ba), in the gas phase: intrinsic effect of cation size on zwitterion stability

Interactions between divalent metal ions and biomolecules are common both in solution and in the gas phase. Here, the intrinsic effect of divalent alkaline earth metal ions (Be, Mg, Ca, Sr, Ba) on the structure of glycine in the absence of solvent is examined. Results from both density functional and Moller-Plesset theories indicate that for all metal ions except beryllium, the salt-bridge form of the ion, in which glycine is a zwitterion, is between 5 and 12 kcal/mol more stable than the charge-solvated structure in which glycine is in its neutral form. For beryllium, the charge-solvated structure is 5-8 kcal/mol more stable than the salt-bridge structure. Thus, there is a dramatic change in the structure of glycine with increased metal cation size. Using a Hartree-Fock-based partitioning method, the interaction between the metal ion and glycine is separated into electrostatic, charge transfer and deformation components. The charge transfer interactions are more important for stabilizing the charge-solvated structure of glycine with beryllium relative to magnesium. In contrast, the difference in stability between the charge-solvated and salt-bridge structure for magnesium is mostly due to electrostatic interactions that favor formation of the salt-bridge structure. These results indicate that divalent metal ions dramatically influence the structure of this simplest amino acid in the gas phase.     

Salt effects on solute exchange in sodium dodecyl sulfate micelles

We describe the influence of sodium chloride on the rate of solute exchange in aqueous SDS micelles for a water-insoluble solute, a pyrene-containing triglyceride 1. The initially prepared solutions contained a small fraction of micelles containing two molecules of 1 and a large excess of empty micelles. These solutions showed a measurable excimer emission (of intensity I(E)) that was stable for days to weeks in the absence of added salt. Following additions of salt, I(E) decayed exponentially (rate constant, k(obs)) accompanied by an increase in pyrene monomer emission. Values of k(obs) increased strongly with ionic strength (k(obs) similar [Na(+)](4)). There was no contribution of the empty micelle concentration beyond its contribution to the sodium ion concentration. We conclude that the solute exchange involves spontaneous fragmentation of the SDS micelles into two submicelles, each bearing a molecule of 1, which then grow back to normal micelles through condensation of SDS monomers. We propose a model for the fragmentation process in which large amplitude surface fluctuations "pinch off" a subunit that becomes a submicelle. These fluctuations bring sulfate headgroups into close proximity. Fluctuations leading to fission become important only in the presence of sufficient counterion concentration to reduce the electrostatic repulsion between neighboring headgroups.     

Release of lysozyme from the branched polyelectrolyte-lysozyme complexation

On the basis of the discretely charged sphere model of lysozyme, the release behavior of lysozyme from the branched polyelectrolyte-lysozyme complexation is investigated by adding salt and changing the pH values of the solution. It is found that, with the increase of the salt ionic strength of the solution, the lysozymes are gradually released from the oppositely charged polyelectrolyte as a result of the screening of electrostatic attraction between the two ionic species by adding the salt. Interestingly, there exists a critical salt ionic strength at which all proteins are released from the branched polyelectrolyte, and the polyelectrolyte-protein complexation is broken completely. Beyond the critical value, the increase of the salt ionic strength causes self-association of the proteins released from the branched polyelectrolyte-protein complexation. The self-association of the protein is detrimental in biological systems. By calculating the second virial coefficient, we found that the optimal salt content for the dispersion of proteins coincides with the critical ionic strength, because the second virial coefficient reaches its maximum at the critical ionic strength. Similarly, increasing the pH value of the solution can also release the lysozymes from the polyelectrolyte, because the increase of pH value of the solution changes the charge distribution and net charge of the lysozyme, weakens the attraction between lysozymes mediated by polyelectrolyte, and finally leads to the dissolution of the complexation of branched polyelectrolyte with lysozymes in strong alkaline solution. In addition, by exploring the effect of architecture of the polyelectrolyte on the release behavior of proteins, we found that it is more difficult to release proteins from the branched polyelectrolyte than from the linear polyelectrolyte.     

Effect of size, proteic composition, and heat treatment on the colloidal stability of proteolyzed bovine casein micelles

The casein micelles of reconstituted nonfat milk that have been fractionated by controlled pore glass chromatography showed a relationship between their size and their proteic composition: The fractions containing the smaller particles were richer in κ-casein than the fractions containing the bigger ones, in accordance with the casein micelle model of submicelles. The initial aggregation rate of micelles of different sizes, partially proteolyzed with chymosin (para-casein micelles), was measured in conditions of enzyme excess in which aggregation is the rate-limiting step of enzymatic coagulation, showing higher rates for the smaller micelles with the production of less compact para-casein micelle networks. This behavior could be explained in terms of electrostatic and steric colloidal stabilization due to their lower negative net charge and size and to a higher surface density of hydrophobic “patches” of proteolyzed κ-casein related to a higher probability of effective collisions between particles. Differences in the β-casein content did not seem to affect the initial aggregation rate of the micelles. On the contrary, the modifications of the micelle surface by heating affected the colloidal stability of the hydrolyzed micelles in different ways. The denaturation of the whey proteins and the formation of covalent complexes with κ-casein modify the micelle surface, increasing specially the steric stabilization, and produces a diminution in the number of hydrophobic sites that could be able to give interparticle hydrophobic interactions.