热诱导白蛋白与壳聚糖在溶液中的自组装

80℃热诱导牛血清白蛋白(BSA)变性,BSA疏水残基暴露在分子表面,并进一步凝胶化.采用紫外-可见光光度仪(UV-Vis)和动态激光光散射仪(DLS)考察了热处理时间、溶液p H值、壳聚糖(CS)与BSA配比等因素对CS与BSA自组装行为的影响.加热时间介于15~20 min,BSA与CS发生自组装;BSA/CS混合体系p H大于BSA等电点(p I=4.7)时,BSA与壳聚糖静电作用增强,随着p H增大,出现沉淀.BSA浓度过高,变性BSA之间聚集作用增强,导致体系出现沉淀.研究结果显示,CS阻碍了BSA自身凝胶化进程,并与BSA发生自组装.在p H=5.4的溶液中制备了BSA-CS自组装体.采用透射电镜(TEM)观察了自组装体的形态,采用DLS对其粒径及其分布进行了测试.自组装体是以BSA聚集体为核、CS分子链为壳的核壳纳米结构.制备的自组装体室温贮存40天后,其粒径和分布无明显变化.     

L-半胱氨酸自组装膜诱导草酸钙结晶研究

在CaCl2.H2O和Na2C2O4配制的过饱和溶液中,利用L-半胱氨酸(L-Cys)在金片上形成的自组装膜为模板,研究了草酸钙(CaOxa)在自组装膜上的结晶行为,并探讨了溶液pH对CaOxa晶体组成、晶型及其形貌的影响。采用X射线衍射(XRD)和扫描电子显微镜(SEM)等技术对CaOxa晶体的结构和形貌进行了表征。实验结果表明:当溶液pH=3.0时,溶液中可以形成一水草酸钙(CaC2O4.H2O,COM)和二水草酸钙(CaC2O4.2H2O,COD)晶体,而在同样pH条件下,在L-Cys自组装膜上只形成COD晶体,表明自组装单层对CaOxa晶体的成核和生长有重要影响。通过改变溶液的pH,在自组装单层上可以得到不同晶型和不同形状的CaOxa晶体。当pH=3.0时得到四方块状的COD晶体,而pH=5.0和pH=7.0时分别得到六边形和拉长六边形的COM晶体。     

开环聚合诱导自组装的挑战与展望

聚合诱导自组装（PISA）是一种新兴的纳米粒子制备技术,它集聚合与组装过程于一体,可在高固含量条件下进行,因此备受青睐.此外,通过改变嵌段聚合度以及固含量等参数,可以精确地控制纳米粒子的形貌,实现从球形胶束到空心囊泡的形貌转变.然而,受限于适用于PISA体系的聚合方法和单体种类,其发展也受到了一定的限制.目前,PISA主要基于可逆加成-断裂链转移聚合（RAFT）,其在聚合诱导自组装机理、形貌控制、结构表征等方面的研究成果,对于高分子化学其他领域具有重要的参考价值.然而,由于RAFT聚合诱导自组装（RAFT-PISA）体系中适用的单体往往局限于（甲基）丙烯酸酯类和苯乙烯类,导致RAFT-PISA制备的纳米粒子限于其碳-碳主链的基本结构难以生物降解,因此生物医用前景并不乐观.为了克服以上缺陷,开环聚合诱导自组装（ROPISA）应运而生,主要包括开环易位聚合诱导自组装（ROMPISA）、氨基酸-N-羧基-环内酸酐开环聚合诱导自组装（NCA-PISA）及自由基开环聚合诱导自组装（rROPISA）.由于ROMPISA体系对诸多功能性基团表现出化学惰性,从而为多功能纳米粒子的原位制备提供了新的方法;而rROPISA和NCA-PISA则使得生物可降解纳米粒子的原位制备成为可能.作为PISA领域崭新的研究方向,ROPISA不仅将新聚合方法引入了PISA体系,而且突破了以往PISA难以制备可降解纳米粒子的瓶颈,为PISA技术在生物医药领域的应用架起了桥梁.作者简要总结了ROPISA的发展现状,着重分析并提出了该领域面临的挑战,最后从机理研究、单体设计及转化应用等方面对ROPISA的发展前景进行了展望.     

聚合诱导自组装(PISA)技术的应用研究进展

聚合诱导自组装(PISA)技术是制备嵌段共聚物纳米自组装体的一种新技术.相较于传统的嵌段共聚物自组装技术,该技术具有边聚合、边组装的操作简便性特点,同时还具有纳米自组装体形态可控、固含量高(高达50％)等优点,使得聚合物纳米自组装体的规模化生产和应用成为可能.经过十多年的发展,基于各种"活性"/可控聚合机理和各种配方组...     

基于蛋白质分子自组装体系的构建

蛋白质是一类功能丰富、结构独特的生物大分子,具有高度的自组装特性。氨基酸通过酰胺键形成序列确定的肽链,是蛋白质的基本构成单元。肽链通过弱相互作用控制肽链折叠以及蛋白质高级结构的形成。同时,蛋白质是一种来源丰富、生物可降解以及生物相容性可再生资源,利用蛋白质的自组装特性构建具有生物功能的可控自组装体系是纳米科学、材料科学以及生物医学等学科潜在的研究课题之一。本文从分子科学的角度解析了蛋白质三维结构的自组装特性,进一步探讨蛋白质热变性后自组装、金属诱导的蛋白质自组装、蛋白质与高分子的自组装以及蛋白质杂化体的自组装。旨在进一步认识和理解蛋白质的自组装特性,并为设计和构建结构可控及功能独特的自组装体系提供思路。     

侧链型偶氮聚电解质自组装和膜结构研究

研究了4种侧链型偶氮聚电解质的自组装过程及其对自组装膜结构的影响.用聚电解质上的偶氮基团作为“探针”,研究了自组装过程中出现的生色团取向、解吸附和非线性增长等现象.这些侧链型偶氮聚电解质均具有较好的自组装性,但其自组装行为有很大差异.在不同的pH条件下,聚电解质的电离程度不同,导致吸附过程和自组装膜结构亦明显不同.自组装膜的增长和结构取决于体系中吸附和解吸的平衡.偶氮生色团端基的亲水或疏水性对自组装膜的增长有明显的影响.偶氮聚电解质自组装过程不同阶段出现的非线性增长现象,分别反映了基底、溶液性质和聚电解质结构等因素的影响.     

有机凝胶自组装模板法制备纳米材料

利用溶胶一凝胶聚合过程人工模拟生物矿化进程的技术,已经融人无机材料和超分子有机化学的研究领域.小分子有机凝胶因子在溶剂中发牛自组装,形成多种形态的有机凝胶超分子结构,以其为模板,经过溶胶一凝胶过程,可以诱导转录形成各种形态的纳米材料.本文介绍了利用有机凝胶因子自组装结构为模板制备形态可控无机材料的研究进展及模板结构诱导转录的两种可能机制.     

一种偶氮聚电解质在不同pH值条件下的静电逐层自组装研究

研究了一种光响应偶氮聚电解质(PEAPE)在不同pH值条件下的自组装,重点讨论了pH值对静电逐层自组装以及对光响应性能的影响.研究表明,在所研究的pH范围内,pH值越低,越有利于生成吸光度高的自组装膜,对应的自组装膜厚度也越大.红外光谱分析表明,偶氮聚电解质在不同pH溶液中存在不同的电离情况.pH值越低,用于自组装的溶液中的聚合物链上的电荷数越少,链构象越卷曲.解释了不同pH值条件下自组装膜吸光度和厚度差别的原因.     

端基结构对超支化聚合物静电吸附自组装行为的影响

研究了3种具有相同骨架结构、不同端基的超支化聚合物与线型聚阳离子(PDAC)的静电吸附自组装.结果表明,超支化聚合物的组装过程与线型弱酸聚合物相似,都受溶液pH值与无机盐浓度的影响,但影响程度随端基结构不同而变化.此外,对以超支化聚合物为最外层的不同自组装膜的表面形貌及接触角进行了表征,其表面形貌及亲水性随端基结构的不同而不同.     

端基对侧链型偶氮聚电解质自组装膜内生色团取向的影响

用偏振紫外光谱研究了 4种带有不同端基的侧链型偶氮聚电解质静电逐层自组装膜中偶氮生色团的初始取向 .讨论了不同的端基对偶氮生色团在自组装膜中初始取向的影响 .进一步探讨了偶氮聚电解质自组装膜的结构特点 .研究表明 ,侧链型偶氮聚电解质自组装膜中偶氮生色团普遍存在一定程度的沿面取向 .偶氮生色团所带端基的类型对其在自组装膜中的取向程度有较大的影响 ,这主要取决于偶氮生色团与聚阳离子基底的电荷相互作用和极性相互作用等 .对偶氮生色团在水溶液中能形成H 聚集体的自组装膜来说 ,H 聚集体对生色团取向也有一定的影响 .结果表明 ,在制备需控制生色团取向性的自组装膜时 ,要考虑生色团上的不同端基对取向的影响     

The separation of racemic crystals into enantiomers by chiral block copolymers

A series of chiral double hydrophilic block copolymers (DHBCs) was synthesized and employed as additives in the crystallization of calcium tartrate tetrahydrate (CaT). We found that appropriate polymers can slow down the formation of the thermodynamically most stable racemic crystals as well as the formation of one of the pure enantiomeric crystals so that chiral separation by crystallization occurs even when racemic crystals can be formed. In addition, the presence of DHBCs results in major modifications of crystal morphology, creating unusual morphologies of higher complexity. Our study demonstrates the potential application of chiral DHBCs in the control of chirality throughout crystallization, in particular for racemic crystal systems, and also shows that enantiomeric excess of one enantiomer can be maximized by the kinetic control of crystallization.     

Nanosized amorphous calcium carbonate stabilized by poly(ethylene oxide)-b-poly(acrylic acid) block copolymers

Particles of amorphous calcium carbonate (ACC), formed in situ from calcium chloride by the slow release of carbon dioxide by alkaline hydrolysis of dimethyl carbonate in water, are stabilized against coalescence in the presence of very small amounts of double hydrophilic block copolymers (DHBCs) composed of poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) blocks. Under optimized conditions, spherical particles of ACC with diameters less than 100 nm and narrow size distribution are obtained at a concentration of only 3 ppm of PEO-b-PAA as additive. Equivalent triblock or star DHBCs are compared to diblock copolymers. The results are interpreted assuming an interaction of the PAA blocks with the surface of the liquid droplets of the concentrated CaCO3 phase, formed by phase separation from the initially homogeneous reaction mixture. The adsorption layer of the block copolymer protects the liquid precursor of ACC from coalescence and/or coagulation.     

Control of the morphogenesis of barium chromate by using double-hydrophilic block copolymers (DHBCs) as crystal growth modifiers

A systematic morphosynthesis of barium chromate particles has been performed by using double-hydrophilic block copolymers (DHBCs), which consist of a hydrophilic solvating block and a hydrophilic binding block, as crystal growth modifiers to direct the controlled precipitation of barium chromate from aqueous solution. Several kinds of DHBCs with different functional groups -COOH, -PO3H2, -SO3H, -SH as well as PEG-poly(aminoamine) block-dendrimer copolymers were explored for crystallization and morphology control of barium chromate. Well-defined morphologies of BaCrO4 particles can be produced, such as more or less dendritic X-shaped, elongated X-shaped, or rodlike particles, flower-like plates, ellipsoids, spheres, nanofiber bundles, nanofibers, and other more complex morphologies. In the presence of the phosphonated copolymer PEG-b-PMAA-PO3H2 (degree of phosphonation: 21%) at pH 5, large conelike bundles of nanofibers ranging from 10 to 20 nm in diameter with lengths up to 150 microns can be produced at room temperature, whereas replacement of the covalently bound phosphonate groups by the ionic salt analogue dopant fails to produce this structure, indicating the importance of the functional polymer block structures. The time-resolved formation process of the bundles of nanofibres was investigated, showing a remarkable self-similarity. At temperatures higher than 50 degrees C, in plastic flasks or when undergoing continuous stirring, only ellipsoids or nearly spherical particles can be obtained. This shows that the fiber formation relies on heterogeneous nucleation and is in agreement with a recently published mechanism where fiber formation is due to the vectorially directed self-assembly of primary particles. Our results demonstrate that the integration of DHBCs, taking advantage of the experimental conditions such as crystallization sites, temperature, pH, and reactant concentration, will extend the possibilities for controlling the shape, size, and microstructures of the inorganic crystals by means of a simple mineralization process.     

Superstructures of temporarily stabilized nanocrystalline CaCO3 particles: morphological control via water surface tension variation

In this paper, the formation of different complex morphologies of nanocrystalline CaCO3 under the control of double hydrophilic block copolymers (DHBCs) carrying phosphate groups is described. The DHBCs consist of a poly(ethylene glycol) (PEG) block and a pendant poly[2-(2-hydroxy ethyl)ethylene] block with different degrees of phosphorylation up to 40%, some of which show surface activity. The polymers furthermore temporarily stabilize CaCO3 nanocrystals, which are formed by slow CO2 evaporation from a supersaturated Ca(HCO3)2 solution (Kitano method). The polymers are active down to concentrations of 10(-4) g/L. In dependence of the nature and concentration of the DHBC, tunable complex shuttlecock flowerlike and other superstructures are formed, which are aggregates of CaCO3 vaterite nanoparticles with an enhanced stability of at least 2 months. It is shown that the aggregation starts around template CO2 gas bubbles at the air/water interface. The size and morphology of the growing aggregates depends on the polymer concentration, phosphorylation degree, and water surface tension. The latter determines when the aggregate sinks to the bottom, interrupting the further growth process. Variation of the water surface tension by addition of the nonionic surfactant Antharox CO880 also allows a variation of the aggregate morphology, thus implying the described method as simple and versatile for the generation of complex CaCO3 morphologies.     

Fabrication of a Thermoresponsive Biohybrid Double Hydrophilic Block Copolymer by a Cofactor Reconstitution Approach

The fabrication of a thermoresponsive biohybrid double hydrophilic block copolymer (DHBC) by a cofactor reconstitution approach is reported. Poly(N‐isopropylacrylamide) (PNIPAM) bearing a porphyrin moiety at the chain terminal, PPIXZn‐PNIPAM, is synthesized by the combination of ATRP and a click reaction. The subsequent cofactor reconstitution process between apomyoglobin and PPIXZn‐PNIPAM affords well‐defined myoglobin‐b‐PNIPAM protein–polymer bioconjugates. Behaving as typical responsive DHBCs, the obtained myoglobin‐b‐PNIPAM biohybrid diblock copolymer exhibits thermo‐induced aggregation behavior in aqueous solution as a result of the presence of the thermoresponsive PNIPAM block, as revealed by temperature‐dependent transmittance, dynamic laser light scattering measurements, transmission electron microscopy, and scanning electron microscopy. This work represents the first report of the preparation of responsive biohybrid DHBCs by the cofactor reconstitution process.

     

Dissipative particle dynamics simulation on a ternary system with nanoparticles, double-hydrophilic block copolymers, and solvent

Dissipative particle dynamics (DPD) simulations are performed to study the aggregation of hydrophobic nanoparticles in the presence of double-hydrophilic block copolymer (DHBC). A single compact spherical nanoparticle aggregate is formed in the absence of DHBC. The response of the aggregate to a continuous increase in the concentration of DHBC has been investigated in detail. We observe the evolvement from single spherical aggregate, through single ellipsoidal aggregate, single platelike aggregate, single long and curly rod, dispersed aggregates, then to hexagonally packed cylinders, and ultimately to ordered lamellar structures upon slow addition of DHBC chains. However, when nanoparticles and DHBCs are added into the system simultaneously at the beginning of simulation, we only obtain single spherical aggregate, dispersed aggregates, hexagonally packed cylinders, and ordered lamellar structures at different concentrations of DHBC. Phase diagrams of structures against concentration of DHBC are presented for these two methods, and the stabilities of structures obtained with the two methods are compared.     

Synthesis of well-defined poly(N-isopropylacrylamide)-b-poly(L-glutamic acid) by a versatile approach and micellization

A novel Fmoc-protected chain transfer agent (CTA) was synthesized and applied in the reversible addition-fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide (NIPAAm), resulting in well-defined Fmoc-protected PNIPAAm and the amino-end capped PNIPAAm by the subsequent hydrolysis. Poly(N-isopropylacrylamide)-b-poly(l-glutamic acid) (PNIPAAm-b-PLGA) with controlled molecular weight and narrow molecular weight distribution was synthesized successfully via ring-opening polymerization (ROP) of alpha-amino acid N-carboxyanhydrides (NCAs) by using PNIPAAm-NH2 as the macroinitiator. Both pH- and thermo-responsive micellization behaviors of the block copolymer PNIPAAm55-b-PLGA35 in dilute aqueous solution were investigated by means of the pyrene fluorescence, circular dichroism, 1H NMR, transmission electron microscopy and dynamic and static light scattering. Spherical PLGA-core and rod-like PNIPAAm-core micelles are formed in response to pH and temperature. The reversible transition between the PLGA-core and PNIPAAm-core micelles was observed. This work provides a versatile approach for synthesizing well-defined stimuli-responsive polypeptide-based double hydrophilic diblock copolymers (DHBCs), and is of great potential for generating useful stimuli-responsive materials in biomedical applications.     

Control of aggregation of nanoparticles by double-hydrophilic block copolymers: a dissipative particle dynamics study

Double-hydrophilic block copolymer (DHBC)-directed mineralization is investigated by dissipative particle dynamics (DPD) simulation. By mineralization, we refer to the formation of inorganic crystals from the solution. In the current study, the DHBCs are modeled as chains of A and B blocks with repulsion between unlike blocks, while the mineralization is approximated by aggregation of hydrophobic nanoparticles from the solution. Depending on the relative concentrations of nanoparticles and DHBC, dispersed spherical aggregates, hexagonally packed cylinders, and ordered lamellae structures are obtained. The structures formed are seen to be controlled by competing forces between aggregation of nanoparticles, the interaction of DHBC with nanoparticles, and the self-assembly of DHBC in the solution. The time evolutions of hexagonally packed cylinders and ordered lamellae are studied. For the development of cylinders, nanoparticles first aggregate into orientationally disordered small cylinders, then these cylinders slowly grow into hexagonally packed long cylinders. For the development of ordered lamellae, nanoparticles first form a disordered structure, then grow into disordered lamellae, and at last evolve into ordered lamellae. The simulation demonstrates that addition of DHBC can effectively control the aggregation of inorganic particles and lead to formation of a variety of nanostructures.     

超支化双亲水性嵌段共聚物对CaCO3结晶影响的研究

采用合成的聚乙二醇-超支化聚酯(PEG-hb-DMPA)的线性-超支化杂化二嵌段共聚物, 探讨了羧端基树状功能化的杂化嵌段共聚物对CaCO₃结晶的影响，并用FTIR、XRD、SEM等对产物进行了表征。结果表明，羧端基的双亲水性嵌段共聚物对CaCO₃结晶形貌乃至晶型均具有显著调控作用，比较高的浓度(1.67 g·L^-1, >10 min)或较低浓度作用较长时间(0.33 g·L^-1, 24 h)均得到了呈较均匀球粒形态的球霰石CaCO₃结晶。     

Supramolecular Self‐Assembly of Nonlinear Amphiphilic and Double Hydrophilic Block Copolymers in Aqueous Solutions

Supramolecular self‐assembly of block copolymers in aqueous solution has received ever‐increasing interest over the past few decades due to diverse biological and technological applications in drug delivery, imaging, sensing and catalysis. In addition to relative block lengths, molecular weights and solution conditions, chain architectures of block copolymers can also dramatically affect their self‐assembling properties in selective solvents. This feature article mainly focuses on recent developments in the field of supramolecular self‐assembly of amphiphilic and double hydrophilic block copolymers (DHBCs) possessing nonlinear chain topologies, including miktoarm star polymers, dendritic–linear block copolymers, cyclic block copolymers and comb‐shaped copolymer brushes.