【作者】 李兆楼；

【导师】 郝爱友；

【作者基本信息】 山东大学 ， 有机化学， 2014， 博士

【摘要】 本论文依据超分子化学的理论观点,以β-环糊精(β-CD)为凝胶子,设计、合成了多个功能性的有机超分子凝胶材料。从理论框架来看,本论文所依赖的基本的科研思想及观点主要来自三个领域,即超分子化学、环糊精化学和凝胶化学等。按照Lehn的定义,所谓超分子,即超越共价键的分子；超分子化学,即分子组装(assembly)的化学和分子间键的化学。超分子化学以分子间的非共价键即低能键(键能1-80kJ)为基础,以分子聚集体等超分子体系为构筑对象,其目的在于发展复杂有序、具有某种特定功能和性质的高度复杂聚集体,并将信息存储在分子部件中。所以,根据体系内部不同分子的结构特点,依据可能的非共价键作用方式,可以设计、自组装成具有一定功能的超分子材料。环糊精有机分子是一种环状多糖,其独特的大环结构特点使之成为超分子化学研究的热点。本文选择了β-CD做最基本的原料来构筑有机凝胶材料。凝胶化学是胶体化学的一个分支。它更注重于溶胶与凝胶之间的转变关系,同时又要探讨凝胶本身的比较复杂的非均质结构及其形成机理。我们以超分子化学为基础,研究有机小分子凝胶(物理凝胶)的工作是一个较新的领域。特别是新凝胶体系的结构的描述与表征,以及对形成机理的阐述等都是新的课题。本文所涉及的超分子凝胶体系,是β-CD的溶液并含有少量的盐类,如LiCl或K2CO3等。在物理刺激(如热刺激)或者化学试剂作用下,β-CD分子以自组装方式形成凝胶纤维或以凝胶粒子(即为网络结构亚单元)。这些亚单元的网络结构凭借毛细管吸附力或表面吸附作用力,捕获了溶剂分子于网络中,从而使凝胶本身具有一定的结构特点和性能。这类材料内部的超分子作用力,主要是氢键、分子-离子作用、范德华力等；这些超分子作用力始终影响着凝胶的刺激响应性,并为我们设计不同性能的功能性凝胶材料所利用。本论文主要研究内容如下：(1)β-环糊精自身、无需客体分子的嵌入其空腔,在热刺激下就具有胶凝能力,是早先未发现的。试验表明,在N,N-二甲基甲酰胺(DMF)溶剂与少量氯化锂(LiCl)存在下,适当升温β-CD能够自组装而可逆地形成有机凝胶。实验证明,这种凝胶的微结构是一种β-CD分子簇,它由笼型结构的β-CD为核心,其上生长着各个方向上的管道型β-CD纤维束。我们使用光学显微镜(OM)和电子扫描显微镜(SEM)等方法证实了这种凝胶的微观形貌。这种凝胶的结构和形成过程由FTIR,TR-FTIR,1HNMR和XRD等手段得到证实。我们讨论了凝胶体系内存在的主要的超分子作用力。分子动力学模拟实验与上述方法所确定的凝胶的结构一致。试验表明,能够形成凝胶的β-CD浓度范围是0.13-0.28mol/L,由溶液到凝胶的相转移的近似热焓ΔH是28kJ/mol。该研究对于应用低廉的β-CD原料来开发新型的热控材料具有很大的意义。(2) β-CD/LiC1/DMF溶胶体系被开发为常温下的凝胶,即无需加热,只需往体系里引入一种羧酸：甲酸(FA)、或乙酸(AA)或丙酸(PA)即可完成。但是,试验表明,不同羧酸如FA、或AA或PA刺激作用原溶胶体系后得到的凝胶具有不同的形貌。这主要是因为FA、或AA或PA的分子极性和氢键能力的差别,影响到所生成的凝胶的微结构和物理化学性质,PA凝胶里β-CD自组装有序化明显较大,而FA凝胶粒子里结晶度最小,这些被SAXS、 WAXS、 FT-IR和XRD证实。这些凝胶的形貌、热稳定性和机械强度上的差别,也利用OM、SEM、DSC和流变学等手段进行了研究。在实验的基础上,我们还描绘了β-CD体系与FA凝胶化相转变的相图(具有代表性)。小分子羧酸刺激溶胶发生凝胶化的机理也被阐明：由于溶剂化的DMF-β-CD复合物通过氢键转变而成为DMF-羧酸分子复合物,其间导致β-CD溶剂化破坏、β-CD自聚合发生。通过引入添加剂,来调剂溶胶-凝胶相转变的方法,在研究可控性的刺激-响应性材料方面将会具有潜在意义。(3)对于β-CD/K2CO3/1,2-丙二醇体系的凝胶A,我们使用了甲酸HCOOH进行刺激作用后,凝胶A演化成另一个凝胶B,实现了凝胶-溶胶-凝胶的连续的相转变。其间,K2CO3为盐桥的凝胶A的网络解体且释放出CO2；而后,凝胶B的网络得以重新组合,它却是在新盐桥HCOOK的协助下形成的。针对A和B这两个凝胶,我们使用了OM、 SEM、 SAXS、WAXS、 FTIR、 XRD等手段进行了研究。凝胶B具有较大的弹性模量(G’1×105Pa),能够屈服于较高的应力作用(应力屈服点为300Pa),这相比于凝胶A而言的(G’3×104Pa；应力屈服点180Pa)；热分析的DSC曲线表明,与凝胶A的相转移温度(34.4℃)相比,凝胶B具表现出较高的相转移温度(161.75℃)。凝胶-溶胶-凝胶转变过程的真正原因,是盐桥K2CO3-HCOOK的转变造成的。此类相转移是首次报道,相转移是因甲酸添加剂诱导引发而完成的。对于开发药物的控制和释放材料,以及其它更复杂的刺激响应性材料将有更大的意义。另外,在分子水平上描述凝胶结构和分子自组装-聚集过程,其表征手段采取的多是物理技术与手段。目前用于研究凝胶结构和性质的方法,主要有光散射、红外光谱、X光和中子衍射、显微镜、核磁共振、粘弹性测定法,以及热性能、光学性能等,也是本论文中使用涉及到的一些物理手段和方法。这些现代科技手段,对我们认识分子自组装过程以及理性地设计新的凝胶提供了依据。总之,本文研究的所采取的调控β-CD体系发生胶凝的主要方法有：外部刺激诱发β-CD凝胶子自身以氢键为主的胶凝能力、利用盐类转变及其在凝胶体系中的不同作用、利用共溶剂氢键转换作用对溶剂化的破坏作用等。这些调控方式与结果,不仅对开发β-CD体系凝胶材料的发现有意义,而且对β-CD参与的超分子化学及超分子作用有新的贡献。因此,这些结论具有一定学术价值和应用价值。我们希望这些新成果在控温应用材料、智能材料、药物控制与释放材料以及其它更复杂的刺激响应性材料等领域有良好的应用前景,也希望有更充分的时间和适宜的应用平台,更多地开展应用性研究尝试。本论文的主要创新点如下：(1)在加热刺激下,β-环糊精自身具有胶凝能力,可形成β-CD/LiC1/DMF热致可逆凝胶。这是新的发现。(2)对于β-CD/LiC1/DMF体系,提出了受热生成凝胶的机理及其微结构模型。该凝胶的微结构是一种β-CD分子簇,它由笼型结构的β-CD为核心,其上生长着各个方向上的管道型β-CD纤维束。(3)对于β-CD/LiC1/DMF体系,同样地可以用小分子羧酸进行化学诱导,可直接使其转化为凝胶,无需加热。形成凝胶的机理,涉及羧酸的羧基所参与的氢键作用。溶剂化的DMF-β-CD复合物,在小分子羧酸作用下,通过氢键转变而成为DMF-羧酸分子复合物,其间导致β-CD溶剂化破坏而β-CD自聚合发生。(4)对于β-CD/LiC1/DMF体系,在小分子羧酸作用下,可引致β-CD借助氢键作用自聚合成为凝胶。小分子羧酸的分子极性和氢键能力的差别,影响到所生成的凝胶的微结构和物理化学性质。(5)对β-CD/K2CO3/1,2-丙二醇体系的凝胶A,通过甲酸化学作用。可使凝胶A转化成另一个凝胶B,实现了凝胶-溶胶-凝胶的连续的相转变。这是前所未有的一个新发现。(6)研究了β-CD/K2CO3/1,2-丙二醇体系发生的凝胶-溶胶-凝胶转变的原因,主要是盐桥K2CO3向HCOOK所引致的。使用这种新体系,对于开发药物的控制和释放材料,以及其它更复杂的刺激响应性材料有重要的意义。更多还原

【Abstract】 The functional materials of supramolecular organogels based on β-cyclodextrin (β-CD) were designed and synthetized depending on the viewpoints of supramolecular chemistry in this thesis. Supramolecular Chemistry is the chemistry involving molecular assemblies with non-covalent bonds. In brief, Supramolecular Chemistry is a science for various functional systems formed by non-covalent bonds among multiple molecules.The basic research ideas in this thesis depended mainly on the three academic sectors from Supramolecular Chemistry, Cyclodextrin Chemistry and Sol-gel Chemistry. According to the definition provided by J.-M. Lehn, supramolecular complex is a combination beyond the molecules of covalent bonds. Supramolecular Chemistry is aimed at developing complex and ordered aggregates with certain function and property based on non-covalent bonds among multiple molecules in a system. Therefore, some supramolecuar materials can be designed and self-assembled depending on specific non-covalent bonds from the structural characteristics of molecules in a system. Cyclodextrin is a kind of macrocyclic polysaccharides with unique structures as the investigated candidates of supramolecular chemistry. Therefore, we have chosen P-cyclodextrin as basic material to construct supramolecular organogels. The Sol-gel Chemistry is one branch of Colloidal Chemistry. It focused more on a state exchange from solution to gel state, or in reverse. It is a new field to study the low-molecular weight organogels. The characterization of new gel system and explaination of formation mechanisms are all new subjects.The systems of supramolecular gels here mostly are some β-CD solutions with a small quantity of salts such as LiCl or K2CO3, etc. Facing physical stimuli or chemical additives, β-CD molecules in the systems constructed to form gel fibers or colloidal particles as subunits of gel network by self-assembling. The network trapped solvent molecules by capillary force or face adsorption to form a gel with specific structural characteristics and performance. The supramolecular interactions within this kind of gel materials mainly are hydrogen-bonds, molecule-ion interaction and van der Waals force, etc. And these supramolecular interactions influenced the stimuli-responsive performance of gels and were employed to design various functional gel materials.This thesis mainly consists of three parts as follows:i) It had not been found ever before that β-Cyclodextrin (β-CD) itself has gelling abilities under heating, without the help of the guest molecules embedding in cavities. The experiments showed that P-CD can self-assemble an organogel with a very small amount of lithium chloride (LiC1) in N,N-dimethylformamide (DMF) by heat. The experiments also showed that the β-CD organogel microstructures were β-CD molecular clusters composed of many channel-type β-CD fibers extending from a cage-type β-CD core in various directions. The morphology of the organogel was characterized by OM and SEM. The process of the gel formation and the structure were suggested based on FTIR, TR-FTIR,’H NMR and XRD results. The main supramolecular interactions among the various molecules in the system were discussed for gelation. A molecular dynamics simulation of the gel structure was performed in agreement with the results. The experiments showed that the concentration of P-CD for the gel formation ranged from0.13to0.28mol/L. The approximate heat effect of the phase transition was28kJ/mol. This investigation results will be of great significance to develop new temperature-controlling materials with native P-CD of low cost in application.ii) The β-CD/LiCl/DMF solution can be developed to become supramolecular organogels by introducing formic (FA), acetic (AA) or propanoic acid (PA) into the system without heating. However, the experiments showed that the gel morphologies were diverse depending on different additives of FA, AA or PA into the system. The polarities and H-bond abilities of FA, AA or PA influenced micro-structures and physicochemical properties of these gels. More orderly β-CD self-assembly was in PA gel, while lower crystallinity of colloidal particles was in FA gel, which was revealed by SAXS, WAXS, FT-IR and XRD. The diversity of the gels in morphology, thermostablility and mechanical strength were studied by OM, SEM, DSC and rheology. The phase diagram of theβ-CD system with FA was described for such gel formation. A common mechanism of the gels formation was clarified, namely, H-bonds exchange from DMF-β-CD complex to DMF-carboxylic acid complex resulted in destruction of solvent shell on β-CD gelator and β-CD self-aggregation in the co-solvent system. By introducing an additive to manipulate sol-gel transitions, this approach would be a potential implication in controllable stimuli-responsive materials.iii) For supramolecular "gel A" of β-CD/K2CO3/1,2-propylene glycol system, it can be activated by the addition of HCOOH to evolve into another "gel B". This manipulation achieved the gel-sol-gel’phase transition. In the process, the release of CO2dissociated the network of the "gel A" bridged by K2CO3and the new network of the "gel B" can be reorganized with the help of the newborn HCOOK. The two gels,"A and B", were investigated by OM, SEM, SAXS, WAXS, FTIR and XRD. The"gel B" with greater elastic modulus (G’,1×105Pa) could endure higher applied stress (the yield point300Pa) than the "gel A"(G’,3X104Pa; the yield point180Pa). The "gel B" also exhibited the higher phase transition temperature (161.75℃) than that (34.4℃) of the "gel A" in DSC analysis. The reason behind the gel-sol-gel’phase transition was the salt bridge evolution. This work is the first report on gel evolution with phase reorganization triggered by chemical additive (HCOOH), which may be of great significance to develop drug controlled release materials, and other more complex stimuli-responsive materials.In addition, physical techniques often are used in characterizing gel structures and self-assembly process. The main physical techniques are small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), optical microcopy (OM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and rheology. These techniques had also been used to design and describe the new gel systems in this thesis.In all, the main methods with supramolecular interactions we used were the utilization of hydrogen-bonds between β-CD molecules for gelation of β-CD gel, the use of molecule-ion interaction from salts, and destruction of solvent shell of β-CD molecules, etc. These findings may be of great significance not only to develop gel materials but also to extend CD chemistry and supramolecular science.The innovated points in this thesis mainly include:i) It is firstly proposed that β-Cyclodextrin (β-CD) itself has gelling abilities under heating. Without the help of the guest molecules embedding P-CD cavities, the reversible organogel of β-CD/LiCl/DMF system can be formed.ii) We proposed that the organogel microstructures were P-CD molecular clusters composed of many channel-type β-CD fibers extending from a cage-type β-CD core in various directions. This suggests the gelation mechanism of the β-CD/LiCl/DMF system.iii) The β-CD/LiCl/DMF solution can also be developed to become supramolecular organogels by introducing formic, acetic or propanoic acid into the system without heating. The mechanism of the gels formation involved in hydrogen-bonds interaction from the carboxyl group of carboxylic acids. The DMF-P-CD complex for salvation with hydrogen exchange became DMF-carboxylic acid complex, resulted in destruction of solvent shell on P-CD molecules and P-CDs self-aggregation in the co-solvent system.iv) For theβ-CD/LiCl/DMF system, the destruction of solvation forβ-CD resulted in β-CD gel formation under chemical additive of small carboxylic acid. The polarities and H-bond abilities of FA, AA or PA influenced micro-structures and physicochemical properties of these gels.v) For "gel A" of P-CD/K2CO3/1,2-propylene glycol system, it can be activated by adding HCOOH to evolve into "gel B". This manipulation achieved the gel-sol-gel’ phase transition. This gave us an unprecedented opportunity.vi) The reason behind the gel-sol-gel’phase transition was the salt bridge evolution. This approach may be of great significance to develop drug controlled release materials, and other more complex stimuli-responsive materials.更多还原