【作者】 张笑；

【导师】 李国文；

【作者基本信息】 吉林大学 ， 高分子化学与物理， 2009， 博士

【摘要】 DNA借助两条链上互补碱基对之间形成的氢键维系其有规则的双螺旋结构,互补碱基间多重氢键的形成已经被广泛用作人工超分子聚集体构筑的驱动力。然而,互补碱基间的氢键通常仅仅在有机介质中是有效的,这是因为水分子对自组织体系的氢键形成的激烈竞争性。双亲性生物大分子能够在含水微环境中聚集成不同形态的聚集体,这些聚集体以一个独立的不溶的整体存在而排除了介质水的竞争,从而能够使互补碱基在水溶液中实现分子识别。因此,本文模拟DNA的分子结构,用无毒、亲水、具有较好生物相容性的聚乙二醇(PEG)作为共聚物的亲水基团,用间苯二甲酸酯作为亲脂段接枝功能基团核酸碱基,设计、合成了一系列生物相容性好、可降解的双亲共聚物。并使该共聚物通过自组织作用在水溶液中形成聚集体,利用扫描电镜观测不同结构的共聚物与各种具有互补结构的功能基团间形成的氢键对聚集体形态的影响;接枝的底物核酸碱基功能基团由于疏水亲脂作用进入聚集体的疏水区域,排除环境水的竞争性干扰,使受体与底物间形成氢键,利用傅立叶红外及变温红外测试了氢键的形成和断裂过程。双亲性高分子在溶液中可以形成聚集体应用于药物载体,而氢键的形成可以增强受体与底物间的分子相互作用,提高受体对底物的负载量,如果底物是含有互补基团的药物,则通过分子识别可以增强受体与药物间的相互作用,进而提高受体的载药能力,进而为开发含有相应互补基团的药物聚集体的分子识别以及制备新型纳米球药物制剂提供了可行的途径。更多还原

【Abstract】 Biological macromolecules with a complex structure had a high degree of selectivity and the role of non-covalent characteristics in the assembly of biological systems. Compared with the biological system, to investigate the molecular gathering behavior and various forms in-depth, control the structure of these aggregates and morphology especially with the aggregation patterns which is similar to DNA double helix structure, simulate some specific functions of different kinds of aggregations, explore the formation and building the rules and mechanisms, it will be great significance for understanding of the lives of some physical phenomenon and chemical processes, physiological functions and pathological mechanism in the chemical system with relatively simple and determine composition.Nucleic acid is a linear polymer which composed by nucleotide as the basic unit, and an important material of life to determine the genetic. From the chemical point of view, the poly-deoxynucleotide chain of DNA is an amphiphilic polymers which composed by hydrophobic deoxycytidine and hydrophilic phospholipid. It gathered into a double helix structure with the genetic features material through self-organization and molecular recognition. It is the essential of the formation of DNA double helix structure by self-organizing, which drives by hydrophobic-lipophilic and Watson-Crick base pairs recognize. It is well known that the molecular self-organization and the molecular recognition are the basic functions and essential phenomenon in living systems, and the hydrophobic micro-environment provided by the bio-supramolecular structure is the key to molecular recognition. For example, monomeric nucleosides fail to recognize with each other through hydrogen bonding in aqueous solution because the environment is too competitive to shield their binding sites from water.In order to mimic the progress of self-organization and the molecular recognition in biological system, we designed and synthesized a series of amphiphilic polymers grafted with nucleic acid bases, which simulate of the structure of DNA. It is a simple strategy for molecular recognize to incorporate the functional groups containing hydrogen bonding sites into hydrophobic-lipophilic regions, to shield their binding sites from water. Meanwhile, the amphiphilic aggregation can be used as drug carrier and targeted drug delivery system if it is biodegradable and biocompatible. The details of this paper are as follows.1. Synthesis of the copolymersIn this paper, we design and synthesis a series of biocompatibility and amphiphilic biodegradable copolymers by simulation of the structure of DNA. We used polyethylene glycol (PEG) which is avirulent, hydrophilic and with good biocompatibility as a hydrophilic group and isophthalate graft nucleobases as the hydrophobic. They are Poly(polyoxyethylene-600) -oxy-5-(6-(1-thymine)hexyl)) isophthaloyl (PPETHI), Poly(polyoxyethylene- 600)-oxy-5-(6-(9-adenine)hexyl)) isophthaloyl (PPEAHI), Poly(polyoxyethylene-600)-methylene-5-(1-thymine) isophthaloyl (PPEMTI) and Poly(polyoxyethylene-600)-methylene-5-(9-adenine) isophthaloyl (PPEMAI). We confirmed the structure of every molecular we synthesized by 1H NMR and the purity of those monomer molecules which used for polymerization by elemental analysis. We characterized every copolymer by 1H NMR and GPC. It did not affect the function of nucleic acid bases with polymerization process thought 1H NMR results. The amino on thymine of copolymer or the adenine remained the former structure. This is of great significance for the molecular recognition between nucleobases. This provides the basis for us to simulate the DNA aggregates.2. Study of the morphology of the copolymer with with its complementary baseThe copolymer and its complement base were dissolved in spectroscopic grade chloroform (for example, PPETHI /adenine, molar ratio 1:1) and then removed the solvent by N2 flow to obtain the amphiphilic film. The resulting film was covered with double distilled water and ultrasonic grinding in the ice water bath in order to make the aggregates better dissolved in water. The solutions were cooled with ice-water for half an hour and then rose to room temperature, dropped on silica plate and dried under vacuum for SEM.From the experimental results, we found that the aggregates are formed spheroid or ellipsoid shapes expect the copolymer PPEAHI with substrate barbituric acid, which was rod-like in the system of copolymer PPETHI, PPEAHI with its complementary base. In the PPEAHI/VB2 system or the PPETHI/PPEAHI system, the nanoparticles will cluster together among each other when the substrate molecular is large, for example. In the system of copolymer PPEMTI, PPEMAI with its complementary base, it still formed spherical or ellipsoid aggregates when the two copolymers dissolved into water separately. Nevertheless, the shapes changed when its substrate added in. it formed special shapes such as cube or strips.We know that the receptor will achieve the best combination of conformation with the substrate when they recognize with each other so that the hydrogen bonds could achieve the most stable state. This is called conformation re-organization of the identify process. Therefore, we deemed that the single form of the aggregates in the copolymer PPETHI and PPEAHI system is because of the long alkyl chain which grafting group of nucleic acid bases. This has led to the identification of groups were separated by the alkyl chain in the hydrophobic aggregates. It cannot have a greater impact on the shapes of the aggregates by the formation of different hydrogen bonds space three-dimensional structure. We improved the structure of copolymer composition in the copolymer PPEMTI and PPEMAI system. We removed the hexyl chain, which linked the benzene ring and the nucleic acid bases, so that nucleic acid bases could link directly with the rigid benzene ring. This led to a great impact on the shapes of the aggregates by the formation of different hydrogen bonds space three-dimensional structure. This differences in morphology showed that it has evident impact by the length of alkyl chain in hydrophobic groups.In addition, we freeze out the aqueous solution of PPETHI copolymer aggregates on the silicon directly to test their form. It shows that lyophilization does not impact the shapes of the aggregates. It could remain their shape as they are in the aqueous solution. This provides a theoretical basis for us to use solid FT-IR for the test of hydrogen bonds formation.3. Study of molecular recognize between the copolymer and its complementary baseWe lyophilized the aqueous solution of aggregates in order to test the formation of hydrogen bonds. From the FT-IR spectrum of recognition, we found that the amino and hydroxyl on the complementary base pairs have varying degrees of displacement. In the PPETHI / adenine system, for example, the free band at 3352 cm-1 disappeared and a new band at 3373 cm-1 emerges, which is assigned to the hydrogen-bond formation between C=O of thymine and N-H of adenine in PPETHI/adenine nanospheres. The band at 3109 cm-1 and 3054 cm-1 are related to the bonded N-H stretching vibrations and the band of 3109 cm-1 might be shifted from 3122 cm-1of adenine, and band of 3054 cm-1 was from 3064 cm-1of thymine in PPETHI copolymer respectively. It is found that the characteristic vibration band of thymine at 1685 cm-1 shifted to 1680 cm-1, However, the band of the C2=O of the thymine did not changed at 1722 cm-1. Similarly, the 1595 cm-1 band did not change. The shift of C4=O stretching band to lower frequency suggested that the hydrogen-bond formation between C4=O and N-H in the hydrophobic region of the nanospheres.In the variable temperature FT-IR spectrum of the PPETHI/adenine nanospheres, upon heating from 25 oC, the peak of 3373 cm-1 basically remain unchanged with increasing temperature, and gradually undergoes a decrease in intensity and an increase in bandwidth with increasing temperature prior to 115 oC, which indicates that the hydrogen-bonding interaction between the thymine and adenine is gradually reduced. However, the peak of 3373 cm-1 changed abruptly to 3312 cm-1, which is close to 3309 cm-1 of adenine at 115 oC. The band at 1722 cm-1 does unchanged with heating from 25 oC to 130 oC, however, the band at 1680 cm-1 changed to 1685 cm-1. Upon heating further above 115 oC, the band at 1685 cm-1 does not change.We also observed that in the recognition system, the hydrogen bond will formed between the four carbonyl (C4=O) of thymine and the amino-adenine when thymine as receptor, for example, in PPETHI / adenine system, PPEAHI / PPETHI system, PPEMTI / adenine system and PPEMTI / PPEMAI system. The hydrogen bond will formed between the two carbonyl (C2=O) of thymine and the amino-adenine when thymine or its derivatives as substrate, for example, in PPEAHI / thymine system, PPEAHI/5-FU system, PPEAHI / BA system, PPEAHI/VB2 system, PPEMAI / thymine system and PPEMAI/5-FU system. This maybe caused by two reasons. First, the differences between the carbonyl oxygen atom electronegativity on thymine or its derivatives. Second, in order to achieve the best combination of conformation when the receptor with the combination of substrate, they formed different kinds of space three-dimensional structure of hydrogen bonds affects the stability.In conclusion, we designed and synthesized two series of copolymers could enhance the receptor and the substrate interaction through hydrogen bonding. It could increase the capacity of drug receptors if the substrate is drug that contained the complementary group. The morphology of the aggregates could change by adjust the length of alkyl chain. It provided a possible way to mimic the double helix structure of biology in chemical system.更多还原