Preparation And Self-assembly Of Dna-g-Polymer

Extensive efforts have been devoted to the development of hybrid structures consisting of DNA and organic polymers connected through covalent bonds. The hybrid materials not noly have the physiological functions of DNA molecules but also keep the unique properties of the polymer segment. This kind of biological materials are supposed to have unique advantages to serve as gene carriers. In this paper, we studied the chemical reactions of DNA with synthetic polymers such as polyethylene glycol (PEG), carboxymethyl cellulose (CMC) and hydroxyl silicone oil (PDMS) to form block copolymers or graft copolymers. In addition, block copolymer assemblies with more complex structures were achieved through biological methods as well as the hydrophobic effect of synthetic polymers.1. First of all, chemical synthesis and biosynthesis were adopted to the preparation of DNA and PEG block copolymer. Carboxyl terminated PEG was obtained by the reaction of PEG and maleic anhydride. After beening further activated by EDC and NHS, PEG with N-hydroxy-succinimide group was obtained. The PEG-NHS could react with the amino-terminated oligonucleotides (NH2-ODN) to form ODN-PEG and ODN-PEG-ODN block copolymers at room temperature. To achieve the final DNA-PEG-DNA or DNA-PEG block copolymers, the polymerase chain reaction (PCR) was performed and the ODN was expanded to double-stranded DNA with 1.3k base pairs. When the molecular weight of PEG was 3.4k, the reaction yields of PEG and ODN could reach more than 90%. While, when the molecular weight of PEG was 20k, the yields will be only 30%. However, the existing of PEG had no effect for the PCR process of ODN. After connecting with PEG, the gel electrophoresis migration rate of the ODN and 1.3k DNA will slow down. The presence of PEG allows the DNA evenly distributed on the mica under a certain concentration. In another experiment where the α- amylase was modified with PEG, the activity of the enzyme remained the same. What’s more, through the BAS action and the role of complementary base pairing, new DNA/protein complexes were generated.2. Further, the hybrid copolymers of CMC side chain grafted DNA was obtained by the method similar to the reaction of PEG and DNA. There are many carboxyl groups along the side of CMC which could be modified into NHS. Under acidic conditions, the EDC and NHS-activated carboxyl groups on the CMC backbone could react with the ODN-NH2, to get the side chain grafted ODN of CMC-g-ODN. Negatively charged CMC and 1.3k bp DNA could accelerate the rate of migration on a 1% horizontal agarose gel electrophoresis process, which slows down the rate of migration in denaturing polyacrylamide vertical slab gel electrophoresis.3. Finally, chemical synthesis method was used to prepare the DNA with side chain graftedPDMS to get amphiphilic hybrid copolymer, and the product had the capability of self-assembly. The strong chemical reactivity of isophorone diisocyanate was used to connect the terminal hydroxy group of PDMS and the amino groups on the DNA backbone to get DNA-g-PDMS. After the products being dissolved in acetonitrile and aqueous solution respectively, they could conceive opposite spherical micelles with core-shell structures. Micelle size in the two solutions were at 250nm and 300nm respectively. When the biomacromolecule bovine serum albumin was added to the micelle, it could be found that the micelles aggregated in the organic solvent but dispersed well in aqueous solution.