Synthesis And Application Of Nanomaterials Templated By G-rich DNA

Polymorphic conformations of G-rich DNAs through Hoogsteen bonding make them one of the most promising templates to control motions and organize matter with nanometer precision for nanotechnology. Due to the numerous and complicated G-quadruplexes from various G-rich sequences, as well as regulation of the polymorphic nature of the G-quadruplexes are manifold, synthesis and application of spatially nanoscale inorganic materials by using G-rich DNA templates have not been fully explored. Here, the polymorphic G-quadruplexes are increasingly studied as the intriguing building block to orient silica nanostructure, to synthesize Ag nanoparticles and to deposite TiO2 film.Firsly, we designed a series of G-rich oligunucleotides with 5'terminal one guanine missing from Oxytricha nova telomere G₄T₄G₄. G₂T₄G₄, G3T4G4 and G₄T₄G₄ in the presence of Na+ form dimeric antiparallel quadruplex structures, characterized by circular dichroism (CD), native polyacrylamide gel electrophoresis (PAGE), atomic force microscopy (AFM) and surface-enhanced raman spectra (SERS). When the number of guanine at 5'terminus of the sequences increases from 2 to 3 and then 4, the stability and the symmetry of the G-quadruplexes increase, and their behavior distinguishes with addition of ethanol. G₂T₄G₄ shows the potential of self-aggregation and modulation, it forms single-stranded structure at pH 2.0 and pH 4.0, anti-parallel and parallel mixture G-quadruplex under K+, and multi-stranded aggregates under Ba2+. Upon addition of aminopropyltrimethoxysilane (APTMS), G₂T₄G₄ template, which transforms form the antiparallel G-quadruplex to multi-stranded supermolecular assemblies in the presence of Na+, was integrated through sol-gel process to construct an interesting leaf-vein nanostructure of silica with regular branch intervals characterized by AFM and transmission electron microscope (TEM). Regulation of the polymorphic nature of the G-quadruplexes of G₂T₄G₄ by changing solution condition presents a novel methodology for modulating the silica architectures as a template. At low pH of 2.0, single-stranded G₂T₄G₄ oriented unordered organization of silica nanoparticles. Under 40% (v/v) ethanol aqueous solution, leaf-vein silica structures with shorter branch intervals and smaller particles were constructed. In the presence of Ba2+, club-shaped silica formed.Secondly, polymorphic DNA templates were emplored, including G-quadruplex of A8G12, I-motif of C12T8, and duplex of A8G12/C12T8 1:1 mixture. The influence of polymorphic DNA templates structure on the interaction between Ag+ and DNA was studied by using CD, PAGE and density functional theory (DFT) simulations. For G-quadruplex, the Ag+ is firstly chemically adsorbed at the center formed by eight O6 atoms of the two adjacent tetrad guanines (which denoted as type I interaction), then the Ag+ would bind with N3 of guanine, which was shown as type II interaction. For I-motif, Ag+ is trapped in C-C mismatches. Reduction of Ag+ in the presence of polymorphic DNA structures with equal NaBH4 resulted in the appearance of Ag nanoparticles. It is indicated that the size distribution (1.6 nm-3.9 nm), lattice spacings (111, 200) and the fluorescence performance of the silver nanocrystals are greatly dependent on the conformation of DNA templates. The reduction reaction of nitryl to amido was used to characterize the catalytic performance of the as synthesized Ag nanoparticles. Over Im-Ag the reaction has the highest rate constants. The reduction reaction of 4-nitrophenol over Im-Ag has the rate constant of 0.573 min-1 at the concentration of 0.360 mg/L, and for 4-nitrobenzoic acid the rate constant is 2.503 min-1 at the concentration of 0.720 mg/L.Thirdly, methyl terminal group of APTMS bonds with hydroxyl group on the Si surface and aldehyde group of glutaraldehyde is attack by amino groups of APTMS and DNA to form a covalent bond, G-quadruplex and duplex DNA were immobilized to a substration. Crystal TiO2 film was deposited on the substrate immobilizated DNA from solution of 10 mM TiCl4/0.05 mM HCl at 40 oC after 48 h. Characterized by raman spectra and TEM, amorphous-anatase TiO2 film forms under G-quadruplex and amorphous-anatase-rutile TiO2 film forms under duplex template. For contrast, phosphate-SAMs which immersed in 5 mM TiCl4/0.1 M HCl at 80 oC induced anatase TiO2 film.