Syntheses, Characterization Of The Metal Complexes Involving Biimidazole And Their Interaction With DNA

Imidazole, with the prestige of 'life ligand', has distinguished talents of proton acceptor, conjugated acid-base and recognition ability for coordination. In nature, imidazole participates in many important biochemical reactions, acting as the functional group in enzymes' active centers. 2,2'-biimidazole (Hzbiim), as a bidentate chelating ligand with multi-proton donor sites, has two imidazole rings and can coordinate to many metals, forming complexes with particular structures. Therefore, it is one of the most important objects that interested in coordination chemistry, supramolecular chemistry and other related fields. At the same time, it is an important biological molecule that used abroad in biology, especially in enzyme mimics. Therefore, on the one hand, a more profound study on the mechanism of the interaction of the complexes involving H₂biim with DNA, and the relationships between the molecular structure and biological activity will not only help us to understand the process of life on a molecular level and pathogenic mechanism of some illness, but also provide rationales for new drug designs, as well as a means to develop novel agents for exploring the structures of nucleic acids. On the other hand, it is significant to study hydrogen-bonded assemblies involving H₂biim and its complexes to build supramolecular systemIn this thesis, firstly, we synthesized several metal complexes from H₂biim and its derivatives, characterized their structures with the methods of elemental analyses (EA), IR and X-ray Crystallography. We also investigated the interaction between these complexes and DNA by using UV, fluorescent spectra, electrochemistry, viscosity measurements, gel electrophoresis and molecular modeling. Secondly, starting from H₂biim, we synthesized five supramolecular compounds assemblied through hydrogen-bonding, investigated the H-bonding patterns andÏ€-Ï€interactions. The main results include:1. Two complexes, i.e. Mn(H₃biim)₂(NCS)₂Cl₂ and Cd(H₃biim)₂(NCS)₂Cl₂ have been synthesized from H₂biim, their structures were determined by X-ray crystallography. The two complexes have similar structures and both are neutral compounds. One N atom in H₂biim is protonated, forming a H3biim+ cation. The later is an unidentate ligand, the central metal, Cd or Mn is six coordinated and adopts a distorted octahedral environment. Molar electrolytic conductivity and quantum chemistry calculations reveal that the two complexes are disociated in solution, forming the cations, [Mn(H₃biim)₂(H₂O)₂]⁴⁺ or [Cd(H₃biim)₂(H₂O)₂]⁴⁺. Investigations on the interaction between DNA and the complexes show that the binding mode of the two complexes with DNA is mainly electrostatic. We found that DNA can quench the fluorescence intensity of the complexes, and thus obtained their, binding constants to be 1.48×10⁴ L/mol for Mn(H₃biim)₂(NCS)₂Cl₂ and 1.98×10⁴ L/mol for Cd(H₃biim)₂(NCS)₂Cl₂, respectively. We also found that the complex [Mn(H₃biim)₂(NCS)₂Cl₂] can cleave plasmid pBR322 DNA at pH 7.2 and 37℃. Studies on the mechanism of DNA cleavage implicate that DNA cleavage mediated by [Mn(H₃biim)₂(NCS)₂Cl₂] occurs via a hydrolytic path. Also, the complex [Cd(H₃biim)₂(NCS)₂Cl₂] can cleave plasmid pBR322 DNA at pH 7.2 and 37℃.The binuclear copper(â…¡) complex with 1,1'-dimethyl-2,2'-biimidazole ligand, [Cu₂(Dmbiim)₄(H₂O)₂](ClO₄)₄·6H₂O (Dmbiim=1,1'-dimethyl-2,2'-biimidazole) was synthesized and determined by X-ray crystallography. The crystal structure reveals that the complex is cage-shaped, with two Cu atoms bridged by Dmbiim. The distance between the two Cu atoms is 3.065A and two channels crossed each other were formed. Such type of channels would be significant in the field of supramolecuar material. DNA-binding investigations show that the copper(â…¡) complex interacts with DNA through minor groove binding. In addition, we found that the copper(â…¡) complex can cleave circular plasmid pBR322 DNA efficiently in the presence of AH₂ (ascorbic acid) at pH 8.0 and 37℃.2. Supramolecular assemblies of 2,2'-biimidazole with 4-aminobenzoic acid(PABA), 3,4,5-trihydroxy benzoic acid(THBA) and 5-sulfosalicylic acid(5-S SA), i.e. 2-(2-1H-imidazolyl)-1H-imidazolium chloride-4-aminobenzoic acid (â… ), 2,2'-bi-1H-imidazolium bis(3,4,5-trihydroxy benzoate) tetrahydrate (â…¡) and bis(2-(2-1H-imidazolyl)-1H-imidazolium) 3-carboxy-4-hydroxybenzene-sulfonate monohydrate (â…¢) have been synthesized and characterized by X-ray diffraction methods. Various H-bonds modes were found in these compounds owing to the protonization of N atoms in H₂biim. In compound (â… ), a fundamental unit of the crystal structure consisting a hydrogen-bonded trimer: PABA…H₃biim⁺…Cl^- via R₂² (9) and R₂¹ (7) forms a 1D ribbon through H-bond interactions. This 1D structure then extends into 3D via further H-bond andÏ€-Ï€interactions. In compound (â…¡), a fundamental unit of crystal structure consists of a hydrogen-bonded trimer: THBA^-…H₄biim²⁺…THBA via R₂² (9), which forms a 3D network by H-bonds. The 3D stacking is strengthened in further byÏ€-Ï€interactions between phenyl and adjacent imidazole rings, phenyl and phenyl rings. In compound (â…¢), there are two different H₃biim⁺ (H₃biim⁺-1 involving N1, N2, N3, N4 and H_biim⁺-2 involving N5, N6, N7, N8). Two adjacent H₃biim⁺-2 species connect each other by a direct side-by-side interaction, forming a centrosymmetric [H₃biim⁺-2…H₃biim⁺-2] dimer via R₂² (10). While two adjacent H₃biim⁺-1 species connect each other, yielding an unsymmetrical [H₃biim+-1…H₃biim⁺-1] dimer via R₂² (10), which maybe the result of the more contorted H₃biim⁺-1 than H₃biim⁺-2. In addition, the H₃biim⁺-1 cation and adjacent 5-SSA^2- anion species connect each other through cyclic R₂² (9) interaction, the H₃biim⁺-2 cation and adjacent 5-SSA^2- anion species connect each other through cyclic R₂² (7) interaction. And more, there exist some O—H…O hydrogen-bonds between water molecules and O atoms of sulfonate groups in 5-SSA^2-, weak C—H…O H-bonds and cation-anionÏ€-Ï€stacking interactions in the compound. The overall interactions aforesaid result in the formation of the 3D network.Another two complexes, [Ni(H₂biim)₂(PABA)₂]Cl₂·2H₂O (PABA=4-aminobenzoic acid) and [Co(H_biim)₂(H₂O)₂](isophthalate)·4H₂O, deriving from H₂biim, have been synthesized and characterized by. X-ray crystallography. In Ni(â…¡) complex, the cation [Ni(H₂biim)₂(PABA)₂]²⁺, Cl^- anion and H₂O molecule connects together via R₂¹(7) and R₄⁴(12), forming 2D network. This network then forms to layer structure byÏ€-Ï€interactions between adjacent benzene rings. In Co(â…¡) complex, the cation [Co(H₂biim)₂(OH₂)₂]²⁺ connects with two isophthalate anions via R₂² (9), forming a 1D-extended chain. The relative position of the carboxylate groups confers a wavy form to the 1D-array. This 1D structure then extends into 2D network structure via further O—H…O H-bonds andÏ€-Ï€interactions between imidazole and adjacent phenyl rings, imidazole and imidazole rings.