Research On Construction And Performance Of Metal-organic Octahedra And Macrocycles

Metal-organic polyhedra and macrocycles are important models to realize the process of enzyme catalysis and recognition. These structures discussed exhibit well-defined cavities with gated pores providing specific inner environments for selective uptaking and binding of guest molecules. Yet only a few "artificial systems" achieved the detection and imaging techniques in biological systems and the magnificent catalysis of natural enzymes. The major challenge at stake here goes beyond the introducing of an optical measurable output, the active sites and specific weak effect response sites. On the basis of this context, by combining these functional groups into metal-organic polyhedra/macrocycles with considerable stabilities, we constructed relatively enclosing metal-organic octahedra and relatively open metal-organic macrocycles for biological molecules recognition and simulating enzyme catalysis researches.1. Metal-organic octahedra research(1) Biological molecules recognition:By combining three quinoline groups as fluorophores, constituting amide groups as guest binding sites and communicators, we created metal-tunable octahedral nanocages Co-PT1/Zn-PTl [PT1(N’,N",N"’-tris(quinolin-2-yl-methylene)benzene-1,3,5-tricarbohydrazide)]. Such a special two-fold hydrogen bonding pattern which only occurs between the cytidine and PT1is important for compounds Co-PT1/Zn-PTl to selectively recognize cytidine over others by both Uv-vis and luminescent responses.(2) MRI Contrast Agent: By combining high-spin Gd3+ions with PT2(N’,N",N"’-tris(pyridin-2-yl-methylene)-benzene-1,3,5-tricarbohydrazide) to form octahedral nanocages Gd-PT2. Gd-PT2exhibited quite high longitudinal relaxivity (r1=388.5mM-1a-1), and could apply images of a living mouse hypodermis, could be described as the glucosamine-specific probes in the MR responses. The glucosamine molecules in the solution substitute the coordinated water molecules, and interact with Gd3+ions directly to induce the decreasing of MR responses.(3) Heterogeneous catalysis:Through incorporating having characteristic green luminescence Tb3+ions as Lewis acid sites and amide groups as guest-accessible functional weak base sites, we constructed porous molecular materials having one-dimensional channels, for size-selectively heterogeneous catalyzing the cyanosilylation and aldol reactions. The cyanosilylation reactions mostly took part in the channel of the catalysts and the aldehydes substrates were activated by the Tb3+ions, while the aldol reactions mainly occurred in the octahedral cavities and the cyclohexanone substrates possibly interacted with the amide groups through a hydrogen bond, respectively.2. Metal-organic macrocycles research(1) Chiral catalysis:A. Through incorporation of a L-proline moiety within ligand PT3(N’,N",N"’-bis(pyridin-2-ylmethylene)-5-((S)-pyrrolidine-2-carboxamido)isophthalohydrazide) containing amide groups, we have developed a new approach to create metal-tunable homochiral triangles Co-PT3/Ni-PT3. With the asymmetric catalytic active sites to stabilize the potential transition state and the helical cavity to increase the local concentration of the substrates, triangles work as asymmetric enzyme-like catalysts prompting the well-known aldol reactions with size-and stereoselectivity [(anti:syn)max=10.3:1].B. By using L-/D-proline as a chiral adduct, we performed the homochiral lanterns of the two enantiomorphs L-CePT4/D-CePT4[L-PT4(N’,N",N"’-bis((2-hydroxynaphthalen-1-y1)-methylene)-5-((S)-pyrrolidine-2-carboxamido)isophthalohydrazide); D-PT4(N’,N",N"’-bis((2-hydroxynaphthalen-1-y1)methylene)-5-((R)-pyrrolidine-2-carboxamido)isophthalohydrazide)], having coordinatively unsaturated metal sites Ce3+. Asymmetric cyanosilylations of aromatic aldehydes were dispalyed to validate the excellent enantioselectively catalytic performance of the lanterns (eemax>99%).(3) Biological molecules recognition:By combining anthracene groups as fluorophores, constituting amide groups as guest binding sites and communicators, we created metal-organic squares Co-PT7[PT7(N’,N",N"’-bis(1-(pyridin-2-yl)ethylidene)anthracene-9,10-dicarbohydrazide)]. These squares can be ATP-specific probes in luminescence responses as compared to other nucleotides, by utilizing the synergistic effects of electrostatic.π-stacking. hydrogen-bonding and coordinative interactions inside the cavity.