Recognition Of Biomacromolecules By Multifunctional Complexes And Its Biological Applications

Biomacromolecules present in living organisms, like DNA, proteins are closely associated with life. The recognition of biomacromolecule has great significance in signal transduction, genome duplication, proteomics, clinical diagnostics, and development of targeting drugs. Metal complexes can react with such macromolecules with many metal-binding sites and have diversely biological applications. Owing to the advantageous luminescence, lanthanide complexes have received much attention as luminescent probes to detect biomacromolecules. Platinum-based anticancer drugs have exhibited their high activity via targeting to DNA nucleobases, however, they also might bind to several other biomacromolecules before DNA is reached. Therefore platinum complexes as potential drugs may also interact with some proteins related with other diseases. The dissertation is composed of five chapters, focusing on exploring novel multifunctional terbium and/or platinum-based complexes to recognize DNA or proteins and its biological applications.Chapter 1, the recognition of biomacromolecules was reviewed including structures and reactive sites of DNA and proteins, the advantage of lanthanide luminescence and lanthanide complexes as luminescent probes for biomacromolecules, the interactions between platinum-based anticancer drugs and DNA or proteins.Chapter 2, a novel terbium complex (TbL) was synthesized as a time-resolved luminescence probe for human serum albumin (HSA) in aqueous solution at physiological pH. TbL is constituted by a luminescent terbium(Ⅲ) center and a polydentate ligand, where the diethylenetriaminepentaacetate (DTPA) moiety functions as the reporter and two 2-methyl-5-nitroimidazole (metronidazole) moieties as the sensor. The luminescence intensity of TbL significantly enhanced upon reacting with HSA via multiplex interactions with amino acid residues in HSA. TbL exhibits a higher selectivity for HSA than other proteins or enzymes. Furthermore, this probe can also detect the changes of HSA induced by therapeutic drugs like cisplatin and phospholipids. Nitro groups are indispensable element for the luminescence enhancement and hydrogen bonding between nitro groups and amino acid residues in HSA is the predominant interaction. Besides nitro groups, the proper space configuration of HSA, the hydrogen bonding between the coordinated water and functional groups on the surface of HSA, and the high affinity of HSA for metronidazole moieties may also play roles synergistically in detection. By virtue of the excellent water-solubility, near physiological expetimental condition and high sensitivity, TbL may become a convenient tool to detect interactions between drugs and HSA.Chapter 3, the luminescence changes of TbL were further investigated in presence of DNA. TbL exhibits a remarkable selectivity for adenine and guanine nucleobases in single-stranded oligonucleotides and calf thymus DNA, accompanied with a significant enhancement in luminescence. Interestingly, TbL is not responsive to nucleotide monophosphates containing either a purine or a pyrimidine base. On above results, TbL sensitively and fleetly gives instant luminescence response to the depurination of DNA caused by Methyl methanesulfonate (MMS) and acidic conditions. TbL selectively interacts with purine nucleobases in DNA with some intercalative mode owing to the preferred binding of nitroimidazole moieties with guanine and adenine bases. Nitro groups are also the predominant element for the luminescence enhancement of TbL. Owing to its excellent selectivity, high sensitivity, and instantaneity, TbL may usefully detect the DNA damage or repair involving depurination in real-time.Chapter 4, a novel heterotrinuclear terbium-platinum complex (TPC) has been designed as a selective time-resolved luminescence probe for guanine base and N7-guanine modification of DNA. The probe consists of a luminescent terbium(III) center and two monofunctional platinum(Ⅱ) moieties with a multifunctional polydentate ligand as the linker. TPC exhibits a remarkable selectivity for monophosphate of guanosine (GMP) over other nucleotides, accompanied with a significant luminescence enhancement. Moreover, the probe is capable of detecting guanine in single-stranded oligonucletides and calf thymus DNA. Mechanistic studies using the electrospray mass spectrometry and the NMR spectroscopy revealed that the luminescence enhancement resulted from the preferential binding of platinum(II) to N7 of guanine. More meaningfully, TPC can also detect the N7-guanine modification of DNA by MMS or cisplatin in aqueous solution. In view of its high sensitivity, excellent specificity, superior water solubility, and wide pH window, TPC may serve as an effective tool to detect guanine nucleobase and N7-guanine modification in DNA by anticancer drugs and carcinogens.Charpter 5, two macrocyclic platiniferous chelators (PC1, PC2) derived from cyclen have been designed as novel bifunctional inhibitors of the metal-induced amyloid-β(Aβ) aggregation. PC1 and PC2 contain two moieties:cyclen as the metal-chelating unit(s) and Pt(bipyridine)Cl2 as the A/?-binding unit. The interaction between the chelators and Aβaggregates was studied by the tandem mass spectrometry and 1H NMR. Platinum centers in PC1 and PC2 were proved to coordinate with histidine residue (His-14 or-13) of Aβ40. The inhibitory effect of the chelators on Aβ40 aggregation induced by Zn2+ and Cu2+ ions was investigated using turbidometry, thioflavin T fluorescence spectroscopy, and BCA protein assay. PC1 and PC2 inhibit the Aβaggregation more effectively than the unmetalated macrocyclic chelator, cyclen. By contrast, the related anticancer drug cisplatin exhibits no inhibition on the Aβaggregation. Both PC1 and PC2 can suppress the generation of reactive oxygen species by Cu-Aβ40 and their neurotoxicity in cortical neuronal cells of mice. Moreover, they also showed decrease of Aβaggregation interacted with transgenic mice brain homogenates. These compounds represent a new type of chelators as potential anti-AD agents.