Syntheses, spectra and crystal structures of ruthenium(II) complexes with polypyridyl: [Ru(bipy)2(phen)](ClO4)2 · H2O and [Ru(bipy)2(Me-phen)](ClO4)2

Two ruthenium(II) complexes with polypyridyl, Ru(bipy)₂(phen)](ClO₄)₂·H₂O (1) and [Ru(bipy)₂(Me-phen)](ClO₄)₂ (2), (phen = 1,10-phenanthroline, bipy = 2,2′-bipyridine, Me-phen = 5-methyl-1,10-phenanthroline), were synthesized and characterized by IR, MS and NMR spectra. Their structures were determined by single crystal X-ray diffraction techniques. The strong steric interaction between the polypyridyl ligands was relieved neither by the elongation of the Ru---N bonds nor increase of the N---Ru---N bite angles. The coordination sphere was distorted to relieve the ligand interaction by forming specific angles (δ) between the polypyridyl ligand planes and coordination planes (N---Ru---N), and forming larger twisted angles between the two pyridine rings for each bipy. The bond distances of Ru---N(bipy) and Ru---N(phen) were virtually identical with experimental error, as expected of π back-bonding interactions which statistically involve each of the ligands present in the coordination sphere.     

Synthesis, DNA-binding and photocleavage studies of cobalt(III) mixed-polypyridyl complexes: [Co(phen)(2)(dpta)](3+) and [Co(phen)(2)(amtp)](3+)

Two novel cobalt(III) mixed-polypyridyl complexes [Co(phen)(2)(dpta)](3+) and [Co(phen)(2)(amtp)](3+) (phen=1,10-phenanthroline, dpta=dipyrido-[3,2-a;2',3'-c]- thien-[3,4-c]azine, amtp=3-amino-1,2,4-triazino[5,6-f]1,10-phenanthroline) have been synthesized and characterized. The interaction of these complexes with calf thymus DNA was investigated by spectroscopic, cyclic voltammetry, and viscosity measurements. Results suggest that the two complexes bind to DNA via an intercalative mode. Moreover, these Co(III) complexes have been found to promote the photocleavage of plasmid DNA pBR322 under irradiation at 365nm. The mechanism studies reveal that hydroxyl radical (OH()) is likely to be the reactive species responsible for the cleavage of plasmid DNA by [Co(phen)(2)(dpta)](3+) and superoxide anion radical (O(2)(-)) acts as the key role in the cleavage reaction of plasmid DNA by [Co(phen)(2)(amtp)](3+).     

Ruthenium(II) mixed-ligand complexes containing 2-(6-methyl-3-chromonyl)imidazo[4,5-f][1,10]-phenanthroline: Synthesis, DNA-binding and photocleavage studies

Two novel Ru(II) complexes [Ru(bpy)₂(MCMIP)]²⁺ (1) and [Ru(phen)₂(MCMIP)]²⁺ (2) (bpy = 2,2′-bipyridine; phen = 1,10-phenanthroline; MCMIP = 2-(6-methyl-3-chromonyl)imidazo[4,5-f][1,10]-phenanthroline) have been synthesized and characterized by elemental analysis, mass spectra and ¹H NMR. The DNA-binding properties of the complexes were investigated by absorption, emission, melting temperature and viscosity measurements. Experimental results indicate that the two complexes can intercalate into DNA base pairs. Upon irradiation at 365 nm, two Ru(II) complexes were found to promote the cleavage of plasmid pBR 322 DNA from supercoiled form I to nicked form II, and the mechanisms for DNA cleavage by the complexes were also investigated.     

DNA-binding and photocleavage properties of cationic porphyrin-anthraquinone hybrids with different lengths of links

Four cationic porphyrin–anthraquinone (Por–AQ) hybrids differing in lengths of flexible alkyl linkage, 5-[4-(1-N-anthraquinonon-yl)-l-oxophenyl]-10,15,20-tris(N-methylpyridinium-4-yl)porphyrin triiodide, (l = acetyl, pentanoyl, octanoyl, undecanoyl, designed as [AQATMPyP]I₃, [AQPTMPyP]I₃, [AQOTMPyP]I₃ and [AQUTMPyP]I₃, respectively, see Fig. 1), were synthesized and their interactions with DNA were investigated. The results of spectroscopic, denaturation and viscosity measurements suggest that [AQATMPyP]I₃ binds to DNA through non-intercalative mode while the other three hybrids with longer links bind via bis-intercalative mode. Ethidium bromide (EB) competition experiment was carried out to determine the binding constants (K_b) of these compounds for CT DNA, and [AQPTMPyP]I₃ shows the largest K_b among these hybrids. The photocleavage mechanism and wavelength-dependent cleaving abilities of these hybrids to pBR322 plasmid DNA were also comparably investigated.     

Screening and Mutagenesis of Aspergillus niger for the Improvement of Glucose-6-Phosphate Dehydrogenase Production

The Aspergillus niger strain ZBY-7 was selected as the original strain of glucose-6-phosphate dehydrogenase production. After mutagenesis of the strain by means of UV irradiation and nitrosoguanidine, mutants of Aspergillus niger resistant to a certain metabolic inhibitor were obtained. Five of the mutants showed increased glucose-6-phosphate dehydrogenase production. The mutant resistant to antimycin A (Aspergillus niger AM-23) produced the highest level of glucose-6-phosphate dehydrogenase (695.9% of that produced by the original strain).     

Increased thermostability and phenol removal efficiency by chemical modified horseradish peroxidase

Horseradish peroxidase was modified by phthalic anhydride and glucosamine hydrochloride. The thermostabilities and removal efficiencies of phenolics by native and modified HRP were assayed. The chemical modification of horseradish peroxidase increased their thermostability (about 10- and 9-fold, respectively) and in turn also increased the removal efficiency of phenolics. The quantitative relationships between removal efficiency of phenol and reaction conditions were also investigated using modified enzyme. The optimum pH for phenol removal is 9.0 for both native and modified forms of the enzyme. Both modified enzyme could suffer from higher temperature than native enzyme in phenol removal reaction. The optimum molar ratio of hydrogen peroxide to phenol was 2.0. The phthalic anhydride modified enzyme required lower dose of enzyme than native horseradish peroxidase to obtain the same removal efficiency. Both modified horseradish peroxidase show greater affinity and specificity of phenol.     

Impacts of Cd(II) on the conformation and self-aggregation of Alzheimer's tau fragment corresponding to the third repeat of microtubule-binding domain

Environmental exposure to some heavy metals such as cadmium appears to be a risk factor for Alzheimer's disease (AD), however, definite mechanism of their toxicity in AD remains to be elucidated. Previous studies largely focused on the metal ions binding to beta-amyloid, however, very few papers concerned the interaction between tau and metal ions. For the first time, we investigated the impacts of Cd(II) on the conformation and self-aggregation of Alzheimer's tau peptide R3, corresponding to the third repeat of microtubule-binding domain. The initial state of R3 was proven to be dimeric linked by intermolecular disulfide bond, in the non-reducing buffer (Tris-HCl buffer pH7.5, containing no reducing reagent). In this paper, we show that Cd(II) can accelerate heparin-induced aggregation of R3 or independently induce the aggregation of R3, as monitored by ThS fluorescence. In the presence of Cd(II), the resulting R3 filaments became much smaller, as revealed by electron microscopy. Binding to the Cd(II) ion, the dimeric R3 partially lost its random coil, and converted to alpha-helix structure, as revealed by CD and Raman spectrum. Stoichiometric analysis of CD signal against the ratio of [Cd(II)]/[R3] suggested that the coordination intermediate consisted of two R3 dimers binding to a central cadmium ion. As the seed, the coordination intermediate could extensively accelerate the self-aggregation of R3 via promoting the nucleation step. On the other hand, gain in alpha-helix structure on the peptide chain, by coordinating with Cd(II), could be a critical role to promote self-aggregation, as revealed by Raman spectrum. These results provide a further insight into the mechanism of tau filament formation and emphasize the possible involvement of Cd(II) in the pathogenesis of AD.     

Synthesis, characterization, and DNA-binding of chiral complexes delta- and lambda-[Ru(bpy)2(pyip)]2+

New chiral Ru(II) complexes delta and lambda-[Ru(bpy)(2)(pyip)](PF(6))(2) [(bpy = 2,2'-bipyridine; pyip = (2-(1-pyrenyl)-1H-imidazo[4,5-f] [1,10]phenanthroline] were synthesized and characterized by elemental analysis, (1)H NMR, ESI-MS, IR, and CD spectra. Their DNA-binding properties were studied by means of UV-vis, emission spectra, CD spectra and viscosity measurements. A subtle but detectable difference was observed in the interaction of both enantiomer with CT-DNA. Spectroscopy experiments indicated that each of these complexes could interact with the DNA. The DNA-binding of the Delta-enantiomer was stronger than that of Lambda-enantiomer. DNA-viscosity experiments provided evidence that both Delta- and Lambda-[Ru(bpy)(2)(pyip)](PF(6))(2) bound to DNA by intercalation. At the same time, the DNA-photocleavage properties of the complexes were investigated too. Under irradiation with UV light, Ru(II) complexes showed different efficiency of cleaving DNA.     

Studies on synthesis, characterization, and G-quadruplex binding of Ru(II) complexes containing two dppz ligands

In this work, the interaction between the guanine-rich single-strand oligomer AG₃(T₂AG₃)₃ quadruplex and two Ru(II) complexes, [Ru(L¹)(dppz)₂](PF₆)₄ (1) and [Ru(L²)(dppz)₂](PF₆)₄ (2) (L¹ = 5,5′-di(1-(trimethylammonio)methyl)-2,2′-dipyridyl cation, L² = 5,5′-di(1-(triethylammonio)methyl)-2,2′-dipyridyl cation, dppz = dipyrido[3,2-a:2′,3′-c] phenazine), has been studied by UV-Visible, fluorescence, DNA melting, and circular dichroism in K⁺ buffer. The two complexes after binding to G-quadruplex have shown different DNA stability and fluorescence enhancement. The results show that both complexes can induce the stabilization of quadruplex DNA. ΔT_m values of complexes 1 and 2 at [Ru]/[DNA] ratio of 1:1 were 9.4 and 7.0, respectively. Binding stoichiometry along with the quadruplex was investigated through a luminescence-based Job plot. The major inflection points for complexes 1 and 2 were 0.49 and 0.46, respectively. The data were consistent with the binding mode at a [quadruplex]/[complex] ratio of 1:1. In addition, the conformation of G-quadruplex was not changed by the complexes at the high ionic strength of K⁺ buffer.