Qianling Zhang

DNA-binding and photocleavage studies of cobalt(III) polypyridyl complexes: [Co(phen)2IP]3+ and [Co(phen)2PIP]3+

Two complexes of [Co(phen)2IP]3+ (IP=imidazo[4,5-f][1,10]phenanthroline) and [Co(phen)2PIP]3+ (PIP=2-phenylimidazo[4,5-f][1,10]phenanthroline) have been synthesized and characterized by UV/VIS, IR, EA and mass spectra. The binding of the two complexes with calf thymus DNA has been investigated by absorption spectroscopy, cyclic voltammetry, viscosity measurements and DNA cleavage assay. The spectroscopic studies together with cyclic voltammetry and viscosity experiments support that both of the complexes bind to CT DNA by intercalation via IP or PIP into the base pairs of DNA. [Co(phen)2PIP]3+ binds more avidly to CT DNA than [Co(phen)2IP]3+, which is consistent with the extended planar and π system of PIP. Noticeably, the two complexes have been found to be efficient photosensitisers for strand scissions in plasmid DNA.

DNA-binding and cleavage studies of macrocyclic copper(II) complexes

Three hexaaza macrocyclic copper (II) complexes with different functional groups have been synthesized and characterized by elemental analysis and infrared spectra. Absorption and fluorescence spectral, cyclic voltammetric and viscometric studies have been carried out on the interaction of [CuL(1)]Cl(2) (L(1)[double bond]3,10-bis(2-methylpyridine)-1,3,5,8,10,12-hexaazacyclotetradecane), [CuL(2)]Cl(2) (L(2)[double bond]3,10-bis(2-propionitrile)-1,3,5,8,10,12-hexaazacyclotetradecane) and [CuL(3)]Cl(2) (L(3)=3,10-bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane) with calf thymus DNA. The results suggest that three complexes can bind to DNA by different binding modes. The spectroscopic studies together with viscosity experiments and cyclic voltammetry suggest that [CuL(1)](2+) could bind to DNA by partial intercalation via pyridine ring into the base pairs of DNA. [CuL(2)](2+) may bind to DNA by hydrogen bonding and hydrophobic interaction while [CuL(3)](2+) may be by weaker hydrogen bonding. The functional groups on the side chain of macrocycle play a key role in deciding the mode and extent of binding of complexes to DNA. Noticeably, the three complexes have been found to cleave double-strand pUC18 DNA in the presence of 2-mercaptoethanol and H(2)O(2).

Nitrogen and Sulfur Dual-Doped Non-Noble Catalyst Using Fluidic Acrylonitrile Telomer as Precursor for Efficient Oxygen Reduction

In order to make polyacrylonitrile (PAN) fluidic, acrylonitrile telomer (ANT) is synthesized by radical telomerization and used as a nitrogen and carbon precursor to prepare a non-noble oxygen reduction reaction (ORR) catalyst. This fluidic precursor greatly increases the contact between Fe salt aggregates and the polymer so that more active sites are formed during stabilization and carbonization. Such prepared catalysts and the commercial Pt/C catalyst have comparable ORR performance and stability.

Effects of the ancillary ligands of polypyridyl ruthenium(II) complexes on the DNA-binding behaviors

A new polypyridyl ligand PMIP {PMIP = 2-(4-methylphenyl)imidazo[4,5-f]1,10-phenanthroline}, and its Ru(II) complexes, [Ru(bpy)2PMIP]2+1 (bpy = 2,2′-bipyridine), [Ru(phen)2PMIP]2+2 (phen = 1,10-phenanthroline) and [Ru(dmp)2PMIP]2+3 (dmp = 2,9-dimethyl-1,10-phenanthroline), have been synthesized and characterized. The binding of the three complexes to calf thymus DNA (CT DNA) has been investigated with spectrophotometic methods, viscosity measurements, as well as equilibrium dialysis and circular dichroism spectroscopy. Complexes 1 and 2 can bind to CT DNA through intercalation. Complex 3 binds to CT DNA via partial intercalative mode. All the three complexes can enantioselectively interact with CT DNA in a way. Complex 3 is a much better candidate as an enantioselective binder to CT DNA than complex 1 and complex 2. The Δ enantiomer of complex 1 is slightly predominant for binding to CT DNA to the Λ enantiomer. The experimental results suggest that the ancillary ligands of polypyridyl Ru(II) complexes have significant effects on the spectral properties and the DNA-binding behaviors of the complexes. On the basis of the experiments, the theoretical calculations applying the density functional theory (DFT) on the level of B3LYP/LanL2DZ basis set for these three complexes have been used to further discuss the trend in the binding strength or binding constants (Kb) of the complexes to DNA, as well as predict roughly some of their spectral properties.

Synthesis, characterization and the effect of ligand planarity of [Ru(bpy)2L]2+ on DNA binding affinity.

Two structurally related ligands (L) 4,5,9,18-tetraazaphenanthreno[9,10-b] triphenylene (taptp) and 2,3-diphenyl-1,4,8,9-tetraazatriphenylene (dptatp), and their related complexes of [Ru(bpy)2L]2+ have been synthesized and characterized by elemental analyses, 1H NMR and mass spectra. Their electrochemical properties were also examined. Both complexes emit intense luminescence in organic solvent but are quenched in water to different extents. The interactions of the complexes with calf thymus DNA have been investigated by viscosity, absorption, emission and circular dichroism spectra. The intrinsic binding constants of [Ru(bpy)2(taptp)]2+ and [Ru(bpy)2(dptatp)]2+ are 1.7 x 10(5) and 3.8 x 10(4) M-1, respectively. All data indicate that both complexes bind enantioselectively to double-stranded calf thymus DNA via the intercalative mode, with stronger affinity for the fully planar ligand complex of [Ru(bpy)2(taptp)]2+.

Effect of intramolecular hydrogen-bond on the DNA-binding and photocleavage properties of polypyridyl cobalt(III) complexes

Abstract Two polypyridyl cobalt(III) complexes containing intramolecular hydrogen-bond [Co(phen) 2 HPIP] 3+ (HPIP=2-(2-hydroxyphenyl)imidazo[4,5- f ][1,10]phenanthroline) and [Co(phen) 2 HNAIP] 3+ (HNAIP=2-(2-hydroxy-l-naphthyl)imidazo[4,5- f ][1,10]phenanthroline) have been synthesized and characterized by UV–Vis, EA and MS spectra. Binding of both complexes with calf thymus DNA has been investigated by cyclic voltammetry, absorption spectroscopy, luminescence titration, viscosity measurements and DNA cleavage assay. The results suggested that the complex [Co(phen) 2 HPIP] 3+ bound to CT DNA by intercalation via HPIP into the base pairs of DNA, while [Co(phen) 2 HNAIP] 3+ bound with DNA by partial intercalating the ligand HNAIP. In addition, both complexes have been found to promote the single-stranded cleavage of plasmid pBR 322 DNA upon irradiation, and [Co(phen) 2 HPIP] 3+ exhibited the higher cleaving efficiency.

Optimization of glucose oxidase production by Aspergillus niger in a benchtop bioreactor using response surface methodology

Response surface methodology (RSM) was applied to optimize the speed of agitation and the rate of aeration for the maximum production of glucose oxidase (GOD) by Aspergillus niger. A 22 central composite design using RSM was employed in this investigation. A quadratic model for GOD production was obtained. Aeration had more negative effect on GOD production than agitation. Significant negative interaction existed between agitation and aeration. The quadratic term of agitation presented significant positive effect. The maximum level of GOD was achieved when the speed of agitation and the rate of aeration were 756 rev min−1 and 0.9 v/v/m, respectively. The fermentation kinetics of GOD by Aspergillus niger were also studied in a batch system. A simple model was proposed using the Logistic equation for growth, the Luedeking–Piret equation for GOD production and Luedeking–Piret-like equation for glucose consumption. The kinetic model parameters X0, Xm, μm, α, k, YX/S, mS and S0 is 0.24 mg ml−1, 1.65 mg ml−1 and 0.23 h−1, 3.45 U mg−1, −0.81 U ml−1, 1.60 g g−1, 9.72 g g−1 h−1 and 97.6 g l−1, respectively. The model appeared to provide a reasonable description for each parameter during the growth phase. The production of GOD was growth-linked.

A mathematical model for gluconic acid fermentation by Aspergillus niger

Abstract The fermentation kinetics of gluconic acid by Aspergillus niger were studied in a batch system. A simple model was proposed using the logistic equation for growth, the Luedeking–Piret equation for gluconic acid production and Luedeking–Piret-like equation for glucose consumption. The model appeared to provide a reasonable description for each parameter during the growth phase. The production of gluconic acid was growth-associated.

Enantiomeric ruthenium(II) complexes binding to DNA: binding modes and enantioselectivity

Δ- and Λ-[Ru(bpy)2(HPIP)](PF6)2 (Δ-1 and Λ-1; bpy =2,2′-bipyridine, HPIP=2-(2-hydroxyphenyl)imidazo[4,5-f][1,10]phenan-throline), Δ- and Λ-[Ru(bpy)2(HNAIP)](PF6)2 (Δ-2 and Λ-2; HNAIP=2-(2-hydroxy-1-naphthyl)imidazo[4,5-f][1,10]phenanthroline), Δ- and Λ-[Ru(bpy)2 (HNOIP)](PF6)2 (Δ-3 and Λ-3; HNOIP=2-(2-hydroxy-5-nitrophenyl)imidazo[4,5-f][1,10]phenanthroline), and Δ- and Λ-[Ru(bpy)2(DPPZ)](PF6)2 (Δ-4 and Λ-4; DPPZ=dipyridophenazine), have been synthesized. Binding behavior of these chiral complexes to calf thymus DNA (CT-DNA) has been investigated by electronic absorption, steady-state emission, and circular dichroism spectroscopies, as well as by viscosity measurements and equilibrium dialysis binding studies. Several points came from the results. (1) The DNA-binding properties were distinctly different for the [Ru(bpy)2L]2+ (L=HPIP, HNAIP, HNOIP) series of ruthenium(II) complexes, which indicates that the photophysical behavior of the complexes on binding to DNA can be modulated through ligand design. (2) Different binding rates of individual enantiomers of complexes 1 and 4 to DNA were observed through dialysis experiments. The Λ enantiomer bound more rapidly than the Δ enantiomer and their different intercalative binding geometries were suggested to be responsible. (3) Both Δ-2 and Λ-2 bound weakly to CT-DNA; Δ-2 may bind through a partial intercalation mode, whereas Λ-2 may bind in the DNA groove. (4) There was no noticeable enantioselectivity for complexes 1, 3, and 4 on binding to CT-DNA. Both of their enantiomers can intercalate into DNA base pairs. It is noted that Δ-3 and Λ-3 exhibited almost identical spectral changes on addition of CT-DNA, and a similar binding manner of the isomers to the double helix was proposed.

Synthesis, characterization and DNA-binding studies of cobalt(III) polypyridyl complexes

Abstract [Co(bpy) 2 (HNOIP)] 3+ and [Co(phen) 2 (HNOIP)] 3+ (HNOIP=2-(2-hydroxy-5-nitrophenyl)imidazo[4,5- f ][1,10]phenanthroline) have been synthesized and characterized by UV–Vis, EA and mass spectra. The binding of the two complexes with calf thymus DNA has been investigated by absorption spectroscopy, fluorescence spectroscopy, cyclic voltammetry and viscosity measurements. The spectroscopic studies together with cyclic voltammetry and viscosity experiments support that both complexes bind to CT DNA by intercalation via HNOIP into the base pairs of DNA. The NO 2 and OH substitute groups have no significant effect on the spectral properties and DNA-binding behavior of both complexes. Both complexes have also been found to promote cleavage of plasmid pBR 322 DNA from the supercoiled form I to the open circular form II upon irradiation. The cleaving mechanism for the two complexes has been proposed.