Studies on Interaction of Norfloxacin,Cu<Superscript>2+</Superscript>, and DNA by Spectral Methods

The interactions of norfloxacin (NFA), DNA, and Cu²⁺ are studied by fluorescence and UV-spectra method. According to the experimental results, it can be concluded that NFA can form a steady binary complex with Cu²⁺. There is a linear relationship between the Fluorescence intensity of the norfloxacin–Cu²⁺–DNA system and the concentration of DNA. And when the concentration of the NFA is 1.95×10⁻⁵ mol L⁻¹, they possess a good linearity in the concentration of DNA ranged from 4.7×10⁻⁶ to 2.8×10⁻⁵ mol L⁻¹.It is a good method due to the high sensitivity and selectivity.     

Bis‐4,9‐diazapyrenium dications: synthesis of the methylenedibenzyl‐analogue,interactions with nucleotides,DNA, RNA. The antitumour activity of all till now prepared analogues

Novel bis‐4,9‐diazapyrenium dication has shown reversible pH dependent formation of 4,9‐ diazapyrenium pseudobase in water characteristic for most 4,9‐diazapyrenium derivatives. The compound has formed non‐covalent complexes with nucleotides in water, whose stability is controlled dominantly by aromatic stacking interactions. No cooperativity between two 4,9‐diazapyrenium subunits was observed in binding of nucleotides. Novel bis‐4,9‐diazapyrenium dication formed mono‐intercalative complexes with studied double stranded DNA and RNA. Additional interactions of non‐intercalated part were found to depend significantly on the polynucleotide secondary structure, yielding strong DNA over RNA preference. Appearance of ICD band of 3 was found to be specific for DNA polynucleotides and together with observed destabilisation of double stranded RNA is attributed to the aggregation of compound in one of the RNA grooves. All bis‐4,9‐diazapyrenium dications prepared till now have shown considerable antiproliferative activity against five human tumour cell lines, which suggested mechanism of action by interacting with cell DNA. Copyright © 2007 John Wiley & Sons, Ltd.     

Quercetin-Iron Complex: Synthesis,Characterization, Antioxidant,DNA Binding,DNA Cleavage,and Antibacterial Activity Studies

Quercetin-iron (II) complex was synthesized and characterized by elemental analysis, ultraviolet-visible spectrophotometry, fourier transform infrared spectroscopy, mass spectrometry, proton nuclear magnetic resonance spectroscopy, thermogravimetry and differential scanning calorimetry, scanning electron micrography and molar conductivity. The low molar conductivity value investigates the non-electrolyte nature of the complex. The elemental analysis and other physical and spectroscopic methods reveal the 1:2 stoichiometric ratio (metal:ligand) of the complex. Antioxidant study of the quercetin and its metal complex against 2, 2-di-phenyl-1-picryl hydrazyl radical showed that the complex has much more radical scavenging activity than free quercetin. The interaction of quercetin-iron (II) complex with DNA was determined using ultraviolet visible spectra, fluorescence spectra and agarose gel electrophoresis. The results showed that quercetin-iron (II) complex can intercalate moderately with DNA, quench a strong intercalator ethidium bromide and compete for the intercalative binding sites. The complex showed significant cleavage of pBR 322 DNA from supercoiled form to nicked circular form and these cleavage effects were dose-dependent. Moreover, the mechanism of DNA cleavage indicated that it was an oxidative cleavage pathway. These results revealed the potential nuclease activity of complex to cleave DNA. In addition, antibacterial activity of complex on E.coli and S. aureus was also investigated. The results showed that complex has higher antibacterial activity than ligand.     

Antioxidant effects of phenothiazine,phenoxazine, and iminostilbene on free‐radical‐induced oxidation of linoleic acid and DNA

Antioxidant effects of phenothiazine (PtzNH), phenoxazine (PozNH), and iminostilbene (IsbNH) on the oxidation of linoleic acid (LH) and DNA induced by 2,2′‐azobis(2‐amidinopropane) dihydrochloride (AAPH) were investigated in this work. LH was suspended in the liposome of dipalmitoyl phosphatidylcholine (DPPC) to mimic a biomembrane. In the course of AAPH‐induced oxidation of LH, the inhibition period (t_inh) generated by PtzNH, PozNH, and IsbNH was proportional to the concentrations of PtzNH, PozNH, and IsbNH employed. The abilities of PtzNH, PozNH, and IsbNH to protect LH were similar to that of trolox (6‐hydroxyl‐2,5,7,8‐tetramethylchroman‐2‐carboxylic acid). Quantum chemical calculations elucidated that the nonplanar configurations of PtzNH, PozNH, and IsbNH transformed to planar ones when they were converted into radicals. In addition, spin‐densities (SDs) on the N atom in the radicals derived from PtzNH, PozNH, and IsbNH were calculated. The N atom in the radical of PtzNH possessed the lowest SD, indicating that the radical of PtzNH was the most stable one. Moreover, PtzNH, PozNH, and IsbNH were applied to protect the DNA against AAPH‐induced oxidation, in which PozNH and IsbNH were able to generate t_inh. The t_inh generated from PozNH and IsbNH was also proportional to their concentrations. The antioxidant effect of PozNH on the oxidation of DNA was higher than that of IsbNH. Copyright © 2009 John Wiley & Sons, Ltd.     

Comment on paper “the bulk modulus and Poisson's ratio of “incompressible” materials” by P.H. Mott, J.R. Dorgan, C.M. Roland

A widespread error related to Poisson's ratio and its limiting value 0.5 provokes complex explanations of fully coherent experimental data.     

Exons, introns, and DNA thermodynamics

The genes of eukaryotes are characterized by protein coding fragments, the exons, interrupted by introns, i.e., stretches of DNA which do not carry useful information for protein synthesis. We have analyzed the melting behavior of randomly selected human cDNA sequences obtained from genomic DNA by removing all introns. A clear correspondence is observed between exons and melting domains. This finding may provide new insights into the physical mechanisms underlying the evolution of genes.