A novel bis-phenanthridine triamine with pH controlled binding to nucleotides and nucleic acids

The new bis-phenanthridine triamine is characterised by three pK(a) values: 3.65; 6.0 and >7.5. A significant difference in the protonation state of at pH = 5 (four positive charges) and at pH = 7 (less than two positive charges) accounts for the strong dependence of -nucleotide binding constants on nucleotide charge under acidic conditions, whereas at neutral pH all -nucleotide complexes are of comparable stability. All experimental data point at intercalation as the dominant binding mode of to polynucleotides. However, there is no indication of bis-intercalation of the two phenanthridine subunits in binding to double stranded polynucleotides, the respective complexes being most likely mono-intercalative. Thermal stabilisation of calf thymus DNA (ct-DNA) and poly A-poly U duplexes upon addition of is significantly higher at pH = 5 than at neutral conditions. This is not the case with poly dA-poly dT, indicating that the specific secondary structure of the latter, most likely the shape of the minor groove, plays a key role in complex stability. At pH = 5 acts as a fluorimetric probe for poly G (emission quenching) as opposed to other ss-polynucleotides (emission increase), while at neutral conditions this specificity is lost. One order of magnitude higher cytotoxicity of compared to its "monomer" can be accounted for by cooperative action of two phenanthridinium units and the charged triamine linker. The results presented here are of interest to the development of e.g. sequence-selective cytostatic drugs, and in particular for the possibility to control the drug activity properties over binding to DNA and/or RNA by variation of the pH of its surrounding.     

Permeability of hydrophilic and hydrophobic Shirasu-porous-glass (SPG) membranes to pure liquids and its microstructure

Morphological properties of hydrophilic and hydrophobic Shirasu-porous-glass (SPG) membranes were investigated over a wide range of mean pore sizes (0.252–20.3 μm) by liquid permeability measurements, scanning electron microscopy and Hg porosimetry. Hydrophobic modification of membrane surface was made by surface coating with silicone resin. The results are discussed using the non-uniform capillary bundle model of membrane permeability. The mean pore tortuosity of 1.28 was kept constant over the whole range of mean pore sizes investigated. The SEM images confirmed that the geometry of pore network was similar for all SPG membranes, irrespective of their mean pore size. The span of pore size distribution ranged from 0.28 to 0.68 and the number of pores per unit cross-sectional membrane area from 10⁹ to 10¹³ m⁻². The membrane resistance was unchanged after surface treatment with silicone resin, which means that the pores were not plugged by the resin, even in the submicron range of mean pore sizes.     

Mixed cobalt(III) complexes with aromatic amino acids and di­amines. III.

The title compound, [Co(C₉H₁₀NO₃)₂(C₂H₈N₂)]Cl·4H₂O, is one of six possible diastereomers of the (1,2‐di­amino­ethane)­bis(S‐tyrosinato)­cobalt(III) complex. The cobalt(III) ion has an octahedral coordination, with three five‐membered chelate rings which have deformed coordination angles and coordinated O atoms in trans positions. In comparison with the previously reported crystal structure of the Δ‐C₁‐cis(O) diastereomer [Miodragovi?et al. (2001). Enantiomer, 6 , 299–308], the compound presented in this paper has more planar five‐membered amino­carboxyl­ate rings. Complex cations, chloride anions and water mol­ecules of crystallization are linked together by a network of hydrogen bonds. The chloride anions lie approximately between two Co atoms and form hydrogen bonds with all coordinated NH₂ groups. In the crystal structure, there is a weak intermolecular π?π interaction between the phenyl rings.     

AlFe-pillared clay catalyst for phenol oxidation in water solution

Catalytic wet peroxide oxidation of phenol over AlFe-pillared montmorillonites, with different iron contents, was carried out at room temperature, in a glass batch reactor, under constant airflow and halogen lamp light. At lower concentration (0.5 mg phenol/100 cm³ water) a phenol conversion of 100% was achieved independently of the iron content in pillared clay catalyst. However, at higher phenol concentration (5.0 mg phenol/100 cm³ water) retardation of the catalyst activity was observed. This revised version was published online in June 2006 with corrections to the Cover Date.     

PRIMARY MECHANISMS OF ERYTHROCYTE PHOTOLYSIS INDUCED BY BIOLOGICAL SENSITIZERS AND PHOTOTOXIC DRUGS

Abstract— The elucidation of the molecular mechanism of photosensitized hemolysis of red blood cells may give important clues to the primary events underlying the phototoxic reactions observed in pathological conditions such as porphyria and induced by photosensitizing drugs. Sensitizers effective in photo-hemolysis are porphyrins, the tryptophan metabolite kynurenic acid, and phototoxic drugs such as chlor-promazine and demethylchlortetracycline. Utilizing the singlet oxygen quenchers. jS-carotene and histi-dine and the large deuterium effect on the lifetime of singlet oxygen previously described by us, good evidence of the participation of this excited molecular species in the photohemolysis in the presence of kynurenic acid was obtained. Chlorpromazine and demethylchlortetracycline clearly act by a non-singlet oxygen pathway. The situation observed with haematoporphyrin is less clear and may represent a mixed Type I-Type II mechanism.     

Detection of hydrogen atom adduct of spin-trap DEPMPO. The relevance for studies of biological systems

We proposed EPR spectroscopy using spin-trap DEPMPO as a novel method for the detection of a hydrogen atom (*H) produced by chemical and biological systems. In complex EPR spectra of DEPMPO adducts in biological systems, spectral lines of unknown origin have been observed. We have assumed (Baci?, G.; Mojovi?, M. Ann. N. Y. Acad. Sci. 2005, 1048, 230-243) that those lines represent the spectrum of a hydrogen atom (*H) adduct i.e., DEPMPO/H. An electrochemical system known to produce only *H radicals was used here in order to obtain a separate spectrum of the DEPMPO/H adduct. An acquired spectrum as well as a computer spectral simulation of the DEPMPO/H adduct showed considerable resemblance with additional lines in the EPR spectra of DEPMPO adducts in biological systems-plant plasma membranes and cell walls. This shows that such a radical is produced by plants as well as that DEPMPO is suitable for detection in both electrochemical and biological systems.     

Rheological model optimization using advanced evolutionary computation for the analysis of the influence of recycled rubber on rubber blend dynamical behaviour

Rheological models of tested rubber blend samples, with different ratios of smut/recycled material, were developed, analyzed and discussed according to experimental data. The experimental measurements show the dynamical behavior of these samples after a short-term axial load. The rheological model of samples was assumed as a viscoelastic Voigt-Maxwell and hyperelastic Mooney-Rivlin model. Real coded genetic algorithms were implemented for optimal model parameters identification in order to minimize the difference between the real sample behavior and dynamical model output. Numerical results obtained for analyzed mixture were compared with the original sample to verify the presented method. In purpose of predicting the dynamical characteristics for desirable rubber blends, an interrelation was formed based on the concentration of recycled material in sample blends and dynamical model parameters dependence.     

Benefits of mesopores in sulfated zirconia catalyst

Activities of two catalysts obtained from hydroxide and alkoxide precursors were correlated to their different structural and textural properties. Activity is mainly determined by the presence of active tetragonal phase, which is more stable at high temperatures in the catalyst of alkoxide origin than in one from hydroxide. An appropriate structure must be accompanied with beneficial pore structure, as is the case of mesopores of the catalyst from alkoxide. In the case of very small pores of the catalyst from hydroxide precursor, activity is negligible due to pores plugged by coke.     

A new method for finding cycles by semilinear control

In the paper two new results that prove typically real and local univalent properties of certain class of rational functions in the unit disc $\mathbb{D}$ are presented. They provide a theoretical justification of a new method for finding periodic solutions of the discrete vector dynamical systems. The main goal of the paper is to propose and investigate the two-delays generalization of the scheme introduced by Ö. Morgül. The analysis shows that the coefficients in the proposed method can be chosen in a way that improves the admissible range of parameters. The method is elementary and easy to implement. Furthermore, numerical experiments with several well known maps show effectiveness of the control scheme.