Antioxidant vs. Prooxidant Properties of the Flavonoid,Kaempferol, in the Presence of Cu(II) Ions: A ROS-Scavenging Activity,Fenton Reaction and DNA Damage Study

Kaempferol is a flavonoid that occurs in tea and in many vegetables and fruits, including broccoli, cabbage, beans, grapes, apples, and strawberries. The efficacy of Kaempferol has been demonstrated in the treatment of breast, esophageal, cervical, ovarian, and liver cancers and leukemia, which very likely arises from its prooxidant properties and the activation of pro-apoptotic pathways. Indeed, this matter has already been the focus of a number of published studies and reviews. The aim of the present study was to elucidate the antioxidant vs. prooxidant properties of flavonoids in the presence of the redox-active metal, copper (II) ion, by means of the Fenton reaction. The specific motivation of this work is that, since an increased level of Cu(II) ions is known to be associated with many disease states such as neurological conditions (Alzheimer’s disease) and cancer, any interaction between these ions and flavonoids might affect the outcome of therapeutic uses of the latter. The structure of the Cu-kaempferol complex in DMSO was investigated by means of low temperature EPR spectroscopy, which confirmed the existence of at least two distinct coordination environments around the copper (II) ion. UV vis-spectra of kaempferol and its Cu(II) complex in DMSO revealed an interaction between the 5-OH (A ring) group and the 4-CO (C ring) group of kaempferol with Cu(II) ions. An ABTS assay confirmed that kaempferol acted as an effective radical scavenger, and that this effect was further enhanced in the form of the Cu(II)-kaempferol complex. Quantitative EPR spin trapping experiments, using DMPO as the spin trap, confirmed suppression of the formation of a mixture of hydroxyl, superoxide, and methyl radicals, in a Fenton reaction system, upon coordination of kaempferol to the redox-active Cu(II) ions, by 80% with respect to the free Cu(II) ions. A viscometric study revealed a better DNA-intercalating ability of the Cu-kaempferol complex than for free kaempferol, essential for conferring anticancer activity of these substances. The results of the viscometric measurements were compared with those from a DNA damage study of Cu-kaempferol complexes in a Fenton reaction system, using gel electrophoresis. At low concentrations of kaempferol (Cu–kaempferol ratios of 1:1 and 1:2), a very weak protective effect on DNA was noted, whereas when kaempferol was present in excess, a significant DNA-protective effect was found. This can be explained if the weakly intercalated kaempferol molecules present at the surface of DNA provide protection against attack by ROS that originate from the Fenton reaction involving intercalated Cu(II)-kaempferol complexes. Following the application of ROS scavengers, L-histidine, DMSO, and SOD, gel electrophoresis confirmed the formation of singlet oxygen, hydroxyl radicals, and superoxide radical anions, respectively. We propose that the prooxidant properties of Cu-kaempferol complexes may provide anticancer activity of these substances. When present in excess, kaempferol displays antioxidant properties under Cu-Fenton conditions. This suggests that kaempferol might prove a suitable candidate for the prevention or treatment of oxidative stress related medical conditions that involve a disturbed metabolism of redox metals such as copper, for example, Menkes disease, and neurological disorders, including Alzheimer’s disease. For the potential use of kaempferol in clinical practice, it will be necessary to optimize the dose size and critical age of the patient so that this flavonoid may be beneficial as a preventive drug against cancer and neurological disorders.     

Irregular structures in polyvinylchloride II. Unsaturated structures

In the present paper, considerations are made on the mechanism of the dehydrochlorination of PVC, mainly from information summarized from studies with unsaturated model compounds. A semi-empirical evaluation of the activation energy has been carried out for the monomolecular elimination of hydrogen chloride involving unsaturated structures in PVC. The semi-empirical method proposed by VEDENEYEV was used to study the C-Cl, C-H and C-C bonds in PVC. Activation energies for elimination of hydrogen chloride were calculated on the basis of the additivity of bond energies of the four-centre activated complex for various irregular structures in the polymer chain such as branching, head-to-head or tail-to-tail addition, and double bonds. From a number of possible structural abnormalities controlled by polymerization conditions only a few give a contribution to the initiation of the thermal dehydrochlorination but internal allyl type chlorine and branched structures having a tertiary chlorine appear to have significant effect as the initiators of the decomposition, while abnormal structures at the chain ends are rather stable. It should be pointed out that increasing delocalization or resonance stabilization in the case of unsaturated internal-irregular structures will lower the activation energy of elimination of hydrogen chloride in consequence of decreased thermal stability of PVC.     

裂缝非达西渗流对气井水力压裂设计的影响

水力压裂技术是低渗透致密气藏增产的主要手段。在水力压裂裂缝中,气体在裂缝内高速流动产生的非达西渗流使裂缝的有效导流能力和裂缝长度大大减小,从而影响了水力压裂井的产能。在考虑气体非达西渗流的基础上,建立了非达西渗流条件下裂缝有效渗透率和裂缝参数的计算方法,研究了非达西渗流对水力压裂设计参数(裂缝长度、宽度)和产能的影响。结果表明,考虑非达西渗流时的水力压裂必须设计比达西渗流条件下更短和更宽的裂缝;由于裂缝非达西渗流的存在,气井的产能也有较大幅度的降低。考虑非达西渗流进行水力压裂设计和计算时,不能直接用流体在多孔介质或裂缝中的真实渗透率来计算水力压裂气井的产量,而必须用非达西有效渗透率。     

The absorption of direct dyes by crosslinked cellulose. II. Rate of dyeing and diffusivity

The effect of crosslinking in the dry state on the rate of dyeing of cellophane with two direct dyes, Chrysophenine G and Chlorazol Sky Blue FF, has been studied. Dimethylolethyleneurea and bis(hydroxyethyl) sulfone were the crosslinking agents. It was found that the rate of dyeing was reduced at high degree of crosslinking by more than 90%, whereas the amount of dye absorbed at equilibrium was reduced by only 40%. It was concluded that the major factor in the practical undyeability of the crosslinked cellulose fibers in commerce is the reduction of the rate of dyeing rather than that of the absorption at final equilibrium. The average diffusivities of the dyes in the cellulose film were calculated from the rate data. The diffusion coefficients as functions of the dye concentration in the films were estimated from the diffusivity values. The two models of swollen cellulose, the pore model and the gel model, were applied to explain the effect of crosslinking on the diffusion coefficients. The pore model offers a satisfactory explanation by assuming that crosslinking reduces the average pore diameter and therefore increases the drag and also the tortuosity. The gel model offers an equally satisfactory explanation by assuming that crosslinking reduces the free volume by increasing the rigidity and concentration of the cellulose chains in the cellulose gel.     

The role of tensides in the covering, formation and power loss properties of amorphous metallic ribbons by glassy coatings

Tensides are surface active substances which play an essential role in the formation of glassy coatings from aqueous solutions of H₃BO₃, H₃PO₄ and their salts. Firstly, they ensure the wettability of the hydrophobic metallic ribbon at the phase boundary in very low concentrations and, in addition, they adjust both specifically and effectively the reaction conditions between the depositing solution and the surface of the amorphous metallic ribbon. They penetrate into the interlayer of the ribbon changing its physico-chemical properties and in this way influence its magnetic characteristics. This paper deals with the effect of commercially produced non-ionic tensides (Slovanik NT, Slovasol EL, Slovasol O) and an anionic tenside (Slovafos 3) in the process of the formation of glassy coatings vs. power loss for amorphous Fe₈₂Si₆B₁₂, Fe₄₀Ni₄₀B₂₀ and Co₇₀Fe₅Si₇B₁₈ ribbons. The influence of different amounts of tensides in borate and phosphate deposition solutions and of heat treatment of these solutions on power loss is discussed.     

Status of the Lisbon experiment on neutrino mass determination

We report the status of a ¹⁸⁷Re beta decay spectrum measurement using a technique based on the detection of decay-induced magnetic flux penetration into a geometrically metastable superconducting foil.