Induction of DNA-double-strand breaks by auger electrons from 99mTc complexes with DNA-binding ligands

The potential of certain Auger electron emitting nuclides for systemic radiotherapeutic applications has recently gained much attention. In particular, the ability of several nuclides, including 111In, 125I, and 123I, to induce DNA double-strand breaks (dsb), a good indicator of cytotoxicity, has been extensively studied. However, this ability has never previously been shown experimentally for 99mTc, which, besides the well-known gamma radiation that is used for diagnostic applications, also emits an average of 1.1 conversion electrons and 4 Auger or Coster-Kronig electrons per decay. Owing to the short range of Auger electrons, the radionuclide needs to be located very close to the DNA for dsb to occur. We synthesized two cationic 99mTcI-tricarbonyl complexes with pendant DNA binders, pyrene and anthraquinone. The X-ray crystal structures of the two complexes could be elucidated. Linear dichroism and UV/Vis spectroscopy revealed that the complex with pyrene intercalates DNA with a stability constant, K, of 1.1 x 10(6) M(-1), while the analogous complex with anthraquinone interacts with DNA in a groove-binding mode and has an affinity value of K=8.9 x 10(4) M(-1). We showed with phiX174 double-stranded DNA that the corresponding 99mTc complexes induce a significant amount of dsb, whereas non-DNA-binding [TcO4]- and nonradioactive Re compounds did not. These results indicate that the Auger electron emitter 99mTc can induce dsb in DNA when decaying in its direct vicinity and this implies potential for systemic radiotherapy with 99mTc complexes.     

PORE-MOUTH POISONING OF NON-UNIFORM CATALYSTS

Impurity poisoning of a catalyst particle having a non-uniform activity distribution is analyzed. Equations that relate the position of the poison-front with time for different activity profiles are derived. It is shown that the effect of the activity distribution on the poisoning rate is apparent in the case of intraparticle-diffusion control. The performance of a non-uniform bifunctional catalyst in such conditions is also studied.     

Small‐angle X‐ray scattering study of modified porous suspension–poly(vinyl chloride) particles

Small‐angle X‐ray scattering (SAXS) was applied to investigate the microstructure of unmodified and modified porous commercial suspension‐type poly(vinyl chloride) (PVC) particles. The modified PVC particles were prepared by an in situ stabilizer‐free polymerization/crosslinking of particles absorbed with a monomer/crosslinker/peroxide solution. The modifying polymers include styrene with or without divinyl benzene (DVB) as a crosslinker and methyl methacrylate (MMA) with or without ethylene glycol dimethacrylate (EGDMA) as a crosslinker. The SAXS method was used to highlight the effect of polystyrene (PS) on the microstructure of PVC particles and to evaluate the characteristic lengths, both in the PVC/PS and the PVC/XPS (PS crosslinked with 0 and 5% DVB, respectively) systems. A model is suggested, where during the synthesis modification process, swelling of PVC by styrene and styrene polymerization occur simultaneously. PVC swelling by styrene causes destruction of the PVC subprimary particles, whereas styrene polymerization leads to phase separation resulting from incompatibility of the polymers. It was further suggested that because of PVC swelling by styrene, structure of the subprimary particles is lost. Therefore the characteristic lengths of PVC/PS and PVC/XPS, as calculated from the SAXS measurements, were attributed to the size of the phase‐separated PS and XPS inclusions, respectively. The SAXS method also shows that PMMA and XPMMA do not influence the PVC microstructure. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1024–1031, 2005     

Heat Induced Structure Modifications in Polymer‐Layered Silicate Nanocomposites

Summary: The success of the use of layered silicates in polymer nanocomposites, to improve physical and chemical properties is strictly related to a deeper knowledge of the mechanistic aspects on which the final features are grounded. This work shows the temperature induced structural rearrangements of nanocomposites based on poly[ethylene‐co‐(vinyl acetate)] (EVA) intercalated‐organomodified clay (at 3–30 wt.‐% silicate addition) which occur in the range between 75 and 350 °C. In situ high temperature X‐ray diffraction (HT‐XRD) studies have been performed under both nitrogen and air to monitor the modifications of the nanocomposite structure at increasing temperatures under inert/oxidative atmosphere. Heating between 75 and 225 °C, under nitrogen or air, causes the layered silicate to migrate towards the nanocomposite surface and to increase its interlayer distance. The degradation of both the clay organomodifier and the VA units of the EVA polymer seems to play a key role in driving the evolution of the silicate phase in the low temperature range. The structural modifications of the nanocomposites in the high temperature range (250–350 °C), depended on the atmosphere, either inert or oxidizing, in which the samples were heated. Heating under nitrogen led to deintercalation and thus a decrease of the silicate interlayer space, whereas exfoliation was the main process under air leading to an increase of the silicate interlayer space.

Heat induced structural modification of EVA‐clay nanocomposite under nitrogen and air.     

Dielectric Properties of the "Twinned" 8H-Hexagonal Perovskite Ba8Nb4Ti3O24

The dielectric properties of dense ceramics of the "twinned" 8H-hexagonal perovskite Ba₈Nb₄Ti₃O₂₄ are reported. Single-phase powders were obtained from the mixed-oxide route at 1325°C and ceramics (>92% of the theoretical X-ray density) by sintering in air or flowing O₂ at 1400°–1450°C. The ceramics are dc insulators with a band gap >3.4 eV that resonate at microwave frequencies with relative permittivity, ɛ_r∼44–48, quality factor, Q × f _r∼21 000–23 500 GHz (at f _r∼5.5 GHz) and temperature coefficient of resonant frequency, TC _f,∼+115 ppm/K.     

Natural fiber composites of high‐temperature thermoplastic polymers: Effects of coupling agents

Our earlier paper (Jana, S.C.; Prieto, A. J Appl Polym Sci 2002, 86, 2159) on the development of natural fiber composites of high‐performance thermoplastic polymers described a new methodology for the manufacturing of composite materials of a high‐temperature thermoplastic polymer, poly(phenylene ether) (PPE) and wood flour, a cellulosic natural filler. A thermosetting epoxy, used as a reactive solvent, reduced the processing temperature of PPE/epoxy blends to well below the decomposition temperature of natural fillers. In addition, the epoxy component, upon polymerization, formed coating layers around the filler particles to provide resistance against moisture diffusion and attacks by acids and alkali. This article describes the results of an investigation on two outstanding issues: (1) the influence of cellulosic wood particles and coupling agents on the speed of epoxy curing and reaction‐induced phase separation and (2) the effects of coupling agents on the morphology of crosslinked epoxy at the surfaces of natural fillers and mechanical properties of the composites. It was found that wood particles expedited epoxy curing in the composites; the extent of epoxy curing, however, was reduced in the presence of coupling agents. Also, the coupling agents promoted complete coverage of wood flour particles by polymerized epoxy, although the mechanical properties deteriorated over systems without coupling agents. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2168–2173, 2002     

Thermodynamic interactions of branched polyethylene in polar and nonpolar systems

The thermodynamic properties of polymer solutions are frequently described in terms of the Flory-Huggins equation. This equation includes a parameter χ, which depends upon the intermolecular forces acting between the molecules in a solution. The experimental determination of χ was performed by an improved microtechnique and extended to a wide range of polar and nonpolar diluents of polyethylene. Careful correlations are prescribed for calculating χ from pure-component properties; they are based on an extension of the Hildebrand-Scatchard theory of solutions and on the theory of intermolecular forces. Polar (τ) and nonpolar (δ) solubility parameters are presented for a variety of solvents. For polyethylene—nonpolar solvent systems we have emphasized the factor deciding the sign of heat of mixing, while for polyethylene-polar solvent systems we have determined the contribution of dipole-induced dipole interactions ψ (δτ) in interchange-energy density B and, hence, χ.     

Guanine and plasmid DNA binding of mono- and trinuclear fac-[Re(CO)3]+ complexes with amino acid ligands

We have synthesized and fully characterized four new complexes comprising the fac-[Re(CO)3]+ moiety and the ligands NH3, L-proline (Pro), or N,N-dimethylglycine (dmGly). The reaction of [Re(H2O)3(CO)3]+ with the two amino acids gives trinuclear complexes of general formula [Re(L)(CO)3]3 (where L = amino acid). We have studied the in vitro behavior of these compounds with guanine and DNA in order to understand whether the cytotoxicity exhibited by certain rhenium complexes based on the fac-[Re(CO)3]+ core is due to the formation of nucleobase complexes and inter- or intrastrand links between DNA bases. We have performed model studies with guanine and studied the structural effects induced by different rhenium(I) tricarbonyl complexes on PhiX174 plasmid DNA by electrophoretic methods. Our results show that rhenium complexes with two available coordination sites interact with plasmid DNA to form a stable adduct that is likely to involve two bases.