Behaviour of the Antitumor Agent Vanadocene Dichloride in Physiological and Therapeutic Media, Blood Plasma and Human Blood - An EPR Study

By means of EPR spectroscopy the behaviour of the vanadocene dichloride (I), Cp(2)VCl(2) (Cp=eta(5)-C(5)H(5)), in various deoxygenated and non-deoxygenated physiological media and therapeutic solution as well as in blood plasma and stabilized human blood was studied. On the basis of measured values of isotropic spectroscopic splitting factor g(iso) and isotropic hyperfine coupling constant A(iso), the vanadocene species, [Cp(2)V(H(2)O)Cl](+) (II; g(iso)= 1.985, |A(iso)| = 7.68 mT), [Cp(2)V(H(2)O)(2)](2+) (III; g(iso)= 1.983, |A(iso)| = 7.92 mT), [Cp(2)V(OH(2) (IV; g(iso)= 1.991, |A(iso)| = 6.285 mT), [Cp(2)VCl(DMSO)](+) (V; g(iso)= 1.985, |A(iso)| = 7.69 mT), the vanadyl species [VO(DMSO)(5)](2+) (VI; g(iso)= 1.964, |A(iso)| = 10.78mT) and [VO(H(2)O)(5)](2+) (VII; g(iso)= 1.955, |A(iso)| = 11.56 mT) have been identified. From the measurements it follows that I does not react in its first coordination sphere with any component of a system used other than water and DMSO, resp. As to water-containing media, its behaviour is fully consistent with that of I in pure aqueous media. It was found the only vanadocene species present after application of the therapeutic solution of I into human blood to be IV not interacting in its first coordination sphere with any blood component.     

The effect of reaction conditions on montmorillonite-catalysed peptide formation

Oligomerization of glycine (gly) and diglycine (gly₂) on montmorillonite was performed as cyclic, drying-wetting process at temperatures below 100°C, under varying reaction conditions. The influence of substrate/clay ratio, temperature and pH was found to be different for amino acid (AA) dimerization, cyclic anhydride (CA) formation and peptide chain elongation. High temperatures and neutral pH favour CA formation over diglycine production. An AA/catalyst ratio of 0.2 mmol/g leads to optimal yields. This supports the assumption that amino acid dimerization and CA formation take place at the edges of clay particles. Peptide chain elongation, starting from gly₂, produces higher yields at higher temperatures and neutral pH.     

Artificial ageing of low density polyethylene film containing chemically bound UV - stabilizer

This paper deals with photostabilization of low density polyethylene films (LDPE) grafted with the UV-stabilizer 2-hydroxy-4-(3-methacryloxy-2-hydroxy-propoxy) benzophenone (HMB). The influence of grafting yield and the other grafting conditions upon photostabilization efficiency of LDPE films were then studied. The chemically bound monomer (HMB) was localized mainly near the surface of an LDPE film. The grafted LDPE film was exposed to an ultraviolet radiation source, and the degree of oxidation and other photooxidative changes were determined by transmission IR and ATR IR spectroscopy. Experimental results show that radiation grafting of a UV-stabilizer upon LDPE films is an efficient photostabilization method.     

Dynamic mechanical behavior of chlorosubstituted derivatives of poly(ethyl methacrylate) and poly(ethyl acrylate)

A freely oscillating torsional pendulum was used in the investigation of the influence of trichloroethyl, tetrachloroethyl, trichloromethoxyethyl, and trichloroethoxyethyl side groups on the molecular mobility in the glassy state and on the glass transition temperature of poly(meth)acrylates. All the polymers under study, which may be used as fire retardants, exhibit a simple relaxation behavior. While the parameters of the low-temperature and secondary relaxation process in the glassy state are not noticeably affected by the substituents used, the glass transition temperature T_g, increases with rising polarity and volume of side chains. The increase is larger in the series of polyacrylates, so that differences in the softening temperatures of polymethacrylates and polyacrylates having the same side chains decrease considerably with growing substitution.     

Fault-Tolerant Formation Driving Mechanism Designed for Heterogeneous MAVs-UGVs Groups

A fault-tolerant method for stabilization and navigation of 3D heterogeneous formations is proposed in this paper. The presented Model Predictive Control (MPC) based approach enables to deploy compact formations of closely cooperating autonomous aerial and ground robots in surveillance scenarios without the necessity of a precise external localization. Instead, the proposed method relies on a top-view visual relative localization provided by the micro aerial vehicles flying above the ground robots and on a simple yet stable visual based navigation using images from an onboard monocular camera. The MPC based schema together with a fault detection and recovery mechanism provide a robust solution applicable in complex environments with static and dynamic obstacles. The core of the proposed leader-follower based formation driving method consists in a representation of the entire 3D formation as a convex hull projected along a desired path that has to be followed by the group. Such an approach provides non-collision solution and respects requirements of the direct visibility between the team members. The uninterrupted visibility is crucial for the employed top-view localization and therefore for the stabilization of the group. The proposed formation driving method and the fault recovery mechanisms are verified by simulations and hardware experiments presented in the paper.     

Upgrading of gas oils: the HDS kinetics of dibenzothiophene and its derivatives in real gas oil

The hydrodesulphurization (HDS) of dibenzothiophene (DBT), 4-methyl dibenzothiophene (4 M-DBT), 4,6-dimethyl dibenzothiophene (4,6 DM-DBT) and 4,6-diethyl dibenzothiophene (4,6 DE-DBT) as real gas oil components on NiMo/Al₂O₃ catalyst was investigated. On the basis of the first order rate constants of HDS of the individual sulphur compounds reactivities of the investigated compounds decreased in the order DBT ≫ 4 M-DBT > 4,6 DE-DBT ≈ 4,6 DM-DBT. Apparent activation energies of HDS of above sulphur compounds increased from 80.0 to 120.5 kJ/mol.     

Statistical prediction of fracture parameters of concrete and implications for choice of testing standard

This article shows how the fracture energy of concrete, as well as other fracture parameters such as the effective length of the fracture process zone, critical crack-tip opening displacement and the fracture toughness, can be approximately predicted from the standard compression strength, maximum aggregate size, water-cement ratio, and aggregate type (river or crushed). A database, consisting of 238 test data, is extracted from the literature and tabulated, and approximate mean prediction formulae calibrated by this very large data set are developed. A distinction is made between (a) the fracture energy, G_f, corresponding to the area under the initial tangent of the softening stress-separation curve of cohesive crack model, which governs the maximum loads of structures and is obtained by the size effect method (SEM) or related methods (Jenq-Shah two-parameter method and Karihaloo's effective crack model, ECM) and (b) the fracture energy, G_F, corresponding to the area under the complete stress-separation curve, which governs large postpeak deflections of structures and is obtained by the work-of-fracture method (WFM) proposed for concrete by Hillerborg. The coefficients of variation of the errors in the prediction formulae compared to the test data are calculated; they are 17.8% for G_f and 29.9% for G_F, the latter being 1.67 times higher than the former. Although the errors of the prediction formulae taking into account the differences among different concretes doubtless contribute significantly to the high values of these coefficients of variation, there is no reason for a bias of the statistics in favor of G_f or G_F. Thus, the statistics indicate that the fracture energy based on the measurements in the maximum load region is much less uncertain than that based on the measurement of the tail of the postpeak load-deflection curve. While both G_f and G_F are needed for accurate structural analysis, it follows that if the testing standard should measure, for the sake of simplicity, only one of these two fracture energies, then G_f is preferable.     

Structure and dynamics of a pentablock copolymer of polystyrene-polybutadiene in a butadiene-selective solvent

We have examined solutions of a polystyrene-polybutadiene pentablock copolymer in n-heptane, a strongly selective solvent for polybutadiene. Small angle neutron scattering from 7 to 15% samples reveals domains about 10 nm in radius formed by the association of 200 polystyrene blocks. Dynamic light scattering measurements on 8 and 9% samples showed three modes: a fast diffusive mode related to the collective diffusion in semidilute solutions/gels; a relaxational mode related to the local dynamics of polystyrene domains trapped in the gel formed by bridging the domains with the polybutadiene chains; and a very slow diffusive mode. The relaxational dynamics persisted over the entire temperature range, becoming faster with increasing temperature, indicating a decreased microviscosity at higher temperatures. The slow dynamics seems to be connected with heterogeneities in the physical gel due to microsyneresis and almost disappeared above 50 °C. Macroscopic phase separation into two liquid phases was observed in a dilute solution of the un-associated copolymer, and into a liquid and gel phase at higher concentrations. The absence of flower-like micelles in dilute solutions and the macroscopic phase seperation suggest that the gels in the pentablock are formed by random association of multiplet domains and not by bridging of micellar domains.     

Equilibrium and dynamics of acetylene sorption in multiwalled carbon nanotubes

Multiwalled carbon nanotubes (MWCNT) were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and by adsorption of N₂ and acetylene. The dynamics of acetylene sorption was studied by frequency response spectroscopy. The average tube dimension and the shell number were determined from a statistical evaluation of the TEM images. This value agreed with that obtained from XRD via the Scherrer equation only if a shape factor of 0.49 was used. The diffusion of acetylene in the nanotubes of the MWCNT sample was found to be the rate-controlling step of the sorption process. Relationships between the tube dimensions and the equilibrium and dynamic sorption properties were demonstrated.     

Effect of γ-irradiation on strength of concrete for nuclear-safety structures

Concrete applied for construction of nuclear power plant (NPP) Temelín (Czech Republic) has been exposed to γ-irradiation up to dose 6×10⁵ Gy. Depending on the level of irradiation, changes in strength, porous structure and phase composition of the concrete have been studied. It is found that irradiation lowers both the strength of concrete (about 10%) and volume (resp. surface) of porous space. On the other hand, γ-irradiation increases the ratio of calcite, CaCO₃, in the concrete. Observed effects are discussed with respect to safety of NPPs.