Novel rapid in vitro cytotoxicity test on mammalian cells based on an electrochemical measuring method

The proliferation of pharmaceuticals and chemicals and the increasing manufacture of medical goods have made an assessment of their potential toxicological risks to man and the environment indispensable. Hence, a wide range of tests has been developed in order to generate data on the harmful effects of chemicals and pharmaceuticals on organisms. Initially, toxicological data were commonly collected from tests involving animals; however, on account of ethical objections, they are gradually being replaced by in vitro cytotoxicity tests. In this work, a new in vitro screening method for the determination of cytotoxicity, based on a novel electrochemical bioactivity sensor system, was implemented. The evaluation was based on current–time curves of a potentiostatic measurement proportional to the reduction of mediator molecules by mammalian cells. Depending on the number of reduced mediator molecules used by the cells, a current signal is produced, which provides information about the viability of living cells. By adding a toxic test substance to the cell, a reduction in the current signal can be observed, depending on the cytotoxicity of the substance. It is possible to quickly create a specific cytotoxic curve and to determine the corresponding inhibitory concentrations (IC₅₀ value). First tests were performed on three mammalian cell lines and eight model compounds using this electrochemical measurement system. The IC₅₀ values obtained corresponded well with the toxicity determined with an established reference cytotoxicity assay (MTT test) and with data reported in the literature.     

Time domain 1H NMR as a new method to monitor softening of gelatin and HPMC capsule shells

Defined mechanical properties are an essential requirement for any pharmaceutical dosage form and this is particularly important in the case of liquid-filled capsules. Changes in the mechanical properties may be induced by exposure of the capsules to humidity or by a shift of the water equilibrium that typically occurs when hydrophilic or amphiphilic fill masses are used, for example, in self-emulsifying drug delivery systems. This study aims to characterize the softening of empty hard gelatin and hydroxypropyl methylcellulose (HPMC) capsules by means of mechanical tests, a Bareiss hardness test, and a stiffness test using a texture analysis method. A benchtop time domain NMR method is applied in addition to characterize the physico-chemical state of water in the capsule shells and to correlate this with the results of the mechanical tests. Hardness and stiffness measurements resulted in corresponding values, showing a softening for both capsule materials in a humid environment, which was most pronounced beyond 60% relative humidity. The capsules made of gelatin exhibited in general higher stiffness and hardness values compared to the HPMC capsules. The physico-chemical state of water in the capsule shells, as probed by a time domain NMR method, was interpreted in terms of a population balance model. Three different water populations were identified that differ in their molecular mobility, as indicated by their characteristic spin-lattice relaxation times, T1. The most loosely bound water fraction dominated in the capsule shells in the range beyond 60% relative humidity. Numerical correlation of the data led to a heuristic equation between the NMR-derived fraction of loosely bound water in the capsule shells and their mechanical stiffness and hardness. Adequate models were obtained for both capsule types, gelatin, and HPMC. Mechanical measurements of pharmaceutical capsules are generally destructive and time consuming. Testing is usually performed in an analytical laboratory, off-line from the manufacturing process, and involves only a small number of samples. Based on the here presented correlation between mechanical stiffness measurements and benchtop time domain NMR data, the latter method may be used as a nondestructive alternative for mechanical testing. This study also opens the possibility to investigate liquid-filled capsules and to establish a process analytical technology (PAT) during manufacturing.     

Exergy based fluid selection for a geothermal Organic Rankine Cycle for combined heat and power generation

In this study the option of combined heat and power generation was considered for geothermal resources at a temperature level below 450 K. Series and parallel circuits of an Organic Rankine Cycle (ORC) and an additional heat generation were compared by second law analysis. Depending on operating parameters criteria for the choice of the working fluid were identified. The results show that due to a combined heat and power generation, the second law efficiency of a geothermal power plant can be significantly increased in comparison to a power generation. The most efficient concept is a series circuit with an organic working fluid that shows high critical temperatures like isopentane. For parallel circuits and for power generation, fluids like R227ea with low critical temperatures are to be preferred.     

Exergy analysis of multi-effect water–LiBr absorption systems: From half to triple effect

An exergy analysis, which only considers the unavoidable exergy destruction, is conducted for single, double, triple and half effect Water–Lithium bromide absorption cycles. Thus, the obtained performances represent the maximum achievable performance under the given operation conditions.The coefficient of performance (COP), the exergetic efficiencies and the exergy destruction rates are determined and the effect of the heat source temperature is evaluated. As expected, the COP increases significantly from double lift to triple effect cycles. The exergetic efficiency varies less among the different configurations. In all cycles the effect of the heat source temperature on the exergy destruction rates is similar for the same type of components, while the quantitative contributions depend on cycle type and flow configuration. Largest exergy destruction occurs in the absorbers and generators, especially at higher heat source temperatures.     

Criteria for the comparison of electron microscopical 3D reconstructions of individual particles

Similarity criteria for electron microscopical 3D reconstructions can be defined in different ways. It is shown that the choice of the zero level in 3D reconstructions plays an important role, (a) for the discrimination of stained versus non-stained structural parts ("discrimination level"), and (b) for the physical definition of the signal ("zero potential level"). Of special interest are further structural features (artifacts) introduced by the reconstruction method chosen (single axis tilting in our papers). A crude estimate of the zero potential level is only possible if we neglect electron scattering from light atoms (concept of the "holey stain structure"). We calculate for the reconstructions of stained ribosome particles (W. Hoppe and H. Oettl and H. Tietz, J. Mol. Biol., in press) a signal-to-noise ratio of the order 3:1 (smaller by a factor of ca. 3 than the ratio calculated from electron noise). This explains why structural details can be recognized in single-particle reconstructions and why averages over only a few particles can already lead to consistent results. An analysis of the contrast decrease along the optical axis shows that this result is only true for strongly stained structural parts; averaging over large numbers of particles is required for the structural study of weakly stained parts. Possibilities of pattern recognition are discussed. The structural feature complementarity is explained by means of a model example; it can drastically reduce cross-correlation coefficients.     

Dephosphorization equilibria between pure molten iron and CaO-saturated FeOn–CaO–SiO2 and FeOn–CaO–Al2O3 slags

Metal-slag refining reactions have been investigated to determine dephosphorization equilibria in steelmaking using CaO-saturated slags, low in P₂O₅–content, based on the systems FeO_n–CaO–SiO₂ and FeO_n–CaO–Al₂O₃. Slag compositions have been optimized with respect to basicity and oxygen potential to achieve maximum partition ratios wt.%(P₂O₅)/wt.%[P] and minimum phosphorus contents in pure molten iron at 1550, 1600 and 1700°C. Both slag systems prove to be effective dephosphorizers. Optimal slag compositions are around 10 wt.% SiO₂ near the CaO–3CaO · SiO₂ double saturation in the case of FeO_n–CaO–SiO₂ slags and at Al₂O₃ contents tending to zero in the case of FeO_n–CaO–Al₂O₃ slags. Attempts were also made to present phosphate capacities C_PO4^3?, fractions of free oxygen ions x_O^2? and theoretical optical basicities Λ as a function of the FeO_n content of slags.     

Rubber composites based on graphene nanoplatelets,expanded graphite,carbon nanotubes and their combination: A comparative study

Solution styrene butadiene rubber (S-SBR) composites reinforced with graphene nanoplatelets (GnPs), expanded graphite (EG), and multiwalled carbon nanotubes (MWCNTs) were prepared and the electrical and various mechanical properties were compared to understand the specific dispersion and reinforcement behaviours of these nanostructured fillers. The electrical resistivity of the rubber composite gradually decreased with the increase of filler amount in the composite. The electrical percolation behaviour was found to be started at 15 phr (parts per hundred rubber) for GnP and 20 phr for EG filled systems, whereas a sharp drop was found at 5 phr for MWCNT based composites. At a particular filler loading, dynamic mechanical analysis and tensile test showed a significant improvement of the mechanical properties of the composites comprised of MWCNT followed by GnP and then EG. The high aspect ratio of MWCNT enabled to form a network at low filler loading and, consequently, a good reinforcement effect was observed. To investigate the effect of hybrid fillers, MWCNT (up to 5 phr) were added in a selected composition of EG based compounds. The formation of a mixed filler network showed a synergistic effect on the improvement of electrical as well as various mechanical properties.     

Synthesis,structure, and thermal behavior of [Cu70Se35(PEt2Ph)24]

We investigated the molecular and crystal structure as well as the thermal behavior of [Cu₇₀Se₃₅(PEt₂Ph)₂₄] using single-crystal X-ray diffraction, high-resolution transmission electron microscopy (HRTEM), X-ray powder diffractometry, and thermal gravimetric analysis (TGA). The use of a He-cooled sample head in HRTEM makes possible for the first time the investigation of semiconductor cluster molecules under the extreme conditions of the experiment and, thus, comparison with the results of single-crystal X-ray diffraction. The lattice spacings and packing symmetry of the three-dimensional cluster molecule superlattice found in HRTEM are in good agreement with the ones determined by X-ray structure diffraction. The atomic ordering inside the cluster molecules, which resembles a hexagonal packing of the selenium atoms, could not be resolved in the HRTEM measurements, since upon irradiation with the electron beam the clusters start to move after a few seconds and the images go out of focus. This movement is possibly affected by cleavage processes of the phosphine ligands, as could be observed in thermal gravimetric analysis under comparably mild conditions. Powder diffraction measurements show that this cleavage of ligand molecules is accompanied by the formation of larger copper selenide cluster cores and ends up at high temperatures in the formation of bulk α-Cu₂Se.