Diffusion and concentration of molecular probes in thermoresponsive poly(N-isopropylacrylamide) hydrogels: effect of the volume phase transition

Poly(N-isopropylacrylamide), NIPA, thermoresponsive hydrogels with well-defined concentrations of an electroactive probe, 1,1'-ferrocenedimethanol, Fc(MeOH)2, were prepared. The discontinuous reversible volume phase transition of such gels occurs at 32 +/- 1 degrees C and results in a release of approximately 93% of the solution from the polymeric network. Transport of Fc(MeOH)2 in both swollen and collapsed gels was studied using steady-state voltammetry and chronoamperometry at platinum microelectrodes. The diffusion coefficient of Fc(MeOH)2 in collapsed gels was approximately 2 orders of magnitude smaller than that in swollen gels. UV/vis spectroscopic studies showed that for 3.0% NIPA gel, the concentration of Fc(MeOH)2 in the collapsed phase was approximately 6 times higher than that in released solution and 4.5 times higher than in the original swollen gel.     

Elucidation of a polychlorinated bipyrrole structure using enantioselective GC

A hexachloro congener (Q1-hex) of the natural heptachloro-1'-methyl-1,2'-bipyrrole Q1 was recently observed as a byproduct of the Q1 synthesis. NMR investigation confirmed that Q1-hex has a proton on a carbon in beta-position to a nitrogen. Three isomers are possible that fulfill this prerequisite; unfortunately, however, the NMR data were not sufficient to distinguish among the three structural variants. Because only one isomer of Q1-hex is expected to be chiral, we utilized enantioselective gas chromatography and two chiral stationary phases to separate the atropisomers. Baseline separation of the Q1-hex atropisomers was obtained on 10% chemically bonded permethyl-beta-cyclodextrin. In the full-scan mode, it was found that Q1-hex was racemic and that both atropisomers had identical mass fragmentation patterns. Partial resolution of the Q1-hex atropisomers was obtained on 25% tert-butyldimethylsilylated beta-cyclodextrin diluted in PS086. In concert with previous NMR data, these enantioseparations prove that the structure of Q1-hex is 2,3,3',4',5,5'-hexachloro-1'-methyl-1,2'-bipyrrole (5). To our knowledge, this is the first gas chromatographic separation of atropisomers of an axially chiral 1,2'-bipyrrole derivative.     

Integrated microfluidic system enabling (bio)chemical reactions with on-line MALDI-TOF mass spectrometry

A continuous flow micro total analysis system (micro-TAS) consisting of an on-chip microfluidic device connected to a matrix assisted laser desorption ionization [MALDI] time-of-flight [TOF] mass spectrometer (MS) as an analytical screening system is presented. Reaction microchannels and inlet/outlet reservoirs were fabricated by powderblasting on glass wafers that were then bonded to silicon substrates. The novel lab-on-a-chip was realized by integrating the microdevice with a MALDI-TOFMS standard sample plate used as carrier to get the microfluidic device in the MALDI instrument. A novel pressure-driven pumping mechanism using the vacuum of the instrument as a driving force induces flow in the reaction microchannel in a self-activating way. Organic syntheses as well as biochemical reactions are carried out entirely inside the MALDI-MS ionization vacuum chamber and analyzed on-line by MALDI-TOFMS in real time. The effectiveness of the micro-TAS system has been successfully demonstrated with several examples of (bio)chemical reactions.     

Near-infrared diode laser based spectroscopic detection of ammonia: a comparative study of photoacoustic and direct optical absorption methods

A photoacoustic spectroscopic (PAS) and a direct optical absorption spectroscopic (OAS) gas sensor, both using continuous-wave room-temperature diode lasers operating at 1531.8 nm, were compared on the basis of ammonia detection. Excellent linear correlation between the detector signals of the two systems was found. Although the physical properties and the mode of operation of both sensors were significantly different, their performances were found to be remarkably similar, with a sub-ppm level minimum detectable concentration of ammonia and a fast response time in the range of a few minutes.     

Thermoluminescence dating of archaeological artefacts from the Middle Neolithic,Bronze Age and the Roman Empire period

Thermoluminescence (TL) dating was applied for artefacts found near the small village of Michelstetten, Lower Austria. Settlements in this region can be traced hack a long time and, according to archaeologists, the discovered artefacts may be as old as 6000 years. A modified sample preparation technique based on the fine-grain method was developed. This technique results in a higher reproducibility and reduces the overall preparation time. For some artefacts the new information of the TL dating leads to an unforeseen re-interpretation of the archaeological age. Furthermore, an iron furnace from the period of the Roman Empire could be dated. For the first time, it was possible to estimate correctly the point of time of the burn-down of an ancient wooden house via an analysis of the house's clay plaster. The fire took place in the sixth century; this was confirmed by dating ceramic artefacts.     

Possible implications of non-linear radiobiological effects for the estimation of radiation risk at low doses

Possible implications of the effects of low LET radiation on the induction of cancer at low doses are studied. Low dose hypersensitivity and adaptive response were identified as candidates which may give a non-linear dose effect curve for acute exposures, whereas adaptive response may influence protracted exposures. In this paper acute exposures are studied. Several radiobiological reports on studies with mammalian cell lines have indicated the presence of a hypersensitive region in the radiation survival response at low doses followed by an increase in radioresistance. The two step clonal expansion (TSCE) model for the process of carcinogenesis was adapted in such a way that cell killing after acute radiation induces increased clonal expansion for some time and thus gives a promoting effect of radiation. As a first step, the Radiation Effects Research Foundation (RERF) data on the lung cancer incidence are fitted to study how such a model would influence the assessment of the cancer risk at low doses.     

Monte Carlo code for microdosimetry of inhaled alpha emitters

A Monte Carlo code has been developed to calculate the local energy deposited by alpha emitters deposited on the inner surface in the lung airway. Developed to deal further with airway bifurcations, this code has been as a first step validated in a cylindrical airway configuration by comparison with well-established analytical codes in the case of contamination of bronchiolar airways with actinides. The code has then been applied to the study of uniform and non-uniform contamination of cylindrical bronchial airways by radon progeny in indoor and mine exposure conditions. In addition to the microdosimetric spectra, the average microdosimetric parameters (zp, n, z) have been evaluated. The work currently in progress consists in adapting this developed Monte Carlo code to the configuration of an airway bifurcation with realistic particles deposition.     

Polarity determination of III-V compound semiconductors by large-angle convergent beam electron diffraction

The large-angle convergent beam electron diffraction (LACBED) technique is used for determining the crystal polarity of GaP and GaAs single crystals from < 1 1 0 > cross-sectional samples. The method which is based on an earlier approach using convergent beam electron diffraction (CBED) evaluates the polarity-sensitive contrast of high odd-index Bragg-lines in [0 0 2] dark-field patterns. The polarity is determined by application of a simple contrast rule as well as by direct comparison with dynamical simulations. For the two materials the ranges of applicability are determined by a detailed analysis of the Bragg-line contrast as a function of the sample thickness. The coexistence of the Bragg-line pattern and the of shadow image of the defect in correct rotational relationship to each other makes the analysis straightforward and free from possible sources of errors. As an example, the crystal polarity of GaP is related to the morphology of facetted voids. The LACBED method is shown to be suitable for relating the analysis of extended crystal defects. The advantages and the disadvantages of the LACBED method are discussed in comparison with the corresponding CBED method and with a recent method based on the analysis of bend contours.