Voltammetric determination of arsenic in high iron and manganese groundwaters

Determination of the speciation of arsenic in groundwaters, using cathodic stripping voltammetry (CSV), is severely hampered by high levels of iron and manganese. Experiments showed that the interference is eliminated by addition of EDTA, making it possible to determine the arsenic speciation on-site by CSV. This work presents the CSV method to determine As(III) in high-iron or -manganese groundwaters in the field with only minor sample treatment. The method was field-tested in West-Bengal (India) on a series of groundwater samples. Total arsenic was subsequently determined after acidification to pH 1 by anodic stripping voltammetry (ASV). Comparative measurements by ICP-MS as reference method for total As, and by HPLC for its speciation, were used to corroborate the field data in stored samples. Most of the arsenic (78 ± 0.02%) was found to occur as inorganic As(III) in the freshly collected waters, in accordance with previous studies. The data shows that the modified on-site CSV method for As(III) is a good measure of water contamination with As. The EDTA was also found to be effective in stabilising the arsenic speciation for longterm sample storage at room temperature. Without sample preservation, in water exposed to air and sunlight, the As(III) was found to become oxidised to As(V), and Fe(II) oxidised to Fe(III), removing the As(V) by adsorption on precipitating Fe(III)-hydroxides within a few hours.     

Thermo‐/moisture‐responsive shape‐memory effect of poly(2‐ethyl‐2‐oxazoline) networks

In this work, poly(2‐ethyl‐2‐oxazoline) (PEtOx) is crosslinked to realize a moisture‐ and thermo‐responsive shape‐memory polymer. The obtained PEtOx networks exhibit excellent shape‐memory properties with storable strains of up to 650% and recovery values of 100% over at least 10 shape‐memory cycles. The trigger temperature (T_trig) of 68 °C of a PEtOx network at a relative humidity (RH) of 0% decreases with increasing moisture and equals room temperature at an RH of 40%. Thus, programmed PEtOx networks trigger sensitively on a certain temperature/moisture combination and, further, can be programmed as well as triggered at room temperature exclusively by varying humidity. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1053–1061     

Spectral diffusion of quasi localized excitons in single silicon nanocrystals

Evolution in time of photoluminescence spectra of SiO_x capped single silicon nanocrystals has been investigated by means of confocal optical spectroscopy at room temperature. Large spectral jumps between subsequent spectra of up to 40 meV have been detected leading to noticeable line broadening and variation in the electron–phonon coupling. Further, a correlation between emission energy and emission intensity has been found and discussed in terms of an intrinsic Stark effect. Anti-correlated variations of the electron–phonon coupling to Si and SiO₂ phonons as a function of photoluminescence energy indicate that the nearly localized excition is to some extent coupled to phonons in the shell covering the silicon nanocrystal. However, coupling is reduced upon increasing Stark effect, while at the same time coupling to phonons of the Si core increases.     

Development of a magnetic lab-on-a-chip for point-of-care sepsis diagnosis

We present design criteria, operation principles and experimental examples of magnetic marker manipulation for our magnetic lab-on-a-chip prototype. It incorporates both magnetic sample preparation and detection by embedded GMR-type magnetoresistive sensors and is optimized for the automated point-of-care detection of four different sepsis-indicative cytokines directly from about 5 μl of whole blood. The sample volume, magnetic particle size and cytokine concentration determine the microfluidic volume, sensor size and dimensioning of the magnetic gradient field generators. By optimizing these parameters to the specific diagnostic task, best performance is expected with respect to sensitivity, analysis time and reproducibility.     

Vapor‐Based Polymer Gradients

Chemical vapor deposition (CVD) co‐polymerization was used to fabricate polymer coatings, which comprise of reactive surface composition gradients. Two functionalized derivatives of [2.2]paracyclophane were fed into a two‐source CVD system at a 180 ° angle, then copolymerized and deposited as a polymer gradient. Infrared and X‐ray photoelectron spectroscopy (XPS) confirmed the compositional changes within the bulk polymer and at the surface. By manipulating process parameters, gradients of tailored compositional slope can be deposited on a wide range of substrates. We also were able to selectively immobilize fluorescence‐labeled ligands onto the reactive polymer gradients, making CVD‐based gradient surfaces a flexible platform for fabricating biomolecular substrates.

     

Taxol Inclusion Complexes with a Cyclodextrin Dimer: Possibilities to Detoxify Chemotherapeutics and to Target Drugs Specifically to Tumors?

The natural drug, paclitaxel (taxol), is highly effectiveas a tumor chemotherapeuticwith a low probability of inducing chemoresistance,but shows severe toxic side effectsat the therapeutic dose. How can this toxicitybe overcome? Here we report the synthesisof cyclodextrin dimers connected at thesecondary face by amide-bonded aliphatic spacers. The spacer length of one of the dimers referred to asdiβCD(2N-A4C5A4) or dimer 7cmatches the distance between the twobenzoic acid residues of paclitaxel. We investigated the physical inclusion of taxol into this dimer using the TNS-label competition method. Affinity constants with the dimer in comparison to free β-cyclodextrin are found to be of the order of 10⁷ l/mole.When included into the cyclodextrin dimer, the drug shows a considerable time delay of incorporation into human tumor cell cultures (OAT SCLC cells) or a total exclusion from the cells. This is the prerequisite to avoid intoxication of other organs of a patient. Possibilities are discussed to detoxify chemotherapeutics and to target their inclusioncomplexes specifically to tumors using specific biological signals.     

Impact of the Ga concentration on the microstructure of CuIn1–x Gax Se2

Cross‐sectional samples of CuIn_1–x Ga_x Se₂ layers grown by a three‐stage process were studied by means of electron backscatter diffraction (EBSD) in completed thin‐film solar cells. The microstructural analysis reveals a dependence of the average grain size on the gallium content x = [Ga]/([Ga] + [In]), with a maximum at x = 0.23. This result is correlated with structural measurements on CuIn_1–x Ga_x Se₂ powder samples showing that the ratio of the lattice constants c /a is equal to 2 for about the same x value. The pseudocubic crystal structure at about x = 0.23 may lead to reduced strain in the growing CuIn_1–x Ga_x Se₂ layer and therefore larger average grain sizes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Renormalization flow of QED

We investigate textbook QED in the framework of the exact renormalization group. In the strong-coupling region, we study the influence of fluctuation-induced photonic and fermionic self-interactions on the nonperturbative running of the gauge coupling. Our findings confirm the triviality hypothesis of complete charge screening if the ultraviolet cutoff is sent to infinity. Though the Landau pole does not belong to the physical coupling domain owing to spontaneous chiral-symmetry-breaking (chiSB), the theory predicts a scale of maximal UV extension of the same order as the Landau pole scale. In addition, we verify that the chiSB phase of the theory which is characterized by a light fermion and a Goldstone boson also has a trivial Yukawa coupling.