Control of Intrachain Morphology in the Formation of Polyfluorene Aggregates on the Single-Molecule Level

Controlling the morphology of π-conjugated polymers for organic optoelectronic devices has long been a goal in the field of materials science. Since the morphology of a polymer chain is closely intertwined with its photophysical properties, it is desirable to be able to change the arrangement of the polymers at will. We investigate the π-conjugated polymer poly(9,9-dioctylfluorene) (PFO), which can exist in three distinctly different structural phases: the α-, β-, and γ-phase. Every phase has a different chain structure and a unique photoluminescence (PL) spectrum. Due to its unique properties and the pronounced spectral structure-property relations, PFO can be used as a model system to study the morphology of π-conjugated polymers. To avoid ensemble averaging, we examine the PL spectrum of single PFO chains embedded in a non-fluorescent matrix. With single-molecule spectroscopy the structural phase of every single chain can be determined, and changes can be monitored very easily. To manipulate the morphology, solvent vapor annealing (SVA) was applied, which leads to a diffusion of the polymer chains in the matrix. The β- and γ-phases appear during the self-assembly of single α-phase PFO chains into mesoscopic aggregates. The extent of β- and γ-phase formation is directed by the solvent-swelling protocol used for aggregation. Aggregation unequivocally promotes formation of the more planar β- and γ-phases. Once these lower-energy more ordered structural phases are formed, SVA cannot return the polymer chain to the less ordered phase by aggregate swelling.     

Freeze-drying for the stabilisation of shellfish toxins in mussel tissue (<Emphasis Type="Italic">Mytilus edulis</Emphasis>) reference materials

Two samples of mussels (Mytilus edulis) were collected from the southwest of Ireland. One sample contained domoic acid, the other sample contained okadaic acid, dinophysistoxin-2 and azaspiracid-1, -2 and -3. Wet and freeze-dried reference materials were prepared from each of the two samples to test for differences in homogeneity, stability and extractability of the analytes in either condition. Wet materials were homogenised, aliquoted and hermetically sealed under argon and subsequently frozen at −80 °C. Dry materials were similarly homogenised but frozen in flat cakes prior to freeze-drying. After grinding, sieving and further homogenisation, the resulting powder was aliquoted and hermetically sealed. Domoic acid materials were characterised using HPLC–UV, while LC–MS was used for the determination of lipophilic toxins. The extractabilities of all phycotoxins studied were comparable for wet and freeze-dried materials once a sonication step had been carried out for reconstitution of the freeze-dried materials prior to extraction. Homogeneity was assessed through replicate analysis of the phycotoxins (n = 10), and was found to be similar for wet and freeze-dried materials, for both hydrophilic and lipophilic toxins. Water contents were determined for both wet and freeze-dried materials, and particle size was determined for the freeze-dried materials. Stability was evaluated isochronously over eight months at four temperatures (−20, +4, +20 and +40 °C). The freeze-dried material containing domoic acid was stable over the whole duration at all temperatures, while in the wet material domoic acid degraded to some extent at all temperatures except −20 °C. In freeze-dried and wet materials containing lipophilic toxins, okadaic acid, dinophysistoxin-2, azaspiracid-1 and azaspiracid-2 were stable over the whole duration at all conditions, while concentrations of azaspiracid-3 changed significantly in both materials at some storage temperatures. Figure Aliquots of freeze-dried and wet mussel tissue reference materials containing the various shellfish toxins examined in the study     

On the equivalence of acidic centers in H-beta zeolites tested by Fries rearrangement of phenyl acetate

The heterogeneously catalyzed liquid phase Fries rearrangement reaction of phenyl acetate was carried out on Beta zeolites reexchanged with different amounts of metal cations. The aim of this work was to determine the influence of the amount of Brønsted acid sites as the catalytic active centers on the conversion. Sodium and potassium ions as well as divalent calcium and zinc ions were used in the reexchange procedure. The conversion shows a linear dependency on the degree of ion reexchange following the theoretically expected values. So the results prove that the bridged hydroxyl groups are indeed the dominating active centers and that their strength seems to be independent of the degree of reexchange; consequently, their acidic strength should be identical. A special emphasis was placed on the reexchange with divalent metal ions. It was shown that one divalent ion is not able to replace two protons as is supposed to be necessary for the charge balance—so a 1:1 stoichiometry is needed to assume to explain the catalytic results.     

Novel aflatoxin derivatives and protein conjugates

Aflatoxins, a group of structurally related mycotoxins, are well known for their toxic and carcinogenic effects in humans and animals. Aflatoxin derivatives and protein conjugates are needed for diverse analytical applications. This work describes a reliable and fast synthesis of novel aflatoxin derivatives, purification by preparative HPLC and characterisation by ESI-MS and one- and two-dimensional NMR. Novel aflatoxin bovine serum albumin conjugates were prepared and characterised by UV absorption and MALDI-MS. These aflatoxin protein conjugates are potentially interesting as immunogens for the generation of aflatoxin selective antibodies with novel specificities.     

Synthesis and characterisation of the SrxBa1−xFeO3−y-system and the fluorinated phases SrxBa1−xFeO2F

Compounds in the system Sr_xBa_1?xFeO_3?y have been prepared under different partial pressures of oxygen. In this system, different perovskite-type structures are found depending highly on the values of x and y. Fluorination using polyvinylidenedifluoride (PVDF) gives oxyfluoride materials of composition Sr_xBa_1?xFeO₂F, which normally crystallize in the cubic perovskite structure. Rietveld refinement results provide information about the packing density for oxide and oxyfluoride samples and allow a general comparison between these two different types of materials. Furthermore, the determination of the average iron oxidation state also showed that the oxygen deficiency, y, depends significantly on the value of x and the structure determined by the Sr/Ba ratio.     

An asymptotic Reissner–Mindlin plate model

A mathematical study via variational convergence of a periodic distribution of classical linearly elastic thin plates softly abutted together shows that it is not necessary to use a different continuum model nor to make constitutive symmetry hypothesis as starting points to deduce the Reissner–Mindlin plate model.     

Crystal Structure and Mass-, Electronic-, Infrared Spectral Studies on Hexaaqua Ni(II) Bis(O-Tolylazo-Citrazinate) Hexahydrate Complex

A new crystalline octahedral hexaaqua Ni(II) bis(o-tolylazo-citrazinate)hexahydrate complex was synthesized. The analytical data proved the formation of 1:2 stoichiometry. An X-ray structure investigation has been carried out. The triclinic space group is p and the unit cell parameters are a = 585.5 pm, b = 993 pm, c = 1139.4 pm, α = 101.6°, β = 97.4°, γ = 102.4°. Evaluation of intensity data revealed the structure with an R-value of 0.03 (2316 observed independent reflections). The compound consists of hexaaqua nickel(2+) ions, univalent anions of the carboxylic acid and six additional water molecules per