Wetting phenomena in the two-dimensional ANNNI model in a field

Wetting phenomena at various interface types in the ordered phases of the two-dimensional axial next-nearest neighbour Ising (or ANNNI) model in a field are studied using a transfer matrix approach and Monte Carlo techniques. Different types of wetting at distinct wetting lines or at the bulk phase boundary are identified, which may be tested experimentally in adsorbate systems with a (p×1) ordering, forp equal to two, three or four.     

FLUORESCENCE ENERGY TRANSFER BETWEEN DIMETHYLDIAZAPEROPYRENIUM DICATION AND ETHIDIUM INTERCALATED IN POLY d(A-T)

Dimethyldiazaperopyrenium is one of the largest known DNA intercalators. Fluorescence energy transfer occurred between dimethyldiazaperopyrenium (donor) and ethidium (acceptor) when these dyes were bound to a double-stranded polynucleotide such as poly d(A-T). The addition of increasing amounts of ethidium bromide led to a marked shortening of the fluorescence lifetime of the donor, whereas the excited state of the acceptor was progressively populated via energy transfer from the donor. Critical Förster distance between these two chromophores was calculated to be 3.8 nm. The observed transfer efficiency was lower than that calculated on the basis of this critical distance and a statistical distribution of bound drugs. These results are discussed taking into account the conformational change induced by intercalation of dimethyldiazaperopyrenium in the double-stranded polynucleotide.     

An overview of polylactides as packaging materials

Polylactide polymers have gained enormous attention as a replacement for conventional synthetic packaging materials in the last decade. By being truly biodegradable, derived from renewable resources and by providing consumers with extra end-use benefits such as avoiding paying the "green tax" in Germany or meeting environmental regulations in Japan, polylactides (PLAs) are a growing alternative as a packaging material for demanding markets. The aim of this paper is to review the production techniques for PLAs, summarize the main properties of PLA and to delineate the main advantages and disadvantages of PLA as a polymeric packaging material. PLA films have better ultraviolet light barrier properties than low density polyethylene (LDPE), but they are slightly worse than those of cellophane, polystyrene (PS) and poly(ethylene terephthalate) (PET). PLA films have mechanical properties comparable to those of PET and better than those of PS. PLA also has lower melting and glass transition temperatures than PET and PS. The glass transition temperature of PLA changes with time. Humidity between 10 and 95% and storage temperatures of 5 to 40 degrees C do not have an effect on the transition temperature of PLA, which can be explained by its low water sorption values (i.e. <100 ppm at Aw = 1). PLA seals well at temperatures below the melting temperature but an appreciable shrinking of the films has been noted when the material is sealed near its melting temperature. Solubility parameter predictions indicate that PLA will interact with nitrogen compounds, anhydrides and some alcohols and that it will not interact with aromatic hydrocarbons, ketones, esters, sulfur compounds or water. The CO2, O2 and water permeability coefficients of PLA are lower than those of PS and higher than those of PET. Its barrier to ethyl acetate and D-limonene is comparable to PET. The amount of lactic acid and its derivatives that migrate to food simulant solutions from PLA is much lower than any of the current average dietary lactic acid intake values allowed by several governmental agencies. Thus, PLA is safe for use in fabricating articles for contact with food.     

Simultanbestimmung organischer und anorganischer Anionen aus verwitterten Natursteinoberfl?chen mittels Gradienten-Ionen-Chromatographie

Summary Inorganic anions as well as carboxylic acids in eluates of stone can be separated by anion-exchange chromatography using a gradient elution system. This separation required a HPIC-AS5A(5 ) (DIONEX) separator column, anion micro membrane suppressor (AMMS) (DIONEX) and a continous NaOH-gradient. The gradient started with an initial concentration of 0.75 mmol/l NaOH, 203 mmol/l NaOH was added. An Anion Trap Column (4×50 mm) between injector and pump served to clean the NaOH-eluents. Reproducibility and linearity of the gradient method were satisfactory.     

Photoemission of protons from4He in theΔ-resonance region

High resolution proton energy spectra from the⁴He(γ,p) reaction have been measured with tagged photons in the range E_γ = 130?525 MeV using the large Mainz NaI(T1) spectrometer atΘ _p ^lab =37.1°. Three separate reaction channels were identified, viz.⁴He(γ,p)t two-body breakup,⁴He photodisintegration via two-nucleon photon absorption processes and the quasifree pion production channel. Differential cross sections are presented for each of these channels as a function of photon energy. The sum of the two-nucleon photon absorption and the quasifree pion production differential cross sections, in the CM system, resembles that of the corresponding free-nucleon differential cross section when Fermi motion is taken into account.     

Singlet Oxygen Quenching by Resveratrol Derivatives†

We investigated the singlet oxygen quenching ability of several derivatives of trans-resveratrol which have been reported to have significant antioxidant ability, including photoprotective activity. We measured the total rate constants of singlet oxygen removal (k_T) by the methylated resveratrol derivative 1,3-dimethoxy-5-[(E)-2-(4-methoxyphenyl)ethenyl]benzene, and the partially methylated resveratrol derivatives 4-((E)-2-(3,5-dimethoxyphenyl)ethenyl)phenol (pterostilbene), 5-[(E)-2-(4-methoxyphenyl)ethenyl]benzene-1,3-diol and (2R,3R)-3,5,7-trihydroxy-2-(3,4,5-trihydroxyphenyl)-2,3-dihydrochromen-4-one (dihydromyricetin). A protic solvent system results in higher k_T values, except for the completely methylated derivative. We also investigated the ability of trans-resveratrol to directly act as a photosensitizer (rather than via secondary photoproducts resulting from other primary photochemical reactions) for the production of singlet oxygen but found that neither resveratrol nor any of its derivatives are able to do so. We then studied the chemical reactions of the methylated derivative with singlet oxygen. The main pathway consists of a [4 + 2] cycloaddition reaction involving the trans-double bond and the para-substituted benzene ring similar to what has been observed for trans-resveratrol. Unlike trans-resveratrol, the primary singlet oxygen product undergoes a second [4 + 2] cycloaddition with singlet oxygen leading to the formation of diendoperoxides. A second reactivity pathway for both trans-resveratrol and the methylated derivative leads to the formation of aldehydes via cleavage of a transient dioxetane.     

Novel mixed ligand coordination compounds of some rare earth metal cations containing acesulfamato/N,N-diethylnicotinamide

The mixed ligand coordination compounds containing acesulfamato and N,N -diethylnicotinamide biomolecules of some rare earth metal cations (Eu³⁺, Tb³⁺, Ho³⁺, Er³⁺ and Yb³⁺) were synthesized, and their structural properties were investigated. Possible structural formulas have been proposed by determining the chemical composition of molecules (elemental analysis), binding properties (infrared spectroscopy, mass analysis, solid-state UV-vis spectroscopy), thermal degradation properties (TGA / DTA curves). Based on the data collected, it is suggested that rare earth metal cations with a 3+ oxidation state have sextet coordination. The geometries of the structures were thought to be distorted octahedral. The charge balance of the coordination sphere is balanced by a monoanionic acesulfamato located outside the coordination sphere. When the thermal behaviours of the complexes were examined, it was determined that the compounds with Eu³⁺, Tb³⁺, and Yb³⁺ metal cations contained one hydrate water outside the coordination sphere. Hydrate waters do not exist in the Ho³⁺ and Er³⁺ metal cation-centred complexes. At the end of the thermal decomposition analysis of all complex structures, it was determined that they leave the relevant metal oxides in the reaction vessels as final decomposition products.     

Surface Critical Behavior of Two-Dimensional Dilute Ising Models

Ising models with nearest neighbor ferromagnetic random couplings on a square lattice with a (1, 1) surface are studied, using Monte Carlo techniques and a star-triangle transformation method. In particular, the critical exponent of the surface magnetization is found to be close to that of the perfect model, Β₁ = 1/2. The crossover from surface to bulk critical properties is discussed.