Molecular dynamics simulations of water droplets on polymer surfaces

Molecular dynamics simulations were used to study the wetting of polymer surfaces with water. Contact angles of water droplets on crystalline and two amorphous polyethylene (PE) and poly(vinyl chloride) (PVC) surfaces were extracted from atomistic simulations. Crystalline surfaces were produced by duplicating the unit cell of an experimental crystal structure, and amorphous surfaces by pressing the bulk polymer step by step at elevated temperature between two repulsive grid surfaces to a target density. Different-sized water droplets on the crystalline PE surface revealed a slightly positive line tension on the order of 10(-12)-10(-11) N, whereas droplets on crystalline PVC did not yield a definite line tension. Microscopic contact angles produced by the simple point charge (SPC) water model were mostly a few degrees smaller than those produced by the extended SPC model, which, as the model with lowest bulk energy, presents an upper boundary for contact angles. The macroscopic contact angle for the SPC model was 94 degrees on crystalline PVC and 113 degrees on crystalline PE. Amorphicity of the surface increased the water contact angle on PE but decreased it on PVC, for both water models. If the simulated contact angles on crystalline and amorphous surfaces are combined in proportion to the crystallinity of the polymer in question, simulated values in relatively good agreement with measured values are obtained.     

Electronic structure of the Sr2MgSi2O7:Eu persistent luminescence material

The electronic structures of the distrontium magnesium disilicate (Sr₂MgSi₂O₇(:Eu²⁺)) materials were studied by a combined experimental and theoretical approach. The UV-VUV synchrotron radiation was applied in the experimental study while the electronic structures were investigated theoretically by using the density functional theory. The structure of the valence and conduction bands and the band gap energy of the material as well as the position of the Eu²⁺ 4f ground state were calculated. The calculated band gap energy (6.7 eV) agrees well with the experimental value of 7.1 eV. The valence band consists mainly of the oxygen states and the bottom of the conduction band of the Sr states. The calculated occupied 4f ground state of Eu²⁺ lies in the energy gap of the host though the position depends strongly on the Coulomb repulsion strength. The position of the 4f ground state with respect to the valence and conduction bands is discussed using the theoretical and experimental evidence available.     

Enzymatic Bromocyclization of α- and γ-Allenols by Chloroperoxidase from Curvularia inaequalis

Vanadate-dependent chloroperoxidase from Curvularia inaequalis catalyzes 5-endo-trig bromocyclizations of α-allenols to produce valuable halofunctionalized furans as versatile synthetic building blocks. In contrast to other haloperoxidases, also the more challenging 5-exo-trig halocyclizations of γ-allenols succeed with this system even though the scope still remains more narrow. Benefitting from the vanadate chloroperoxidase‘s high resiliency towards oxidative conditions, cyclization-inducing reactive hypohalite species are generated in situ from bromide salts and hydrogen peroxide. Crucial requirements for high conversions are aqueous biphasic emulsions as reaction media, stabilized by either cationic or non-ionic surfactants.     

Pyridine-substituted hydroxythiophenes. II. Alkylation of o-(2-, 3- and 4-pyridyl)-3-hydroxythiophenes: Regiospecific formation of o-pyridyl-3-alkoxythiophenes

The alkylation of o-(2-, 3- and 4-pyridyl)-3-hydroxythiophenes has been investigated. In the case of 4-(2-, 3- and 4-pyridyl)-3-hydroxythiophene systems, the soft alkylating reagent, methyl iodide, using sodium hydride as the base and dimethylimidazolidinone as the solvent, gave rise to a mixture of O-alkylated and O,C-dialkylated products in the proportions of 4.6–6.5 to 1. However, in the case of 2-(2-, 3- and 4-pyridyl)-3-hydroxythiophene systems, the same reaction conditions brought about exclusively O-alkylated compounds in yields of 45–53%. In both cases, the hard alkylating reagent, methyl p-toluenesulfonate, with the same base and solvent, only give O-alkylated compounds in yields of 51–77%. These latter conditions resulted in a good preparative route for the regiospecific formation of o-pyridyl-3-alkoxythiophenes by using ethyl 2-bromopro-pionate as well as methyl p-toluenesulfonate as alkylating reagents. The hydrolysis of the esters, derived from alkylation with ethyl 2-bromopropionate, has also been investigated.     

Synthesis of various 5-arylsubstituted cytosines

Some Pd-catalyzed coupling reactions have been evaluated for the synthesis of 5-substituted cytosines. A large number of 5-arylcytosines were prepared in good yields by using 2,4-O,N-bis-trimethylsilyl-5-iodocytosine with various aryl tin compounds. The use of trimethylsilyl groups proved to be essential for the reaction, attempted coupling of 5-iodocytosine and 2-trimethylstannylthiazole was not successful. One convenient alternative, which unfortunately was not successful, would have been to reverse the coupling functionalities and couple commercial arylhalides with 5-trimethylstannyl- or 5-tributylstannyl-derivatives or the corresponding 2,4-O,N-bis-trialkylsilylcytosines.     

An example concerning the zero set of the Jacobian

Let f∈W1,1(Ω,Rn) be a homeomorphism of finite distortion K. It is known that if K1/(n−1)∈L¹(Ω), then the Jacobian Jf of f is positive almost everywhere in Ω. We will show that this integrability assumption on K is sharp in any Orlicz-scale: if α is increasing function (satisfying minor technical assumptions) such that limt→∞α(t)=∞, then there exists f such that K1/(n−1)/α(K)∈L¹(Ω) and Jf vanishes in a set of positive measure.     

An HPLC study of tinidazole hydrolysis

Summary The high-performance liquid chromatographic (HPLC) method herein described allows the simultaneous determination of the hydrolysis kinetics of tinidazole and the formation kinetics of the hydrolysis products. Tinidazole is easily hydrolysed under basic conditions at raised temperature. The rate varies with the pH and the temperature of the solution, and the decomposition follows apparent first-order kinetics. The Arrheinius equation can be used to describe the effect of temperature on the half-life.     

Sorption of inorganic radiocarbon on iron oxides

Journal of Radioanalytical and Nuclear Chemistry - The sorption of inorganic radiocarbon on goethite, hematite and magnetite was studied as a function of carbon concentration, pH and ionic...     

Synthesis of Lanthanide(III) Chelates by Using ‘Click’ Chemistry

The copper(I)‐catalyzed dipolar [2+3] cycloaddition reaction of an azide and a terminal alkyne is exploited in the preparation of various europium(III), terbium(III), and dysprosium(III) chelates (Schemes 1–3). By changing the nature of the alkyne and the azide, a wide range of chelates and biomolecule‐labeling reactants were obtained. The photophysical properties (Table) of the synthesized chelates are also discussed.