Numerical simulation of shock propagation in a polydisperse bubbly liquid

The effect of distributed bubble nuclei sizes on shock propagation in a bubbly liquid is numerically investigated. An ensemble-averaged technique is employed to derive the statistically averaged conservation laws for polydisperse bubbly flows. A finite-volume method is developed to solve the continuum bubbly flow equations coupled to a single-bubble-dynamic equation that incorporates the effects of heat transfer, liquid viscosity and compressibility. The one-dimensional shock computations reveal that the distribution of equilibrium bubble sizes leads to an apparent damping of the averaged shock dynamics due to phase cancellations in oscillations of the different-sized bubbles. If the distribution is sufficiently broad, the phase cancellation effect can dominate over the single-bubble-dynamic dissipation and the averaged shock profile is smoothed out.     

Reductive coupling of aromatic N,N-acetals using zinc and chlorotrimethylsilane

The reductive coupling of aromatic N,N-acetals and N,O-acetal activated by chlorotrimethylsilane proceeded smoothly in the presence of zinc to give the corresponding diamines in good yields.     

Cellulose as matrix component of conducting films

Conjugated polymers gain growing importance as conductive materials in industrial applications in various fields of electronic devices. Cellulose with its extraordinary supramolecular structure and material properties can help to awake the possibilities for conducting polymers in interplay of the two materials. The ability of additional derivatization, the stiff and oriented molecular structure and the inherent strength, stability and film-forming properties give cellulose a complementary role to the brittle conjugated polymers, cellulose imparting the features of a stable and robust carrier component. To go forward this way, making a composite out of cellulose and conducting polymers is a prerequisite. Different strategies to form composite materials of non-derivatized cellulose and conductive organic polymers were tested. Significant differences between various mixing strategies as well as between the conducting polymers polyaniline (PAni), polypyrrole (PPy), and polythiophen (PTh) were observed. In situ synthesis of the conducting polymers in cellulose solutions and microcellulose dispersions as well as blending of pre-synthesized conducting polymers in these cellulose systems were tested. Unexpectedly, not homogenous mixtures showed best results in respect to film formation and conductivity, but composites formed by heterogeneous mixtures of the conducting polymers within a cellulose gel. Best results were obtained with finely dispersed PAni. The results support development studies towards circuitry and photo-current systems based on cellulose carriers.     

Ab initio study of magnetic interactions of manganese-oxide clusters

The manganese clusters have attracted much attention in relation with the oxygen evolving center (OEC) in photosystem II (PS II) system, which catalyzes the water oxidation reaction. Previously, we examined various spin-structures of Mn(II)₄O₄ model clusters, of which all of magnetic interactions are antiferromagnetic. In this study, we investigated electronic and magnetic structures of simple model clusters, Mn₄O₄(OAc)₆ and Mn₃CaO₄(OAc)₆ using spin unrestricted B3LYP (UB3LYP) method. The UB3LYP method is a standard tool for this study and has been in fact employed by many researchers. However, several peculiar features are observed for these model clusters: for instance the most stable spin state becomes the highest spin state for Mn(IV)₄O₄(OAc)₆ although this model cluster consists of superexchange type of units, Mn(IV)₂O₂ that usually favors antiferromagnetic spin alignments. Implications of the comparative results are discussed in relation to the electrophilic (or radical) mechanism for the O-O bond formation in the OEC.     

Span 80 vesicles have a more fluid, flexible and "wet" surface than phospholipid liposomes

The surface properties of Span 80 vesicles at various cholesterol contents, together with those of various liposomes, were characterized by using fluorescence probes. The membrane fluidity of the Span 80 vesicles was measured by 1,6-diphenyl-1.3.5-hexatriene (DPH) and trimethlyammonium-DPH (TMA-DPH), and the results suggested that the surface of the Span 80 vesicles was fluid due to the lateral diffusion of Span 80 molecules. The depolarization measured by TMA-DPH and the headgroup mobility measured by dielectric dispersion analysis indicated the high mobility of the head group of Span 80 vesicles. This suggested that the surface of Span 80 vesicles was flexible due to the head group structure of Span 80, sorbitol. In addition, spectrophotometric analysis with 6-dodecanoyl-N, N-dimethyl-2-naphthylamine and 8-anilino-1-naphthalenesulfonic acid indicated that the water molecules could easily invade into the interior of the Span 80 vesicle membrane, suggesting that the membrane surface was more wet than the liposome surface. These surface properties indicated that the protein could interact with the interior of vesicle membranes, which was similar to the case of cholesterol. Thus the present results confirmed that the Span 80 vesicle surfaces showed the unique characteristics of fluidity, flexibility, and "wetness", whereas the liposome surfaces did not.     

The selenite-capped polyoxo-4-aurate(iii), [Au(III)(4)O(4)(Se(IV)O(3))(4)](4-)

The discrete heteropolyaurate [Au(III)(4)O(4)(Se(IV)O(3))(4)](4-) () represents only the second member of this class ever reported, and was synthesized via one-pot room temperature condensation in aqueous medium. was structurally characterized in the solid state and in solution by single-crystal XRD, TGA, FT-IR, (77)Se NMR, mass spectrometry and electrochemistry.     

A tubular macrocycle from covalently linked anthracenes and meta-phenylene spacers

A novel tubular macrocycle containing four anthracene panels covalently linked by meta-phenylene spacers was synthesized. The tube is approximately 1 nm long with anthracene panels delimiting a columnar cavity with a diameter of ~1 nm and exhibits strong blue fluorescence.     

Synthesis of fluorinated N-aminoaziridines: access to new CF3-peptidomimetics

A series of fluorinated N-aminoaziridines have been synthesized by the PhI(OAc)₂-mediated aziridination procedure. The reaction was carried out with various protected hydrazides and fluorinated alkenes. The reaction was extended to alkenes bearing an amino acid and the ring opening of the CF₃–N-aminoaziridines has been investigated.     

Colorless poly(ester imide)s derived from hydrogenated trimellitic anhydride

Tetracarboxylic dianhydrides were synthesized from hydrogenated trimellitic anhydride (HTA) and some diols to obtain novel poly(ester imide)s (PEsIs). The HTA-derived tetracarboxylic dianhydrides showed much higher reactivity with various diamines than conventional cycloaliphatic tetracarboxylic dianhydrides and led to PEsI precursors with high molecular weights (M_w). The results can be explained in terms of a spacer effect. The PEsI films were essentially colorless regardless of diol and diamine components owing to inhibited charge-transfer interactions. The HTA-derived PEsIs also exhibited excellent combined properties: relatively high glass transition temperatures (T_g), relatively low water absorption (W_A), and relatively low dielectric constants. The outstanding processability (thermoplasticity and solubility) observed for the HTA-derived PEsIs was discussed on the basis of a non-planar/bent structure at the HTA-based imide units. The use of a fluorene-containing diol component was effective for enhancing T_g’s by restricted internal rotation and for reducing W_A by a decreased imide group content. On the other hand, the use of 4,4′-biphenol as another diol gave rise to a prominent toughening effect without sacrificing other target properties. One of the HTA-derived PEsI systems can be a promising candidate as plastic substrates because of its excellent combined properties: a high T_g close to 300 °C, high optical transparency, significant toughness (elongation at break > 100%), and good thermo- and solution-processability.     

Crystalline Complex of Syndiotactic Polystyrene with Poly(ethylene Glycol) Dimethyl Ethers

It has been clarified that syndiotactic polystyrene (sPS) forms co‐crystalline structures with polyethylene glycol dimethyl ethers (PEGDMEs) with molecular weights ranging from 178 to 1 000 g · mol⁻¹ through a guest exchange procedure assisted by a plasticizing agent. The PEGDME molecules are incorporated into the spaces between sPS polymer sheets consisting of (T₂G₂)₂ helices. The results of X‐ray diffraction and gravimetric measurements suggest that one or less molecules are included per unit cell for PEGDME with average molecular weight of 1 000 g · mol⁻¹, which indicates the possibility that longer polymeric molecules can be introduced into sPS lattices with multiple site occupation.