Emulsion Combustion and Flame Spray Synthesis of Zinc Oxide/Silica Particles

Two flame spray methods, emulsion combustion method (ECM) and flame spray pyrolysis (FSP), were compared for synthesis of pure and mixed SiO₂ and ZnO nanoparticles. The effect of silicon precursor was investigated using liquid hexamethyldisiloxane (HMDSO) or SiO₂ sol, while for ZnO zinc acetate (ZA) was used. Gas phase reaction took place when using HMDSO as Si precursor, forming nanoparticles, whereas the SiO₂ sol used as Si source was not evaporated in the flame, creating large aggregates of the sol particles (e.g. 1 m). The FSP of ZA produced ZnO homogeneous nanoparticles. Lower flame temperatures in ECM than in FSP resulted in mixed gas and liquid phase reaction, forming ZnO particles with inhomogeneous sizes. The FSP of HMDSO and ZA led to intimate gas-phase mixing of Zn and Si, suppressing each other's particle growth, forming nanoparticles of 19 nm in BET-equivalent average primary particle diameter. Nucleation of ZnO and SiO₂ occurred independently by ECM of HMDSO and ZA as well as by FSP of the SiO₂ sol and ZA, creating a ZnO and SiO₂ mixture. The reaction of ZnO with SiO₂ was likely to be enhanced by ECM of the SiO₂ sol and ZA where both Zn and Si species were not evaporated completely, resulting in ZnO, -willemite and Zn_1.7SiO₄ mixed phase.     

Simultaneous determination of cationic surfactants and nonionic surfactants by ion-association titration.

A simultaneous determination of cationic and nonionic surfactants has been developed using ion-association titration. Tetrabromophenolphthalein ethyl ester (TBPE) was used as an indicator. Benzalkonium reacted with TBPE to form a blue ion-associate in the organic phase. When tetrakis(4-fluorophenyl)borate was added dropwise to the solution, the color of the organic phase turned to yellow at the equivalence point. In addition, when a large amount of potassium ion was added to a solution including Triton X-100, Triton X-100 could be determined by the same technique as described above because of formation of the K+-Triton X-100 cation. The proposed method is available for the stepwise determination of cationic and nonionic surfactants in mixtures.     

Thermoresponsive behavior of charged <Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide-based hydrogels containing gold nanostructures

We report the synthesis of N-isopropylacrylamide-based hydrogels containing either an anionic (acrylic acid) or cationic ([2-(acryloyloxy)ethyl]trimethylammonium chloride) co-monomer. These hydrogels were cross-linked with a cleaveable (N,N′-cystaminebisacrylamide) and/or inert (N,N′-methylenebisacrylamide) molecule in four combinations. Gold nanostructures were then synthesized within these hydrogel matrices by in situ reduction of a metal ion precursor. The resulting eight nanocomposites and their non-gold-containing (native) analogs were characterized with several analytical methods. UV–visible and infrared spectroscopy revealed differences among the samples based largely on the concentration and identity of cross-linking agent. Equilibrium swelling masses and phase transition behavior point to differences among samples on charge of the hydrogel backbone, cross-linker type, and presence or absence of gold nanostructures. A molecular level explanation for these observations is described.     

Synthesis of 6,6-dimethyltricyclo[5.4.0.02,8]undecane-2,9-diol for (ent-)longipinane-type sesquiterpenoids using two types of radical cyclization reactions

A synthetic route to 6,6-dimethyltricyclo[5.4.0.0^2,8]undecane-2,9-diol, a key precursor to (ent-)longipinane-type sesquiterpenoids, is described. This unique core common to (ent-)longipinanes was constructed using two types of intramolecular radical cyclization reactions, namely, intramolecular coupling of an acid chloride and an alkyl iodide mediated by SmI₂, TBAI and HMPA, and the coupling of a ketone and an epoxide mediated by Cp₂TiI₂ and SmI₂.     

Efficient synthesis of syn-α-alkoxy epoxide via a diastereoselective Darzens reaction

A highly diastereoselective Darzens reaction was developed by using a MEM- or TBDPS-protected α-hydroxy aldehyde with di-tert-butyl bromomalonate. This method effectively provides a syn-α-alkoxy epoxide, and a possible reaction mechanism was proposed to explain the high syn selectivity.     

Intense terahertz emission from undoped GaAs/n-type GaAs and?InAs/AlSb structures grown on Si substrates in the transmission-geometry excitation

Intense terahertz radiation was generated from femtosecond laser-irradiated InAs and GaAs layers on Si substrates. Results show that InAs/Si and GaAs/Si films can be excited in reflection and transmission geometries. The InAs/Si film exhibited weaker emission for both excitation cases but it will be more feasible as a spectroscopic THz source due to the absence of complex spectral features in its emission spectrum. The GaAs/Si emission is characterized by Fabry?CPerot oscillations but it is 90% of that of p-InAs bulk crystal emission intensity in the reflection geometry. Excitation fluence measurements showed that the InAs/Si film saturates easily due to the laser??s shallow penetration depth in InAs.     

Viscoelastic properties of semidilute poly(methyl methacrylate) solutions

Viscoelastic properties were examined for semidilute solutions of poly(methyl methacrylate) (PMMA) and polystyrene (PS) in chlorinated biphenyl. The number of entanglement per molecule, N, was evaluated from the plateau modulus, G _N . Two time constants, _s and ₁, respectively, characterizing the glass-to-rubber transition and terminal flow regions, were evaluated from the complex modulus and the relaxation modulus. A time constant _k supposedly characterizing the shrink of an extended chain, was evaluated from the relaxation modulus at finite strains. The ratios ₁/ _s and _k / _s were determined solely by N for each polymer species. The ratio ₁/ _s was proportional to N ^4.5 and N ^3.5 for PMMA and PS solutions, respectively. The ratio _k / _s was approximately proportional to N ^2.0 in accord with the prediction of the tube model theory, for either of the polymers. However, the values for PMMA were about four times as large as those for PS. The result is contrary to the expectation from the tube model theory that the viscoelasticity of a polymeric system, with given molecular weight and concentration, is determined if two material constants _s and G _N are known.     

Evaluation of 13C-phenylalanine and 13C-tyrosine breath tests for the measurement of hepatocyte functional capacity in patients with liver cirrhosis.

Liver disease is associated with an abnormal elevation of the plasma concentrations of the aromatic amino acids phenylalanine and tyrosine. The liver is the main site of aromatic amino acid metabolism, particularly the hydroxylation of phenylalanine to tyrosine and further tyrosine degradation. In the present study, we have examined the usefulness of the L-[1-13C]phenylalanine breath test (13C-PheBT) and L-[13C]tyrosine breath test (13C-TyrBT) for the detection of hepatic damage in patients with liver cirrhosis. First, the time courses of 13CO2 excretion after the administration of L-[1-13C]phenylalanine and L-[1-13C]tyrosine were compared. The peak times (the time expressed in minutes at which 13CO2 excretion was maximal) were 20 min in both breath tests, but 13C-TyrBT gave a higher peak than 13C-PheBT. Next, the parameters of 13C-PheBT and 13C-TyrBT were compared with biochemical liver function test values. These parameters were well correlated with several liver blood test values conventionally regarded as measures of hepatocyte functional reserve. Therefore, 13C-PheBT and 13C-TyrBT may be useful to assess the degree and progression of hepatic dysfunction.