π-π* Emission from a tetrazine derivative complexed with zinc ion in aqueous solution: a unique water-soluble fluorophore

A 3,6-bis(5-amino-2-pyridyl)-1,2,4,5-tetrazine exhibits strong π-π* fluoresce in the presence of zinc ion (Zn(2+)) in aqueous solution, whereas it is not fluorescent in the absence of Zn(2+) as well as in the presence of competing metal ions.     

Determination of stable lead isotope ratios in environmental samples: Combination of microwave digestion and ICP-MS

Microwave digestion was applied as pretreatment of environmental samples for the determination of lead isotope ratios by ICP-MS. Microwave digestion decomposed the samples easily and rapidly without lead contamination. The lead isotope ratios could be measured directly by ICP-MS without tedious lead purification, because the influence of the matrix elements on measurements of lead isotope ratios is small enough to be ignored.     

The effect of sulfur stereochemistry of l-β,β-dimethylmethionine S-oxide on the physicochemical properties of truncated polytheonamides

l-β,β-Dimethylmethionine S-oxide is a unique amino acid found in polytheonamides. Four designed hexapeptides containing the sulfide, (S_R)-sulfoxide, (S_S)-sulfoxide, and sulfone derivatives of l-dimethylmethionine were synthesized and functionally analyzed. Our results indicate that the sulfoxide stereochemistry of the peptides controls their overall physicochemical properties.     

Quadrature Frequency Conversion Scheme Using CsLiB6O10 Crystals for the Efficient Second-Harmonic Generation of High Power Nd:YAG Laser

The ability of CsLiB_6O10 (CLBO) crystals for high power second-harmonic generation (SHG) of a 1064-nm Nd:YAG laser in a quadrature arrangement was experimentally demonstrated. A 532-nm second harmonic output pulse energy of 2.25 J was obtained with 3.21 J of an input 1064-nm fundamental pulse energy at a repetition rate of 10 Hz, corresponding to a power conversion efficiency in excess of 70%.     

Attenuation of weak shock waves along pseudo-perforated walls

In order to attenuate weak shock waves in ducts, effects of pseudo-perforated walls were investigated. Pseudo-perforated walls are defined as wall perforations having a closed cavity behind it. Shock wave diffraction and reflection created by these perforations were visualized in a shock tube by using holographic interferometer, and also by numerical simulation. Along the pseudo-perforated wall, an incident shock wave attenuates and eventually turns into a sound wave. Due to complex interactions of the incident shock wave with the perforations, the overpressure behind it becomes non-uniform and its peak value can locally exceed that behind the undisturbed incident shock wave. However, its pressure gradient monotonically decreases with the shock wave propagation. Effects of these pseudo-perforated walls on the attenuation of weak shock waves generated in high speed train tunnels were studied in a 1/250-scaled train tunnel simulator. It is concluded that in order to achieve a practically effective suppression of the tunnel sonic boom the length of the pseudo-perforation section should be sufficiently long. Received 23 June 1997 / Accepted 16 September 1997     

Synthesis, characterization, and catalytic reactivity of a highly basic macrotricyclic aminopyridine

The synthesis methods, physicochemical and structural characteristics, and catalytic reactivity of new macrocyclic proton chelators, N,N',N'-tris(p-tolyl)azacalix[3](2,6)(4-pyrrolidinopyridine) and N,N',N'-tris(p-tolyl)azacalix[3](2,6)(4-piperidinopyridine), are studied. The introduction of pyrrolidino and piperidino groups into the pyridine unit enables the enhancement of the synergistic proton affinity of the cavity of the macrotricycle giving a high basicity (pK(BH+) = 28.1 and 27.1 in CD(3)CN), resulting in a catalytic activity for the Michael addition of nitromethane with α,β-unsaturated carbonyl compounds.     

Improving the Heat Resistance of Ribonuclease A by the Addition of Poly(N,N‐diethylaminoethyl methacrylate)‐graft‐poly(ethylene glycol) (PEAMA‐g‐PEG)

Poly(N,N‐diethylaminoethyl methacrylate)‐graft‐poly(ethylene glycol) (PEAMA‐g‐PEG) has previously been used as a novel additive to improve the heat resistance of lysozyme, which has a positive net charge and a negatively charged active site. In the present study, we show that PEAMA‐g‐PEG prevents heat inactivation of ribonuclease A (RNase A), which has a positive net charge and a positively charged active site. After treatment at 98 °C for 10 min, the enzymatic activity of RNase A complexed with PEAMA‐g‐PEG was maintained at up to 75% of the level of the native RNase A. The extents of inactivation of RNase A and the complex of RNase A with PEAMA‐g‐PEG were strongly dependent upon the heating temperature and incubation time. Circular dichroism (CD) spectral analysis revealed that heat‐induced irreversible inactivation was largely suppressed when RNase A was complexed with PEAMA‐g‐PEG. These findings suggest that the heat resistance of RNase A is improved by the external addition of PEAMA‐g‐PEG.

     

Molecular imaging contrast media for visualization of liver function

Background and Aims

Diagnosis of liver disease has improved because of progress in imaging technology. Among the imaging methods, magnetic resonance imaging (MRI) has the advantage of a lack of radiation exposure, but the basis of the method (imaging of hydrogen atoms in water molecules) makes it hard to detect changes in tissue or the location of the diseased tissue in the liver. The aims of this study are to develop new contrast media for visualization of functional changes in the liver and to check the effectiveness of the media.

Methods

We developed a new molecular imaging contrast media that targets the asialoglycoprotein receptor (ASGP-R), a membrane protein that is specific to hepatocytes. We first checked the contrast media diameter and the cytotoxicity. Next, we examined the interaction of the media with ASGP-R through observation of fluorescein isothiocyanate (FITC)-labeled molecular imaging contrast media bound to normal hepatocellular ASGP-R using confocal laser scanning microscopy. Finally, we used MRI to observe hepatocyte interactions with the molecular imaging contrast media.

Results

The contrast media forms a nanoparticle of about 30 nm diameter in aqueous solution and the cytotoxicity is low. In vitro, the media has high specificity for ASGP-R in normal rat hepatocyte RLN-8 cells and this interaction was blocked by lactose (which has a similar molecular structure to that of galactose) and by an anti-ASGP-R antibody. The contrast media markedly enhanced T1-weighted images in MRI of normal rat hepatocytes compared to the signal strength for rat liver cancer cells.

Conclusions

We have shown that our new contrast media for molecular imaging of hepatocytes by MRI is effective in vitro.     

Characterization of epitaxial MgO growth on Si(001) surface

MgO epitaxial growth on a Si(001) surface by ultrahigh-vacuum molecular beam epitaxy was investigated. Epitaxial orientation and crystalline quality were characterized based on the three-dimensional reciprocal map obtained by Weissenberg RHEED. The epitaxial orientation and crystallinity were strongly dependent on the initial condition of the substrate. When MgO was deposited on a clean Si(001) surface at room temperature a MgO(001) film grew on the Si(001) substrate with two in-plane orientations:MgO[110]//Si[100] and MgO[100]//Si[100]. This is the first observation of MgO epitaxy with the former orientation, which has a smaller mismatch than the latter orientation. When the substrate was exposed to O₂ or thermally oxidized, the latterorientation predominantly grew on the substrate. Deposition of Mg on the substrate also produced the latter orientation. These results imply that nucleation sites on the initial substrate play an important role in determining the epitaxial orientation.