Synthesis of detoxininolactone derivatives and the revised absolute stereochemistry of detoxinine

A stereospecific synthesis of acetyl-$\text{L}$-valyl-detoxininolactone has been performed and the absolute stereochemistry of detoxinine has been revised to (2$\text{S}$, 3$\text{R}$, 1′$\text{S}$)-2-(2′-carboxy-1′-hydroxyethyl)-3-hydroxypyrrolidine.     

Effect of specific adsorbed anions on the electrode kinetics of the V(III)/V(II) and Eu(III)/Eu(II) couples

Electrochemical kinetic parameters of the V(III)/V(II) and Eu(III)/Eu(II) couples in sulfuric, perchloric, hydrochloric, and hydrobromic acids were measured by potentiostatic and double pulse galvanostatic methods. The ₂ potentials in these solutions were calculated from electrocapillary measurements and the effect of the ₂ potentials on the electrode kinetics was discussed. The kinetic data after the Frumkin correction was applied show a very good agreement in H₂SO₄, HClO₄, and HCl solutions, if we assume that the non-complexed ion, which is partially supplied by the dissociation of complex ions, participates in the electrode reaction. The corrected rate constants in the bromide solution were about ten times larger than those to be expected from the ₂ potentials in the case of the V(III)/V(II) couple and a small acceleration effect was observed for the Eu(III)/Eu(II) couple. The greater reaction rate in the bromide solution is explained by the bridging effect.     

Removal of iron for the spectrophotometric determination of humic substances in fresh waters

More than 95% iron in water is removed by sorption on a cation-exchange resin after reduction to iron(II) with hydroxylammonium chloride at pH 3.5 for 24 h. The absorbance is then measured at 350 nm for the reliable determination of humic substances.     

Quasi one-dimensional nanopores in single-wall carbon nanohorn colloids using grand canonical Monte Carlo simulation aided adsorption technique

The average interstitial nanopore structure of single-wall carbon nanohorn (SWNH) assemblies was determined using X-ray diffraction and grand canonical Monte Carlo (GCMC) simulation aided N(2) adsorption at 77 K. The interstitial nanopores of SWNH assemblies can be regarded as quasi one-dimensional pores due to the partial orientation of the SWNH particles; the average pore width of the interstitial pores is 0.6 nm. Good agreement between the GCMC simulation of a structural model with one-dimensional interstitial nanopores and an experimental adsorption isotherm below P/P(0) = 10(-4) is evidence of the quasi one-dimensionality of the interstitial nanopores. A snapshot from the GCMC simulation showed one-dimensional growth of adsorbed N(2) molecules.     

Improvement of the Derjaguin-Broekhoff-de Boer theory for capillary condensation/evaporation of nitrogen in mesoporous systems and its implications for pore size analysis of MCM-41 silicas and related materials

In this work, we propose an improvement of the classical Derjaguin-Broekhoff-de Boer (DBdB) theory for capillary condensation/evaporation in mesoporous systems. The primary idea of this improvement is to employ the Gibbs-Tolman-Koenig-Buff equation to predict the surface tension changes in mesopores. In addition, the statistical film thickness (so-called t-curve) evaluated accurately on the basis of the adsorption isotherms measured for the MCM-41 materials is used instead of the originally proposed t-curve (to take into account the excess of the chemical potential due to the surface forces). It is shown that the aforementioned modifications of the original DBdB theory have significant implications for the pore size analysis of mesoporous solids. To verify our improvement of the DBdB pore size analysis method (IDBdB), a series of the calcined MCM-41 samples, which are well-defined materials with hexagonally ordered cylindrical mesopores, were used for the evaluation of the pore size distributions. The correlation of the IDBdB method with the empirically calibrated Kruk-Jaroniec-Sayari (KJS) relationship is very good in the range of small mesopores. So, a major advantage of the IDBdB method is its applicability for small mesopores as well as for the mesopore range beyond that established by the KJS calibration, i.e., for mesopore radii greater than approximately 4.5 nm. The comparison of the IDBdB results with experimental data reported by Kruk and Jaroniec for capillary condensation/evaporation as well as with the results from nonlocal density functional theory developed by Neimark et al. clearly justifies our approach. Note that the proposed improvement of the classical DBdB method preserves its original simplicity and simultaneously ensures a significant improvement of the pore size analysis, which is confirmed by the independent estimation of the mean pore size by the powder X-ray diffraction method.     

The surface of TiO2 gate of 2DEG-FET in contact with electrolytes for bio sensing use

In order to apply two-dimensional electron-gas-field-effect-transistors (2DEG-FETs) for cell-viability sensors, we investigated the chemical/electrical properties of TiO₂ thin films (13-17 nm) prepared with the sol-gel technique on the gate surface of AlGaAs/GaAs 2DEG-FETs. Photochemical/electrochemical reactions on GaAs surface in electrolytes, which induce the degradation of 2DEG-FET performance, are effectively suppressed by introducing a TiO₂ thin film on the gate area of 2DEG-FETs. Compared to conventional ion-selective FETs (ISFETs), the TiO₂/2DEG-FETs in this study exhibit a high sensitivity (410 mV/mM) for H₂O₂ detection. TiO₂ surfaces show better biocompatibility than GaAs surfaces as demonstrated by direct cell culture on these surfaces.     

Structural changes of silica particles in elongated rubber by two-dimensional small-angle X-ray scattering and extended reverse Monte Carlo analysis

Two-dimensional pattern reverse Monte Carlo method is applied to investigate structural changes of silica particle filler in uniaxially elongat ed rubber. We calculated three-dimensional confor mations of spherical silica particles using a series of two-dimensional patterns of structure factors during elongation. The structure factors we used are inter polated from experimentally observed structure factors for the elongation ratio ε?=?0.0, 0.5, 1.0, and 1.5. To make a continuous motion of particles, we set the elongation ratio with small interval Δε?=?0.001. It is found that the structural change of the particles seem to be reliable at least for small ε regions because spurious motions like the Brownian motions are not observed.     

Chiral separation of NBD-amino acids by ligand-exchange micro-channel electrophoresis.

The chiral separation of amino acid derivatives by ligand-exchange electrophoresis in a microchannel chip was performed for the first time. A Cu(II) complex with L-prolinamide was used as a chiral selector. The migration behaviors of eleven NBD-DL-amino acids were investigated by ligand-exchange capillary electrophoresis (LE-CE). The enantiomer of five NBD-amino acids (Ser, Thr, Val, Phe and His) could be separated by LE-CE using a 20 mM ammonium acetate buffer (pH 9.0) containing 10 mM copper acetate, 20 mM L-prolinamide and 1 mM SDS. NBD-His was eluted in the order D-form and L-form, while the elution order of another enantiomers was L-form and D-form. Under this condition, the enantioseparation of these five NBD-amino acids by ligand-exchange microchip electrophoresis (LE-ME) was investigated using a glass microchip. The enantioseparation of NBD-Ser, -Thr and -His could be successfully accomplished by LE-ME. LE-ME was superior to LE-CE in terms of the short migration time and a good enantiomeric separation.     

Preparation of a novel bromine complex and its application in organic synthesis

Although molecular bromine (Br₂) is a useful brominating reagent, it is not easy to handle. Herein, we describe the preparation of a novel air-stable bromine complex prepared from 1,3-dimethyl-2-imidazolidinone (DMI) and Br₂, which was identified to be (DMI)₂HBr₃ by spectral and X-ray techniques. This complex was then used to brominate olefins, carbonyl compounds, and aromatics, as well as in the Hofmann rearrangement. Yields of reaction products using this complex were almost the same or superior to those using other bromine alternatives.     

"Click peptide" based on the "o-acyl isopeptide method": control of A beta1-42 production from a photo-triggered A beta1-42 analogue

A clear understanding of the dynamic events of amyloid beta peptide (Abeta) 1-42, such as the folding, self-assembly, and aggregation processes, would be of great significance in Alzheimer's disease (AD) research. However, elucidation of these Abeta1-42 dynamic events is a difficult issue due to uncontrolled polymerization, which also poses a significant obstacle for establishing an experimental system that clarifies the pathological function of Abeta1-42. On the basis of the O-acyl isopeptide method, we herein developed a novel photo-triggered "click peptide" of Abeta1-42, for example, 26-N-Nvoc-26-AIAbeta42, in which the photocleavable 6-nitroveratryloxycarbonyl (Nvoc) group was introduced at the alpha-amino group of Ser26 in 26-O-acyl isoAbeta1-42 (26-AIAbeta42). From the results, (1) the click peptide did not exhibit the self-assembling nature under physiological conditions due to one single modified ester; (2) photoirradiation of the click peptide and subsequent O-N intramolecular acyl migration afforded the intact Abeta1-42 with a quick and one-way conversion reaction (so-called "click"), while the click peptide was stable under nonphotolytic or storage conditions. In addition, it is advantageous that no additional fibril inhibitory auxiliaries were released during conversion to Abeta1-42. This method provides a novel system useful for investigating the dynamic biological functions of Abeta1-42 in AD by inducible activation of Abeta1-42 self-assembly.