Palladium catalyzed synthesis of mandelate derivatives from arylboronic acids and glyoxylate hemiacetals

NHC-coordinated cyclometalated palladium(II) catalyzed addition of arylboronic acids to methyl 2-hydroxy-2-methoxyacetate gave corresponding various functionalized methyl mandelate derivatives in good yields.     

Magnetic uni- and tri-axial grain-orientation in superconductors with layered structures

We report the grain-orientation effects under a modulated rotation magnetic field for Y-based cuprate superconductors and LaFeAsO (La1111). Tri-axial orientation has been successfully achieved only for orthorhombic Y₂Ba₄Cu₇O_y and YBa₂Cu₄O₈ powders without a twin microstructure, while separation of three crystallographic axes could not be observed in twinned YBa₂Cu₃O_y (Y123) and tetragonal La1111 powders. The morphology of grains, in addition to the symmetry of crystal structures, seriously affects the degrees of tri-axial orientation, which means that the control of twin microstructures is required for the tri-axial magnetic orientation in Y123.     

Thermo-responsive mending of polymers crosslinked by thermally reversible covalent bond: Polymers from bisfuranic terminated poly(ethylene adipate) and tris-maleimide

Remending properties of a network polymer with reversible reactivity are described. The network structure is constructed by a Diels-Alder (DA) reaction between furyl-telechelic poly(ethylene adipate) (PEAF₂) and a tris-maleimide, M₃. When a film sample was cut into two pieces and the cut surfaces were kept in contact with each other at 60 °C, rejoining of the cut pieces was observed. This mending was induced by the reversible cross-linking reaction bridging the cut surfaces. At the cut front, the “weak” DA adducts are selectively dissociated sacrificially to release the stress so as to protect the chemical structure of the prepolymer and the linker against the scission or degradation. The dissociated furan and maleimide readily reconnect by forward DA reaction to mend the material. The remending was also observed for the samples kept at room temperature after melting at 60 °C. So, the PEAF₂ network polymer is a thermo-responsive mendable material in which crack healing is induced by a prompt thermal stimulus.     

Total Synthesis of Gambierol by Using Oxiranyl Anions

Gambierol was isolated as a neurotoxin from the cultured cells of the ciguatera causative dinoflagellate Gambierdiscus toxicus and classified as a member of the polycyclic ether family of marine toxins. The structure consists of a ladder‐shaped trans‐fused octacyclic ring system that includes 18 stereogenic centers, two 1,3‐diaxial dimethyl‐substituted tetrahydropyranyl rings, and a partially conjugated triene side chain. The total synthesis of gambierol has been achieved by utilizing an oxiranyl anion strategy in an iterative manner. Synthetic highlights of this route include direct carbon–carbon formation on epoxides, sulfonyl‐assisted 6‐endo cyclization, and an expansion reaction of the tetrahydropyranyl rings to oxepanes to forge the polycyclic architecture of the target molecule.     

A nonparametric method of multi-step ahead forecasting in diffusion processes

This paper provides a nonparametric model of multi-step ahead forecasting in diffusion processes. The model is constructed from the local linear model with the Gaussian kernel. The paper provides simulation studies to evaluate its performance of multi-step ahead forecasting by comparing with the global linear model, showing the better forecasting performance of the nonparametric model than the global linear model. The paper also conducts empirical analysis for forecasting using intraday data of the Japanese stock price index and the time series of heart rates. The result shows the performance of forecasting does not differ much in the Japanese stock price index, but that the nonparametric model shows significantly better performance in the analysis of the heart rates.     

Electrochemical extraction of proteins by reverse micelle formation

The transfer of proteins by the anionic surfactant bis(2-ethylhexyl) sulfosuccinate (AOT) at a polarized 1,2-dichloroethane/water (DCE/W) interface was investigated by means of ion-transfer voltammetry. When the tetrapentylammonium salt of AOT was added to the DCE phase, the facilitated transfer of certain proteins, including cytochrome c (Cyt c), ribonuclease A, and protamine, could be controlled electrochemically, and a well-defined anodic wave for the transfer was obtained. At low pH values (e.g., pH 3.4), the anodic wave was usually well-separated from the wave for the formation of protein-free (i.e., unfilled) reverse micelles. The anodic wave for the protein transfer was analyzed by applying the theory for facilitated transfer of ions by charged ligands and then supplying information regarding the number of AOT anions reacting with one protein molecule and the total charge carried by the protein transfer. However, controlled-potential electrolyses performed for the transfer of Cyt c, which is red, revealed that the protein-AOT complexes were unstable in DCE and liable to aggregate at the interface when the pH of the W phase was 3.4. At pH 7.0, when formation of unfilled reverse micelles occurred simultaneously, the protein-AOT complexes appeared to be stabilized, probably via fusion with unfilled reverse micelles.     

Electron spin resonance studies on the oxidation mechanism of sterically hindered cyclic amines in TiO2 photocatalytic systems

A sterically hindered cyclic amine, 4-hydroxy-2,2,6,6-tetramethylpiperidine (HTMP), is converted to the corresponding aminoxyl radical (nitroxide radical), 4-hydroxy-2,2,6,6-tetramethyl piperidine 1-oxyl (TEMPOL radical) as a result of a photocatalytic reaction in TiO2 aqueous suspension. The time profile of the radical formation and the effect of additives, such as SCN-, I-, methanol, and H2O2, on the initial formation rate were measured in order to elucidate the reaction mechanism. The experimental observations indicated that the direct photocatalytic oxidation of HTMP followed by reaction with O2 is the dominant process in the formation of TEMPOL radicals. Electrochemical measurements showed that HTMP is oxidized at 0.7 V (vs NHE), which is consistent with the proposed mechanism. The possibility of other processes, involving reactions with singlet molecular oxygen, superoxide radical, and hydroxyl radical, were excluded from the reaction mechanism.     

Determination of the purity of acidimetric standards by constant-current coulometry, and the intercomparison between CRMs

The accuracy and uncertainty of the coulometric measurement results of reference materials for acidimetric titration were examined in this study. The results for amidosulfuric acid and potassium hydrogen phthalate are presented. The uncertainty was investigated by examining the dependency on the sample size and on the electrolysis current. Changes in the titration parameters did not result in any significant effects on the titration results. Acidimetric standards with the certified value linked to the SI were developed. In addition, the intercomparison of acidimetric standards was carried out by gravimetric titration, and the relationship between our coulometric results was determined. Furthermore, due to recent internationalization, not only the traceability to the SI but also the relationship and consistency of their analytical data have gained increasing importance. Our results were validated using certified reference materials (CRMs) obtained from different National Metrology Institutes (NMIs), and their relationships are presented. Presented at -- “BERM-10” -- April 2006, Charleston, SC, USA.     

Stability analysis of the two rotational isomers of meta-fluorobenzaldehyde in the S0, S1, and S2 electronic states

For a determination of the stabilization energy between the two rotational isomers of m-fluorobenzaldehyde, the S(1,2)<--S0 absorption spectra were observed in fluid n-hexane solutions at 293 and 198 K. After employing a simulation method for the spectra, we succeeded in determining the stabilization energies in the ground and the relevant excited state at the same time. The energy was estimated to be 1.7 +/- 0.5 kJ mol(-1) for S0 and also for S1 while it was 2.9 +/- 0.5 kJ mol(-1) for S2. Ab initio calculations at MP2/6-311G** computational level predicted that the O-cis form in the S0 state is more stable by 1.9 +/- 0.5 kJ mol(-1) than the counterpart rotamer, O-trans form. In summary, a schematic energy level diagram of the two rotational isomers will be illustrated for the S0, S1, and S2 states in the fluid system.     

A family of low-molecular-weight hydrogelators based on L-lysine derivatives with a positively charged terminal group

A family of L-lysine-based low-molecular-weight compounds with various positively charged terminals (pyridinium and imidazolium derivatives) was synthesized and its gelation behavior in water was investigated. Most of the compounds can be very easily synthesized in high yields (total yields >90 %), and they function as excellent hydrogelators that form hydrogels below 1 wt %; particularly, N(epsilon)-lauroyl-N(alpha)-[11-(4-tert-butylpyridinium)undecanoyl]-L-lysine ethyl ester (2 c) and N(epsilon)-lauroyl-N(alpha)-[11-(4-phenylpyridinium)undecanoyl]-L-lysine ethyl ester (2 d), which are able to gel water at concentration of only 0.2 wt %. This corresponds to a gelator molecule that entraps more than 20 000 water molecules. All hydrogels are very stable and maintain the gel state for at least 9 months. TEM observations demonstrated that these hydrogelators self-assemble into a nanoscaled fibrous structure; a three-dimensional network is then formed by the entanglement of the nanofibers. An FTIR study in [D(6)]DMSO/D(2)O and in CHCl(3) revealed the existence of intermolecular hydrogen bonding between the amide groups. This was further supported by a (1)H NMR study in [D(6)]DMSO/H(2)O. A luminescence study, in which ANS (1-anilino-8-naphtharenesulfonic acid) was used as a probe, indicated that the hydrogelators self-assemble into nanostructures possessing hydrophobic pockets at a very low concentration. Consequently, it was found that the driving forces for self-assembly into a nanofiber are hydrogel bonding and hydrophobic interactions.