Kinetic resolution of d,l-myo-inositol derivatives catalyzed by chiral Cu(II) complex

Kinetic resolution of d,l-myo-inositol derivatives having a 1,2-diol functionality by monobenzoylation was achieved using (R,R)-Ph-BOX-Cu(II) as a catalyst. The monobenzoylation preferentially took place at the 1,2-diol functionality via a highly enantiodiscriminatory process, which was largely influenced by a substituent at the position adjacent to the 1,2-diol functionality. This method was applied to a synthesis of biologically important d-inositol-1-phosphate.     

Ion transport across a bilayer lipid membrane facilitated by valinomycin

The facilitated ion transport from one aqueous phase, W1, to another, W2, across a bilayer lipid membrane, BLM, containing valinomycin, Val, as an ionophore was investigated by voltammetry. Cyclic voltammograms for the ion transfer were symmetrical about the origin (0 V, 0 A) and the magnitude of the ion transfer current increased with an increase in the absolute value of the applied potential. The magnitude of the ion transfer current at a definite potential in the voltammograms depended on the cation species added to W1 and W2 and was proportional to the concentration of Val in the BLM. The magnitude of the ion transfer current at a definite potential also varied in proportion to the hydrophobicity of the counter anion in W1 and W2. Taking into account the conjugated ion transfers at the W1|BLM and BLM|W2 interfaces, the positive current that flowed from W1 to W2 across the BLM was attributable to both the transfer of the complex-forming cation from W1 to the BLM and the transfer of the anion, which was distributed in the BLM as the counter ion from W2 to W1. The transfer from the BLM to W1 occurred at the W1|BLM interface and both the transfer of the cation from the BLM to W2 and the transfer of the anion from W2 to the BLM at the BLM|W2 interface. The negative current was then attributed to the opposite reaction. The voltammograms were asymmetrical with the origin when the ion components in W1 and W2 were different.     

Synthetic studies of halichondrin B, an antitumor polyether macrolide isolated from a marine sponge. 8. Synthesis of the lactone part (C1C36) via horner-emmons coupling between C1C15 and C16C36 fragments and Yamaguchi lactonization

The lactone part (2) of halichondrin B (1) was synthesized by Yamaguchi macrolactonization of the seco-acid (3), which was synthesized via coupling of C1C15(4) with C16C36 (5), prepared through stereoselective construction of the E ring starting from C16C26 (7) and C27C36 (8).     

Optical Learning Neural Network Using Photorefractive Waveguides

A model of an optical neural network with learning ability is proposed. We numerically evaluate the learning ability of the proposed network by using parameters determined by experiments. Adaptive connections between artificial neurons are implemented using photorefractive (PR) waveguides that can be optically modified by guided beams. The network consists of three layers and has bipolar weights within the limited range. The bipolar weight is encoded as the difference between optical power transmittances of signal beams in two channels of the PR waveguides. The adaptivity of the transmittance of PR waveguide is experimentally evaluated and is incorporated into the proposed network simulated in a computer. The proposed network is trained by a simplified local learning algorithm. Numerical results showed that the proposed three-layered network with six hidden neurons can solve the exclusive-or problem.     

Photochemistry of amphiphilic copolymers: Fluorescence spectra of copolymers of 1-(2-naphthyl)ethyl methacrylate and sodium 2-acrylamido-2-methylpropanesulfonate in solution

Amphiphilic copolymers containing 1-(2-naphthyl)ethyl ester groups were prepared and their fluorescence properties were examined. The fluorescnce spectra of the copolymers with a higher naphthyl content showed predominantly a broad monomer emission with λ_max at 340 nm in methanol, whereas a structured emission with λ_max at 344 and 362 nm was observed in aqueous solution. The former spectra changed rapidly to the latter ones upon UV irradiation. Photolysis of the copolymers and the monomeric model compound in methanol gave 2-vinylnaphthalene, whose fluorescence agreed with those of copolymers in water, together with methyl ether, alkylnaphthalenes, and other products. These results indicate that the copolymers hold vinylnaphthalene-like traps, which may emit preferentially in water because of efficient sensitization. © 1995 John Wiley & Sons, Inc.     

A 1H NMR study of the effects of Ni additions on the behavior of hydrogen in β-vanadium hydride

The behavior of hydrogen in the hydrides of vanadium metal containing small amounts of nickel was studied by ¹H NMR spectroscopy. FT spectra and spin-spin and spin-lattice relaxation times for VH_0.77, V_0.95Ni_0.05H_0.73, and V_0.90Ni_0.10H_0.65 were measured at temperatures between 77 and 400 K. On the addition of nickel the number of hydrogen atoms on O₂₂ sites decreases and the superstructure of hydrogen is altered. Different effects of nickel on hydrogen diffusion are observed above and below about 200 K, and, therefore, the mechanism of hydrogen diffusion is assumed to change at this temperature.     

A study to control chemical reactions using Si:2p core ionization: site-specific fragmentation

In an aim to create a "sharp" molecular knife, we have studied site-specific fragmentation caused by Si:2p core photoionization of bridged trihalosilyltrimethylsilyl molecules in the vapor phase. Highly site-specific bond dissociation has been found to occur around the core-ionized Si site in some of the molecules studied. The site specificity in fragmentation and the 2p binding energy difference between the two Si sites depend in similar ways on the intersite bridge and the electronegativities of the included halogen atoms. The present experimental and computational results show that for efficient "cutting" the following conditions for the two atomic sites to be separated by the knife should be satisfied. First, the sites should be located far from each other and connected by a chain of saturated bonds so that intersite electron migration can be reduced. Second, the chemical environments of the atomic sites should be as different as possible.     

Modification of the σ-framework of [60]fullerene for bulk-heterojunction solar cells

Modification of the σ-framework of [60]fullerene has been shown to be a new avenue toward n-type materials for bulk-heterojunction solar cells. This approach allowed distinct control of the LUMO level of the C(60)π-system and resulted in a clear improvement of an open-circuit voltage.     

Multiple photosynthetic reaction centres composed of supramolecular assemblies of zinc porphyrin dendrimers with a fullerene acceptor

Multiple photosynthetic reaction centres have successfully been constructed using supramolecular complexes of zinc porphyrin dendrimers [D(ZnP)(n): n = 4, 8, 16] with fulleropyrrolidine bearing a pyridine ligand (C(60)py). Efficient energy migration occurs completely between the ZnP units of dendrimers prior to the electron transfer with increasing the generation of dendrimers to attain an extremely long charge-separation lifetime.     

Total synthesis of a novel tetracyclic alkaloid, cassiarin F from the flowers of Cassia siamea

A novel alkaloid, cassiarin F (1), which showed potent antiplasmodial activity against Plasmodium falciparum in vitro, was isolated from the flowers of Cassia siamea, and its structure was elucidated on the basis of 2D NMR analyses. A total synthesis of 1 was also achieved by employing the Suzuki coupling constructing biaryl unit, nucleophilic aromatic substitution, and Houben-Hoesch type ring construction as key steps.