LiV2O4 spinel as a heavy-mass fermi liquid: anomalous transport and role of geometrical frustration

Transport and specific heat measurements on hydrothermally grown single crystals reveal the formation of a heavy-mass Fermi liquid in the LiV2O4 spinel, below a coherence temperature of T* = 20-30 K. A few observations which illustrate the uniqueness of this spinel are discussed in connection with the origin of the heavy mass, such as the anomalous absence of resistivity saturation above T* and the close proximity to a spin glass phase where the influence of the magnetic frustration is evident.     

Studies on antianaphylactic agents—III : A novel conversion reaction of 4-oxo-4H-1-benzopyran-3-carboxaldehydes to 3-halogenochromones

4-Oxo-4H-1-benzopyran-3-carboxaldehydes in acetic acid react with sodium hypochlorite (aqueous solution) to yield 3-chlorochromones. The reaction of sodium hypobromite with 1 yields 3-bromochromone 15 and other compounds depending on the conditions. Under the normal laboratory lighting hydroxyacetophenone 14, 15 and hydroxychromanone 16 were obtained, whereas 15 and acetoxychromanone 17 were produced by the reaction in the dark. The addition-elimination mechanism described is the most likely in these reactions.     

Construction of azacycles based on endo-mode cyclization of allenes

A new procedure for constructing monocyclic five- and six-membered azacycles by the endo-mode ring-closing reaction of allenylazido derivatives under neutral conditions has been developed. The azabicyclo[m.n.0] compounds were prepared by applying this newly developed procedure. The seven-membered azacycle was prepared when the allene possessing an unsubstituted carboxyl amido functionality was submitted to the basic conditions. In addition, indole and quinoline skeletons were synthesized using this procedure.     

Novel intramolecular cyclization of 2-(buta-1,3-dienyl)-3-methylpyrazines and 3-(buta-1,3-dienyl)-4-methyl-1,2,5-oxadiazoles into 5H-cycloheptapyrazines and 4H-cyclohepta-1,2,5-oxadiazoles

2-(Buta-1,3-dienyl)-3-methylpyrazines (5) and 3-(buta-1,3-dienyl)-4-methyl-1,2,5-oxadiazoles (10) were synthesized starting from base-induced reaction of 2,3-dimethylpyrazine or 3,4-dimethyl-1,2,5-oxadiazole with α,β-unsaturated carbonyls. The thus obtained heteroaromatics bearing a butadienyl moiety and a methyl at the adjacent position underwent intramolecular cyclization by the action of LDA to give the corresponding heteroaromatics fused with a seven-membered ring [7 (8)] and [11 (12)] in moderate to high yields.     

A new lignan glycoside and phenylethanoid glycosides from Strobilanthes cusia BREMEK

The root of Strobilanthes cusia BREMEK. (Acanthaceae), popularly known as Da-Ching-Yeh, has been commonly used in traditional Chinese medicine. It is used to treat influenza, epidemic cerebrospinal meningitis, encephalitis B, viral pneumonia, mumps, and severe acute respiratory syndrome (SARS). In this study, we found a new lignan glycoside (6) and two new phenylethanoid glycosides (7, 8) together with five known compounds as chemical constituents of Strobilanthes cusia root. Some samples were examined for anti-herpes simplex virus type-1 (HSV-1) activity. Among the tested samples, lupeol showed anti-HSV-1 activity (EC(50): 11.7 microM) and showed 100% inhibition of virus plaque formation at 58.7 microM.     

Dispersive excitations in the high-temperature superconductor La2-xSrxCuO4

High-resolution neutron scattering experiments on optimally doped La2-xSrxCuO4 (x=0.16) reveal that the magnetic excitations are dispersive. The dispersion is the same as in YBa2Cu3O6.85, and is quantitatively related to that observed with charge sensitive probes. The associated velocity in La2-xSrxCuO4 is only weakly dependent on doping with a value close to the spin-wave velocity of the insulating (x=0) parent compound. In contrast with the insulator, the excitations broaden rapidly with increasing energy, forming a continuum at higher energy and bear a remarkable resemblance to multiparticle excitations observed in 1D S=1/2 antiferromagnets. The magnetic correlations are 2D, and so rule out the simplest scenarios where the copper oxide planes are subdivided into weakly interacting 1D magnets.     

Raman study of the orbital-phonon coupling in LaCoO3

The magnetic state in LaCoO3 changes from the low spin state (S=0) to the mixed state with a thermally excited intermediate spin state (IS) (S=1) above about 50 K. The partially filled e(g) orbital in the IS state has a nature of Jahn-Teller (JT) distortion. The cooperative JT distortion causes an orbital order. We found that all Raman active phonon modes are affected by the excitation of IS Co3+ ions. Especially, the JT vibration mode shows anomalous temperature dependence.     

Two novel long-chain alkanoic acid esters of lupeol from alecrim-propolis

Two new long-chain alkanoic acid esters of lupeol were isolated together with known triterpenoids, alpha-amyrin, beta-amyrin, cycloartenol, lanosta-7,24-diene-3beta-ol and lupeol from Alecrim-propolis collected in Brazil. The structures were characterized by spectroscopic means.     

Four new halimane-type diterpenes, vitetrifolins D-G, from the fruit of Vitex trifolia

Four new halimane-type (rearranged labdane-type) diterpenes, vitetrifolins D-G were isolated from the fruit of Vitex trifolia L. (Verbenaceae). Their chemical structures were determined on the basis of spectroscopic data as well as chemical evidence.