Stryphnosides A-F, six new triterpene glycosides from the pericarps of Stryphnodendron fissuratum

Six new triterpene glycosides stryphnosides A-F (1-6) were isolated from the pericarps of Stryphnodendron fissuratum (Leguminosae). The structures of 1-6 were determined on the basis of extensive spectroscopic analysis, including two-dimensional (2D) NMR data, and the results of hydrolytic cleavage. The sugar moieties of 3-6 are very unique in structure having not only novel sugar sequences but also the terminal α-l-arabinopyranosyl unit with a ¹C₄ conformation. Stryphnosides C (3)-F (6) are the first representative of naturally occurring glycosides with the ¹C₄ terminal α-l-arabinopyranosyl group.     

Crystal-face dependence and photoetching-induced increases of dye-sensitized photocurrents at single-crystal rutile TiO2 surfaces

Dye-sensitized photocurrents at (100)-, (001)-, and (110)-cut TiO(2) rutile surfaces were increased by photoetching of TiO(2), but the increasing ratio strongly depended on the cut crystal faces and the illumination intensity for the photoetching. For the (110)-cut surface, the photocurrent increase was moderately large and in proportion to the increase in the surface area of TiO(2) induced by the photoetching, irrespective of the illumination intensity for the photoetching. On the other hand, the photocurrent increases for the (001)- and (100)-cut surfaces, especially that for the (001)-cut surface, were prominent and largely exceeded the increases in the surface area. The results were explained by taking into account the following factors: (1) The (001)- and (100)-cut surfaces were thermodynamically unstable in contrast to the (110)-cut surface and had thicker inactive surface layers (or higher densities of surface defects), produced by surface reconstruction during heat treatment of TiO(2) at 550 degrees C in a hydrogen atmosphere for getting n-type semiconductivity. (2) Photoetching not only increased the surface area through formation of nanoholes and grooves at the surface but also effectively removed the thin inactive surface layers (or surface defects).     

High-performance liquid chromatography with photodiode array detection for determination of nobiletin content in the brain and serum of mice administrated the natural compound

We recently demonstrated that nobiletin, a citrus flavonoid, exhibits anti-dementia action in animals. However, no determination methods for the content of nobiletin with beneficial action in the brain of nobiletin-administered animals have been developed, nor has its pharmacokinetics been revealed completely. Here, we established the high-performance liquid chromatography/photodiode array detection method for nobiletin determination using Bond Elut C18 SPE cartridges for extraction, where the calibration curve was linear over 0.025-10 ng, with coefficient of variation of less than 6.76%. This method enabled us to determine pharmacokinetic parameters of nobiletin given intraperitoneally or per os in the brain of mice.     

Photoresponsive change of oxygen-binding affinity of a cobalt schiff-base complex with an axially coordinating stilbazole residue of a copolymer

The reversible binding reaction of oxygen to N,N'-ethylene bis(salicylideneiminato) cobalt(II) (CoS), to which a photoisomerizable stilbazole residue of copolymer 1 coordinated, was investigated. The E form of the stilbazole residues coordinating to CoS, (E)-1-CoS, showed photoisomerization into the Z form, (Z)-1-CoS, on direct ultraviolet irradiation and negligible reverse isomerization. The oxygen-binding equilibrium constant (K) values for (E)-1-CoS and (Z)-1-CoS in toluene were 3.3 x 10(-2) mmHg-1 and 4.8 x 10(-3) mmHg(-1), respectively, at 10 degrees C. Although the pK(a) values of the E and Z forms of the stilbazole residue were similar, the oxygen-binding affinity of (Z)-1-CoS was small in terms of the linear correlation of the logarithm of K (ln K) versus the pK(a). Steric hindrance of the polymer chain of 1 on the coordination of the stilbazole residue of (Z)-1 to CoS was thought to cause the small K. A photoresponsive change of apparent oxygen-binding affinity of 1-CoS along with the E/Z isomerization of the stilbazole residues was observed. The ratio of (Z)-1-CoS converted from (E)-1-CoS by the ultraviolet irradiation could be estimated from analysis of absorption spectra for the oxygen binding of a resulting mixture of (E)-1-CoS and (Z)-1-CoS.     

Biosynthesis of violacein: a genuine intermediate, protoviolaceinic acid, produced by VioABDE, and insight into VioC function

A biosynthetic intermediate of violacein produced by the mixed enzymes of VioABDE was elucidated to be 5-(5-hydroxy-1H-indol-3-yl)-3-(1H-indol-3-yl)-1H-pyrrole-2-carboxylic acid, named protoviolaceinic acid, indicating that VioC, responsible for the final biosynthetic step, works to oxygenate at the 2-position of the right side indole ring, and that the oxygenation reaction to form the central pyrrolidone core proceeds in a non-enzymatic fashion.     

Sesquiterpenoids and flavonoids from the aerial parts of Tithonia diversifolia and their cytotoxic activity

Cytotoxicity-guided fractionation of the 80% EtOH extract of Tithonia diversifolia has resulted in the isolation of twelve sesquiterpenoids (1-12), including three new ones (4, 10, 12), and three known flavonoids (13-15). The structures of the new compounds were determined by analysis of their spectroscopic data. The isolated compounds showed cytotoxic activity against HL-60 leukemia cells with IC(50) values ranging from 0.13 to 13.0 microM, when etoposide used as a positive control gave an IC(50) value of 0.43 microM. The cancer growth inhibitory property of 9, the main cytotoxic compound in T. diversifolia, was examined using a disease-oriented panel composed of 39 human cancer cell lines in the Japanese Foundation for Cancer Research.     

In situ AFM studies on self-assembled monolayers of adsorbed surfactant molecules on well-defined H-terminated Si(111) surfaces in aqueous solutions

The formation of self-assembled monolayers (SAMs) of adsorbed cationic or anionic surfactant molecules on atomically flat H-terminated Si(111) surfaces in aqueous solutions was investigated by in situ AFM measurements, using octyl trimethylammonium chloride (C8TAC), dodecyl trimethylammonium chloride (C12TAC), octadecyl trimethylammonium chloride (C18TAC)) sodium dodecyl sulfate (STS), and sodium tetradecyl sulfate (SDS). The adsorbed surfactant layer with well-ordered molecular arrangement was formed when the Si(111) surface was in contact with 1.0x10(-4) M C18TAC, whereas a slightly roughened layer was formed for 1.0x10(-4) M C8TAC and C12TAC. On the other hand, the addition of alcohols to solutions of 1.0x10(-4) M C8TAC, C12TAC, or SDS improved the molecular arrangement in the adsorbed surfactant layer. Similarly, the addition of a salt, KCl, also improved the molecular arrangement for both the cationic and anionic surfactant layers. Moreover, the adsorbed surfactant layer with a well-ordered structure was formed in a solution of mixed cationic (C12TAC) and anionic (SDS) surfactants, though each surfactant alone did not form the well-ordered layer. These results were all explained by taking into account electrostatic repulsion between ionic head groups of adsorbed surfactant molecules as well as hydrophobic interaction between their alkyl chains, which increases with the increasing chain length, together with the increase in the hydrophobic interaction or the decrease in the electrostatic repulsion by incorporating alcohol molecules into the adsorbed surfactant layer, the decrease in the electrostatic repulsion by increasing the concentration of counterions, and the decrease in the electrostatic repulsion by alternate arrangement of cationic and anionic surfactant molecules. The present results have revealed various factors to form the well-ordered adsorbed surfactant layers on the H-Si(111) surface, which have a possibility of realizing the third generation surfaces with flexible structures and functions easily adaptable to circumstances.     

In-situ FTIR studies on self-assembled monolayers of surfactant molecules adsorbed on H-terminated Si(111) surfaces in aqueous solutions

The adsorption of a surfactant, sodium di-2-ethylhexyl sulfosuccinate (SDES), [C4H9CH(C2H5)CH2OCO][C4H9CH(C2H5)CH2OCOCH2]CHSO3- Na+, in an aqueous solution on an atomically flat H-terminated Si(111) [abbreviated as H-Si(111)] surface with a hydrophobic property was investigated by in-situ FTIR measurements. Immersion of the H-Si(111) surface in a solution of 1.0 x 10(-2) M SDES for more than 2 h led to formation of a self-assembled monolayer (SAM) with the alkyl chains having a tendency to be assembled perpendicular to the Si surface. The in-situ FTIR observation revealed that the adsorption was nearly complete about 60 min after the start of the immersion, and after that the adsorbed molecules changed their arrangement into an ordered mode. The Si-H peak in the FTIR spectrum remained unchanged with time in aqueous surfactant solution, in contrast to the case of immersion in pure water, indicating that the adsorbed surfactant protects the H-Si(111) surface from oxidation. No structural change in the SAM was observed when a negative potential of -700 mV vs Ag/AgCl was applied to the Si, whereas the adsorbed molecules changed their arrangement, accompanied by their substantial desorption and oxidation of the Si surface, when a positive potential of +700 mV was applied.     

Rheological behavior in water of complexes formed from poly(sodium 2-(acrylamido)-2-methylpropanesulfonate) and positively charged rodlike micelles

The viscoelastic behavior of aqueous solutions of an ionic complex formed from poly(sodium 2-(acrylamido)-2-methylpropanesulfonate) and rodlike mixed micelles of dimethyloleylamine oxide (DMOAO) and hexadecyltrimethylammonium chloride (CTAC) was investigated under oscillatory conditions. The DMOAO/CTAC mixed micelles exhibited high zero-shear viscosities (eta0) depending on the mole fraction of CTAC in the mixed micelle (Y) in the range 0Y0.25. The addition of the polyanion had no effect on the rheological behavior of the mixed micelles when Y<0.02 at an ionic strength (mu) of 0.2. However, when Y was increased to a certain level (Yc), eta0 decreased drastically; Yc depended on mu but not on the polymer concentration. These observations indicate the formation of an ionic complex between the polymer and micelle when YYc. The reciprocal of steady-state compliance (Je(-1)) began to decrease gradually at Y approximately Yc and then leveled off at Y>0.06. The relaxation time (tau) was found to be more strongly dependent on Y. Thus, the large decrease in eta0 was attributed mainly to a decrease in tau while the number density of junctions decreased only slightly. Therefore, it is concluded that polymer-micelle complex maintains a rodlike structure with some entanglements remaining at Y<0.12.     

Tuning of luminescence spectra of neutral ruthenium(II) complexes by crystal waters

Neutral ruthenium(II) complexes [RuLL'(CN)2] (L, L' = bpy, dmb, dbb; bpy = 2,2'-bipyridine, dmb = 4,4'-dimethyl-2,2'-bipyridine, dbb = 4,4'-tert-butyl-2,2'-bipyridine) were prepared, and the luminescence characteristics of the complexes in the solid state were measured. The luminescence was tuned by crystal waters included in the crystals; for example, [Ru(dbb)2(CN)2] x 2H2O, [Ru(dbb)2(CN)2] x H2O, and [Ru(dbb)2(CN)2] emit luminescence at 640, 685, and 740 nm, respectively.