Ardisiphenols A-C, novel antioxidants from the fruits of Ardisia colorata.

Novel alk(en)ylphenols, named ardisiphenols A--C (1--3) were isolated from the fruits of Ardisia colorata, together with known alk(en)ylresorcinols (4--6). Their structures were determined by the NMR and MS/MS analyses. All compounds showed scavenging activities towards 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and cytotoxicities against murine breast cancer cell line, FM3A.     

Experimental study of annular bright field (ABF) imaging using aberration-corrected scanning transmission electron microscopy (STEM)

Experimental parameters used in the annular bright field (ABF) imaging method were tested using images simulated with the multislice method. Images simulated under identical conditions were found to agree well with experimental images. The ABF technique was shown to be relatively insensitive to the sample thickness and the defocus. In experimental ABF images, atomic columns exhibited dark contrast over a wide range of specimen thickness and defocus values, from 10 to 70 nm and ?20 to +20 nm, respectively. A series of diffraction patterns at atomic columns, obtained using the diffraction imaging method, exhibited higher intensities in their central regions (0–11 mrad) for light elements and in their peripheral regions (11–22 mrad) for heavy elements. The results indicated that the contrast of light elements is enhanced by subtraction of the central region of the transmitted beam, since this is blocked by a circular mask in the ABF-STEM technique. Thus, the overall contrast of light elements is greatly improved, allowing them to be clearly visualized.     

Nucleophilic substitution at the 4'-position of nucleosides: new access to a promising anti-HIV agent 2',3'-didehydro-3'-deoxy-4'-ethynylthymidine

For the synthesis of 2',3'-didehydro-3'-deoxy-4'-ethynylthymidine (8: 4'-Ed4T), a recently reported promising anti-HIV agent, a new approach was developed. Since treatment of 1-(2,5-dideoxy-beta-L-glycero-pent-4-enofuranosyl)thymine with Pb(OBz)4 allowed the introduction of the 4'-benzoyloxy leaving group, nucleophilic substitution at the 4'-position became feasible for the first time. Thus, reaction between the 4'-benzoyloxy derivative (14) and Me3SiCCAl(Et)Cl as a nucleophile led to the isolation of the desired 4'-"down"-ethynyl derivative (18) stereoselectively in 62% yield. As an application of this approach, other 4'-substituted nucleosides, such as the 4'-allyl (24a) and 4'-cyano (26a) derivatives, were synthesized using organosilicon reagents. In these instances, pretreatment of 14 with MeAlCl2 was necessary.     

Enhanced cell-killing effect of potassium hexachloroplatinum(IV) solution irradiated by60Co γ-rays under the presence of NH4Cl

The enhancement of cell-killing effect induced by⁶⁰Co γ-rays on the aqueous solutions of potassium hexachloroplatinum(IV) (K₂PtCl₆) irradiated in the presence of various concentrations of NH₄Cl was examined. HeLa S-3 cells were treated with the irradiated solutions for 60 minutes at 37°C, and cell survival was measured by colony forming efficiency. The mean lethal concentration (D ₀) for the cells treated with non-irradiated K₂PtCl₆ solution (1 mg/ml) was 34.5 μl/ml. However, it decreased, namely the cell-killing effect of the solution increased with increasing radiation dose up to 2.64·10⁴ Gy in the case of 0.1M NH₄Cl solution (in this condition, theD ₀ decreased to 9.6 μl/ml). No or only a slight enhancement was observed in the case of K₂PtCl₆ solutions irradiated in the presence of NaCl, (NH₄)₂HPO₄, ammonium acetate or glycine. Observations using high performance liquid chromatography (HPLC) of irradiated K₂PtCl₆ solutions revealed the formation of cis- and/or trans-diaminedichloroplatinum (IV) (DDPs(IV)). However, the observed cell-killing action of the solution was too high to be explained by the amount of both the DDPs(IV) formed by γ-rays.     

Spin transport in bimetallic pentalene complexes

Spin transport in bimetallic pentalene complexes (CpM(pentalene)M′Cp;M,M′=Fe,Co,Ni) between two gold electrodes was investigated, using a Green’s function formalism under density functional theory. Variation of the metal atom species in the complexes gives a considerable change in their spin properties, with hetero-bimetallic complexes containing an odd number of electrons exhibiting spin filter behaviour. In contrast, alternation in the contact condition, whether Cp-anchoring or adducting by sulphur-gold bonds, had almost no effect on spin filter behaviour, but did lead to variation in electrical conduction. We examined suitable bimetallic pentalene complexes in order to enhance their spin filter efficiency.     

Four-dimensional geometric element definitions and interferences via five-dimensional homogeneous processing

Abstract  

We have systematized various studies on 4-D visualization and interaction thus far, and we proposed 4-D geometric algorithms via 5-D homogeneous processing. Our framework uses 5 × 5 matrices and 5 × 5 determinants to express various types of transformations, and it simplifies geometric operations without the use of division operations. Using the proposed scheme, we developed an interactive 4-D space display system. The simplicity, generality, and duality of 5-D homogeneous processing are effective not only for 4-D geometric operations but also for interference problems among various 4-D objects. However, the processing regarding geometric characteristics of 4-D objects was not considered in our previous works. In this paper, we describe 4-D geometric elements, in general, and we discuss 4-D computational geometry via 5-D homogeneous processing. Unified geometric operations without the use of division operations constitute the most important part of 5-D homogeneous processing. We systematize the methods for 4-D geometric element definitions and interferences via 5-D homogeneous processing. In the field of 4-D visualization, the proposed algorithms can be potentially used in a user interface for feature detection of a 4-D object and collision detection of several 4-D objects. We comprehensively develop and advance the theoretical framework in the field of 4-D graphics. It is expected that this method of processing will be useful for the performance improvement of 4-D graphics systems.     

Self-motion of an oil droplet: a simple physicochemical model of active Brownian motion

The self-motion of an oil droplet in an aqueous phase on a glass surface is reported. The aqueous phase contains a cationic surfactant, which tends to be adsorbed onto the glass surface. The oil droplet contains potassium iodide and iodine, which prefers to make an ion pair with the cationic surfactant. Since the ion pair is soluble in the oil droplet, dissolution of the surfactant into the oil droplet is promoted, i.e., the system is far from equilibrium with regard to surfactant concentration. The oil droplet is self-driven in a reactive manner by the spatial gradient of the glass surface tension. We discuss the intrinsic nature of this self-motion by developing a simple mathematical model that incorporates adsorption and desorption of the surfactant on the glass surface. Using this mathematical model we were able to construct an equation of motion that reproduces the observed self-motion of an oil droplet. This equation describes active Brownian motion. Theoretical considerations were used to predict the generation of the regular mode of oil-droplet motion, which was subsequently confirmed by experiments.     

Suppression of Thermochromism in a Poly(di‐n‐hexylsilane)‐Zirconia Hybrid

Summary: Poly(di‐n‐hexylsilane) (PDHS)‐containing zirconia hybrid thin films were prepared by a sol‐gel reaction of PDHS copolymers and zirconium alkoxide, and it was found that the thermochromic properties of PDHS due to the transformation of the Si Si main chain were suppressed in the PDHS‐zirconia hybrid thin film.

Structure of poly(di‐n‐hexylsilane)‐zirconia hybrid.     

Total Syntheses of (+)‐Polygalolide A and (+)‐Polygalolide B: Elucidation of the Absolute Stereochemistry and Biogenetic Implications

The total syntheses of (+)‐polygalolide A and (+)‐polygalolide B have been completed by using a carbonyl ylide cycloaddition strategy. Three of the four stereocenters, including two consecutive tetrasubstituted carbon atoms at C2 and C8, were incorporated through internal asymmetric induction from the stereocenter at C7 by a [Rh₂(OAc)₄]‐catalyzed carbonyl ylide formation/intramolecular 1,3‐dipolar cycloaddition sequence. The arylmethylidene moiety of these natural products was successfully installed by a Mukaiyama aldol‐type reaction of a silyl enol ether with a dimethyl acetal, followed by elimination under basic conditions. We have also developed an alternative approach to the carbonyl ylide precursor based on a hetero‐Michael reaction. This approach requires 18 steps, and the natural products were obtained in 9.8 and 9.3 % overall yields. Comparison of specific rotations of the synthetic materials and natural products suggests that polygalolides are biosynthesized in nearly racemic forms through a [5+2] cycloaddition between a fructose‐derived oxypyrylium zwitterion with an isoprene derivative.