Electronic structure of DNA nucleobases and their dinucleotides explored by soft X-ray spectroscopy

The electronic structures of a series of DNA nucleobases and their dinucleotides were investigated by N 1s X-ray absorption, X-ray photoemission, and resonant X-ray emission spectroscopy. Resonant X-ray emission spectra of the guanine base and its dinucleotide indicate that it has a weak structure at the lowest binding energy; at this energy, it isolates from the main valence band and forms the HOMO state. This indicates that the HOMO state is localized in the guanine base, as claimed by valence and core photoemissions and expected from theoretical predictions. In addition, the XAS and XES profiles of the guanine dinucleotide indicate that disruption of the aromatic character of the six-membered ring results in the localization of the pi state at the imine (-N=) site of the guanine base; this may favor charge transfer among stacked guanine bases and further influence the conductivity of DNA.     

A new method for the conversion of allyl alcohol into pi-allyl species promoted by nucleophilic interaction with a CO ligand

Upon treatment with an iridium carbonyl complex, [(PN)Ir(CO)2]+, allyl alcohol can be smoothly converted into pi-allyliridium species at ambient temperature via nucleophilic interaction of the alcohol with a CO ligand followed by C(allyl)-O bond cleavage in the resultant protonated allyloxycarbonyl intermediate.     

Magnetic transitions of single-component molecular metal [Au(tmdt)2] and its alloy systems

A single-component molecular conductor [Au(tmdt)2] (tmdt = trimethylenetetrathiafulvalenedithiolate) undergoes an antiferromagnetic phase transition at unprecedentedly high temperature (TN = 110 K). Black microcrystals of alloys, [Ni1-xAux(tmdt)2] (0.0 < x < 1.0) were prepared. The Au-rich system exhibited an antiferromagnetic transition. Metallic single crystal was obtained for x = 0.25.     

Studies on Nepalese crude drugs. XXIX. Chemical constituents of Dronapuspi, the whole herb of Leucas cephalotes SPRENG

From the whole herb of Leucas cephalotes SPRENG., new labdane-, norlabdane- and abietane-type diterpenes named leucasdins A (1), B (2) and C (3), respectively, and two protostane-type triterpenes named leucastrins A (4) and B (5) were isolated, together with a known triterpene, oleanolic acid, five sterols, 7-oxositosterol, 7-oxostigmasterol, 7alpha-hydroxysitosterol, 7alpha-hydroxystigmasterol and stigmasterol, and eight flavones, 5-hydroxy-7,4'-dimethoxyflavone, pillion, gonzalitosin I, tricin, cosmosin, apigenin 7-O-beta-D-(6-O-p-coumaroyl)glucopyranoside, anisofolin A and luteolin 4'-O-beta-D-glucuronopyranoside. The structures of 1--5 were determined as (3S,6R,8R,9R,13S,16S)-9,13,15,16-bisepoxy-3,16-diacetoxy-6-formyloxylabdane, (3S,6R)-3-acetoxy-6-formyloxy-iso-ambreinolide, (4R,9S,12R,13R)-12,13-dihydroxyabiet-7-en-18-oic acid, (3S,17S,20S,24S)-3,20-dihydroxy-24-methylprotost-25-en, and (3S,17S,20S,24S)-3,20,24-trihydroxyprotost-25-en respectively, based on spectral and chemical data.     

Association kinetics of wild- and mutant-type Ynd1p in relation to quality of grown crystals

The intermolecular interaction and association dynamics of the Ynd1p protein were investigated using dynamic and time-resolved static light scattering measurements. The mutual diffusion coefficients of wild- and mutant-type (a single amino acid substitution) Ynd1p monomer were measured in 50 mM 2-(N-morpholino)ethanesulfonic acid (MES) buffer with 5 mM MnCl2 and 7.5% (v/v) ethylene glycol. Both translational diffusion coefficients at a zero protein concentration were (40.3 +/- 0.2) x 10(-12) m2/s at 20 degrees C and a pH of 7.0, so the hydrodynamic radius of the monomers was 4.1 +/- 0.1 nm. The measured intermolecular interaction between monomers, however, showed that the mutant-type Ynd1p had a stronger attractive force. Time-resolved static light scattering measurements showed that the association of mutant-type Ynd1p yielded a larger number of aggregates than that of wild-type Ynd1p. The time dependence of aggregate gyration radius differed between the two types. Fractal dimension analysis using scattering intensity data suggested that the inner structure of the aggregates changed from loose to rigid with time. Although this phenomenon is common for wild and mutant types, the differences in the number of aggregates yielded in the initial stages and in the intermolecular interaction affected the quality of the final grown crystals. That is, single crystals of Ynd1p grew in the mutant-type protein solution and polycrystals of Ynd1p grew in the wild-type protein solution.     

Binding of Multivalent Anionic Porphyrins to V3 Loop Fragments of an HIV‐1 Envelope and Their Antiviral Activity

Interactions of multivalent anionic porphyrins and their iron(III) complexes with cationic peptides, V3_Ba‐L and V3_IIIB, which correspond to those of the V3 loop regions of the gp120 envelope proteins of the HIV‐1_Ba‐L and HIV‐1_IIIB strains, respectively, are studied by UV/Vis, circular dichroism, ¹H NMR, and EPR spectroscopy, a microcalorimetric titration method, and anti‐HIV assays. Tetrakis(3,5‐dicarboxylatophenyl)porphyrin (P1), tetrakis[4‐(3,5‐dicarboxylatophenylmethoxy)phenyl]porphyrin (P2), and their ferric complexes (Fe^IIIP1 and Fe^IIIP2) were used as the multivalent anionic porphyrins. P1 and Fe^IIIP1 formed stable complexes with both V3 peptides (binding constant K>10⁶ M ^?1) through combined electrostatic and van der Waals interactions. Coordination of the His residues in V3_Ba‐L to the iron center of Fe^IIIP1 also played an important role in the complex stabilization. As P2 and Fe^IIIP2 form self‐aggregates in aqueous solution even at low concentrations, detailed analysis of their interactions with the V3 peptides could not be performed. To ascertain whether the results obtained in the model system are applicable to a real biological system, anti‐HIV‐1_BA‐L and HIV‐1_IIIB activity of the porphyrins is examined by multiple nuclear activation of a galactosidase indicator (MAGI) and 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assays. There is little correlation between chemical analysis and actual anti‐HIV activity, and the size rather than the number of the anionic groups of the porphyrin is important for anti‐HIV activity. All the porphyrins show high selectivity, low cytotoxicity, and high viral activity. Fe^IIIP1 and Fe^IIIP2 are used for the pharmacokinetic study. Half‐lives of these iron porphyrins in serum of male Wistar rats are around 4 to 6 h owing to strong interaction of these porphyrins with serum albumin.     

Luminous, fully aliphatic polyamides: Multicolor photoluminescence, their pH and solvent dependency

Novel luminous aliphatic polyamides were obtained from a condensation reaction of ethylene diamines and malonyl dichloride in the presence of triethylamine. These polymers appeared in blackish red and reddish orange solids and unusually exhibited a visible light-emission. Their fluorescence properties were significantly dependent on the excitation wavelength, media polarity, and acidity. These polymers emitted fairly strong visible lights in a wide range from blue to near yellow when excited at wavelengths longer than 305 nm. The emission bands significantly shifted to longer wavelengths during the increase in the polarity of the solvent used. Their fluorescence intensities significantly increased under acidic conditions.     

Graph-theoretical analysis of the clar's aromatic sextet : Mathematical properties of the set of the kekulé patterns and the sextet polynomial for polycyclic aromatic hydrocarbons

The mathematical structure of a set of the Kekulé patterns for a polycyclic aromatic hydrocarbon has been analysed graph-theoretically. By defining the proper and improper sextets, sextet pattern, Clar transformation, and sextet rotation, one can prove the important property of the sextet polynomial B_G(x) as B_G(1) = K(G), where K(G) is the number of the Kekulé patterns for thin polyhex graph G. For fat polyhex graphs such as coronene the above relation is found to be also valid by introducing the concept of a super sextet. All the Kekule patterns for a given G are shown to form a hierarchical tree structure by the sextet rotation. The theory developed in this paper gives a mathematical basis and interpretation for the concept of the Clar's aromatic sextet.     

Gelation of colloidal crystals without degradation in their transmission quality and chemical tuning

A single-domain colloidal crystal with high transmission quality, prepared by a shear-induced process, was fixed as a hydrogel film by photopolymerization. Upon gelation, the original optical quality was almost perfectly preserved. By replacing the solvent, the gelled crystal could be converted to smaller lattice constant crystals without significant degradation in its transmission characteristics. The conversion results in a stop-band wavelength coverage across the entire visible light range.     

Synthesis of (±)-pyranonaphthoquinone derivatives, a Cdc25A phosphatase inhibitor

The novel pyranonaphthoquinone 2, carrying Cdc25A phosphatase inhibitory activity, has been successfully synthesized through tricyclic compound 16, which was obtained from 15 by using the intramolecular Michael addition. The precursor 9 was derived from 5-bromoveratraldehyde.