Nitration reactions of astaxanthin and β-carotene by peroxynitrite

The in vitro reactivities of astaxanthin and β-carotene toward peroxynitrite were investigated and the reaction products after scavenging with peroxynitrite were analyzed. A series of carotenoids substituted with nitro group, 14′-s-cis-15′-nitroastaxanthin, 10′-s-cis-11′-cis-11′-nitroastaxanthin, 14′-s-cis-15′-nitro-β-carotene and 10′-s-cis-11′-cis-11′-nitro-β-carotene, were isolated from the reaction products of carotenoids with peroxynitrite. Carotenoids with nitro derivatives were reported for the first time. These results indicated that astaxanthin and β-carotene could catch peroxynitrite or nitrogen dioxide radical (NO₂) in their molecule to form nitrocarotenoids.     

Fluorescence study on the nyctinasty of Phyllanthus urinaria L. using novel fluorescence-labeled probe compounds

We report the synthesis of fluorescence-labeled probes based on phyllanthurinolactone 1, which is a leaf-closing substance of Phyllanthus urinaria L. The fluorescence study using biologically active probe 2 and inactive probes (epi-2 and 31) revealed that the target cell for 1 is a motor cell and suggested that some receptors, which recognize the aglycon of 1 exist on the plasma membrane of the motor cell, as with leaf-opening substances. Moreover, binding of probe 2 was specific to the plant motor cell contained in the plants belonging to the genus Phyllanthus. These results showed that the binding of probe 2 with a motor cell is specific to the plant genus and suggested that the genus-specific receptor for the leaf-closing substance would be involved in nyctinasty.     

Anisotropic polymerization of a long-chain diacetylene derivative Langmuir-Blodgett film on a step-bunched SiO2/Si surface

Alternating facet/terrace nanostructures were fabricated on a SiO2 surface by step-bunching and thermal oxidation of a vicinal Si(111) substrate, and their influence upon the polymerization direction of a long-chain diacetylene derivative monolayer film was investigated by angle-dependent polarized near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. It was found that the peak intensity of the C 1s-pi transition was stronger when the electric vector plane of the incident X-ray was parallel to the direction of the periodic facet/terrace structures rather than perpendicular to them. On the contrary, a polymer film fabricated on a flat SiO2 surface showed no in-plane anisotropy of the peak intensity. These results indicate that the diacetylene groups in the diacetylene derivative monolayer are preferentially photopolymerized in the direction not across but along the periodic one-dimensional structures on the step-bunched and thermally oxidized SiO2/Si(111) surface.     

Kinetic appearance of first-order gas-liquid expanded and liquid expanded-liquid condensed phase transitions below the triple point

Phase diagram of Gibbs monolayers of mixtures containing n-hexadecyl phosphate (n-HDP) and L-arginine (L-arg) at a molar ratio of 1:2 has been constructed by measuring surface-pressure-time (pi-t) isotherms with film balance and by observing monolayer morphology with Brewster angle microscopy (BAM). This phase diagram shows a triple point for gas (G), liquid expanded (LE), and liquid condensed (LC) phases at around 6.7 degrees C. Above this triple point, a first-order G-LE phase transition occurring at 0 surface pressure is followed by another first-order LE-LC phase transition taking place at a certain higher surface pressure that depends upon temperature. The BAM observation supports these results. Below the triple point, the pi-t measurements show only one first-order phase transition that should be G-LC. All of these findings are in agreement with the general phase diagram of the spread monolayers. However, the BAM observation at a temperature below the triple point shows that the thermodynamically allowed G-LC phase transition is, in fact, a combination of the G-LE and LE-LC phase transitions. The latter two-phase transitions are separated by time and not by the surface pressure, indicating that the G-LC phase transition is kinetically separated into these two-phase transitions. The position of the LE phase below the triple point in the phase diagram is along the phase boundary between the G and LC phases.     

Novel 2,1,3-benzothiadiazole-based red-fluorescent dyes with enhanced two-photon absorption cross-sections

This paper reports the two-photon absorbing and orange-red fluorescence emitting properties of a series of new 2,1,3-benzothiadiazole (BTD)-based D-pi-A-pi-D-type and star-burst-type fluorescent dyes. In the D-pi-A-pi-D-type dyes 1-6, a central BTD core was connected with two terminal N,N-disubstituted amino groups via various pi-conjugated spacers. The star-burst-type dyes 8 and 10 have a three-branched structure composed of a central core (benzene core in 8 and triphenylamine core in 10) and three triphenylamine-containing BTD branches. All the BTD-based dyes displayed intense orange-red color fluorescence in a region of 550-689 nm, which was obtained by single-photon excitation with good fluorescent quantum yield up to 0.98 as well as by two-photon excitation. Large two-photon absorption (TPA) cross-sections (110-800 GM) of these BTD dyes were evaluated by open aperture Z-scan technique with a femtosecond Ti/sapphire laser. The TPA cross-sections of D-pi-A-pi-D-type dyes 2-6 with a benzene, thiophene, ethene, ethyne, and styrene moiety, respectively, as an additional pi-conjugated spacer are about 1.5-2.5 times larger than that of 1c with only a benzene spacer. The TPA cross-sections significantly increased in three-branched star-burst-type BTDs 8 (780 GM) with a benzene core and 10 (800 GM) with a triphenylamine core, which are about 3-5 times larger than those of the corresponding one-dimensional sub-units 9 (170 GM) and 11 (230 GM), respectively. The ratios of sigma/e(pi) between three-branched and one-dimensional dyes were 6.5:3.8 (for 8 and 9) and 6.0:4.0 (for 10 and 11), which are larger than those predicted simply on the basis of the chromophore number density (1:1), according to a cooperative enhancement of the two-photon absorbing nature in the three-branched system.     

Rhodium-catalyzed isomerization of unactivated alkynes to 1,3-dienes

A rhodium/binap complex has been found to effectively catalyze the isomerization of unactivated internal alkynes to the corresponding 1,3-dienes in the presence of an azomethine imine as the reaction promoter.     

Supramolecular assemblies and redox modulation of pyromellitic diimide-based cyclophane via noncovalent interactions with naphthol

This paper reports the electroscopic and electrochemical properties of [2 + 2] pyromellitic diimide-based cyclophane 1 as well as acyclic N,N'-bis(2-methoxybenzyl)pyromellitic diimide 2 and the clathrate compounds formed by 1. Compound 1 was synthesized by direct cyclocondensation. Its structure was determined by an X-ray crystallographic analysis of a single crystal obtained by recrystallization from DMF. The intramolecular charge-transfer interactions of 1 and 2 were characterized by UV/vis spectroscopy and MO calculations. The UV/vis spectra showed that the tail of a longer wavelength absorption of both 1 and 2 reached the visible region. MO calculations (B3LYP/6-31G*) showed that the HOMO and LUMO orbitals of 1 and 2 substantially localize in the xylyl and pyromellitic diimide moieties across the methylene linker, respectively. The X-ray crystallographic analyses demonstrated that single crystals grown from a mixture of 1 and alpha-naphthol and a mixture of 1 and beta-naphthol were the clathrate compounds with 1D and 2D supramolecular assemblies, respectively, which are formed by a combination of hydrogen-bonding and charge-transfer interactions. From the cyclic voltammetry measurements, both 1 and 2 showed reversible reduction processes, and the reduction potential observed at -1.09 V vs Ag/Ag+ for 2 split into two potentials at -1.01 and -1.14 V for 1. The addition of alpha- and beta-naphthol induced a decrease in the potentials due to the diradical anion of 1 and radical anion of 2 by about 80 mV, and their reduction processes were reversible.     

Divergent chemical synthesis of prolines bearing fluorinated one-carbon units at the 4-position via nucleophilic 5-endo-trig cyclizations

N-[3-(Trifluoromethyl)homoallyl]sulfonamides, prepared via ring opening of (S)-glycidyl ethers or 2-aryloxiranes with 1-(trifluoromethyl)vinyllithium, underwent intramolecular addition or S(N)2'-type reaction in the normally disfavored 5-endo-trig fashion, leading to 2-substituted 4-(trifluoromethyl)- or 4-(difluoromethylene)pyrrolidines. Both alpha- and beta-face-selective hydrogenation of the 4-difluoromethylene group afforded syn- and anti-4-(difluoromethyl)pyrrolidines, respectively. These sequences, followed by the oxidation of a 2-hydroxymethyl or 2-aryl group, successfully provided prolines with a trifluoromethyl, difluoromethylene, or difluoromethyl group at the 4-position, including optically active prolines.     

The first definitive example of oxidative addition of acyclic vinyl selenide to M(0) complex

The principle of C-S bond activation of acyclic vinlyl sulfide by platinum(0)-complex was applied to the C-Se bond fission of vinyl selenide. The substrate possessing Ph and ArSe (Ar = C₆H₄Cl-p) substituents at the β-carbon successfully reacted with Pt(0)-complex at 25 °C to produce the vinyl platinum in good yield and its structure was unambiguously determined by X-ray crystallographic analysis. When (Z)-(Me₃Si)(ArSe)C(H)(SeAr) was employed as a reaction substrate, following β-Se elimination took place to liberate Me₃SiCCH with the production of [trans-Pt(SeAr)₂(PPh₃)₂]. The oxidative addition of C-Se bond of (E)-(Ph)(H)CC(H)(SeAr) to Pt(0) was also confirmed at 25 °C, while no C-S bond-breaking occurred when the corresponding vinyl sulfide was exposed to the same reaction conditions, demonstrating that the cleavage of C-Se bond was more facile than that of C-S bond.     

Experimental and theoretical elastic cross sections for electron collisions with the C3H6 isomers

In the present work we report cross sections for electron collisions with the isomers propene (C3H6) and cyclopropane (c-C3H6). Electron-scattering differential cross sections (DCS) are reported for measurements carried out for energies 1.5-100 eV and the angular range of 20 degrees-120 degrees. Elastic integral cross sections (ECS), DCS, and momentum-transfer cross sections (MTCS) are reported for calculations carried out using the Schwinger multichannel method with pseudopotentials for the energy range of 2.0-40 eV and angular range of 0 degrees-180 degrees. The resemblance of the pi* shape resonance in the cross sections, observed at 1.5-2.0 eV for propene, to those in C2H4 and C2F4 clearly points to the effect of the double bond in the molecular structures for these molecules. Below 60 eV, we observed clear differences in peak positions and magnitudes between the DCS, ECS, and MTCS for C3H6 and c-C3H6, which we view as the isomer effect.