γ-irradiation of polypropylene in vacuum and in air

Polypropylene films were irradiated with ⁶⁰Co γ-rays in vacuum or in air and stored in air. Just after irradiation, the concentration of carbonyl group of the sample irradiated in air only increased with dose. The concentrations of both samples increased with storage time. The more the absorbed doses, the higher the increasing rates. The increasing rate of the concentration of carbonyl group during irradiation in air was higher than those during storage in air. Just after irradiation, the tensile strengths and the elongations of the both samples somewhat increased with dose at the doses less than 5 Mrad, but decreased at doses more than 13 Mrad. The tensile strength and the elongation of the sample irradiated in air decreased with storage time. Those of the sample irradiated in vacuum also decreased with storage time but the decreasing rates were much smaller than those in the sample irradiated in air. The gel fractions of the samples irradiated in vacuum and annealed in vacuum were somewhat higher than those irradiated in vacuum and not annealed. To elucidate high oxidation rate in the sample irradiated in air during and after irradiation, reaction mechanisms were discussed. To clarify the difference of mechanical properties between the samples irradiated in vacuum and in air, the effect of crosslink was considered, together with the oxidation.     

Trapping effect of eugenol on hydroxyl radicals induced by L-DOPA in vitro

Many researchers have stated that eugenol might inhibit lipid peroxidation at the stage of initiation, propagation, or both, and many attempts have been made to elucidate the mechanism of its antioxidant activity. Nevertheless, details of its mechanism are still obscure. This study was carried out to investigate the trapping effect of eugenol on hydroxyl radical generated from L-3,4-dihydroxyphenylalanine (DOPA) in MiliQ water and the generation mechanism of the hydroxyl radical by this system which uses no metallic factor. This was studied by adding L-DOPA and 5,5-dimethyl-1-pyrroline N-oxide (DMPO) to phosphate buffered saline (PBS) or MiliQ water, and the generation of hydroxyl radical was detected on an ESR spectrum. By this method, the effect of antioxidants was detected as a modification of ESR spectra. We found that the eugenol trapped hydroxyl radicals directly, because it had no iron chelating action, did not trap L-DOPA semiquinone radical and inhibited hydroxyl radicals with or without iron ion.     

Polyether-bridged sexithiophene as a complexation-gated molecular wire for intramolecular photoinduced electron transfer

The porphyrin-sexithiophene-fullerene triad 2, where the two central thiophene units of the sexithiophene spacer are bridged with a crown-ether-like polyether chain, undergoes efficient intramolecular electron transfer from the photoexcited porphyrin moiety to the fullerene through the sexithiophene. However, complexation with a sodium cation in the crown ether ring causes complete suppression of electron transfer as a result of a drastic conformational change of the sexithiophene backbone. Furthermore, decomplexation resumes the photoinduced electron transfer. This on/off switching phenomenon indicates that the polyether-bridged sexithiophene can function as a complexation-gated molecular wire.     

Speciation of arsenic in body fluids

Inorganic arsenic is metabolized by consecutive reduction and methylation reactions to dimethylated arsenic (DMA), and then excreted into the urine mostly in the form of DMA. Therefore, arsenic metabolites in the body fluids and organs/tissues are present in the form of inorganic (arsenite and arsenate) and methylated arsenics (MMA and DMA). Although pentavalent arsenics can be present mostly in the form of free ions, trivalent ones may be present more in the forms conjugated with thiol groups of glutathione (GSH) or proteins. Arsenic in the body fluids (plasma, bile and urine) is present in the soluble forms and can be speciated on ion exchange columns by HPLC with on-line detection by an inductively coupled argon plasma-mass spectrometer (ICP-MS). Free forms of arsenite, arsenate, and monomethylarsonous, monomethylarsonic, dimethylarsinous and dimethylarsinic acids in the body fluids have been demonstrated to be speciated simultaneously within 10 min or so on both anion and cation exchange columns together with arsenobetaine (AsB) and arsenocholine (AsC). Trivalent arsenics conjugated with GSH were eluted in intact forms on an anion exchange column but were liberated into free forms on a cation exchange column. Thus, free and GSH-conjugated arsenic metabolites in the bile and urine have been speciated simultaneously on ion exchange columns by HPLC-ICP-MS.     

Power-free poly(dimethylsiloxane) microfluidic devices for gold nanoparticle-based DNA analysis

An extremely simple, power-free pumping method for poly(dimethylsiloxane)(PDMS) microfluidic devices is presented. By exploiting the high gas solubility of PDMS, the energy for the pumping is pre-stored in the degassed bulk PDMS, therefore no additional structures other than channels and reservoirs are required. In a Y-shaped microchannel with cross section of 100 microm width x 25 microm height, this method has provided flow rate of 0.5-2 nL s(-1), corresponding to linear velocity of 0.2-0.8 mm s(-1), with good reproducibility. As an application of the power-free pumping, gold nanoparticle-based DNA analysis, which does not rely on the cross-linking mechanism between nanoparticles, has been implemented in a microchannel with three inlets. Target 15mer DNA has been easily and unambiguously discriminated from its single-base substituted mutant. Instead of colorimetric detection in a conventional microtube, an alternative detection technique suitable for microdevices has been discovered-observation of deposition on the PDMS surfaces. The channel layout enabled two simultaneous DNA analyses at the two interfaces between the three laminar streams.     

Kinetic study of the quenching reaction of singlet oxygen by flavonoids in ethanol solution

The quenching rate of singlet oxygen (1O2) by seven kinds of flavonoids (flavone, flavonol, chrysin, apigenin, rutin, quercetin, and myricetin) with 2,3-double bonds has been measured spectrophotometrically in ethanol at 35 degrees C. The overall rate constants kQ (= kq + kr, physical quenching + chemical reaction) increased as the number of OH groups substituted to the flavone skeleton (that is, the total electron-donating capacity of flavonoids) increases. The existence of catechol or pyrogallol structure in the B-ring is essential for the 1O2 quenching of flavonoids. Log kQ was found to correlate with their peak oxidation potentials, E(P); the flavonoids that have smaller E(P) values show higher reactivities. Similarly, log kQ values of flavonoids correlate with the energy level of the highest occupied molecular orbital (E(HOMO)), calculated by the PM3 MO method, and the longest wavelength pi pi* excitation energy (E(ex)). The contribution of the chemical reaction (kr) was found to be negligible in these flavonoids. The kQ values of rutin, quercetin, and myricetin [(1.21 approximately 5.12) x 10(8) M(-1) s(-1)] were found to be larger than those of lipids [(0.9 approximately 6.4) x 10(4) M(-1) s(-1)], amino acids (<3.7 x 10(7) M(-1) s(-1)), and DNA (5.1 x 10(5) M(-1) s(-1)). The result suggests that these flavonoids may contribute to the protection of oxidative damage in foods and plants, by quenching 1O2.     

Synthesis of marine guanidine alkaloids and their application as chemical/biological tools

Ptilomycalin A and crambescidins, novel marine guanidine alkaloids, have a unique pentacyclic guanidine structure, and exhibit a considerable array of biological activities. The first method developed for the synthesis of the pentacyclic guanidine core structure involved successive 1,3-dipolar cycloaddition reactions and resulted in the first total synthesis of crambescidin 359. The synthesis of other pentacyclic guanidine derivatives has been based on this methodology and applied as tools for studying biological activities, and as chemical reaction catalysts.     

Synthesis,stability, and spectroscopic and electronic properties of three benzocyclohepta[alpha]azulenylium ions

Novel pi-systems, three benzocyclohepta[alpha]azulenylium ions, 7a-c, are synthesized, and their stability and properties have been characterized in terms of the position of the benzo-annulation and compared with those of the parent cyclohepta[alpha]azulenylium ion 4. Benzocyclohepta[6,7-alpha]azulenylium ion (7a) (p K R+ = 7.3, E red = -0.567 V vs Ag/Ag+) and benzocyclohepta[6,5-alpha]azulenylium ion (7b) (p K R+ = 5.1, E red = -0.482 V vs Ag/Ag+), which are annulated with benzene on the position having a high bond order of 4, are not appreciably destabilized compared with cyclohepta[alpha]azulenylium ion (4) (p K R+ = 7.3, E red = -0.458 V vs Ag/Ag+). On the other hand, benzocyclohepta[7,6-alpha]azulenylium ion (7c) (p K R+ = 1.6, Ered = -0.197 V vs Ag/Ag+) is considerably destabilized, probably due to enhanced contribution of the quinoid structure of the benzene ring, which is annulated on the position having a low bond order of the cyclohepta[alpha]azulenylium ion moiety. Furthermore, the cations 7a and 7b are more stable than 12,13-dihydrobenzocyclohepta[7,6-alpha]azulenylium ion (25) (p K R+ = 4.8, E red = -0.513 V vs Ag/Ag+), which is a dihydrogenated compound of 7a, while 7c is less stable than 25. These features are reflected in the considerable red shift of the longest absorption maximum of the electronic spectrum of 7c, as compared with those of 4, 7a, and 7b, and in the chemical shifts of the protons and their coupling constants of the (1)H NMR spectra. Furthermore, the (1)H NMR spectra and electronic spectra of 5H-benzocyclohepta[6,7-alpha]azulen-5-one (8a) and 7H-benzocyclohepta[6,5-alpha]azulen-7-one (8b) in acidic media have also been studied to clarify the spectral characteristics similar to those of 7a and 7b.     

Reverse permeation of sodium ions driven by pH difference across a liquid membrane: time dependencies of membrane resistance and membrane potential in a reverse permeation system

The diffusional flux of sodium ions across a liquid membrane was observed as a reverse permeation phenomenon: sodium ions were transported across the membrane against their own concentration difference. A supported liquid membrane having stearic acid as an ionic carrier was used. The internal aqueous phase contained NaCl and HCl and the external aqueous phase contained NaOH of the same initial concentration as NaCl in the internal aqueous phase. The reverse permeation occurred with a long time delay. During the delay, sodium ions flowed from the acidic to alkaline solution. The diffusion coefficient of sodium ion estimated from the flux equation taking into account the Donnan equilibrium at the interface was found to be much greater than that in the membrane solvent, 1-octanol. In the same membrane system as for the flux measurement, the membrane conductance and the membrane potential were measured as a function of time. The time dependence of the membrane potential in the presteady state showed a biphasic behavior. The initial rapid phase could be attributed to the change in the phase boundary potential and the subsequent slow step to the change in the diffusion potential within the membrane. Before the steady membrane potential had been reached, the reverse permeation of sodium ions against their own concentration difference was not observed. During the slow relaxation process of the membrane potential, the membrane resistance decreased to approach the steady state. Moreover, the oscillation of membrane potential abruptly started at a time in the slow step of the potential change and continued during the steady state. It was suggested that, at the presteady state, the increase in the amount of water in the membrane would drive a drastic change in the state of the liquid membrane in the filter pore, e.g. an inverted micellar structure making.     

Simultaneous determination of bromide and iodide ions by capillary isotachophoresis using quaternary ammonium salts

Bromide and iodide ions were determined simultaneously by capillary isotachophoresis using an aqueous electrolyte system; the separation principle was based on the ion-pairing equilibria between tetradecyldimethylbenzylammonium ion and these anions in the leading electrolyte. The interaction between iodide ion and tetradecyldimethylbenzylammonium ion was stronger than that for bromide ion. Thus complete separation of bromide and iodide ions could be obtained by using a leading electrolyte containing 1.5 mM tetradecyldimethylbenzylammonium ion. The pH of the leading electrolyte was adjusted to 5.0. The relative standard deviations of the zone length for bromide and iodide ions were 1.1 and 1.2%, respectively, when mixture of 3.0 mM of these ions was analysed. A 150-μl volume could be injected for the simultaneous determination of low concentrations of bromide and iodide ions.