Phase changes of CO2 hydrate under high pressure and low temperature.

High pressure and low temperature experiments with CO(2) hydrate were performed using diamond anvil cells and a helium-refrigeration cryostat in the pressure and temperature range of 0.2-3.0 GPa and 280-80 K, respectively. In situ x-ray diffractometry revealed that the phase boundary between CO(2) hydrate and water+CO(2) extended below the 280 K reported previously, toward a higher pressure and low temperature region. The results also showed the existence of a new high pressure phase above approximately 0.6 GPa and below 1.0 GPa at which the hydrate decomposed to dry ice and ice VI. In addition, in the lower temperature region of structure I, a small and abrupt lattice expansion was observed at approximately 210 K with decreasing temperature under fixed pressures. The expansion was accompanied by a release of water content from the sI structure as ice Ih, which indicates an increased cage occupancy. A similar lattice expansion was also described in another clathrate, SiO(2) clathrate, under high pressure. Such expansion with increasing cage occupancy might be a common manner to stabilize the clathrate structures under high pressure and low temperature.

Gas-phase synthesis and characterization of CH4-loaded hydroquinone clathrates.

A CH(4)-loaded hydroquinone (HQ) clathrate was synthesized via a gas-phase reaction using the alpha-form of crystalline HQ and CH(4) gas at 12 MPa and room temperature. Solid-state (13)C cross-polarization/magic angle spinning (CP/MAS) NMR and Raman spectroscopic measurements confirm the incorporation of CH(4) molecules into the cages of the HQ clathrate framework. The chemical analysis indicates that about 69% of the cages are filled by CH(4) molecules, that is, 0.69 CH(4) per three HQ molecules. Rietveld refinement using synchrotron X-ray powder diffraction (XRD) data shows that the CH(4)-loaded HQ clathrate adopts the beta-form of HQ clathrate in a hexagonal space group R3 with lattice parameters of a = 16.6191 A and c = 5.5038 A. Time-resolved synchrotron XRD and quadrupole mass spectroscopic measurements show that the CH(4)-loaded HQ clathrate is stable up to 368 K and gradually transforms to the alpha-form by releasing the confined CH(4) gases between 368-378 K. Using solid-state (13)C CP/MAS NMR, the reaction kinetics between the alpha-form HQ and CH(4) gas is qualitatively described in terms of the particle size of the crystalline HQ.

Effect of NIP-142 on potassium channel alpha-subunits Kv1.5, Kv4.2 and Kv4.3, and mouse atrial repolarization.

Effects of NIP-142, a benzopyran compound which terminates experimental atrial arrhythmia, on potassium channel alpha-subunits and mouse atrial repolarization were examined. NIP-142 concentration-dependently blocked the outward current through potassium channel alpha subunits Kv1.5, Kv4.2 and Kv4.3 expressed in Xenopus oocytes. In isolated mouse atrial myocardia, NIP-142 prolonged the action potential duration and effective refractory period, and increased the contractile force. These results suggest that NIP-142 blocks the potassium channels underlying the transient and sustained outward currents, which may contribute to its antiarrhythmic activity.

High pressure investigation of alpha-form and CH4-loaded beta-form of hydroquinone compounds.

The high pressure compression behaviors of two hydroquinone compounds have been investigated using a combination of in situ synchrotron x-ray powder diffraction and Raman spectroscopy up to ca. 7 GPa. The structural integrity of the alpha-form hydroquinone clathrate is maintained throughout the pressure range, whereas the CH(4)-loaded beta-form hydroquinone clathrate decomposes and transforms to a new high pressure phase near 5 GPa. The bulk modulus (K) and its pressure derivative (K(')) of the alpha-form and the CH(4)-loaded beta-form hydroquinones are measured to be 8.2(3) GPa and 8.4(4), and 10(1) GPa and 9(2), respectively, representing one of the most compressible classes of crystalline solids reported in the literature. The corresponding axial compression behaviors, however, show greater contrast between the two hydroquinone compounds; the elastic anisotropy of the alpha-form is only marginal, being K(a):K(c) = 1.08:1, whereas that of the CH(4)-loaded beta-form is rather drastic, being K(a):K(c) = 11.8:1. This is attributed to the different dimensionality of the hydrogen bonding networks between the two structures and might in turn explain the observed structural instability of the beta-form, compared to the alpha-form.

Hydrogen molecules trapped in interstitial host channels of alpha-hydroquinone.

Easy come, easy go: Hydroquinone forms a channel structure of cages with hydrogen-bonded hexagons. These may provide an ideal route for the fast inclusion and facile release of hydrogen molecules (see figure), which can lead to reversible hydrogen storage under mild conditions.

Structural changes and preferential cage occupancy of ethane hydrate and methane-ethane mixed gas hydrate under very high pressure.

High-pressure experiments of ethane hydrate and methane-ethane mixed hydrates with five compositions were performed using a diamond anvil cell in a pressure range of 0.1-2.8 GPa at room temperature. X-ray diffractometry and Raman spectroscopy showed structural changes as follows. The initial structure, structure I (sI), of ethane hydrate was retained up to 2.1 GPa without any structural change. For the mixed hydrates, sI was widely distributed throughout the region examined except for the methane-rich and lower pressure regions. For the ethane-rich and intermediate composition regions (73 mol % ethane sample and 53% sample), sI was maintained up to 2.1 GPa. With increasing methane component (34% and 30% samples), sI existed at pressures from 0.1 to about 1.0 GPa. Hexagonal structure (sH) appeared in addition to sI at 1.3 GPa for the 34% sample and at 1.1 GPa for the 30% sample. By further increasing the methane component (22% sample), structure II (sII) existed solely up to 0.3 GPa. From 0.3 to 0.6 GPa, sII and sI coexisted, and from 0.6 to 1.0 GPa only sI existed. At 1.2 GPa sH appeared, and sH and sI coexisted up to 2.1 GPa. Above 2.1 GPa, ethane hydrate and all of the mixed hydrates decomposed into ice VI and ethane fluid or methane-ethane fluid, respectively. The Raman study revealed that occupation of the small cages by ethane molecules occurred above 0.1 GPa in ethane hydrate and continued up to decomposition at 2.1 GPa, although it is thought that ethane molecules are contained only in the large cage.

Structural changes of filled ice Ic structure for hydrogen hydrate under high pressure.

High-pressure experiments of hydrogen hydrate, filled ice Ic structure, were performed using a diamond-anvil cell in the pressure range of 0.1-80.3 GPa at room temperature. In situ x-ray diffractometry (XRD) revealed that structural changes took place at approximately 35-40 and 55-60 GPa, and that the high-pressure phase of hydrogen hydrate survived up to at least 80.3 GPa. Raman spectroscopy showed that the changes in vibrational mode for the hydrogen molecules in hydrogen hydrate occurred at around 40 and 60 GPa, and these results were consistent with those of the XRD. At about 40 GPa, the intermolecular distance of host water molecules consisting the framework attained the critical distance of symmetrization of the hydrogen bond for water molecules, which suggested that symmetrization of the hydrogen bond occurred at around 40 GPa. The symmetrization might introduce some structural change in the filled ice Ic structure. In addition, the existence of the high-pressure phase above 55-60 GPa implies that a denser structure than that of filled ice Ic may exist in hydrogen hydrate.

Potential role of high molecular weight hyaluronan in the anti-Candida activity of human oral epithelial cells.

Candida albicans is both a commensal and a pathogen in the oral mucosa. Previous studies have indicated that epithelial cell-associated carbohydrate moiety can inhibit C. albicans growth. In the present study, the mechanisms by which epithelial cells inhibit Candida growth were studied by examining the effect of hyaluronan (HA). A coculture of C. albicans and KB cells or COS-7 cells inhibited in vitro growth of the fungus by 50-87% at an effector-to-target (E:T) ratio of 80:1. Removing extracellular HA by hyaluronidase caused a significant decrease in the anti-Candida activity of the cells. In addition anti-Candida activity was observed at 1 micro g/ml HA (2000 kDa). The antifungal activity of extracellular HA was further studied by transiently transfecting COS-7 cells with human HSA1, HSA2, or HSA3 in order to produce high levels of extracellular HA. All of the transfectants inhibited C. albicans growth in vitro by 51-65% compared to 38% inhibition by the vector control (P<0.05). These results suggest that the anti-Candida activity of epithelial-cells is mediated by extracellular HA.

Highly selective encaging of carbon dioxide molecules in the mixed carbon dioxide and nitrogen hydrate at low temperatures.

The structural identification and guest compositions of the mixed CO(2) and N(2) hydrates at low temperature conditions were investigated by both theoretical predictions and experimental measurements. From the model calculations, at very low temperatures, the highly CO(2)-concentrated hydrates over 95 mol % CO(2) on the basis of water-free concentration could coexist with the gas mixtures of low CO(2) concentrations in equilibrium. X-ray diffraction measurements of the hydrates formed with the gas mixture of 3.16 mol % CO(2) and balanced N(2) indicate that the formed hydrates at all conditions considered in this study were identified as structure I, whereas the model predicts a structural transition to structure II around 220 K. However, it was also found that the formed hydrate samples contain a considerable amount of hexagonal ice resulting from incomplete conversion of ice to the hydrates. The compositional analysis suggests that a favorable encaging of CO(2) in the mixed hydrate can be obtained by the hydrate formation at low temperatures and relative amount of CO(2) molecules in the mixed hydrates increases with a decrease of temperature.

[Tricresyl phosphate residue in garland chrysanthemum and its origin].

Unknown peaks were detected in the chromatogram of garland chrysanthemum extract in analysis of organophosphorus pesticide residues. The unknown peaks were identified as isomers of tricresyl phosphate (TCP) by GC/MS. TCP is used as a plasticizer in polyvinyl chloride, and there is no report of its detection in foods. Therefore, we investigated the origin of TCP detected in garland chrysanthemum. We found no effect of contact with packaging film or polyvinyl chloride sheet used in greenhouses. However, TCP was detected at 0.03 microg/g (average) in 16 of 20 samples of garland chrysanthemum that had been in contact with polyvinyl chloride tubing used for warming greenhouses. These results indicate that TCP migrated to the garland chrysanthemum from the tubing used to keep greenhouses warm.

Clustering structure of aqueous solution of kinetic inhibitor of gas hydrates.

Poly-[N-vinylcaprolactam] (PVCAP) and its related compounds are specific polymeric compounds for inhibiting hydrate formation. To clarify the inhibition mechanism of these compounds on hydrate nucleation at the molecular level, we measured the mass spectra of clusters generated from the fragmentation of liquid droplets including N-methylcaprolactam (NMCAP; functional group of PVCAP). By comparing the mass spectra of clusters of the solutions--pure D2O, tetrahydrofuran (THF)-D2O, NMCAP-D2O, and THF-NMCAP-D2O--it was found that the interaction of NMCAP with D2O was much stronger than that of THF with D2O. The relative intensity ratio of D+(NMCAP)m(D2O)n clusters to all the clusters observed for the NMCAP-D2O (1:250) mixed solution was 0.45. On the other hand, the relative intensity ratio of D+(THF)1(D2O)n clusters to all the clusters observed for the THF-D2O (1:17) mixed solution was 0.15. In the case of the THF-NMCAP-D2O three-component mixed solution, the NMCAP-D2O interaction was more predominant than the THF-D2O interaction, even at a lower NMCAP concentration. NMCAP reduces free mobile water molecules around NMCAP, but THF does not. This correlates with the facts that THF forms its hydrate below the freezing point and that PVCAP works as an inhibitor of gas hydrates.

[Detection of tris(2,4-di-tert-butylphenyl)phosphite (Irgafos 168, antioxidant in plastics) and its oxide in commercial frozen vegetables].

Two peaks, A and B, detected in chromatograms of commercial frozen vegetable extracts during analysis of organophosphorus pesticide residues by GC-FPD, were identified as tris(2,4-ditert-butylphenyl)phosphite (Irgafos 168) and Irgafos 168 oxide, respectively, from their mass spectra. Irgafos 168 is used as an antioxidant in plastics, and there has been no report of its detection in foods. We analyzed Irgafos 168 and its oxide in 38 samples of commercial frozen vegetables, and they were detected from 4 samples (0.02-0.80 microgram/g as total amount of Irgafos 168 and its oxide).

Possible involvement of prostaglandins F(2alpha) and D(2) in acetylcholine-induced positive inotropy in isolated mouse left atria.

The inotropic action of prostaglandins PGF(2alpha), PGD(2) and PGE(2) on isolated mouse left atria was characterized and compared with the positive inotropic action of acetylcholine, which has previously been shown to be mediated by prostaglandins released from the endocardial endothelium. PGF(2alpha), PGD(2) and PGE(2) produced positive inotropic responses; the time course of the change in contractile force induced by PGF(2alpha) and PGD(2) was about the same as that by acetylcholine, while that by PGE(2) was slower. Fluprostenol and sulprostone, FP and EP receptor agonists, respectively, had positive inotropic effects while BW-245C, a DP receptor agonist, had no effect. AH-6809, a DP receptor antagonist, had no inhibitory effect on the positive inotropic response to PGD(2). Dimethylamiloride, an inhibitor of Na(+)/H(+) exchange, inhibited the positive inotropic response to PGF(2alpha), PGD(2) and acetylcholine, but not PGE(2). Fluorometric pH measurement with carboxy-SNARF-1-loaded atrial myocytes revealed no change in intracellular pH on application of PGF(2alpha). PGF(2alpha) and PGD(2) significantly prolonged the duration of the atrial action potential while PGE(2) had no significant effect. These findings suggest that prostaglandins induce positive inotropic response in mouse atria through FP and EP receptor stimulation and that the former mechanism mediates in part the positive inotropic response to acetylcholine.