Effect of Pressure on the Thermal Cracking and Polymerization of Pentacosane (n-C25), an n-Alkane

Hydrocarbons are important carbon components in the subducting slab and play a crucial role in the Earth's deep carbon cycle. In this study, the thermal reaction of pentacosane (n- C25), a long n-alkane, was experimentally investigated under high-pressure and high-temperature conditions at 0.5-1.5 GPa and 360-400 degrees C. The gas chromatography-mass spectrometry (GC/ MS) analyses of the reaction products revealed that the radical reaction of n-C25 proceeded above 360 degrees C at 0.5 GPa and above 380 degrees C at 1.5 GPa, while the rate constant decreased with increasing pressure. Lighter n-alkanes and heavier straight/branched alkanes were detected in the reaction products. The formation of lighter n-alkanes indicates thermal cracking progression, even at high-pressure conditions. During thermal cracking, lighter 1-alkenes were likely to form but were instead rapidly added to the initial n-C25 to form heavier alkanes when enhanced by pressure. Thus, lighter 1-alkenes were not detected in the reaction products. As the secondary reaction, the heavier alkanes were polymerized with dehydrogenation to form amorphous carbon when the remaining percentage of the initial material became <10% and <20% at 0.5 and 1.5 GPa, respectively, while the lighter n-alkanes were detected simultaneously. Both lighter alkanes with high H/C ratios and amorphous carbon with a low H/C ratio eventually formed through the reaction of n-alkanes at high-pressure and high-temperature conditions of the deep Earth

Behavior of intermolecular interactions in alpha-glycine under high pressure

Pressure-response on the crystal structure of deuterated alpha-glycine was investigated at room temperature, using powder and single-crystal X-ray diffraction, and powder neutron diffraction measurements under high pressure. No phase change was observed up to 8.7 GPa, although anisotropy of the lattice compressibility was found. No significant changes in the compressibility and the intramolecular distance between non-deuterated alpha-glycine and deuterated alpha-glycine were observed. Neutron diffraction measurements indicated the distance of the intermolecular D center dot center dot center dot O bond along with the c-axis increased with compression up to 6.4 GPa. The distance of another D center dot center dot center dot O bond along with the a-axis decreased with increasing pressure and became the shortest intermolecular hydrogen bond above 3 GPa. In contrast, the lengths of the bifurcated N-D center dot center dot center dot O and C-D center dot center dot center dot O hydrogen bonds, which are formed between the layers of the alpha-glycine molecules along the b-axis, decreased significantly with increasing pressure. The decrease of the intermolecular distances resulted in the largest compressibility of the b-axis, compared to the other two axes. The Hirshfeld analysis suggested that the reduction of the void region size, rather than shrinkage of the strong N-D center dot center dot center dot O hydrogen bonds, occurred with compression. Published by AIP Publishing

Polymerization Mechanism of Nitrogen-Containing Heteroaromatic Compound Under High-Pressure and High-Temperature Conditions

Hydrogenated carbon nitride is synthesized by polymerization of 1,5-naphthyridine, a nitrogen-containing heteroaromatic compound, under high-pressure and high-temperature conditions. The polymerization progressed significantly at temperatures above 573 K at 0.5 GPa and above 623 K at 1.5 GPa. The reaction temperature was relatively lower than that observed for pure naphthalene, suggesting that the reaction temperature is considerably lowered when nitrogen atoms exist in the aromatic ring structure. The polymerization reaction largely progresses without significant change in the N/C ratio. Three types of dimerization are identified; naphthylation, exact dimerization, and dimerization with hydrogenation as determined from the gas chromatograph–mass spectrometry analysis of soluble products. Infrared spectra suggest that hydrogenation products were likely to be formed with sp3 carbon and NH bonding. Solid-state 13C nuclear magnetic resonance reveals that the sp3/sp2 ratio is 0.14 in both the insoluble solids synthesized at 0.5 and 1.5 GPa. Not only the dimers but also soluble heavier oligomers and insoluble polymers formed through more extensive polymerization. The major reaction mechanism of 1,5-Nap was common to both the 0.5 and 1.5 GPa experiments, although the required reaction temperature increased with increasing pressure and aromatic rings preferentially remained at the higher pressure

Performance of ceramic anvils for high pressure neutron scattering

Three kinds of ceramics, zirconia-toughened alumina (ZTA), alumina-toughened zirconia (ATZ) and yttria-stabilized zirconia (YSZ), were tested as anvil materials, mainly for the purpose of neutron scattering study under high pressure. ZTA with non-toroidal anvil profile, having the same sample volume as conventionally used double toroidal anvils, sustained pressures up to 11.9 GPa. This is comparable to anvils made of tungsten carbide (TC) with Ni binder with the same dimensions. ATZ would also be an alternative material to TC with pressure performance comparable to ZTA, whereas YSZ is much weaker than the other two ceramics. The attenuation coefficient for YSZ is significantly smaller than that of TC and similar to ZTA and ATZ, the latter being estimated by attenuation calculations. Neutron diffraction on a sample of lead in YSZ anvils as well as quasi-elastic neutron scattering on liquid water in ZTA also demonstrate the outstanding neutron transparency of these ceramics. The gain factor in count rate is up to one order of magnitude

Potent Effects of Flavonoid Nobiletin on Amplitude, Period, and Phase of the Circadian Clock Rhythm in PER2::LUCIFERASE Mouse Embryonic Fibroblasts.

Flavonoids are natural polyphenols that are widely found in plants. The effects of flavonoids on obesity and numerous diseases such as cancer, diabetes, and Alzheimer's have been well studied. However, little is known about the relationships between flavonoids and the circadian clock. In this study, we show that continuous or transient application of flavonoids to the culture medium of embryonic fibroblasts from PER2::LUCIFERASE (PER2::LUC) mice induced various modifications in the circadian clock amplitude, period, and phase. Transient application of some of the tested flavonoids to cultured cells induced a phase delay of the PER2::LUC rhythm at the down slope phase. In addition, continuous application of the polymethoxy flavonoids nobiletin and tangeretin increased the amplitude and lengthened the period of the PER2::LUC rhythm. The nobiletin-induced phase delay was blocked by co-treatment with U0126, an ERK inhibitor. In summary, among the tested flavonoids, polymethoxy flavones increased the amplitude, lengthened the period, and delayed the phase of the PER2::LUC circadian rhythm. Therefore, foods that contain polymethoxy flavones may have beneficial effects on circadian rhythm disorders and jet lag