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Unraveling the mystery of natural rubber biosynthesis. Part II. Composition and growth of in vitro natural rubber using high-resolution size exclusion chromatography
The superior properties of natural rubber (cis-1,4-polyisoprene [NR]) are a function of its structure and composition, properties that still remain a mystery and that are irreplaceable by any synthetic rubber. NR from guayule (Parthenium argentatum) has been gaining special interest for its hypoallergenic properties while maintaining superior mechanical properties that are commonly associated with the Brazilian rubber tree (Hevea brasiliensis), the most common source of NR. Techniques exist to isolate washed rubber particles (WRPs) that contain enzymatically active rubber transferase, to study NR biosynthesis, and previous work on the in vitroNRgrowth in Hevea has demonstrated the presence of around 50wt%of a low molecular weight ([MW], Mn <10 000 g/mol) fraction. Structural and compositional analyses of this low MW fraction in Hevea are challenging due to the high protein content. Here, we discuss the analysis and composition of guayule latex and WRPs using high-resolution Size Exclusion Chromatography. We also discuss the composition of the soluble fraction of inactive guayule latex using matrix-assisted laser desorption ionization/time of flight mass spectrometry.
On the nature of the free radicals of the cold bokkeveld meteorite <sur la nature des radicaux libres de la meteorite cold bokkeveld<
Nature of free radicals in Bokkeveld meteorite from paramagnetic resonance signals
The intercrater plains of Mercury and the Moon: Their nature, origin and role in terrestrial planet evolution. Discussion of the nature, origin and role of the intercrater plains of Mercury and the Moon
The nature and origin of the intercrater plains of Mercury and the Moon as determined through geologic mapping, crater statistics, and remotely sensed data are summarized. Implications of these results regarding scarp formation, absolute ages, and terrestrial planet surfaces are included. The role of the intercrater plains is defined and future work which might lead to a better understanding of these units and terrestrial planet evolution is outlined.
Blending low-carbon hydrogen with natural gas: Impact on energy and life cycle emissions in natural gas pipelines
In this article, hydrogen (H 2 ) is considered an alternative energy carrier to reduce greenhouse gas (GHG) emissions related to power and heat generation. A quantitative analysis was conducted to estimate the energy intensity and GHG emissions associated with the transportation of NG/H 2 mixture in high-pressure transmission pipeline, considering blending ratios up to 100% of low-carbon H 2 . The life cycle emissions were obtained by including upstream supply chain emissions, compression and transportation emissions, and end use combustion emissions of the NG/ H 2 blend. This study accounts for global warming potential of fugitive methane and H 2 emissions associated with pipeline transportation of the blend in the life cycle analysis. A significant reduction in the overall life cycle GHG emissions can be achieved when delivering the same volume throughput but at a reduced energy flow to end users. However, to maintain the nominal energy throughput of the pipeline regardless of the H 2 mole fraction, a maximum reduction of about 6% is obtained as the H 2 mole fraction in the blend will be practically limited to approximately 30% H 2 when the pipeline operates at capacity.
Origin and Nature of Bond Rotation Barriers: A Unified View
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Photonics meets excitonics: natural and artificial molecular aggregates
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Thermodynamic evaluation of solar integration into a natural gas combined cycle power plant
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Photophysical Characterization of the Naturally Occurring Dioxobacteriochlorin Tolyporphin A and Synthetic Oxobacteriochlorin Analogues
Abstract Tolyporphins are tetrapyrrole macrocycles produced by a cyanobacterium‐containing culture known as HT ‐58‐2. Tolyporphins A–J are free base dioxobacteriochlorins, whereas tolyporphin K is an oxochlorin. Here, the photophysical characterization is reported of tolyporphin A and two synthetic analogues, an oxobacteriochlorin and a dioxobacteriochlorin. The characterization (in toluene, diethyl ether, ethyl acetate, dichloromethane, 1‐pentanol, 2‐butanone, ethanol, methanol, N,N ‐dimethylformamide and dimethylsulfoxide) includes static absorption and fluorescence spectra, fluorescence quantum yields and time‐resolved data. The data afford the lifetime of the lowest singlet excited state and the yields of the nonradiative decay pathways (intersystem crossing and internal conversion). The three macrocycles exhibit only modest variation in spectroscopic and excited‐state photophysical parameters across the solvents. The long‐wavelength (Q y ) absorption band of tolyporphin A appears at ~680 nm and is remarkably narrow (full‐width‐at‐half‐maximum ~7 nm). The position of the long‐wavelength (Q y ) absorption band of tolyporphin A (~680 nm) more closely resembles that of chlorophyll a (662 nm) than bacteriochlorophyll a (772 nm). The absorption spectra of tolyporphins B–I, K (which were available in minute quantities) are also reported in methanol; the spectra of B–I closely resemble that of tolyporphin A. Taken together, tolyporphin A generally exhibits spectral and photophysical features resembling those of chlorophyll a .
High Performance Thermoelectricity in Earth-Abundant Compounds Based on Natural Mineral Tetrahedrites
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The Nature of Hydrogen Adsorption on Platinum in the Aqueous Phase
H2 adsorption properties on Pt in aqueous phase was determined by a reaction kinetic measurement of gas H2 reacting with liquid D2O into liquid HDO, gas HD and D2, and a DFT based ab inito molecular dynamic simulation of H2 adsorption on Pt (111) in the presence and absence of water. Both approaches show that the H2 adsorption on Pt in water is much weaker than that in the gas phase. The presence of interfacial water destabilizes the adsorbed H on Pt via decreasing the adsorption heat (hydrogen binding energy) by 19 - 22 kJ·molH2-1 and inducing an extra entropy loss of 50 - 70 J·mol H2-1·K-1. Upon H adsorption on Pt, the closest water layer near Pt surface shifts to a larger distance from the surface and re-orientates to a more ordered structure; in turn, the water layer limits the translation mobility of adsorbed H on Pt. The influence of interfacial water property on H2 adsorption is also reflected by the decrease of adsorption heat with the decrease of local pH provided by the support. Research was funded by the Laboratory Directed Research and Development program at Pacific Northwest National Laboratory.
Ethylene Dehydroaromatization over Ga-ZSM-5 Catalysts: Nature and Role of Gallium Speciation
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Transport and Fate of Natural Gas and Brine Escaping from a Hydrocarbon Reservoir Through a Failed Deepwater Well in the Oceanic Subsurface of the Gulf of Mexico
The possibility of broaching, or the release of fluids at the seafloor due to a damaged or faulty well, is a hazard that must be assessed in the well permitting process. Here, this paper describes a numerical simulation study of a real-life scenario where a complex, permeable sandy formation, connected to the seafloor via known chimneys/seeps, is intersected by a damaged production well that drains another deeper, gas-bearing formation. The objective of the study is to determine the transport and fate of hydrocarbon reservoir fluids (gas and brines) escaping into the sandy formation through the casing shoe of the failed well, and to determine the time it takes for these contaminants to reach the ocean floor. We conducted a detailed simulation study to represent the conditions, properties, and behavior of the system under such failure conditions, and we investigated the migration of gas and brine for a range of reservoir and chimney properties. A key conclusion is that, for such complex systems, modeling the three-dimensional geometry of the system in detail is the key to describing transport and assessing the time and magnitude of potential releases. For the system studied here, transport times range from under 2 years (highest permeabilities) to many decades, ensuring significant time to respond to potential broaching hazards. Lastly, under the conditions investigated in this study, we also determine that gas-dominated releases associated with low rates of water flow into the sandy formation are likely to cause hydrate formation that can reduce permeabilities in the colder, upper regions of the chimneys and possibly mitigate releases.