They gathered myriad samples from the pools — of varying temperatures, salinities and acidities — and used a range of techniques to painstakingly search for biosignatures.
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There exists a large corpus of data concerning acid strengths in aqueous solution (pKa values), and it is tempting to transfer this to other solvents. Such comparisons are, however, fraught with danger, as they only consider the effect of solvation on the stability of the hydrogen ion, while neglecting its effects on the stability of the other species involved in the equilibrium. Gas phase acidities (normally known as proton affinities) can be measured, and their relative order is often quite different from that of the aqueous acidities of the corresponding acids. Few quantitative studies on acidities in nonaqueous solvents have been carried out, although some qualitative data are available.
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Oca grows with very low production inputs, generally on plots of marginal soil quality, and tolerates acidities between about pH 5.3 and 7.8. In traditional Andean cropping systems, it is often planted after potato and therefore benefits from persisting nutrients applied to, or left over from, the potato crop.
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Currently the tidal flows are limited in size and managed for flood control. For years the lake acted as a waste collector. It was regarded as ideal for sewage because of its chemical contents, which have high acidities that cause it to decompose human feces at very high rates.
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For instance it grows in two regions of China with different soil acidities. Tai Shan is granitic while Lao Shan has soluble limestone with mineral water springs. The plant requires full sunlight and cannot grow in shades. The seeds can be grown by winter sow in vented containers set up in a cold frame or unheated greenhouse.
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Taw manroot grows most vigorously by streams or in washes but can also be successful in dryer areas, at elevations up to . It will tolerate a variety of soil types and acidities, but it requires at least seasonally moist soil. Vines can grow in full-sun to heavily shaded conditions. Vines die back in summer and emerge in late winter.
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Coastal manroot grows most vigorously by streams or in washes but can also be successful in dryer areas, at elevations up to 1600 metres. It will tolerate a variety of soil types and acidities, but it requires at least seasonally moist soil. Vines can grow in full-sun to heavily shaded conditions. In mild areas of its range where year- round moisture is available, vines are perennial.
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The California manroot grows most vigorously by streams or in washes but is also successful in dry chaparral, at elevations up to 1600 metres. It ranges through most of California except the far northwest and the Mojave Desert. It will tolerate a variety of soil types and acidities, but it requires seasonally moist soil. Vines can grow in full-sun to partially shaded conditions.
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Chemists use a series of factors developed from physical chemistry -- electronegativity/Induction, bond strengths, resonance, hybridization, aromaticity, and solvation—to predict relative acidities and basicities. The hard/soft acid/base principle is utilized to predict molecular interactions and reaction direction. In general, interactions between molecules of the same type are preferred. That is, hard acids will associate with hard bases, and soft acids with soft bases.
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Since the electrophile is much less acidic than the nucleophile, rapid proton transfer usually transfers the enolate back to the nucleophile if the product is enolizable; however, one may take advantage of the new locus of nucleophilicity if a suitable electrophile is pendant. Depending on the relative acidities of the nucleophile and product, the reaction may be catalytic in base. In most cases, the reaction is irreversible at low temperature.
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Louis Plack Hammett (April 7, 1894 - February 9, 1987) was an American physical chemist. He is known for the Hammett equation, which relates reaction rates to equilibrium constants for certain classes of organic reactions involving substituted aromatic compounds. He is also known for his research into superacids and his development of a scheme for comparing their acidities based on what is now known as the Hammett acidity function. The Curtin–Hammett principle bears his name.
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Fatty acids do not show a great variation in their acidities, as indicated by their respective pKa. Nonanoic acid, for example, has a pKa of 4.96, being only slightly weaker than acetic acid (4.76). As the chain length increases, the solubility of the fatty acids in water decreases, so that the longer-chain fatty acids have minimal effect on the pH of an aqueous solution. Even those fatty acids that are insoluble in water will dissolve in warm ethanol, and can be titrated with sodium hydroxide solution using phenolphthalein as an indicator.
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Because DMSO is only weakly acidic, it tolerates relatively strong bases and as such has been extensively used in the study of carbanions. A set of non-aqueous pKa values (C-H, O-H, S-H and N-H acidities) for thousands of organic compounds have been determined in DMSO solution. Because of its high boiling point, , DMSO evaporates slowly at normal atmospheric pressure. Samples dissolved in DMSO cannot be as easily recovered compared to other solvents, as it is very difficult to remove all traces of DMSO by conventional rotary evaporation.
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Due to its capability to penetrate skin, glycolic acid finds applications in skin care products, most often as a chemical peel. Physician-strength peels can have a pH as low as 0.6 (strong enough to completely keratolyze the epidermis), while acidities for home peels can be as low as 2.5. Once applied, glycolic acid reacts with the upper layer of the epidermis, weakening the binding properties of the lipids that hold the dead skin cells together. This allows the stratum corneum to be exfoliated, exposing live skin cells.
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Because GDGTs have two hydrophilic head groups, they form a lipid monolayer in the cell membrane instead of a bilayer, making GDGT-producing archaea exceptional among all clades of life. Originally, it was believed that GDGT membrane lipids were an adaption to life at high temperatures and acidities. Because the two sides of a monolayer lipid are connected by covalent bonds rather than the weaker intermolecular forces that promote the cohesion of bilayers, they are more stable than typical bilayers. This hypothesis is supported by the observation that some extremophile bacteria synthesize their own membrane-spanning, ether-bound GDGT analogues.
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All three lighter boron trihalides, BX3 (X = F, Cl, Br) form stable adducts with common Lewis bases. Their relative Lewis acidities can be evaluated in terms of the relative exothermicities of the adduct-forming reaction. Such measurements have revealed the following sequence for the Lewis acidity: :BF3 < BCl3 < BBr3 (strongest Lewis acid) This trend is commonly attributed to the degree of π-bonding in the planar boron trihalide that would be lost upon pyramidalization of the BX3 molecule. which follows this trend: :BF3 > BCl3 > BBr3 (most easily pyramidalized) The criteria for evaluating the relative strength of π-bonding are not clear, however.
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The acidity of was found to vastly exceed that of triflic acid, , and bistriflimide, , compounds previously regarded as the strongest isolable acids. Their high acidities stem from the extensive delocalization of their conjugate bases, carboranate anions (CXB11Y5Z6–), which are usually further stabilized by electronegative groups like Cl, F, and CF3. Due to the lack of oxidizing properties and the exceptionally low nucleophilicity and high stability of their conjugate bases, they are the only superacids known to protonate C60 fullerene without decomposing it. Additionally, they form stable, isolable salts with protonated benzene, C6H7+, the parent compound of the Wheland intermediates encountered in electrophilic aromatic substitution reactions.
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As a class, the carborane acids form the most acidic group of well-defined, isolable substances known, far more acidic than previously known single- component strong acids like triflic acid or perchloric acid. In certain cases, like the nearly perhalogenated derivatives mentioned above, their acidities rival (and possibly exceed) those of the traditional mixed Lewis-Brønsted superacids like magic acid and fluoroantimonic acid. (However, a head-to-head comparison has not been possible thus far, due to the lack of a measure of acidity that is suitable for both classes of acids: pKa values are ill-defined for the chemically complex mixed acids while H0 values cannot be measured for the very high melting carborane acids).
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