Citric acid

Citric acid is a weak organic acid that has the chemical formula C6H8O7. It occurs in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in the metabolism of all aerobic organisms. More than two million tons of citric acid are manufactured every year, it is used as an acidifier, as a flavoring and a chelating agent. A citrate is a derivative of citric acid. An example of the former, a salt is trisodium citrate; when part of a salt, the formula of the citrate ion is written as C6H5O3−7 or C3H5O3−3. Citric acid exists in greater than trace amounts in a variety of fruits and vegetables, most notably citrus fruits. Lemons and limes have high concentrations of the acid; the concentrations of citric acid in citrus fruits range from 0.005 mol/L for oranges and grapefruits to 0.30 mol/L in lemons and limes. Industrial-scale citric acid production first began in 1890 based on the Italian citrus fruit industry, where the juice was treated with hydrated lime to precipitate calcium citrate, isolated and converted back to the acid using diluted sulfuric acid.

In 1893, C. Wehmer discovered. However, microbial production of citric acid did not become industrially important until World War I disrupted Italian citrus exports. In 1917, American food chemist James Currie discovered certain strains of the mold Aspergillus niger could be efficient citric acid producers, the pharmaceutical company Pfizer began industrial-level production using this technique two years followed by Citrique Belge in 1929. In this production technique, still the major industrial route to citric acid used today, cultures of A. niger are fed on a sucrose or glucose-containing medium to produce citric acid. The source of sugar is corn steep liquor, hydrolyzed corn starch, or other inexpensive, sugary solution. After the mold is filtered out of the resulting solution, citric acid is isolated by precipitating it with calcium hydroxide to yield calcium citrate salt, from which citric acid is regenerated by treatment with sulfuric acid, as in the direct extraction from citrus fruit juice.

In 1977, a patent was granted to Lever Brothers for the chemical synthesis of citric acid starting either from aconitic or isocitrate/alloisocitrate calcium salts under high pressure conditions. Global production was in excess of 2,000,000 tons in 2018. More than 50% of this volume was produced in China. More than 50% was used as an acidity regulator in beverages, some 20% in other food applications, 20% for detergent applications, 10% for applications other than food, such as cosmetics, in the chemical industry. Citric acid was first isolated in 1784 by the chemist Carl Wilhelm Scheele, who crystallized it from lemon juice, it can exist either as a monohydrate. The anhydrous form crystallizes from hot water, while the monohydrate forms when citric acid is crystallized from cold water; the monohydrate can be converted to the anhydrous form at about 78 °C. Citric acid dissolves in absolute ethanol at 15 °C, it decomposes with loss of carbon dioxide above about 175 °C. Citric acid is considered to be a tribasic acid, with pKa values, extrapolated to zero ionic strength, of 2.92, 4.28, 5.21 at 25 °C.

The pKa of the hydroxyl group has been found, by means of 13C NMR spectroscopy, to be 14.4. The speciation diagram shows that solutions of citric acid are buffer solutions between about pH 2 and pH 8. In biological systems around pH 7, the two species present are the citrate ion and mono-hydrogen citrate ion; the SSC 20X hybridization buffer is an example in common use. Tables compiled for biochemical studies are available. On the other hand, the pH of a 1 mM solution of citric acid will be about 3.2. The pH of fruit juices from citrus fruits like oranges and lemons depends on the citric acid concentration, being lower for higher acid concentration and conversely. Acid salts of citric acid can be prepared by careful adjustment of the pH before crystallizing the compound. See, for example, sodium citrate; the citrate ion forms complexes with metallic cations. The stability constants for the formation of these complexes are quite large because of the chelate effect, it forms complexes with alkali metal cations.

However, when a chelate complex is formed using all three carboxylate groups, the chelate rings have 7 and 8 members, which are less stable thermodynamically than smaller chelate rings. In consequence, the hydroxyl group can be deprotonated, forming part of a more stable 5-membered ring, as in ammonium ferric citrate, 5Fe2·2H2O. Citric acid can be esterified at one or more of the carboxylic acid functional groups on the molecule, to form any of a variety of mono-, di-, tri-, mixed esters. Citrate is an intermediate in the TCA cycle, a central metabolic pathway for animals and bacteria. Citrate synthase catalyzes the condensation of oxaloacetate with acetyl CoA to form citrate. Citrate acts as the substrate for aconitase and is converted into aconitic acid; the cycle ends with regeneration of oxaloacetate. This series of chemical reactions is

Rheumaptera undulata

Rheumaptera undulata, the scallop shell, is a moth of the family Geometridae. It was first described by Carl Linnaeus in his 1758 10th edition of Systema Naturae, it is found in most of North America. The wingspan is 25–30 mm; the ground colour of the forewings is pale. The crosslines are darker, evenly spaced and numerous; the outer margin is pale brown with a scalloped fringe. The hindwings are paler. There is one generation per year with adults on wing from the end of May to August in Europe; the larvae feed on birch and willow species, as well as aspen {Populus tremula), Populus balsamifera, Berberis vulgaris, Ribes alpinum, Spiraea salicifolia, Elaeagnus commutata and Myrica gale. Larvae can be found in September, it overwinters as a pupa. Rheumaptera undulata undulata Rheumaptera undulata sajana Bryk, 1921 Media related to Rheumaptera undulata at Wikimedia Commons

Toyota TF103

The Toyota TF103 was the Gustav Brunner designed machine with which the Toyota F1 team competed in the 2003 Formula One season. Unveiled on January 8, 2003 at the Paul Ricard circuit, its drivers were the Frenchman Olivier Panis and Brazilian Cristiano da Matta, the reigning CART FedEx Championship Series Champion from 2002; the TF103 was quite a conservative design, by the team's admission it was more of a'logical evolution' from its predecessor the TF102. Lighter and with more downforce, the car was a joint effort between Gustav Brunner's design team and Keizo Takahashi, chief of Technical co-ordination; the biggest improvement over the TF102 came with the engine, the RVX-03 had been tested for the first time in September 2002 and offered the team benefits twofold over the RVX-02. The engine was the brainchild of Italian designer Luca Marmorini; the TF103 stepped up a level in terms of performance too, with the car scoring a total of sixteen points between its drivers, da Matta outscoring Panis 10-6.

The most notable race involving the TF103 was at Silverstone for the British Grand Prix when both cars ran 1-2 for a time amidst the confusion brought about by a track invader on the 11th lap. In the constructors standings, Toyota finished in eighth, still some way off the performance their massive budget should have allowed, but too, it was a notable improvement on their 2002 finish. TF103 Evolution at Toyota F1 official site TF103 Facts at