SUBJECTS citric acid

The starting NaY zeolite was an SK-40 from Union Carbide with a framework Si/Al ratio of 2.4. Ultrastable HY zeolites (HYUS) were prepared by steam-calcination of partially ammonium exchanged zeolites at atmospheric pressure and 550-750 °C during 3-20 hours. After dealumination they were exchanged twice with an NH solution at 80 C for one hour and then calcined at 550 °C for 3 hours. In this way dealuminated samples containing less than 2% of the original Na were obtained. One of these (HYUS-8) was subjected to different treatments (1) washed with a solution of citric acid or HCl (pH=3) at 25 °C for one hour (samples HYUSAC and HYUSl, respectively) (2) washed with a solution 0.1 M of NaOH at 40 °C for one hour (HYUSN), and (3) washed with a 38% v/v solution of acetylacetone in ethanol at 20 °C for 2 hours (HYUSA). 

To test the hypothesis that the addition of CCM reduces dental erosion, the erosive effects of four different drinks was compared a citric acid-based orange-flavored soft drink fortified with CCM (pH 4.0, 1344 mg Ca/liter) the same drink without CCM (pH 3.6, 72 mg Ca/liter) and positive and negative controls consisting of a diet phosphoric acid-based cola (pH 3.1, 35 mg Ca/liter) and distilled water, respectively (Rugg-Gurm et ah, 1998). In a randomized cross-over design comprised of four 6-day periods, 11 subjects were required to wear a palatal... 

Brookhaven National Laboratory s (BNL s) biochemical recovery of radionuclides and heavy metals is a patented biochemical recovery process for the removal of metals and radionuclides from contaminated minerals, soil, and waste sites. In this process, citric acid, a naturally occurring organic complexing agent, is used to extract metals and radionuclides from solid wastes by the formation of water-soluble, metal-citrate complexes. The complex-rich extract is then subjected to microbiological biodegradation that removes most of the extracted heavy metals. 

We finally return to the subject of citric acid. We posed the question in Section 2 as to whether the four hydrogen atoms in citric acid (Fig. 4) were distinguishable and we have already seen that HA and HB (or Hc and HD) are diastereotopic and therefore,... 

The third control step in the citric acid cycle is catalyzed by 2-oxoglutarate dehydrogenase. This multienzyme complex is subject to product inhibition by both NADH and succinyl-CoA. Yet again,... 

Citric acid is present in citrus fruits. It is composed of carbon, hydrogen, and oxygen. When a 0.5000 g sample of citric acid was subjected to carbon-hydrogen combustion analysis, 0.6871 g of carbon dioxide and 0.1874 g of water were produced. Using a mass spectrometer, the molar mass of citric acid was determined to be 192 g/mol. 

Subsequent to this breakthrough, the subject was extensively investigated and was subsequently reviewed [390]. The acids most effective are BTCA, tricarballylic acid, and citric acid. Owing to the low cost and wide availability of citric acid, it is undergoing widespread commercial development for esterification cross-linking of cotton and paper products, often with minor amounts of BTCA as an activator, together with suitable catalysts. 

The role of thiamin diphosphate in pymvate dehydrogenase means that, in deficiency, there is impaired conversion of pymvate to acetyl GoA, and hence impaired entry of pymvate into the citric acid cycle. Especially in subjects on a relatively high carbohydrate diet, this results in increased plasma concentrations oflactate and pymvate, which may lead to life-threateninglactic acidosis. 

Gershoff and Prien (G6) found that normal subjects excrete significantly less xanthurenic acid and 4-pyridoxic acid and more citric acid than patients with chronic formation of calcium oxalate. A marked rise in excretion of calcium oxalate followed administration of tryptophan in these patients, whereas ingestion of pyridoxine was followed by a decrease in urinary oxalate. 

These reactions show the relation of citric acid to the two tri-basic acids mentioned at the beginning of this section. When subjected to dry distillation citric acid loses carbon dioxide while at the same time it becomes oxidized, and acetone is produced. 

Vitamin K status can be assessed by a functional test, called the "prothrombin time test," which involves measuring the lime required to form a blood clot. The test is performed as follows. A blood sample is withdrawn from a subject and immediately mixed with citric acid. Citric acid is a chelator, which means that it can form a tight complex with ions, such as calcium ions. The chelator prevents the interaction of calcium ions with the blood-clotting proteins and thus prevents these proteins from forming a blood clot in the sample. Calcium ions, it should be noted, are required for supporting the activity of several blood clotting proteins. The "citrated blood" is placed in a machine called a fibrometer. The fibrometer is used to detect increases in the viscosity of the blood over a period. 

Similar to fumaric acid, L-malic acid is also a naturally occurring four-carbon dicarboxyhc acid and an intermediate in the TCA cycle. It has been used in many food products, primarily as an acidulant. L-Malic acid is compatible with all sugars with low hygroscopicity and good solubihty. In addition, it has therapeutic value for the treatment of hyperammoemia and liver dysfunction and as a component for amino acid infusion. L-Malic acid has been the subject of interest because of its increased application in the food industry as a citric acid replacement and its potential use as a raw material for the manufacture of biodegradable polymers. 

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