Urea, from ammonia

GENERATION OF THE REDUCING AGENT AMMONIA FROM UREA... 

Variation of the nature of the gate electrode results in the different types of FET. For example, in the metal oxide semiconductor FET (MOS-FET) palladium/palladium oxide is used as the gate electrode. This catalyti-cally decomposes gases such as hydrogen sulphide or ammonia with the production of hydrogen ions, which pass into the semiconductor layer. An enzyme may be coated on the palladium, e.g. urease, which catalyses the production of ammonia from urea and thus provides a device for the measurement of this substrate. 

Urease, spread on water, retains only about 5 per cent, of its original power of liberating ammonia from urea and this small activity might be due to a little unspread enzyme. 

Certain intestinal bacteria can release ammonia from urea molecules that diffuse across the membrane into the intestinal lumen. Treatment with antibiotics kills these organisms, thereby reducing blood ammonia concentration. 

The assay is based on the inhibitory effect of mercury on the enzyme urease and hence on its rate of production of ammonia from urea. We also describe the assay of creatinine using dry reagent strips. 

The production of ammonia from urea gives rise to a shift of the C(V)-curve along the voltage cLxis as discussed above. The inhibition of the urease activity by Hg " was estimated from the slope of AV versus time plots, compared to the slope without added mercury(II) chloride. In Fig.5, we have shown the observed relative enzyme activity as a function of the Hg -concentration. The detection limit appears to be about 0.001 /xM Hg " " in this measurement system. One sample could be processed within 5 minutes. 

Bi2(CsH407)] 2K ) which has a complex stmcture. This salt is unstable in the stomach acid and precipitates out to form complex cationic species which form complexes with proteins in the stomach wall protecting ulcers from gastric add and pepsin, and these complexes are also toxic to H. pylori. The basis of the toxidty of bismuth salts to the bacteria may be due to formation of complexes with the tuease (which produces ammonia from urea) that the bacteria produce in large amounts in order to maintain the pH of their environment at around 6 so that they can survive tmder the addic conditions in the stomach/ Bismuth salts are usually used in combination with an H2-receptor antagonist and a tetracydine (see Ch. 22) which is also used to kill the bacteria. 

Ammonia and urea prices from 1968 to 1986 are shown in Figure 22 (82). The average FOB price of ammonia on the U.S. Gulf Coast in early 1991 was 105/t. 

Only one melamine molecule is formed from six urea molecules, whilst three molecules of ammonia carbamate are formed. Whilst this can be recycled to urea the conversion from urea to melamine per cycle is at most 35%. Both the main route and the recycling operation involve high pressures and the low process efficiency offsets some of the apparent economic attractions of the route compared to those from dicy . 

Fig. 10-13. The links between the cycling of C, N, and O2 are indicated. Total primary production is composed of two parts. The production driven by new nutrient input to the euphotic zone is called new production (Dugdale and Goering, 1967). New production is mainly in the form of the upward flux of nitrate from below but river and atmospheric input and nitrogen fixation (Karl et al, 1997) are other possible sources. Other forms of nitrogen such as nitrite, ammonia, and urea may also be important under certain situations. The "new" nitrate is used to produce plankton protoplasm and oxygen according to the RKR equation. Some of the plant material produced is respired in the euphotic zone due to the combined efforts...

Recently, the old alkaline phenol method has been revived, and is being widely used in clinical laboratories, without protein preclpltatlon(27). In this procedure, the serum is added to an alkaline phenol reagent, and the ammonia generated from urea is determined either after the action of urease or after strong alkaline treatment of the serum. The objection to this procedure is first, that all urease is rich in ammonia, and second, the color produced with alkaline phenol is not specific for ammonia. It will react with other compounds, especially for those that liberate ammonia. By this procedure one obtains a useful number from the point of view of determining whether the patient has nitrogen retention, but a value which is somewhere between a urea and an N.P.N. determination. 

The major problems with the substitution of the reducing agent ammonia for urea are on the one hand the homogeneous mixing of urea and exhaust gas and on the other hand the limited residence time in SCR systems for the different decomposition steps, i.e. the evaporation of water from the droplet, the thermolysis of urea to isocyanic acid and the following hydrolysis to ammonia [18]. 

Formation of urea (for removal of ammonia from body fluids)... 

The urea cycle is essential for the detoxification of ammonia 678 Urea cycle defects cause a variety of clinical syndromes, including a metabolic crisis in the newborn infant 679 Urea cycle defects sometimes result from the congenital absence of a transporter for an enzyme or amino acid involved in the urea cycle 680 Successful management of urea cycle defects involves a low-protein diet to minimize ammonia production as well as medications that enable the excretion of ammonia nitrogen in forms other than urea 680... 

Christensen LK, Thinggaard K (1999) Solarization of greenhouse soil for prevention of Pythium root rot in organically grown cucumber. J Plant Pathol 81 137-144 Chun D, Lockwood JL (1985) Reduction of Pythium ultimum, Thielaviopsis basicola, and Macrophomina phaseolina populations in soil associated with ammonia generated from urea. Plant Dis 69 154-158... 

Reaction between phthalic anhydride and urea always affords chlorine-free Copper Phthalocyanine Blue. Chlorinated derivatives are obtained only in the absence of bases (ammonia) or urea. The phase stabilized a-modification is prepared by essentially the same but slightly modified route it is derived from mixed con-... 

Amines other than a-amino acids will also give a colour reaction with ninhydrin but without the production of carbon dioxide. Thus /3-, y-, 8- and e-amino acids and peptides react more slowly than a-amino acids, to give the blue complex, while imino acids result in the formation of a yellow-coloured product which can be measured at 440 nm. Removal of substances such as protein, ammonia and urea from biological samples may be necessary in quantitative work because they also react in a similar manner. 

Nitrates, produced from ammonia or urea, include a variety of nitrogen-based compounds used to make fertilizers, pesticides, and explosives, and they are highly... 

The experiments described above indicated amino acids were oxidatively deaminated in liver and their a-amino groups converted to urea. A start on investigations of the mechanism of urea biosynthesis was made by Schultzen and Nenki (1869) who concluded that amino acids gave rise to cyanate which might combine with ammonia from proteins to produce urea. Von Knieren (1873) demonstrated that when he drank an ammonium chloride solution, or gave it to a dog, there was an increase in the formation of urea, without any rise in urinary ammonia. His results were consistent with the cyanate theory but did not eliminate the possibility that urea arose from ammonium carbonate which could be dehydrated to urea ... 

ERNST, J.W. and MASSEY, H.F. (1960). The effects of several factors on volatilisation of ammonia formed from urea in the soil. Soil Science Society of America Proceedings 24, 87-90. 

Urea, another common example of an amide, is made from the reaction between carbon dioxide gas, CO2, and ammonia, NH3. Urea was the first organic compound to be synthesized in a laboratory. It is found in the urine of many mammals, including humans, and it is used as a fertilizer. 

In prolonged starvation more ammonia than urea is excreted in order to batter the urine from the acidic ketone bodies that are present in the urine. 

Phenylacetamide has been obtained by a wide variety of reactions from benzyl cyanide with water at 250-260° 6 from benzyl cyanide with water and cadmium oxide at 240° 6 from benzyl cyanide with sulfuric acid 7 8 by saturation of an acetone solution of benzyl cyanide with potassium hydrosulfide 9 from benzyl cyanide with sodium peroxide 10 by electrolytic reduction of benzyl cyanide in sodium hydroxide 11 from ethyl phenyl-acetate with alcoholic 12 or aqueous 13 ammonia from phenyl-acetic acid with ammonium acetate 14 or urea 15 from diazoacetophenone with ammoniacal silver solution 16 from phenyl-acetic acid imino ether hydrochloride and water 17 from acetophenone with ammonium poly sulfide at 215° 18 from benzoic acid 19 and by heating the ammonium salt of phenyl-acetic acid.20... 

Urea is a colorless, odorless crystalline substance discovered by Hilaire Marin Rouelle (1718—1779) in 1773, who obtained urea by boiling urine. Urea is an important biochemical compound and also has numerous industrial applications. It is the primary nitrogen product of protein (nitrogen) metabolism in humans and other mammals. The breakdown of amino acids results in ammonia, NH3, which is extremely toxic to mammals. To remove ammonia from the body, ammonia is converted to urea in the liver in a process called the urea cycle. The urea in the blood moves to the kidney where it is concentrated and excreted with urine. 

Solid NH4N03 is very hygroscopic (i.e., it picks up water from the air). Nonoxidizable drying agents such as clays are usually added to suppress this effect and the consequent caking. Calcium carbonate (chalk, crushed limestone) may be added to form a nonexplosive product with 26% N. Alternatively, ammonium nitrate may be marketed as an aqueous solution, also containing ammonia and urea. 

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