Showing papers on "Urea published in 2005"

Rapid dissolution of cellulose in LiOH/urea and NaOH/urea aqueous solutions

Abstract: Rapid dissolution of cellulose in LiOH/urea and NaOH/urea aqueous solutions was studied systematically. The dissolution behavior and solubility of cellulose were evaluated by using (13)C NMR, optical microscopy, wide-angle X-ray diffraction (WAXD), FT-IR spectroscopy, DSC, and viscometry. The experiment results revealed that cellulose having viscosity-average molecular weight ((overline) M eta) of 11.4 x 104 and 37.2 x 104 could be dissolved, respectively, in 7% NaOH/12% urea and 4.2% LiOH/12% urea aqueous solutions pre-cooled to -10 degrees C within 2 min, whereas all of them could not be dissolved in KOH/urea aqueous solution. The dissolution power of the solvent systems was in the order of LiOH/urea > NaOH/urea >> KOH/urea aqueous solution. The results from DSC and (13)C NMR indicated that LiOH/urea and NaOH/urea aqueous solutions as non-derivatizing solvents broke the intra- and inter-molecular hydrogen bonding of cellulose and prevented the approach toward each other of the cellulose molecules, leading to the good dispersion of cellulose to form an actual solution.

Using blood urea nitrogen to predict nitrogen excretion and efficiency of nitrogen utilization in cattle, sheep, goats, horses, pigs, and rats

Abstract: The objectives of this study were to evaluate the potential for using blood urea N concentration to predict urinary N excretion rate, and to develop a mathematical model to estimate important variables of N utilization for several different species of farm animals and for rats. Treatment means (n = 251) from 41 research publications were used to develop mathematical relationships. There was a strong linear relationship between blood urea N concentration (mg/100 mL) and rate of N excretion (g x d(-1) x kg BW(-1)) for all animal species investigated. The N clearance rate of the kidney (L of blood cleared of urea x d(-1) x kg BW(-1)) was greater for pigs and rats than for herbivores (cattle, sheep, goats, horses). A model was developed to estimate parameters of N utilization. Driving variables for the model included blood urea N concentration (mg/100 mL), BW (kg), milk production rate (kg/d), and ADG (kg/d), and response variables included urinary N excretion rate (g/d), fecal N excretion rate (g/d), rate of N intake (g/d), and N utilization efficiency (N in milk and gain per unit of N intake). Prediction errors varied widely depending on the variable and species of animal, with most of the variation attributed to study differences. Blood urea N concentration (mg/100 mL) can be used to predict relative differences in urinary N excretion rate (g/d) for animals of a similar type and stage of production within a study, but is less reliable across animal types or studies. Blood urea N concentration (mg/100 mL) can be further integrated with estimates of N digestibility (g/g) and N retention (g/d) to predict fecal N (g/d), N intake (g/d), and N utilization efficiency (grams of N in milk and meat per gram of N intake). Target values of blood urea N concentration (mg/100 mL) can be backcalculated from required dietary N (g/d) and expected protein digestibility. Blood urea N can be used in various animal species to quantify N utilization and excretion rates.

Mechanism of deposition of gold precursors onto TiO2 during the preparation by cation adsorption and deposition–precipitation with NaOH and urea

Abstract: Gold on TiO2 prepared by cation adsorption (CA) and deposition–precipitation with urea (DP urea) and NaOH (DP NaOH) were characterized by various techniques during the preparation in order to determine the nature of the species deposited and the chemical phenomena occurring during these preparations. In the case of cationic adsorption of the [Au(en)2] 3+ complex, we showed that the preparation has to be performed at room temperature to avoid the decomposition of the complex and the reduction of gold. In such a way, small gold particles are obtained after calcination, but the gold loading is low. The methods of deposition–precipitation (DP NaOH and DP urea) involve both the deposition of a gold(III) species on the TiO2 surface, but the nature of these species is different. For the DP NaOH, we propose that [AuCl(OH)3] � , the main species present at the pH 8 of the preparation, reacts with hydroxyl groups of the TiO2 surface, and forms a grafted hydroxy-gold compound. This may explain the limited amount of gold deposited on TiO2 by this method. For the DP urea method, all the gold present in solution is deposited on the TiO2 surface as a gold(III) precipitate, which is not gold(III) hydroxide, but an amorphous compound containing nitrogen, oxygen and carbon. This compound arises from a reaction between the gold precursor and the products of decomposition of urea. The metallic gold particles obtained after calcination exhibit a decreasing size when the time of DP urea increases. We propose that the progressive increase of pH, due to urea decomposition at 80 8C, results in changes in the surface charge density of the gold precipitate particles, and leads to a fragmentation of the particles. # 2005 Elsevier B.V. All rights reserved.

Urea and urine concentrating ability: new insights from studies in mice.

Abstract: Urea is the most abundant solute in the urine in humans (on a Western-type diet) and laboratory rodents. It is far more concentrated in the urine than in plasma and extracellular fluids. This conce...

Visible-light active N-doped TiO2 prepared by heating of titanium hydroxide and urea

Abstract: Nitrogen-doped titanium dioxide (TiO 2 ) powders were prepared by the heating of titanium hydroxide with urea The samples had a relatively larger specific surface area of 92 ± 2 m 2 g −1 and showed visible-light photocatalytic activity of about 550 nm

Preparation and Properties of a Slow-Release Membrane-Encapsulated Urea Fertilizer with Superabsorbent and Moisture Preservation

Abstract: A slow-release membrane-encapsulated urea fertilizer with a superabsorbent and moisture preservation was prepared by cross-linked starch (the first layer), acrylic acid (AA) and acrylamide (the second layer; AM), ammonia, borax, urea, and so on. The variable affecting the water absorbency was investigated and optimized. The water absorbency of the product was 80 times its own weight if it was allowed to swell in tap water at room temperature for 80 min. Elemental analysis results showed that the product contained 26.74% nitrogen. The water retention property of the product and the slow-release behavior of nitrogen in the product were also investigated, and the results showed that the product not only had good slow-release property but also excellent water retention capacity. This will efficiently improve the utilization of fertilizer and water resources at the same time.

Electrospun biocomposite nanofibers for urea biosensing

Abstract: Urease E.C.3.5.1.5 acts as a catalyst in the hydrolysis of urea to ammonia and carbon dioxide. Presence of this enzyme can increase the rate of reaction by 10 14 . Urea levels are vital in medical diagnosis, environmental and bioindustrial analysis. This paper presents an innovative technique for enzyme immobilization. Nanocomposite fibers of urease and polyvinylpyrrolidone (PVP) were prepared by the electrospinning technique. The non-woven mat formed has potential as a urea biosensor. Its advancements over prior technology are faster response time, sensitivity to lower concentrations of urea, and a more versatile design.

Exhaust gas purification device of internal combustion engine

Abstract: A catalyst (22) suitable for reduction of the NOx in an exhaust gas by ammonia in the presence of excess oxygen is arranged in the exhaust passage (18, 21) of an internal combustion engine. An aqueous urea solution is fed through a flow control valve (33) to the inside of the exhaust passage (21) upstream of the catalyst (22). When the temperature of the catalyst (22) is low, a large amount of the aqueous urea solution is fed to make the urea contained in the aqueous urea solution be stored in the catalyst (22). When the engine is accelerated and the temperature of the catalyst (22) rises, ammonia is released at a little at a time from the inside of the catalyst (22) and the NOx in the exhaust gas is reduced by the released ammonia.

Influence of dietary crude protein concentration and source on potential ammonia emissions from beef cattle manure.

Abstract: Emissions of ammonia, as well as other gases and particulates, to the atmosphere are a growing concern of livestock producers, the general public, and regulators. The concentration and ruminal degradability of CP in beef cattle diets may affect urinary and fecal excretion of N and thus may affect ammonia emissions from beef cattle feed yards. To determine the effects of dietary CP concentration and degradability on potential ammonia emissions, 54 steers were randomly assigned to nine dietary treatments in a 3 x 3 factorial arrangement of treatments. Treatments consisted of three dietary CP concentrations (11.5, 13, and 14.5%) and three supplemental urea:cottonseed meal ratios (100:0, 50:50, and 0:100 of supplemental N). Steers were confined to tie stalls, and feces and urine excreted were collected and frozen after approximately 30, 75, and 120 d on feed. One percent of daily urine and feces excretion were added to polyethylene chambers containing 1,550 g of soil. Chambers were sealed, and ammonia emissions were trapped in an acid solution for 7 d using a vacuum system. As the protein concentration in the diet increased from 11.5 to 13%, in vitro daily ammonia emissions increased (P < 0.01) 60 to 200%, due primarily to increased urinary N excretion. As days on feed increased, in vitro ammonia emissions also increased (P < 0.01). Potential ammonia losses were highly correlated (P < 0.01) to urinary N (r2 = 0.69), urinary urea-N (r2 = 0.58) excretion, serum urea-N concentration (r2 = 0.52), and intake of degradable protein N (r2 = 0.23). Although dietary composition can affect daily ammonia losses, daily ammonia emissions must be balanced with effects on animal performance to determine optimal protein concentrations and forms in the diet.

The burden borne by urease.

Abstract: At the active site of urease, urea undergoes nucleophilic attack by water, whereas urea decomposes in solution by elimination of ammonia so that its rate of spontaneous hydrolysis is unknown Quantum mechanical simulations have been interpreted as indicating that urea hydrolysis is extremely slow, compared with other biological reactions proceeding spontaneously, and that urease surpasses all other enzymes in its power to enhance the rate of a reaction We tested that possibility experimentally by examining the hydrolysis of 1,1,3,3-tetramethylurea, from which elimination cannot occur In neutral solution at 25 degrees C, the rate constant for the uncatalyzed hydrolysis of tetramethylurea is 42 x 10-12 s-1, which does not differ greatly from the rate constants observed for the uncatalyzed hydrolysis of acetamide (51 x 10-11 s-1) or N,N-dimethylacetamide (18 x 10-11 s-1) under the same conditions We estimate that the proficiency of urease as a catalyst, (kcat/Km)/knon, is 8 x 1017 M-1, slightly higher than the values for other metalloenzymes (carboxypeptidase b and cytidine deaminase) that catalyze the hydrolysis of similar bonds

Synthesis and characterization of segmented copoly(ether urea)s with uniform hard segments

Abstract: Employing protective group strategy and novel isocyanate chemistry, segmented copoly(ether urea)s with uniform hard segments were prepared. Amine-terminated poly(tetrahydrofuran) served as the soft segment of these polymers. The size of the hard segments and the number of urea groups it contains were varied systematically, and their influence on the properties was investigated. The strength of hydrogen bonding between the urea groups in monodisperse hard segments containing exactly 1 to exactly 4 urea groups was studied by infrared spectroscopy and compared with materials containing polydisperse hard segments. The strength of hydrogen bonding in polymers possessing exactly two urea groups per hard segment resulted in an optimal balance between excellent mechanical properties and good processability and solubility.

Renal phenotype of UT-A urea transporter knockout mice

Abstract: The urea transporters UT-A1 and UT-A3 mediate rapid transepithelial urea transport across the inner medullary collecting duct (IMCD). In a previous study, using a new mouse model in which both UTA1 and UT-A3 were genetically deleted from the IMCD (UT-A1/3 −/− mice), we investigated the role of these transporters in the function of the renal inner medulla. Here we report a series of studies investigating more generally the renal phenotype of UT-A1/3 −/− mice. Pathological screening revealed abnormalities in both the testis (increased size) and kidney (decreased size and vascular congestion) of UT-A1/3 −/− mice. Total urinary nitrate and nitrite excretion rates in UT-A1/3 −/− mice were more than double those in wildtype mice. Total renal blood flow was not different between UT-A1/3 −/− and wildtype mice, but underwent a greater percentage decrease in response to NG-Nitro-L-arginine Methyl Ester Hydrochloride (L-NAME) infusion. Whole kidney glomerular filtration rate was not different in UT-A1/3 −/− mice compared to controls and underwent a similar increase in response to a greater dietary protein intake. Fractional urea excretion was markedly elevated in UT-A1/3 −/− mice on a 40% protein diet, reaching 102.4 ± 8.8% of the filtered load, suggesting that there may be active urea secretion along the renal tubule. Although there was a marked urinary concentrating defect in UT-A1/3 −/− mice, there was no decrease in aquaporin-2 or -3 expression. Furthermore, although urea accumulation in the inner medulla was markedly attenuated, there was no decrease in NaCl concentration in tissue from outer medulla or 2 levels of the inner medulla.

Urea nitrogen salvage mechanisms and their relevance to ruminants, non-ruminants and man

Abstract: Maintaining a correct balance of N is essential for life. In mammals, the major sources of N in the diet are amino acids and peptides derived from ingested proteins. The immediate endproduct of mammalian protein catabolism is ammonia, which is toxic to cells if allowed to accumulate. Therefore, amino acids are broken down in the liver as part of the ornithine-urea cycle, which results in the formation of urea - a highly soluble, biochemically benign molecule. Mammals cannot break down urea, which is traditionally viewed as a simple waste product passed out in the urine. However, urea from the bloodstream can pass into the gastrointestinal tract, where bacteria expressing urease cleave urea into ammonia and carbon dioxide. The bacteria utilise the ammonia as an N source, producing amino acids and peptides necessary for growth. Interestingly, these microbial products can be reabsorbed back into the host mammalian circulation and used for synthetic processes. This entire process is known as 'urea nitrogen salvaging' (UNS). In this review we present evidence supporting a role for this process in mammals - including ruminants, non-ruminants and man. We also explore the possible mechanisms involved in UNS, including the role of specialised urea transporters.

Cryoprotection by urea in a terrestrially hibernating frog.

Abstract: The role of urea as a balancing osmolyte in osmotic adaptation is well known, but this 'waste product' also has myriad other functions in diverse taxa. We report that urea plays an important, previously undocumented role in freezing tolerance of the wood frog (Rana sylvatica), a northern woodland species that hibernates terrestrially in sites where dehydration and freezing may occur. Wood frogs inhabiting an outdoor enclosure accumulated urea to 65 mmol l-1 in autumn and early winter, when soil moisture was scarce, but subsequently urea levels fell to approximately 2 mmol l-1 as the availability of environmental water increased. Laboratory experiments showed that hibernating R. sylvatica can accumulate at least 90 mmol l-1 urea under relatively dry, warm conditions. During experimental freezing, frogs synthesized glucose but did not accumulate additional urea. Nevertheless, the concentrations of urea and glucose in some tissues were similar. We tested urea's efficacy as a cryoprotectant by measuring lysis and lactate dehydrogenase (LDH) leakage in samples of R. sylvatica erythrocytes frozen/thawed in the presence of physiological levels of urea or other osmolytes. In conferring protection against freeze/thaw damage, urea was comparable to glycerol and as good as or better than glucose, cryoprotectants found in freeze-tolerant frogs and other animals. Urea treatment also improved the viability of intact tissues frozen in vitro, as demonstrated by post-thaw measures of metabolic activity and LDH leakage. Collectively, our findings suggest that urea functions both as an osmoprotectant and a cryoprotectant in terrestrially hibernating amphibians.

Potentiometric enzyme electrode for urea determination using immobilized urease in poly(vinylferrocenium) film

Abstract: A new enzyme electrode for the determination of urea was developed by immobilizing urease in poly(vinylferrocenium) (PVF+) matrix. A PVF+ClO4− film was coated on Pt electrode at +0.7 V by electrooxidation of poly(vinylferrocene) in metylene chloride containing 0.1 M tetrabutylammonium perchlorate (TBAP). The enzyme modified electrode PVF+E− was prepared by anion-exchange in an enzyme solution in 1.0 mM phosphate buffer at pH 7.0. FTIR spectroscopy was used to identify PVF+ClO4−, and PVF+E−. UV spectroscopy was also used to prove the enzyme immobilization. The effects of polymeric film thickness, concentration of enzyme solution, immobilization time of the enzyme, pH and temperature of the medium, concentration of the buffer solution and possible interferents on the measured potential values were investigated. The potentiometric enzyme electrode developed in this study provided linearity to urea in the 5 × 10−5 to 1 × 10−1 M urea concentration range. The detection limit under the optimum working conditions was determined as 5 × 10−6 M for urea. The enzyme electrode was found to be stable for 24 days. The apparent Michaelis-Menten consant (KM app) value and the activation energy, Ea, of this immobilized enzyme system were found to be 4.48 × 10−5 M and 4.97 kcal mol−1 for urea, respectively.

Urea Host Monomers for Stoichiometric Molecular Imprinting of Oxyanions

Abstract: A series of urea-based vinyl monomers was synthesized and investigated for their ability to function as polymerizable hosts for the molecular imprinting of N-Z-d- or l-glutamic acid in polar media (DMSO or DMF). The monomers were synthesized in one step from a polymerizable isocyanate and a nonpolymerizable amine or vice versa, with yields typically over 70%. Prior to polymerization their solution binding properties vis-a-vis tetrabutylammonium benzoate in DMSO were investigated by 1H NMR, UV−vis and fluorescence monitored titrations. The affinities of the urea monomers for benzoate depended upon the substitution pattern of the urea, with all diaryl ureas exhibiting high affinity. EDMA-based imprinted polymers prepared in DMF or DMSO against Z-d-(or l)-glutamic acid using 2 equiv of the urea monomer and 2 equiv of base were able to recognize the imprinted dianion as well as larger molecules containing the glutamic acid substructure. The affinity, reflected in liquid chromatography retention data, correlat...

Impaired urea accumulation in the inner medulla of mice lacking the urea transporter UT-A2.

Abstract: Urea transporter UT-A2, the major urea transporter of the thin descending limb of the loop of Henle in short loop nephrons, has been implicated in urea recycling in the medulla, thereby producing concentrated urine. To investigate the physiological role of UT-A2 in vivo, we generated UT-A2-selective knockout mice by deleting the UT-A2 promoter. Western analysis, immunohistochemistry, and quantitative reverse transcription-PCR were used to confirm the specific deletion of UT-A2 with preservation of other UT-A transporters. Compared to wild-type mice, differences in the urine outputs of UT-A2(-/-) mice consuming a normal protein diet (20% protein) were not observed under normal conditions or with dehydration. Likewise, impairment of urea accumulation in the inner medulla of UT-A2(-/-) mice was not observed. On a low-protein diet (4% protein), however, significantly reduced maximal urine osmolality was observed in dehydrated UT-A2(-/-) mice compared to wild-type littermates (2,500 mosmol versus 3,450 mosmol, respectively). A significant reduction in urea accumulation in the inner medulla was also observed in UT-A2(-/-) mice; however, differences in Na(+) and Cl(-) accumulation were not observed. Thus, UT-A2 is important for maintaining a high concentration of urea in the inner medulla when urea supply to the kidney is limited.

Synthesis of dimethyl carbonate from urea and methanol over zno

Abstract: The synthesis of dimethyl carbonate (DMC) from urea and methanol was investigated, to explore the catalysts and reaction conditions. Among the catalysts, ZnO showed the highest catalytic activity toward DMC synthesis. Based on the experimental investigation, the reaction conditions over ZnO for a batch process were optimized, and the highest DMC yield attained (based on urea) was ∼30%, because of the presence of side reactions. In addition, the reusability test indicated that ZnO had high stability.

Urea analysis in coastal waters: comparison of enzymatic and direct methods

Abstract: This study presents a comparison of two existing methods for the determination of urea concentration in seawater. These methods are referred to here as the enzymatic method, which is based on the use of the enzyme urease, and the direct method, which is based on the reaction of urea with diacetylmonoxime. A room temperature modification of the direct method was adapted for a single reagent and both the enzymatic and the direct method were tested in artificially prepared solutions and in natural samples from estuaries and shelf waters. We were particularly interested in the effects of salinity and humic acids on the accuracy of both methods. The effect of humic acids was negligible. In contrast, salinity ~34 caused a 15% to 40% underestimation in the urea concentrations measured by the enzymatic method and the degree of underestimation varied among enzyme batches. Urea concentrations corrected for the salt effect should, however, be considered estimations, as other factors also interfered with the enzymatic method in natural samples. The direct method as modified in this study presented a low detection limit (0.04 µM urea-N) and high precision (standard deviation: 0.02 µM urea-N; coefficient of variation: 1.1%) comparable to those of the enzymatic method. The direct method was more accurate and less salinity dependent than the enzymatic method. As urea levels could have been underestimated by the enzymatic method, our findings support previous conclusions regarding the important role of urea in the nitrogen cycle and its link with some harmful algal bloom phenomena.

UT-B is expressed in bovine rumen: potential role in ruminal urea transport.

Abstract: The UT-A (SLC14a2) and UT-B (SLC14a1) genes encode a family of specialized urea transporter proteins that regulate urea movement across plasma membranes. In this report, we describe the structure o...