Showing papers on "Urea published in 2011"

Quantifying why urea is a protein denaturant, whereas glycine betaine is a protein stabilizer.

Abstract: To explain the large, opposite effects of urea and glycine betaine (GB) on stability of folded proteins and protein complexes, we quantify and interpret preferential interactions of urea with 45 model compounds displaying protein functional groups and compare with a previous analysis of GB. This information is needed to use urea as a probe of coupled folding in protein processes and to tune molecular dynamics force fields. Preferential interactions between urea and model compounds relative to their interactions with water are determined by osmometry or solubility and dissected using a unique coarse-grained analysis to obtain interaction potentials quantifying the interaction of urea with each significant type of protein surface (aliphatic, aromatic hydrocarbon (C); polar and charged N and O). Microscopic local-bulk partition coefficients Kp for the accumulation or exclusion of urea in the water of hydration of these surfaces relative to bulk water are obtained. Kp values reveal that urea accumulates moderately at amide O and weakly at aliphatic C, whereas GB is excluded from both. These results provide both thermodynamic and molecular explanations for the opposite effects of urea and glycine betaine on protein stability, as well as deductions about strengths of amide NH—amide O and amide NH—amide N hydrogen bonds relative to hydrogen bonds to water. Interestingly, urea, like GB, is moderately accumulated at aromatic C surface. Urea m-values for protein folding and other protein processes are quantitatively interpreted and predicted using these urea interaction potentials or Kp values.

A green slow-release fertilizer composition based on urea-modified hydroxyapatite nanoparticles encapsulated wood

Abstract: In this paper we describe a strategy for sustained release of nitrogen into the soil. Specifically, ureamodified hydroxyapatite nanoparticles were encapsulated under pressure into cavities of the soft wood of Gliricidia sepium. Nitrogen release of the nanofertilizer composition was studied using soil from three elevations in Sri Lanka (pH 4.2, 5.2 and 7) and compared with that of a commercial fertilizer. The nanofertilizer showed an initial burst and a subsequent slow-release even on day 60 compared to the commercial fertilizer, which released heavily early followed by the release of low and non-uniform quantities until around day 30.

Yield and yield components of upland rice as influenced by nitrogen sources

Abstract: Ammonium sulfate and urea are main sources of nitrogen (N) for annual crop production in developing countries. Two greenhouse experiments were conducted using ammonium sulfate and urea as N sources for upland rice grown on a Brazilian Oxisol. The N rates used were 0, 50, 100, 150, 3000, and 400 kg N kg−1 of soil. Yield and yield components were significantly increased in a quadratic fashion with increasing N rate. Ammonium sulfate X urea interaction was significant for grain yield, shoot dry matter yield, panicle number, plant height and root dry weight, indicating a different response magnitude of these plant parameters to two sources of N. Based on regression equation, maximum grain yield was achieved with the application of 380 mg N kg−1 by ammonium sulfate and 271 mg N kg−1 by urea. Grain yield and yield components were reduced at higher rates of urea (>300 mg kg N) but these plant parameters’ responses to ammonium sulfate at higher rates was constant. In the intermediate N rate range (125 to 275 mg k...

Evaluation of preservation methods for improving biogas production and enzymatic conversion yields of annual crops

Abstract: The use of energy crops and agricultural residues is expected to increase to fulfil the legislative demands of bio-based components in transport fuels. Ensiling methods, adapted from the feed sector, are suitable storage methods to preserve fresh crops throughout the year for, for example, biogas production. Various preservation methods, namely ensiling with and without acid addition for whole crop maize, fibre hemp and faba bean were investigated. For the drier fibre hemp, alkaline urea treatment was studied as well. These treatments were also explored as mild pretreatment methods to improve the disassembly and hydrolysis of these lignocellulosic substrates. The investigated storage treatments increased the availability of the substrates for biogas production from hemp and in most cases from whole maize but not from faba bean. Ensiling of hemp, without or with addition of formic acid, increased methane production by more than 50% compared to fresh hemp. Ensiling resulted in substantially increased methane yields also from maize, and the use of formic acid in ensiling of maize further enhanced methane yields by 16%, as compared with fresh maize. Ensiled faba bean, in contrast, yielded somewhat less methane than the fresh material. Acidic additives preserved and even increased the amount of the valuable water-soluble carbohydrates during storage, which affected most significantly the enzymatic hydrolysis yield of maize. However, preservation without additives decreased the enzymatic hydrolysis yield especially in maize, due to its high content of soluble sugars that were already converted to acids during storage. Urea-based preservation significantly increased the enzymatic hydrolysability of hemp. Hemp, preserved with urea, produced the highest carbohydrate increase of 46% in enzymatic hydrolysis as compared to the fresh material. Alkaline pretreatment conditions of hemp improved also the methane yields. The results of the present work show that ensiling and alkaline preservation of fresh crop materials are useful pretreatment methods for methane production. Improvements in enzymatic hydrolysis were also promising. While all three crops still require a more powerful pretreatment to release the maximum amount of carbohydrates, anaerobic preservation is clearly a suitable storage and pretreatment method prior to production of platform sugars from fresh crops.

Microwave-assisted hydrothermal synthesis of nanosized α-Fe2O3 for catalysts and adsorbents

Abstract: Nanosized α-Fe2O3 powder was synthesized by a microwave-assisted hydrothermal reaction of Fe(NO3)3 and urea at 120 °C for 30 min. The products were characterized by X-ray diffraction, transmission electron microscopy, BET measurements, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The catalytic performance of α-Fe2O3 was studied for the oxidation of CO and 2-propanol to CO2, and the adsorption properties were investigated for the removal of As(III) in water treatment. Uniform α-Fe2O3 particles about 5.0 nm in diameter were formed with a surface area of around 173.0 m2 g–1. When 0.1 g of α-Fe2O3 powder worked as a catalyst, CO was oxidized to CO2 over 120 °C and completely transformed to CO2 at 170 °C, and 2-propanol was fully oxidized to CO2 at 350 °C. The adsorption capacity for As(III) reached 51.8 mg g–1 at room temperature. This work facilitates the preparation of nanosized α-Fe2O3 materials with excellent catalytic and adsorption performance.

Efficiency of urease and nitrification inhibitors in reducing ammonia volatilization from diverse nitrogen fertilizers applied to different soil types and wheat straw mulching

Abstract: BACKGROUND: Some authors suggest that the absence of tillage in agricultural soils might have an influence on the efficiency of nitrogen applied in the soil surface. In this study we investigate the influence of no-tillage and soil characteristics on the efficiency of a urease inhibitor (N-(n-butyl)thiophosphoric triamide, NBPT) and a nitrification inhibitor (diciandiamide, DCD) in decreasing ammonia volatilization from urea and ammonium nitrate (AN), respectively. RESULTS: The results indicate that ammonia volatilization in soils amended with urea was significantly higher than in those fertilized with AN. Likewise, the main soil factors affecting ammonia volatilization from urea are clay and sand soil contents. While clay impedes ammonia volatilization, sand favours it. The presence of organic residues on soil surface (no-tillage) tends to increase ammonia volatilization from urea, although this fact depended on soil type. The presence of NBPT in urea fertilizer significantly reduced soil ammonia volatilization. This action of NBPT was negatively affected by acid soil pH and favoured by soil clay content. CONCLUSION: The presence of organic residues on soil surface amended with urea increased ammonia volatilization, and was particularly high in sandy compared with clay soils. Application of NBPT reduced ammonia volatilization although its efficiency is reduced in acid soils. Concerning AN fertilization, there were no differences in ammonia volatilization with or without DCD in no-tillage soils. Copyright © 2011 Society of Chemical Industry

Breath ammonia and trimethylamine allow real-time monitoring of haemodialysis efficacy

Abstract: Non-invasive monitoring of breath ammonia and trimethylamine using Selected-ion-flow-tube mass spectroscopy (SIFT-MS) could provide a real-time alternative to current invasive techniques. Breath ammonia and trimethylamine were monitored by SIFT-MS before, during and after haemodialysis in 20 patients. In 15 patients (41 sessions), breath was collected hourly into Tedlar bags and analysed immediately (group A). During multiple dialyses over 8 days, five patients breathed directly into the SIFT-MS analyser every 30 min (group B). Pre- and post-dialysis direct breath concentrations were compared with urea reduction, Kt/V and creatinine concentrations. Dialysis decreased breath ammonia, but a transient increase occurred mid treatment in some patients. Trimethylamine decreased more rapidly than reported previously. Pre-dialysis breath ammonia correlated with pre-dialysis urea in group B (r(2) = 0.71) and with change in urea (group A, r(2) = 0.24; group B, r(2) = 0.74). In group B, ammonia correlated with change in creatinine (r(2) = 0.35), weight (r(2) = 0.52) and Kt/V (r(2) = 0.30). The ammonia reduction ratio correlated with the urea reduction ratio (URR) (r(2) = 0.42) and Kt/V (r(2) = 0.38). Pre-dialysis trimethylamine correlated with Kt/V (r(2) = 0.21), and the trimethylamine reduction ratio with URR (r(2) = 0.49) and Kt/V (r(2) = 0.36). Real-time breath analysis revealed previously unmeasurable differences in clearance kinetics of ammonia and trimethylamine. Breath ammonia is potentially useful in assessment of dialysis efficacy.

Urea hydrolysis and lateral and vertical movement in the soil: effects of urease inhibitor and irrigation

Abstract: A glasshouse-based study was conducted to investigate the effect of urease inhibitor N-(n-butyl) thiophosphoric triamide (‘Agrotain’) and irrigation on urea hydrolysis and its movement in a Typic Haplustept silt loam soil (in 72 repacked soil cores). Half (36) of these cores were adjusted to soil moisture contents of 80% field capacity (FC) and the remaining 36 cores to 50% FC. Granular urea with or without Agrotain was applied at a rate equivalent to 100 kg N ha−1. There were three replicates to these two sets of soil cores. After 1 day of treatment application, soil cores of the 50% FC were adjusted to 80% FC by applying surface irrigation. Twelve pots were destructively sampled at each day after 1, 2, 3, 4, 7 and 10 days of treatment application to determine urea hydrolysis and its lateral and vertical movement in different soil layers. Agrotain-treated urea delayed urea hydrolysis during the first 7 days after its application. This delay in urea hydrolysis caused by Agrotain enabled added urea, which is uncharged, to move away from the surface soil layer to the sub-surface soil layer both vertically and laterally. In contrast, most urea hydrolysed to soil NH4+ within 2 days of its application. Irrigation after 1 day resulted in further urea movement both laterally and vertically from the surface soil layer (0–10 mm) to the sub-soil layer (30–50 mm) in Agrotain-treated urea. These results suggest that Agrotain delayed urea hydrolysis and allowed more time for rainfall or irrigation to move added urea from the surface layer to sub-soil layers where it is likely to make good contact with plant roots. This distribution of urea in the rooting zone has the potential to enhance N use efficiency and minimize N losses associated with ammonia volatilization from surface-applied urea.

Volatilização de amônia do solo após a aplicação de ureia convencional ou com inibidor de urease

Abstract: Ammonia volatilization is an important process of N loss which decreases the use efficiency of N by plants when urea is applied on the soil surface. To overcome this problem, some chemical compounds were mixed with urea to inhibit the urease action. The purpose of this study was to compare applications of an alternative fertilizer with urease inhibitor to reduce ammonia volatilization with conventional urea, under certain environmental and soil conditions. Four experiments were carried out in 2007 and 2008, under laboratory conditions, with samples of a Humic Haplumbrept. The treatments varied according to each experiment in terms of soil conditions, such as pH (4.0, 5.5, 6.3 and 6.8), soil water content (5, 10 or 20 % moisture), temperature (18 or 35 oC), aside from the fertilizer physical state (solid or liquid) and application method (over the surface or soil-incorporated). The experimental units consisted of plastic trays into which 12 kg of soil (dry basis) were filled in a 15 cm layer. Ammonia gas traps were installed across the soil surface. Frequent measurements were performed during the first 28 days of soil-fertilizer incubation. The peak of ammonia volatilization from the soil occurred in the first week after the application of traditional urea, and two or three days later for urea with urease inhibitor. Ammonia loss was not always higher from conventional than from treated urea, nor from solid than from liquid fertilizers. Ammonia volatilization increased with increases in soil pH, temperature and N rate and was lower at the lowest (5 %) and highest (20 %) soil moisture content. For surface-applied fertilizers, the maximum daily N loss rate was 14 kg ha-1 and the total cumulative loss ranged from 2 to 50 % of the applied N, depending mainly on the physical state of the fertilizer, temperature and on soil moisture. Soil incorporation of urea fertilizers was the best option to minimize ammonia volatilization in all treatments.

A protic ionic liquid attenuates the deleterious actions of urea on α-chymotrypsin.

Abstract: We present a biocompatible ionic liquid, triethyl ammonium acetate (TEAA), that attenuates the denaturation action of a non-ionic chaotrope, urea, on the industrially relevant proteolytic enzyme α-chymotrypsin.

Effects of high environmental ammonia on branchial ammonia excretion rates and tissue Rh-protein mRNA expression levels in seawater acclimated Dungeness crab Metacarcinus magister

Abstract: In the present study of the marine Dungeness crabs Metacarcinus magister , the long term effects of high environmental ammonia (HEA) on hemolymph ammonia and urea concentrations, branchial ammonia excretion rates and mRNA expression levels of the crustacean Rh-like ammonia transporter (RhMM), H + -ATPase (subunit B), Na + /K + -ATPase (α-subunit) and Na + /H + -exchanger (NHE) were investigated. Under control conditions, the crabs’ hemolymph exhibited a total ammonia concentration of 179.3 ± 14.5 μmol L −1 , while urea accounted for 467.2 ± 33.5 μmol L −1 , respectively. Both anterior and posterior gills were capable of excreting ammonia against a 16-fold inwardly directed gradient. Under control conditions, mRNA expression levels of RhMM were high in the gills in contrast to very low expression levels in all other tissues investigated, including the antennal gland, hepatopancreas, and skeletal muscle. After exposure to 1 mmol L −1 NH 4 Cl, hemolymph ammonia increased within the first 12 h to ca. 500 µmol L −1 and crabs were able the keep this hemolymph ammonia level for at least 4 days. During this initial period, branchial RhMM and H + -ATPase (subunit B) mRNA expression levels roughly doubled. After 14 days of HEA exposure, hemolymph ammonia raised up to environmental levels, whereas urea levels increased by ca. 30%. At the same time, whole animal ammonia and urea excretion vanished. Additionally, branchial RhMM, H + -ATPase, Na + /K + -ATPase and NHE mRNA levels decreased significantly after long term HEA exposure, whereas expression levels of RhMM in the internal tissues increased substantially. Interestingly, crabs acclimated to HEA showed no mortality even after 4 weeks of HEA exposure. This suggests that M. magister possesses a highly adaptive mechanism to cope with elevated ammonia concentrations in its body fluids, including an up-regulation of an Rh-like ammonia transporter in the internal tissues and excretion or storage of waste nitrogen in a so far unknown form.