Showing papers on "Urea published in 2008"

Urea denaturation by stronger dispersion interactions with proteins than water implies a 2-stage unfolding

Abstract: The mechanism of denaturation of proteins by urea is explored by using all-atom microseconds molecular dynamics simulations of hen lysozyme generated on BlueGene/L Accumulation of urea around lysozyme shows that water molecules are expelled from the first hydration shell of the protein We observe a 2-stage penetration of the protein, with urea penetrating the hydrophobic core before water, forming a "dry globule" The direct dispersion interaction between urea and the protein backbone and side chains is stronger than for water, which gives rise to the intrusion of urea into the protein interior and to urea's preferential binding to all regions of the protein This is augmented by preferential hydrogen bond formation between the urea carbonyl and the backbone amides that contributes to the breaking of intrabackbone hydrogen bonds Our study supports the "direct interaction mechanism" whereby urea has a stronger dispersion interaction with protein than water

Microbial CaCO3 Precipitation: For the Production of Biocement

Abstract: The hydrolysis of urea by the widely distributed enzyme urease is special in that it is one of the few biologically occurring reactions that can generate carbonate ions without an associated production of protons. When this hydrolysis occurs in a calcium-rich environment, calcite (calcium carbonate) precipitates from solution forming a solid-crystalline material. The binding strength of the precipitated crystals is highly dependent on the rate of carbonate formation and under suitable conditions it is possible to control the reaction to generate hard binding calcite cement (or Biocement). The objective of this thesis was to develop an industrially suitable cost-effective microbial process for the production of urease active cells and investigate the potential for urease active cells to act as a catalyst for the production of Biocement. The biocementation capability of two suitable strains was compared. Sporosarcina pasteurii (formally Bacillus pasteurii) produced significantly higher levels of urease activity compared to Proteus vulgaris, however the level of urease activity was variable with respect to biomass suggesting that the enzyme was not constitutive as indicated by the literature, but subject to regulation. The environmental and physiological conditions for maximum urease activity in S. pasteurii were investigated and it was found that the potential urease capacity of the organism was very high (29 mM urea.min-1.OD-1) and sufficient for biocementation without additional processing (e.g. concentration, cell lysis). The regulation mechanism for S. pasteurii urease was not fully elucidated in this study, however it was shown that low specific urease activity was not due to depletion of urea nor due to the high concentrations of the main reaction product, ammonium. pH conditions were shown to have a regulatory effect on urease but it was evident that another co-regulating mechanism existed. Despite not fully exploiting the urease capability of S. pasteurii, sufficient urease activity to allow direct application of the enzyme without additional processing could still be achieved and the organism was considered suitable for biocementation. Urease was the most expensive component of the cementation process and cost-efficient production was desired, thus an economic growth procedure was developed for large-scale cultivation of S. pasteurii. The organism is a moderate alkaliphile (growth optimum pH 9.25) and it was shown that sufficient activity for biocementation could be cultivated in non-sterile conditions with a minimum of upstream and downstream processing. The cultivation medium was economised and expensive components were replace with a food-grade protein source and acetate, which lowered production costs by 95%. A high level of urease activity (21 mM urea hydrolysed.min-1) was produced in the new medium at a low cost ($0.20 (AUD) per L). The performance of urease in whole S. pasteurii cells was evaluated under biocementation conditions (i.e. presence of high concentrations of urea, Ca2+, NH4 +/NH3, NO3 - and Cl- ions). It was established that the rate of urea hydrolysis was not constant during cementation, but largely controlled by the external concentrations of urea and calcium, which constantly changed during cementation due to precipitation of solid calcium carbonate from the system. A simple model was generated that predicted the change in urea hydrolysis rate over the course of cementation. It was shown that whole cell S. pasteurii urease was tolerant to concentrations of up to 3 M urea and 2 M calcium, and the rate of urea hydrolysis was unaffected up to by 3 M ammonium. This allowed the controlled precipitation of up to 1.5 M CaCO3 within one treatment, and indicated that the enzyme was very stable inspite of extreme chemical conditions. A cost-efficient cementation procedure for the production of high cementation strength was developed. Several biocementation trials were conducted into order to optimise the imparted cementation strength by determining the effect of urea hydrolysis rate on the development of strength. It was shown that high cementation strength was produced at low urea hydrolysis rates and that the development of cementation strength was not linear over the course of the reaction but mostly occurred in the first few hours of the reaction. In addition, the whole cell bacterial enzyme had capacity to be immobilised in the cementation material and re-used to subsequent applications, offering a significant cost-saving to the process. An industry-sponsored trial was undertaken to investigate the effectiveness of Biocement for increasing in-situ strength and stiffness of two different sandy soils; (a) Koolschijn sand and (b) 90% Koolschijn sand mixed with 10% peat (Holland Veen). After biocementation treatment, Koolschijn sand indicated a shear strength of 1.8 MPa and a stiffness of 250 MPa, which represents an 8-fold and 3-fold respective improvement in strength compared to unconsolidated sand. Significantly lower strength improvements were observed in sand mixed with peat. In combination, trials of producing bacteria under economically acceptable conditions and cementation trials support the possibility of on-site production and in-situ application of large field applications.

Enhanced enzymatic hydrolysis of spruce by alkaline pretreatment at low temperature.

Abstract: Alkaline pretreatment of spruce at low temperature in both presence and absence of urea was studied. It was found that the enzymatic hydrolysis rate and efficiency can be significantly improved by the pretreatment. At low temperature, the pretreatment chemicals, either NaOH alone or NaOH-urea mixture solution, can slightly remove lignin, hemicelluloses, and cellulose in the lignocellulosic materials, disrupt the connections between hemicelluloses, cellulose, and lignin, and alter the structure of treated biomass to make cellulose more accessible to hydrolysis enzymes. Moreover, the wood fiber bundles could be broken down to small and loose lignocellulosic particles by the chemical treatment. Therefore, the enzymatic hydrolysis efficiency of untreated mechanical fibers can also be remarkably enhanced by NaOH or NaOH/urea solution treatment. The results indicated that, for spruce, up to 70% glucose yield could be obtained for the cold temperature pretreatment (-15 degrees C) using 7% NaOH/12% urea solution, but only 20% and 24% glucose yields were obtained at temperatures of 23 degrees C and 60 degrees C, respectively, when other conditions remained the same. The best condition for the chemical pretreatment regarding this study was 3% NaOH/12% urea, and -15 degrees C. Over 60% glucose conversion was achieved upon this condition.

Solubility of CO2 in a Choline Chloride + Urea Eutectic Mixture

Abstract: The solubility of CO2 in choline chloride + urea eutectic mixtures was determined at 313.15 K, 323.15 K, and 333.15 K under pressures up to 13 MPa. The mole ratios of choline chloride to urea selected were 1:1.5, 1:2, and 1:2.5. The Henry’s constants and enthalpy of solution of the gas were calculated from the solubility data. The solubility of CO2 in the mixtures increased with increasing pressure, and the solubility is more sensitive to pressure in the low-pressure range. The solubility of CO2 in the mixtures decreased with increasing temperature at all the pressures. The enthalpy of solution is negative at all conditions.

Reducing NH3, N2O and $${\text{NO}}_3^ - $$ –N losses from a pasture soil with urease or nitrification inhibitors and elemental S-amended nitrogenous fertilizers

Abstract: A 3-month field experiment comparing nitrogen (N) losses from and the agronomic efficiency of various N fertilizers was conducted on a sandy loam (Typic Hapludand) soil at Ruakura AgResearch farm, Hamilton, New Zealand during October to December 2003. Three replicates of seven treatments: urea, urea + the urease inhibitor N-(n-butyl) thiophosphoric triamide (trade name Agrotain), urea + Agrotain + elemental sulphur (S), urea + double inhibitor [DI; i.e., Agrotain + dicyandiamide (DCD)], diammonium phosphate (DAP), DAP + S, each applied at 150 kg N ha−1, and control (no N). After fertilizer application, soil ammonium ( $$ \operatorname{NH} ^{ + }_{4} $$ ) and nitrate ( $$ \operatorname{NO} ^{ - }_{3} $$ ) concentrations (7.5-cm soil depth), ammonia (NH3) volatilization, nitrate ( $$ \operatorname{NO} ^{ - }_{3} $$ ) leaching, nitrous oxide (N2O) emission, pasture dry matter, and N uptake were monitored at different timings. Urea applied with Agrotain or Agrotain + S delayed urea hydrolysis and released soil $$ \operatorname{NH} ^{ + }_{4} $$ at a slower rate than urea alone or urea + DI. Urea applied with DI increased NH3 volatilization by 29% over urea alone, while urea + Agrotain and urea + Agrotain + S reduced NH3 volatilization by 45 and 48%, respectively. Ammonia volatilization losses from DAP were lower than those from urea with or without inhibitors. Total reduction in $$ \operatorname{NO} ^{ - }_{3} $$ leaching losses for urea + DI and urea + Agrotain compared to urea alone were 89% and 47%, respectively. Application of S with urea + Agrotain reduced $$ \operatorname{NO} ^{ - }_{3} $$ leaching losses by an additional 6%. Nitrous oxide emissions were higher from the DAP and urea alone treatments. Urea applied with DI and urea + Agrotain reduced N2O emissions by 37 and 5%, respectively, over urea alone. Compared to urea alone, total pasture production increased by 20, 17, and 15% for urea + Agrotain + S, urea + Agrotain, and urea + DI treatments, respectively, representing 86, 71, and 64% increases in N response efficiency. Total N uptake in urea + Agrotain, urea + Agrotain + S, and urea + DI increased by 29, 22, and 20%, respectively, compared to urea alone. These results suggest that the combination of both urease and nitrification inhibitors may have the most potential to reduce N losses and improve pasture production in intensively grazed systems.

Synthesis of Mo and W carbide and nitride nanoparticles via a simple "urea glass" route.

Abstract: A simple, inexpensive, and versatile route for the synthesis of metal nitrides and carbides (such as Mo2N, Mo2C, W2N and WC) nanoparticles was set up. For the first time, metal carbides were obtained using urea as carbon-source. MoCl5 and WCl4 are in a first step contacted with alcohols and an appropriate amount of urea to form a polymer-like, glassy phase, which acts as the starting product for further conversions. Just by heating this phase it was possible to prepare either molybdenum and tungsten nitrides or carbides simply by changing the metal precursor/urea molar ratio. In this procedure, urea plays a double role as a nitrogen/carbon source and stabilizing agent (necessary for the nanoparticle dispersion). Molybdenum and tungsten nitride and carbides synthesized are almost pure and highly crystalline. Sizes estimated by WAXS range around 20 and 4 nm in diameter for Mo and W nitrides or carbides, respectively. The specific surface area was found between 10 and 80 m2/g, depending on the metal and the initial ratio of metal precursor to urea.

Chemical deactivation of V2O5/WO3–TiO2 SCR catalysts by additives and impurities from fuels, lubrication oils, and urea solution: I. Catalytic studies

Abstract: The influence of the combustion products of different lubrication oil additives (Ca, Mg, Zn, P, B, Mo) and impurities in Diesel fuel (K from raps methyl ester) or urea solution (Ca, K) on the activity and selectivity of vanadia-based SCR catalysts were investigated. Standard V2O5/WO3–TiO2 catalysts coated on metal substrates (400 cpsi) were impregnated with water soluble compounds of these elements and calcined at 400 and 550 °C, in order to investigate the chemical deactivation potential of different elements and combinations of them. It was found that potassium strongly reduced the adsorption equilibrium constant K N H 3 of ammonia. At small ammonia concentrations in the feed, only part of the active sites were covered with ammonia resulting in a reduced SCR reaction rate. At high ammonia concentrations, the surface coverage and SCR reaction rate increased, but high SCR activity at concurrent low ammonia emissions was impossible. Calcium caused less deactivation than potassium and did not affect the ammonia adsorption to the same extent, but it lowered the intrinsic SCR reaction rate. Moreover, deactivation by calcium was much reduced if counter-ions of inorganic acids were present (order of improvement: SO42− > PO43− > BO33−). Zinc was again less deactivating than calcium, but the positive effect of the counter-ions was weaker than in case of calcium. The degree of N2O production at T > 500 °C, which is typical for V2O5/WO3–TiO2 catalysts, was not influenced by the different compounds, except for molybdenum, which induced a small increase in N2O formation.

Effects of temperature and molecular weight on dissolution of cellulose in NaOH/urea aqueous solution

Abstract: Dissolution of cellulose having different viscosity-average molecular weight (M η ) in 7 wt%NaOH/12 wt%urea aqueous solution at temperature from 60 to −12.6°C was investigated with optical microscope, viscosity measurements and wide X-ray diffraction (WXRD). The solubility (Sa) of cellulose in NaOH/urea aqueous solution strongly depended on the temperature, and molecular weight. Their Sa values increased with a decrease in temperature, and cellulose having M η below 10.0 × 104 could be dissolved completely in NaOH/urea aqueous solution pre-cooled to −12.6°C. The activation energy of dissolution (Ea,s) of the cellulose dissolution was a negative value, suggesting that the cellulose solution state had lower enthalpy than the solid cellulose. The cellulose concentration in this system increased with a decrease of M η to achieve about 8 wt% for M η of 3.1 × 104. Moreover, cellulose having 12.7 × 104 could be dissolved completely in the solvent pre-cooled to −12.6°C as its crystallinity (χ c) decreased from 0.62 to 0.53. We could improve the solubility of cellulose in NaOH/urea aqueous system by changing M η , χ c and temperature. In addition, the zero-shear viscosity (η 0 ) at 0°C for the 4 wt% cellulose solution increased rapidly with an increase of M η , as a result of the enhancement of the aggregation and entanglement for the relatively long chains.

Ammonia volatilisation from urease inhibitor-treated urea applied to sugarcane trash blankets

Abstract: Legal restrictions from burning sugarcane prior to harvest are causing a sharp increase in acreage which is harvested as green cane. The presence of a thick sugarcane trash mulch left after harvest makes it difficult to incorporate fertilisers in the soil. Since large losses of ammonia may occur when urea is surface applied to trash, it is important to find ways to improve urea-N use efficiency. The urease inhibitor NBPT slows down urea hydrolysis and thus may help decrease ammonia losses. Ammonia traps were set up in seven sugarcane fields covered with trash and fertilised with ammonium sulfate or ammonium nitrate, urea, and NBPT-treated urea. All N fertilisers were surface-applied at rates of 80 or 100 kg N ha-1. Very little N was lost when ammonium nitrate or ammonium sulfate were used. However, volatilisation losses as ammonia from the urea treatments varied from 1% (rainy days after fertilisation) to 25% of the applied N. The percentage of reduction in volatilisation due to NBPT application ranged from 15% to 78% depending on the weather conditions during the days following application of N. Addition of NBPT to urea helped to control ammonia losses, but the inhibitor was less effective when rain sufficient to incorporate urea into the soil occurred only 10 to 15 days or latter after fertiliser application.

Rate and mode of application of the urease inhibitor N-(n-butyl) thiophosphoric triamide on ammonia volatilization from surface-applied urea

Abstract: A laboratory study evaluated the effect of rate (0, 100, 250, 500, 750 or 1000 mg/kg) and mode of application of the urease inhibitor N-(n-butyl) thiophosphoric triamide (nBTPT) (coating the urea granule, adding to the urea melt or adding to urea ammonium nitrate (UAN) solutions) on NH 3 volatilization from urea, at three temperatures (5, 15 and 25 °C), with four contrasting soil types. Daily ammonia loss was measured for up to 21 days after surface N application, using ventilated soil enclosures. Ammonia loss from unamended urea varied with soil type and temperature and ranged from 8.2 to 31.9% of the N applied. nBTPT was highly effective in lowering NH 3 volatilization from urea and in delaying the time of maximum rate of loss. The average % inhibition over all soils, temperatures and formulations was 61.2, 69.9, 74.2, 79.2 and 79.8% for the 100, 250, 500, 750 or 1000 mg/kg nBTPT concentration, respectively. The % inhibition with nBTPT was lower at 15 °C compared with at 5 or 25 °C and was lower in UAN solutions than in granular products. There was little difference between the melted and coated granular products in lowering NH 3 loss or in soil N transformations. The stability of nBTPT in urea products was dependent on its mode of application and on the storage temperature. Incorporating nBTPT in the urea melt produced a more homogeneous product with superior stability than coating the urea granule.

Physiological and Transcriptomic Aspects of Urea Uptake and Assimilation in Arabidopsis Plants

Abstract: Urea is the major nitrogen (N) form supplied as fertilizer in agriculture, but it is also an important N metabolite in plants. Urea transport and assimilation were investigated in Arabidopsis (Arabidopsis thaliana). Uptake studies using 15N-labeled urea demonstrated the capacity of Arabidopsis to absorb urea and that the urea uptake was regulated by the initial N status of the plants. Urea uptake was stimulated by urea but was reduced by the presence of ammonium nitrate in the growth medium. N deficiency in plants did not affect urea uptake. Urea exerted a repressive effect on nitrate influx, whereas urea enhanced ammonium uptake. The use of [15N]urea and [15N]ammonium tracers allowed us to show that urea and ammonium assimilation pathways were similar. Finally, urea uptake was less efficient than nitrate uptake, and urea grown-plants presented signs of N starvation. We also report the first analysis, to our knowledge, of Arabidopsis gene expression profiling in response to urea. Our transcriptomic approach revealed that nitrate and ammonium transporters were transcriptionally regulated by urea as well as key enzymes of the glutamine synthetase-glutamate synthase pathway. AtDUR3, a high-affinity urea transporter in Arabidopsis, was strongly up-regulated by urea. Moreover, our transcriptomic data suggest that other genes are also involved in urea influx.

The dissolution of microcrystalline cellulose in sodium hydroxide-urea aqueous solutions

Abstract: It has been reported that cellulose is better dissolved in NaOH-water when a certain amount of urea is added. In order to understand the mechanisms of this dissolution and the interactions between the components, the binary phase diagram of urea/water, the ternary urea/NaOH/water phase diagram and the influence of the addition of microcrystalline cellulose in urea/NaOH/water solutions were studied by DSC. Urea/water solutions have a simple eutectic behaviour with a eutectic compound formed by pure urea and ice (one urea per eight water moles), melting at −12.5 °C. In the urea/NaOH/water solutions, urea and NaOH do not interact, each forming their own eutectic mixtures, (NaOH + 5H2O, 4H2O) and (urea, 8H2O), as found in their binary mixtures. When the amount of water is too low to form the two eutectic mixtures, NaOH is attracting water at the expense of urea. In the presence of microcrystalline cellulose, the interactions between cellulose and NaOH/water are exactly the same as without urea, and urea is not interacting with cellulose. A tentative explanation of the role of urea is to bind water, making cellulose-NaOH links more stable.

Cells for bioartificial liver devices: the human hepatoma-derived cell line C3A produces urea but does not detoxify ammonia.

Abstract: Extrahepatic bioartificial liver devices should provide an intact urea cycle to detoxify ammonia. The C3A cell line, a subclone of the hepatoma-derived HepG2 cell line, is currently used in this context as it produces urea, and this has been assumed to be reflective of ammonia detoxification via a functional urea cycle. However, based on our previous findings of perturbed urea-cycle function in the non-urea producing HepG2 cell line, we hypothesized that the urea produced by C3A cells was via a urea cycle-independent mechanism, namely, due to arginase II activity, and therefore would not detoxify ammonia. Urea was quantified using (15)N-ammonium chloride metabolic labelling with gas chromatography-mass spectrometry. Gene expression was determined by real-time reverse transcriptase-PCR, protein expression by western blotting, and functional activities with radiolabelling enzyme assays. Arginase inhibition studies used N(omega)-hydroxy-nor-L-arginine. Urea was detected in C3A conditioned medium; however, (15)N-ammonium chloride-labelling indicated that (15)N-ammonia was not incorporated into (15)N-labelled urea. Further, gene expression of two urea cycle genes, ornithine transcarbamylase and arginase I, were completely absent. In contrast, arginase II mRNA and protein was expressed at high levels in C3A cells and was inhibited by N(omega)-hydroxy-nor-L-arginine, which prevented urea production, thereby indicating a urea cycle-independent pathway. The urea cycle is non-functional in C3A cells, and their urea production is solely due to the presence of arginase II, which therefore cannot provide ammonia detoxification in a bioartificial liver system. This emphasizes the continued requirement for developing a component capable of a full repertoire of liver function.

Phosphorylation of UT-A1 urea transporter at serines 486 and 499 is important for vasopressin-regulated activity and membrane accumulation

Abstract: The UT-A1 urea transporter plays an important role in the urine concentrating mechanism. Vasopressin (or cAMP) increases urea permeability in perfused terminal inner medullary collecting ducts and ...

N -carbamylglutamate Markedly Enhances Ureagenesis in N -acetylglutamate Deficiency and Propionic Acidemia as Measured by Isotopic Incorporation and Blood Biomarkers

Abstract: N-acetylglutamate (NAG) is an endogenous essential cofactor for conversion of ammonia to urea in the liver. Deficiency of NAG causes hyperammonemia and occurs because of inherited deficiency of its producing enzyme, NAG synthase (NAGS), or interference with its function by short fatty acid derivatives. N-carbamylglutamate (NCG) can ameliorate hyperammonemia from NAGS deficiency and propionic and methylmalonic acidemia. We developed a stable isotope 13C tracer method to measure ureagenesis and to evaluate the effect of NCG in humans. Seventeen healthy adults were investigated for the incorporation of 13C label into urea. [13C]urea appeared in the blood within minutes, reaching maximum by 100 min, whereas breath 13CO2 reached a maximum by 60 min. A patient with NAGS deficiency showed very little urea labeling before treatment with NCG and normal labeling thereafter. Correspondingly, plasma levels of ammonia and glutamine decreased markedly and urea tripled after NCG treatment. Similarly, in a patient with propionic acidemia, NCG treatment resulted in a marked increase in urea labeling and decrease in glutamine, alanine, and glycine. These results provide a reliable method for measuring the effect of NCG on nitrogen metabolism and strongly suggest that NCG could be an effective treatment for inherited and secondary NAGS deficiency.

Ammonia volatilization and ammonium accumulation from urea mixed with zeolite and triple superphosphate

Abstract: Ammonia volatilization from surface-applied urea fertilizer reduces N fertilizer use efficiency by crops. Beneficial formation of NH4 over NH3 leading to reduction of NH3 loss may be possible through addition of zeolite and acidic materials. The objective of this laboratory study was to evaluate the effect of four different urea-triple superphosphate (TSP)-zeolite mixtures on NH3 volatilization and NH4 and NO3 contents in soil, compared with surface-applied urea without additives. The soil was a sandy clay loam Typic Kandiudults (Bungor Series). The mixtures significantly reduced NH3 loss by 34 to 49% compared with urea (straight urea, 46% N) and larger reductions were obtained with higher rates of zeolite (0.75 and 1 g kg−1 of soil). All the mixtures of acidic P fertilizer and zeolite with urea significantly increased soil NH4 content but not NO3 content. The mixtures with acidic P fertilizer and zeolite also significantly increased soil-exchangeable Ca, K and Mg, and benefited the formation of ...

Lignin and Ethylcellulose as Polymers in Controlled Release Formulations of Urea

Abstract: Lignin and ethylcellulose (EC) have been used for the preparation of controlled release (CR) formulations of urea. The lignin matrixes were prepared by mixing the urea with kraft lignin (UL) under melting conditions. They were also crushed and sieved to obtain granules of size between 0.5–1, 1–2, 2–3 and 3–5 mm. The coated urea granules were produced in a Wurster-type fluidized-bed equipment, using an ethanolic solution of EC on two different polymer levels. Having researched the encapsulation efficiency (EE) and the homogeneity of the CR formulations, kinetic-release experiments were carried out in water. A high EE was reached, it oscillated between 95.12% for the system coated with 20% of EC and 97.18% for the 1 mm < d < 2 mm UL system. The rate of urea release from CR granules diminished in all cases in relation to nonformulated urea, being the latter completely dissolved in less than 0.5 h, but it took at least 48 h to release the 90% of urea from the EC coated formulations. Using an empirical equation, the time taken for 50% of the active ingredient to be released into water (T50) was calculated. From the analysis of the T50 values, we can deduce that the release rate of urea can be controlled mainly by selecting the granule size for lignin CR systems and changing the thickness of the coating film for EC coated granules. The variation order of T50 values, UL (0.5 mm < d < 1.0 mm) < UL (1.0 mm < d < 2.0 mm) < UL (2.0 mm < d < 3.0 mm) < UL (3.0 mm < d < 5.0 mm) < UEC10 < UEC20, showed that the presence of EC in formulations retarded the release of urea in relation to those prepared with lignin. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Acid Gas Permeation Behavior Through Poly(Ester Urethane Urea) Membrane

Abstract: Permeation behavior of pure gases (CO2, N2, CH4) and ternary gas mixtures of CO2, CH4, and H2S through a poly(ester urethane urea) membrane was investigated at different pressures, temperatures, and feed compositions. Permeances of CO2, CH4, and H2S through the membrane were determined at temperatures of 35, 45, and 55 °C, and pressures of 10, 20, and 30 bar. Effects of temperature, pressure, and stage cut on the permeability of gases through the membrane were experimentally studied. Since the main objective of this study was to evaluate the aforesaid membrane for its ability to remove acid gas application, the measured selectivity of poly(ester urethane urea) in this study was compared with that of some other polymeric membranes at nearly the same operating conditions. Maximum selectivities of 43 and 16 were measured for H2S/CH4 and CO2/CH4, respectively. Average permeances of 95 and 45 GPU for H2S and CO2 were achieved, respectively.

Potentiometric urea biosensor based on BSA embedded surface modified polypyrrole film

Abstract: A potentiometric biosensor based on bovine serum albumin (BSA) embedded surface modified polypyrrole has been developed for the quantitative estimation of urea in aqueous solution. The enzyme, urease (Urs), was covalently linked to free amino groups present over the BSA embedded modified surface of the conducting polypyrrole film electrochemically deposited onto an indium–tin-oxide (ITO) coated glass plate. The biosensor has been characterized by UV–visible, infrared spectroscopy and SEM. Potentiometric and spectrophotometric response of the enzyme electrode (Urs/BSA-PPy/ITO) were measured as a function of urea concentration in Tris–HCl buffer (pH 7.0). It has been found that the electrode responds to low urea concentration with wider range of detection. The electrode showed a linear response range of 6.6 × 10−6 to 7.5 × 10−4 M urea. The response time is about 70–90 s reaching to a 95% steady-state potential value and 75% of the enzyme activity is retained for about 2 months. These results indicate an efficient covalent linkage of enzyme to free amino groups of the BSA molecules over the surface of polypyrrole film, which leads to high enzyme loading, an increased lifetime stability of the electrode and an improved wide range of detection of low urea concentration in aqueous solution.