Showing papers on "Urea published in 2014"

Dissolution of cellulose in aqueous NaOH/urea solution: role of urea

Abstract: Urea can improve the solubility and stability of cellulose in aqueous alkali solution, while its role has not come to a conclusion. To reveal the role of urea in solution, NMR was introduced to investigate the interaction between urea and the other components in solution. Results from chemical shifts and longitudinal relaxation times show that: (1) urea has no strong direct interaction with cellulose as well as NaOH; (2) urea does not have much influence on the structural dynamics of water. Urea may play its role through van der Waals force. It may accumulate on the cellulose hydrophobic region to prevent dissolved cellulose molecules from re-gathering. The driving force for the self-assembly of cellulose and urea molecules might be hydrophobic interaction. In the process of cellulose dissolution, OH− breaks the hydrogen bonds, Na+ hydrations stabilize the hydrophilic hydroxyl groups and urea stabilizes the hydrophobic part of cellulose.

Effect of Water on the Density, Viscosity, and CO2 Solubility in Choline Chloride/Urea

Abstract: To study the effect of water on the properties of choline chloride (ChCl)/urea mixtures (1:2 on a molar basis), the density and viscosity of ChCl/urea (1:2) with water were measured at temperatures from 298.15 K to 333.15 K at atmospheric pressure, the CO2 solubility in ChCl/urea (1:2) with water was determined at 308.2 K, 318.2 K, and 328.2 K and at pressures up to 4.5 MPa. The results show that the addition of water significantly decreases the viscosity of ChCl/urea (1:2), whereas the effects on their density and CO2 solubility are much weaker. The CO2 solubility in ChCl/urea (1:2) with water was represented with the Nonrandom-Two-Liquid Redlich–Kwong (NRTL-RK) model. The excess molar volume and excess molar activation energy were further determined. The CO2 absorption enthalpy was calculated and dominated by the CO2 dissolution enthalpy, and the magnitude of the CO2 dissolution enthalpy decreases with the increase of water content.

How a protein can remain stable in a solvent with high content of urea: insights from molecular dynamics simulation of Candida antarctica lipase B in urea : choline chloride deep eutectic solvent

Abstract: Deep eutectic solvents (DESs) are utilized as green and inexpensive alternatives to classical ionic liquids. It has been known that some of DESs can be used as solvent in the enzymatic reactions to obtain very green chemical processes. DESs are quite poorly understood at the molecular level. Moreover, we do not know much about the enzyme microstructure in such systems. For example, how some hydrolase can remain active and stable in a deep eutectic solvent including 9 M of urea? In this study, the molecular dynamics of DESs as a liquid was simulated at the molecular level. Urea : choline chloride as a well-known eutectic mixture was chosen as a model DES. The behavior of the lipase as a biocatalyst was studied in this system. For comparison, the enzyme structure was also simulated in 8M urea. The thermal stability of the enzyme was also evaluated in DESs, water, and 8M urea. The enzyme showed very good conformational stability in the urea : choline chloride mixture with about 66% urea (9 M) even at high temperatures. The results are in good agreement with recent experimental observations. In contrast, complete enzyme denaturation occurred in 8M urea with only 12% urea in water. It was found that urea molecules denature the enzyme by interrupting the intra-chain hydrogen bonds in a “direct denaturation mechanism”. However, in a urea : choline chloride deep eutectic solvent, as a result of hydrogen bonding with choline and chloride ions, urea molecules have a low diffusion coefficient and cannot reach the protein domains. Interestingly, urea, choline, and chloride ions form hydrogen bonds with the surface residues of the enzyme which, instead of lipase denaturation, leads to greater enzyme stability. To the best of our knowledge, this is the first study in which the microstructural properties of a macromolecule are examined in a deep eutectic solvent.

The Emerging Role of Urease as a General Microbial Virulence Factor

Abstract: Urea is generated in humans following the breakdown of amino acids and is evenly distributed throughout the body, including in the central nervous system, subcutaneous adipose tissue, blood serum, and epithelial lining fluid [1], [2]. Various pathogenic microbes are able to utilise urea as a nitrogen source through the activity of the enzyme urease that converts urea into ammonia and carbamic acid, with the spontaneous hydrolysis of carbamic acid to carbonic acid generating a further ammonia molecule. CH4N2O+H2O→NH3+CH3NO2 CH3NO2+H2O→NH3+H2CO3 Under physiological conditions the proton of carbonic acid dissociates, and the ammonia molecules become protonated to form ammonium, causing an increase in local pH that can interfere with host function. The role of urease in the virulence of some bacterial pathogens is well established; however, more recent studies are beginning to highlight the function of urease during human fungal infections, suggesting that this enzyme has a wide role during microbial infection.

Urea degradation by electrochemically generated reactive chlorine species: products and reaction pathways.

Abstract: This study investigated the transformation of urea by electrochemically generated reactive chlorine species (RCS) Solutions of urea with chloride ions were electrolyzed using a bismuth doped TiO2 (BiOx/TiO2) anode coupled with a stainless steel cathode at applied anodic potentials (Ea) of either +22 V or +30 V versus the normal hydrogen electrode In NaCl solution, the current efficiency of RCS generation was near 30% at both potentials In divided cell experiments, the pseudo-first-order rate of total nitrogen decay was an order of magnitude higher at Ea of +30 V than at +22 V, presumably because dichlorine radical (Cl2(-)·) ions facilitate the urea transformation primary driven by free chlorine Quadrupole mass spectrometer analysis of the reactor headspace revealed that N2 and CO2 are the primary gaseous products of the oxidation of urea, whose urea-N was completely transformed into N2 (91%) and NO3(-) (9%) The higher reaction selectivity with respect to N2 production can be ascribed to a low operational ratio of free available chlorine to N The mass-balance analysis recovered urea-C as CO2 at 77%, while CO generation most likely accounts for the residual carbon In light of these results, we propose a reaction mechanism involving chloramines and chloramides as reaction intermediates, where the initial chlorination is the rate-determining step in the overall sequence of reactions

Molecular Dynamics Simulation of Aqueous Urea Solution: Is Urea a Structure Breaker?

Abstract: An aqueous solution of urea is a very important mixture of biological relevance because of the definitive role of urea as protein denaturant at high concentrations. There has been an extended debate over the years on urea’s influence on the structure of water. On the basis of a variety of analysis methods employed, urea has been described as a structure-breaker, a structure-maker, or as neutral toward water structure. Using molecular dynamics simulation and a nearest neighbor approach of analyzing water structure, we present here a detailed analysis of the effect of urea on water structure. By carefully choosing the nearest neighbors, allowing urea also to be a neighbor of a reference water molecule, we have conclusively shown that urea does not break the local tetrahedral structure of water even at high concentrations. A slight change in the distribution of tetrahedral order parameters as a function of urea concentration has been shown to be a result of change in the proportions of n-hydrogen-bonded wate...

Effects of nitrogen fertilizer on the acidification of two typical acid soils in South China

Abstract: A laboratory incubation under constant temperature and humidity was conducted to estimate the impacts of nitrogen (N) fertilizers on the acidification of two acid soils (Plinthudult and Paleudalfs) in south China. The experiment had three treatments, i.e., control (CK), addition of urea (U), and addition of ammonium sulfate (AS). We measured soil pH, nitrate (NO3 −), ammonium (NH4 +), exchangeable hydrogen ion (H+), and aluminum ion (Al3+) concentrations at various intervals during the 90 days of incubation. Soil buffering capacity (pHBC) was also measured at the end of the experiment. The application of N fertilizers resulted in soil acidification. The U treatment caused greater acidification of the Plinthudult soil than the AS treatment, while there were no differences between U and AS treatments on the acidification of the Paleudalfs. At the end of the trial, the pHBC of Plinthudult in AS treatment was greater than that in CK and U treatments, which may be due to the buffering system of NH4 + and NH4OH. However, the pHBC of Paleudalfs was unchanged between treatments. The dynamics of exchangeable H+ and Al3+ corresponded to that of soil pH. Correlation analysis showed that both soil exchangeable H+ and soil exchangeable Al3+ were significantly related to soil pH. Application of urea and ammonium sulfate caused acidification in both soils and increased soil exchangeable Al3+ and H+ concentrations in the Paleudalfs. The application of urea increased exchangeable Al3+, and ammonium sulfate increased pHBC in the Plinthudult.

Overview of Urea and Creatinine

Abstract: Urea, commonly referred to as blood urea nitrogen (BUN) when measured in the blood, is a product of protein metabolism. BUN is considered a non-protein nitrogenous (NPN) waste product. Amino acids derived from the breakdown of protein are deaminated to produce ammonia. Ammonia is then converted to urea via liver enzymes. Therefore, the concentration of urea is dependent on protein intake, the body’s capacity to catabolize protein, and adequate excretion of urea by the renal system. 1 Urea accounts for the majority (up to 80%-90%) of the NPNs excreted by the body. The body’s dependency on the renal system to excrete urea makes it a useful analyte to evaluate renal function. An increase in BUN can be the result of a diet that is high in protein content or decreased renal excretion.

An Eco-Friendly Slow-Release Urea Fertilizer Based on Waste Mulberry Branches for Potential Agriculture and Horticulture Applications

Abstract: Development of a compound fertilizer for agricultural and horticultural applications remains an important challenge in the field of biomass synthesis on account of its raw material source and biodegradability. In this work, an eco-friendly slow-release urea fertilizer (SRUF) employing mulberry branch-g-poly(acrylic acid-co-acrylamide) (MB/P(AA-co-AM)) superabsorbent was prepared. The MB/P(AA-co-AM) superabsorbent was blended with sodium alginate, urea, and CaCl2 solutions to accomplish this synthesis process. The synthesis conditions of the SRUF and its application performance were examined. The results showed that under the optimal synthesis conditions the water absorbency and water absorbency rate of the SRUF reached 420.0 g/g and 60.0 (g/g)/min in deionized water, respectively. The water retention of the SRUF was 7.2 wt % after 25 d. The urea release in deionized water and soil both exhibited a typical slow release behavior. A degradation rate of 32.0 wt % was attained for the SRUF while it was buried ...

Intermolecular Interactions and 3D Structure in Cellulose–NaOH–Urea Aqueous System

Abstract: The dissolution of cellulose in NaOH/urea aqueous solution at low temperature is a key finding in cellulose science and technology. In this paper, 15N and 23Na NMR experiments were carried out to clarify the intermolecular interactions in cellulose/NaOH/urea aqueous solution. It was found that there are direct interactions between OH– anions and amino groups of urea through hydrogen bonds and no direct interaction between urea and cellulose. Moreover, Na+ ions can interact with both cellulose and urea in an aqueous system. These interactions lead to the formation of cellulose–NaOH–urea–H2O inclusion complexes (ICs). 23Na relaxation results confirmed that the formation of urea–OH– clusters can effectively enhance the stability of Na+ ions that attracted to cellulose chains. Low temperature can enhance the hydrogen bonding interaction between OH– ions and urea and improve the binding ability of the NaOH/urea/H2O clusters that attached to cellulose chains. Cryo-TEM observation confirmed the formation of cell...

Excretory nitrogen metabolism and defence against ammonia toxicity in air-breathing fishes.

Abstract: With the development of air-breathing capabilities, some fishes can emerge from water, make excursions onto land or even burrow into mud during droughts. Air-breathing fishes have modified gill morphology and morphometry and accessory breathing organs, which would tend to reduce branchial ammonia excretion. As ammonia is toxic, air-breathing fishes, especially amphibious ones, are equipped with various strategies to ameliorate ammonia toxicity during emersion or ammonia exposure. These strategies can be categorized into (1) enhancement of ammonia excretion and reduction of ammonia entry, (2) conversion of ammonia to a less toxic product for accumulation and subsequent excretion, (3) reduction of ammonia production and avoidance of ammonia accumulation and (4) tolerance of ammonia at cellular and tissue levels. Active ammonia excretion, operating in conjunction with lowering of ambient pH and reduction in branchial and cutaneous NH₃ permeability, is theoretically the most effective strategy to maintain low internal ammonia concentrations. NH₃ volatilization involves the alkalization of certain epithelial surfaces and requires mechanisms to prevent NH₃ back flux. Urea synthesis is an energy-intensive process and hence uncommon among air-breathing teleosts. Aestivating African lungfishes detoxify ammonia to urea and the accumulated urea is excreted following arousal. Reduction in ammonia production is achieved in some air-breathing fishes through suppression of amino acid catabolism and proteolysis, or through partial amino acid catabolism leading to alanine formation. Others can slow down ammonia accumulation through increased glutamine synthesis in the liver and muscle. Yet, some others develop high tolerance of ammonia at cellular and tissue levels, including tissues in the brain. In summary, the responses of air-breathing fishes to ameliorate ammonia toxicity are many and varied, determined by the behaviour of the species and the nature of the environment in which it lives.

High Resolution $^{13}$ C MRI With Hyperpolarized Urea: In Vivo $T_{2}$ Mapping and $^{15}$ N Labeling Effects

Abstract: 13C steady state free precession (SSFP) magnetic resonance imaging and effective spin-spin relaxation time (T2) mapping were performed using hyperpolarized [13C] urea and [13 C,15N2] urea injected intravenously in rats. 15N labeling gave large T2 increases both in solution and in vivo due to the elimination of a strong scalar relaxation pathway. The T2 increase was pronounced in the kidney, with [13 C,15 N2] urea giving T2 values of 6.3±1.3 s in the cortex and medulla, and 11±2 s in the renal pelvis. The measured T2 in the aorta was 1.3±0.3 s. [13C] urea showed shortened T2 values in the kidney of 0.23±0.03 s compared to 0.28±0.03 s measured in the aorta. The enhanced T2 of [13C,15N2] urea was utilized to generate large signal enhancement by SSFP acquisitions with flip angles approaching the fully refocused regime. Projection images at 0.94 mm in-plane resolution were acquired with both urea isotopes, with [13C,15 N2] urea giving a greater than four-fold increase in signal-to-noise ratio over [13C] urea.

pH-switchable electrochemical sensing platform based on chitosan-reduced graphene oxide/concanavalin a layer for assay of glucose and urea.

Abstract: A facile and effective electrochemical sensing platform for the detection of glucose and urea in one sample without separation was developed using chitosan-reduced graphene oxide (CS-rGO)/concanavalin A (Con A) as a sensing layer. The CS-rGO/Con A with pH-dependent surface net charges exhibited pH-switchable response to negatively charged Fe(CN)63–. The principle for glucose and urea detection was essentially based on in situ pH-switchable enzyme-catalyzed reaction in which the oxidation of glucose catalyzed by glucose oxidase or the hydrolyzation of urea catalyzed by urease resulted in a pH change of electrolyte solution to give different electrochemical responses toward Fe(CN)63–. It was verified by cyclic voltammograms, differential pulse voltammograms, and electrochemical impedance spectroscopy. The resistance to charge transfer or amperometric current changed proportionally toward glucose concentration from 1.0 to 10.0 mM and urea concentration from 1.0 to 7.0 mM. On the basis of human serum experime...

Fabrication and characterisation of nanoporous zeolite based N fertilizer

Abstract: A laboratory study was undertaken to improve the nitrogen (N) use efficiency of urea using microporous natural zeolite (Z) and nanoporous zeolite (NZ) as substrate. The fertilizer composite was prepared under ambient conditions by impregnation urea in adsorbents. Z and nanoporous-zeolite measuring a dimension of 794, 87 nm were used for this study. The commercial urea fertilizer and adsorbents were blended or fused at varying w/w ratios of 1:1 to 1:10 using simple liquid immersion with hydrothermal technique. The 1:1 ratio of natural zeolite: urea and NZ: urea registered the highest total N content of 18.5 and 28%, respectively. The adsorbents and fabricated fertilizers such as zeourea (ZU) and nano-zeourea (NZU) of 1: 1 ratios were characterized using particle size analyzer, zeta potential, X-ray diffraction, FT-IR, Raman spectroscopy, and SEM with EDS besides release pattern of N. The data revealed that, the N release from the urea blended with NZ (1:1) was up to 48 days while the conventional Z - urea (1:1) mix was up to 34 day and the N release ceased to exist in urea within 4 days under ambient conditions. This suggests that, nanoporous zeolite based on N fertilizer (NZU) can be used as alternate strategy to improve the N use efficiency in crop production systems. Key words: Nanoporous zeolite, Natural zeolite, Nano-fertilizers, Nitrogen, Slow release N fertilizers.

Hyperammonemia due to urea cycle disorders: a potentially fatal condition in the intensive care setting

Abstract: Disorders of the urea cycle are secondary to a defect in the system that converts ammonia into urea, resulting in accumulation of ammonia and other products. This results in encephalopathy, coma, and death if not recognized and treated rapidly. Late-onset urea cycle disorders may be precipitated by acute disease and can be difficult to recognize because patients are already ill. Diagnosis of urea cycle disorders is based on clinical suspicion and determination of blood ammonia in suspected patients with neurological symptoms in the intensive care setting. Treatment is based on the removal of ammonia by dialysis or hemofiltration, reduction of the catabolic state, abolishment of nitrogen administration, and use of pharmacological nitrogen scavenging agents.

Competitive interactions between methane- and ammonia-oxidizing bacteria modulate carbon and nitrogen cycling in paddy soil

Abstract: . Pure culture studies have demonstrated that methanotrophs and ammonia oxidizers can both carry out the oxidation of methane and ammonia. However, the expected interactions resulting from these similarities are poorly understood, especially in complex, natural environments. Using DNA-based stable isotope probing and pyrosequencing of 16S rRNA and functional genes, we report on biogeochemical and molecular evidence for growth stimulation of methanotrophic communities by ammonium fertilization, and that methane modulates nitrogen cycling by competitive inhibition of nitrifying communities in a rice paddy soil. Pairwise comparison between microcosms amended with CH4, CH4+Urea, and Urea indicated that urea fertilization stimulated methane oxidation activity 6-fold during a 19-day incubation period, while ammonia oxidation activity was significantly suppressed in the presence of CH4. Pyrosequencing of the total 16S rRNA genes revealed that urea amendment resulted in rapid growth of Methylosarcina-like MOB, and nitrifying communities appeared to be partially inhibited by methane. High-throughput sequencing of the 13C-labeled DNA further revealed that methane amendment resulted in clear growth of Methylosarcina-related MOB while methane plus urea led to an equal increase in Methylosarcina and Methylobacter-related type Ia MOB, indicating the differential growth requirements of representatives of these genera. An increase in 13C assimilation by microorganisms related to methanol oxidizers clearly indicated carbon transfer from methane oxidation to other soil microbes, which was enhanced by urea addition. The active growth of type Ia methanotrops was significantly stimulated by urea amendment, and the pronounced growth of methanol-oxidizing bacteria occurred in CH4-treated microcosms only upon urea amendment. Methane addition partially inhibited the growth of Nitrosospira and Nitrosomonas in urea-amended microcosms, as well as growth of nitrite-oxidizing bacteria. These results suggest that type I methanotrophs can outcompete type II methane oxidizers in nitrogen-rich environments, rendering the interactions among methane and ammonia oxidizers more complicated than previously appreciated.

Recovering urea from human urine by bio-sorption onto Microwave Activated Carbonized Coconut Shells: Equilibrium, kinetics, optimization and field studies

Abstract: Microwave Activated Carbonized Coconut Shell (MACCS) was used to recover urea from human urine. Batch adsorption studies were conducted to evaluate the effect of initial adsorbate concentration (25%–100%), contact time, carbon loading (1–3 g) and shaking speed (150–200 rpm) on the removal of urea at 30 °C. Microwave activation was performed at 180 W (microwave output power) for 10 min. The sorption data were fitted to Langmuir, Freundlich, Tempkin, Flory–Huggins and Dubinin–Radushkevich isotherm models. Results showed that the maximum monolayer adsorption capacity of the MACCS powder was 256.41 mg g−1. The Flory–Huggins model was found to best describe the urea uptake process since it demonstrated the minimum deviations from the experimental data. The kinetic data was fitted to pseudo-first-order, pseudo-second-order and intra-particle diffusion models, and was found to follow closely the pseudo-first order kinetic model. Based on the Central Composite Rotary Design, a five factor interaction model and a quadratic model were respectively developed to correlate the adsorption variables to the adsorption capacity. Field studies were conducted to determine the percentage biomass increase and relative agronomic effectiveness for soil treated with the urea adsorbed MACCS powder. Microwave activated carbonized coconut shell was shown to be a promising adsorbent for recovery and removal of urea from human urine solutions.

Phenylalanine-Based Poly(ester urea): Synthesis, Characterization, and in vitro Degradation

Abstract: A new class of l-phenylalanine-based poly(ester urea)s (PEU) was developed that possess tunable mechanical properties and degradation rates. Our preliminary data have shown that 1,6-hexanediol-l-phenylalanine-based poly(ester urea)s possess an elastic modulus nearly double that of poly(lactic acid). The data in this article detail the synthesis of a series of l-phenylalanine-based poly(ester urea)s possessing a variation in diol chain length and how these subtle structural differences influence the mechanical properties and in vitro biodegradation rates. The mechanical data span a range of values that overlaps with several currently clinically available degradable polymers. Increasing the diol chain lengths increases the amount of flexible segment in the chemical structure, which results in reduced elastic modulus values and increased values of elongation at break. The l-phenylalanine-based poly(ester urea)s also exhibited a diol length dependent degradation process that varied between 1 and 5% over 16 we...

Microalgae growth on concentrated human urine.

Abstract: In this study, for the first time, a microalga was grown on non-diluted human urine The essential growth requirements for the species Chlorella sorokiniana were determined for different types of human urine (fresh, hydrolysed, male and female) Batch experimental results using microtiter plates showed that both fresh and synthetic urine supported rapid growth of this species, provided additional trace elements (Cu, Fe, Mn, and Zn) were added When using hydrolysed urine instead of fresh urine, additional magnesium had to be added as it precipitates during hydrolysis of urea C sorokiniana was able to grow on non-diluted urine with a specific growth rate as high as 0104 h−1 under light-limited conditions (105 μmol photons m−2 s−1), and the growth was not inhibited by ammonium up to a concentration of 1,400 mg NH4 +-N L−1 The highest growth rate on human urine was as high as 0158 h−1 Because it was demonstrated that concentrated urine is a rich and good nutrient source for the production of microalgae, its application for a large-scale economical and sustainable microalgae production for biochemicals, biofuels and biofertilizers becomes feasible

Nitrogen Source and Rate Effects on Irrigated Corn Yields and Nitrogen-Use Efficiency

Abstract: Nitrogen rate studies were conducted under furrow-irrigated corn (Zea mays L.) production on a silty clay soil to compare granular urea with polymer-coated urea (PCU) and stabilized urea (SU, contains urease and nitrification inhibitors) effects on corn yields, plant N uptake, and N use efficiency. Polymer-coated urea had a yield advantage over urea 2 (continuous corn) of 3 yr at N rates below maximum yield, which resulted in greater economic returns with PCU (4–14%) at N rates from 168 to 280 kg N ha –1 . The SU fertilizer had no yield or economic advantage over urea. Grain and stover yields and N uptake increased with increasing N rate for all N sources. Expressing grain yields from all N sources as a linear-plateau function of N rate showed that yields were maximized at 14.3 Mg ha –1 at an N rate of 254 kg N ha –1 or available N level (soil NO 3 –N plus fertilizer N) of 295 kg N ha –1 . Nitrogen recovery efficiency (RE) tended not to vary with N rate, with no differences between SU and urea but greater RE (19%) with PCU than urea under continuous corn. Fertilizer N use efficiency did not vary with N rate but was greater for PCU (36%) than for urea (32%) under continuous corn. In contrast to SU, PCU provided grain yield and potential economic advantages over urea under continuous corn production at N rates below those needed with urea for maximum grain yield.

Urea Uptake and Carbon Fixation by Marine Pelagic Bacteria and Archaea during the Arctic Summer and Winter Seasons

Abstract: How Arctic climate change might translate into alterations of biogeochemical cycles of carbon (C) and nitrogen (N) with respect to inorganic and organic N utilization is not well understood. This study combined 15N uptake rate measurements for ammonium, nitrate, and urea with 15N- and 13C-based DNA stable-isotope probing (SIP). The objective was to identify active bacterial and archeal plankton and their role in N and C uptake during the Arctic summer and winter seasons. We hypothesized that bacteria and archaea would successfully compete for nitrate and urea during the Arctic winter but not during the summer, when phytoplankton dominate the uptake of these nitrogen sources. Samples were collected at a coastal station near Barrow, AK, during August and January. During both seasons, ammonium uptake rates were greater than those for nitrate or urea, and nitrate uptake rates remained lower than those for ammonium or urea. SIP experiments indicated a strong seasonal shift of bacterial and archaeal N utilization from ammonium during the summer to urea during the winter but did not support a similar seasonal pattern of nitrate utilization. Analysis of 16S rRNA gene sequences obtained from each SIP fraction implicated marine group I Crenarchaeota (MGIC) as well as Betaproteobacteria, Firmicutes, SAR11, and SAR324 in N uptake from urea during the winter. Similarly, 13C SIP data suggested dark carbon fixation for MGIC, as well as for several proteobacterial lineages and the Firmicutes. These data are consistent with urea-fueled nitrification by polar archaea and bacteria, which may be advantageous under dark conditions.

General Liquid-crystal droplets produced by microfluidics for urea detection

Abstract: pH-sensitive 4-cyano-4′-pentylbiphenyl (5CB) droplets were produced for urea detection by coating with poly(acrylicacid-b-4-cyanobiphenyl-4-oxyundecylacrylate) (PAA-b-LCP) and covalently immobilizing urease on the PAA chains on the 5CB droplets using microfluidics. The functionalized 5CB droplets detected urea based on a bipolar-to-radial orientational change of the droplets observed by polarized optical microscopy using crossed polarizers. The detection limit was as low as 3 mM with a response time of 180 s. Urine was evaluated as a real sample for urea prescreening. This new and sensitive liquid crystal droplet-based urea biosensor has the merits of facile visual detection and is prospectively useful for urea prescreening for human subjects.