Urea Residues Research Articles

Stimuli-Responsive Oligourea Molecular Films.

We have designed and synthesized a helical cysteamine-terminated oligourea foldamer composed of ten urea residues featuring side carboxyl and amine groups. The carboxyl group is located in proximity to the C-terminus of the oligourea and hence at the negative pole of the helix dipole. The amine group is located close to the N-terminus and hence at the positive pole of the helix dipole. Beyond the already remarkable dipole moment inherent in oligourea 2.5 helices, the incorporation of additional charges originating from the carboxylic and amine groups is supposed to impact the overall charge distribution along the molecule. These molecules were self-assembled into monolayers on a gold substrate, allowing us to investigate the influence of an electric field on these polar helices. By applying surface-enhanced infrared reflection-absorption spectroscopy, we proved that molecules within the monolayers tend to reorient themselves more vertically when a negative bias is applied to the surface. It was also found that surface-confined oligourea molecules affected by the external electric field tend to rearrange the electron density at urea groups, leading to the stabilization of the resonance structure with charge transfer character. The presence of the external electric field also affected the nanomechanical properties of the oligourea films, suggesting that molecules also tend to reorient in the ambient environment without an electrolyte solution. Under the same conditions, the helical oligourea displayed a robust piezoresponse, particularly noteworthy given the slender thickness of the monolayer, which measured approximately 1.2 nm. This observation demonstrates that thin molecular films composed of oligoureas may exhibit stimulus-responsive properties. This, in turn, may be used in nanotechnology systems as actuators or functional films, enabling precise control of their thickness in the range of even fractions of nanometers.

Molecular clips with spatially proximal urea residues for efficient transmembrane co-transport of H+/Cl- ions.

We report the design of bis(urea) functionalized amphiphilic molecular clips viz. 1a-1e to achieve efficient transmembrane co-transport of H+/Cl- ions. The most promising molecule 1a demonstrated a low nanomolar EC50 value (6.96 nM) to co-transport H+/Cl- ions via a carrier-mediated pathway and showed selective toxicity against cancerous HeLa cells as a result.

De novo designed self-assembling helicomimetic lipooligoureas with antibacterial activity

The overuse of antibiotics has led to a rise in infections caused by multidrug-resistant bacteria, resulting in a need for new antibacterial compounds with different modes of action. In this paper, we describe a new class of compounds called lipooligoureas, which are foldamer-based mimetics of antimicrobial lipopeptides. The lipooligoureas consist of an acyl chain connected to the N-terminus of an oligourea head group that exhibits a well-defined 2.5-helix secondary structure, which is further stabilized by the attachment of the lipophilic chain to the oligourea moiety. These compounds meet the established criteria for membranolytic compounds by possessing an amphiphilic structure that promotes the internalization and partitioning of the molecules into the lipid membrane. The presence of positively charged urea residues promotes electrostatic interactions with the negatively charged bacterial membrane. The subtle structural differences in oligourea head group influence the compounds' aggregation behavior, with the number and position of positively charged urea residues correlating with their aggregation ability. The biological activity of these compounds in inhibiting bacterial growth is correlated with their ability to aggregate, with stronger antibacterial properties exhibited by those that aggregate more easily. However, the concentration inhibiting bacterial growth is significantly lower than the critical aggregation concentration values, suggesting that the mechanism of action involves the monomeric forms of lipooligoureas. Nonetheless, a mechanism based on membrane-induced aggregation cannot be ruled out. The lipooligoureas exhibit higher activity towards Gram-positive bacteria than against Gram-negative bacteria, which is indicative of certain selectivity of these compounds. It is also demonstrated that lipooligoureas exhibit increased stability against proteolytic degradation in human blood serum.

Effect of nitriding treatment on char reducing nitric oxide at high temperature

To reduce nitric oxide (NO) emissions from coal-fired industrial boilers, char waste could be collected from the tail flue and fed into the furnace to reduce NO, which would also decrease the incomplete combustion loss. Nitriding treatment could be used to enhance the NO reducibility of char waste. In this paper, char with nitriding treatment (nitriding char) was prepared from Shenhua char and urea. The effect of nitriding treatment on char reducing NO at high temperatures (700 °C–900 °C) was studied using a fixed-bed experimental system and various urea masses and pretreatment times. Increasing the urea mass and decreasing the pretreatment time resulted in more urea residue being present in the char, which increased the nitrogen complex which existed in the form of C(N) and caused the surface enrichment of nitrogen element, but blocked the pore structure. In an inert atmosphere, the NO reduction rates of all the nitriding chars were higher than that of the raw char, but there was an optimal limit parameter for the urea mass and pretreatment time. The presence of 2 vol% O2 was not conducive to the NO reduction by nitriding char because of the higher char-nitrogen (char-N) content resulting from the nitriding treatment, which generated more NO and offset the benefit of the nitriding treatment. This paper provides a useful NO control strategy in coal-fired industrial boilers, and the relevant process route has achieved a 20%–35% decrease in NO emissions in engineering applications.

Oligourea molecular lifter triggered by electric field

We have synthesized an oligourea foldamer containing seven urea residues, with a Cys-like residue introduced near the N-terminus of the helix. This enabled the immobilization of the molecules on gold electrode using gold-sulfur chemistry. Molecular layer was characterized by electrochemical and spectroelectrochemical methods. Electrochemical measurements confirmed the formation of a dielectric layer on the electrode surface and the determined potential of zero free charge proved that the molecules are adsorbed with the positive pole of the dipole pointing to the electrode surface. The measurements with the use of in situ surface-enhanced infrared absorption spectroscopy provided insight into the dynamics of molecules under the influence of the electric field. Namely, helical oligourea molecules undergo reversible potential-induced changes in the orientation of the molecules. Our results show that molecular layers of oligourea helical foldamers can be used as building blocks for assembly of stimuli-responsive molecular layers serving as molecular lifters triggered by electric field.

Ferrocene-Terminated Oligourea Foldamer Monolayers

We have designed and synthesized two α-helicomimetic foldamers composed of six urea residues with terminal ferrocene and cysteamine moieties. The direction of the net dipole moment in these two com...

P.228 The polypharmacological profile of psilocybin and potential behavioural effects of very low doses

DNA damage under oxidative stress leads to oxidation of guanine base. The identification of the resulting guanine lesions in cellular DNA is difficult due to the sensitivity of the primary oxidation products to hydrolysis and/or further oxidation. We isolated dehydroguanidino-hydantoin (DGh) (or oxidized guanidinohydantoin), a secondary oxidation product of guanine, and showed that this lesion reacts readily with nucleophiles such as asymmetric peroxides and transforms to 2,4,6-trioxo-1,3,5-triazinane-1-carboxamidine residue. Further hydrolysis of this intermediate leads to cyanuric acid and finally to urea residue. This work demonstrates a new possible pathway for the formation of the well-known carboxamidine precursor of cyanuric acid lesion.

Characteristics of urea under high pressure and high temperature**Project supported by the National Natural Science Foundation of China (Grant Nos. 51772120, 11604246, 51872112, and 11804305) and the Project of Jilin Science and Technology Development Plan, China (Grant No. 20180201079GX).

The properties of urea under high pressure and high temperature (HPHT) are studied using a China-type large volume cubic high-presentation apparatus (CHPA) (SPD-6 × 600). The samples are characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), and Raman spectroscopy. By directly observing the macroscopic morphology of urea with SEM, it is confirmed that the melting point of urea rises with the increase of pressure. The XRD patterns of urea residues derived under different pressures show that the thermal stability of urea also increases with the increase of pressure. The XRD pattern of the urea residue confirms the presence of C3H5N5O (ammeline) in the residue. A new peak emerges at 21.80°, which is different from any peak of all urea pyrolysis products under normal pressure. A more pronounced peak appears at 708 cm−1 in the Raman spectrum, which is produced by C–H off-plane bending. It is determined that the urea will produce a new substance with a C–H bond under HPHT, and the assessment of this substance requires further experiments.

Pathological study on urea utilization by poultry

The present work aimed to investigate the histopathological aspects, growth performance, urea residue in muscle and liver of broilerbirds and chemical composition of the breast muscles in birds fed graded levels of urea –treated ration. 80, day old chicks werereared for 6 weeks. After one week of age, chicks were randomly divided into 4 equal groups fed on 1.25%, 2.5%, 5% and 0% ureain their ration. Five birds from each group were sacrificed at the day 7, 14, 28 and 35 from adding urea. The most clinical signswere respiratory symptoms, watery diarrhea and staggering gait. Body weight and feed consumption were increased in group I &II, while the group III showed mild decrease. Urea residue in muscle and liver increased significantly in group III when comparingwith other groups. The chemical composition of the muscle showed that the moisture content in group III was high thangroup IV. There was non-significant increase in the crude protein level in group II. There was significant increase in ashpercent in group II. The fat content in the muscle of all urea treated groups was significant decrease than IV group. Grossly,kidneys and the liver were severe enlarged with pale anemic and mottled coloration. Lungs and the muscles were severe congestedand dark brownish color with petechial and linear hemorrhage in muscle. The brain showed mild hyperemia. Histopathologicalexamination in the kidneys showed degenerative changes in the epithelial cell lining of the renal tubules. The glomeruli showedshrinkages of their glomerular tuft and hyalinization of the Bowman's capsules. Liver showed focal areas of necrosis in the hepaticparenchyma. There was severe thickening of the hepatic capsule. The bile duct showed hyperplasia of their epithelial cell liningwith the presence of desquamated epithelia in the ductile lumen with newly formed bile ductile. Most of hepatic and pulmonaryblood vessels showed thrombosis. Lungs and muscle and brain showed congestion of the blood vessels. The bronchioles showedcatarrhal bronchopneumonia. There was osseous metaplasia among the pulmonary tissue. The neuron was suffering fromTygrloysis with presence of satellotosis and neurophagia. The intestine showed degenerative changes. Myomalecia of some musclecell and suffering from mild degree of hyaline degeneration. It is recommended that lower inclusion levels of urea diets (1.25%)rather than the 2.5% and 5% used in this study be employed for a short period of time.

A coupled system involving arginase and urease for l-ornithine production

l-Ornithine, a non-protein amino acid, is widely used as a food supplement and nutrition product that is usually produced by the enzymatic hydrolysis of l-arginine. However, urea, a by-product, complicates purification of l-ornithine. Here, we describe a highly efficient coupled system, which involves Rummeliibacillus pycnus arginase and Jack bean urease, for the production of l-ornithine without urea residue. Although R. pycnus arginase exhibited the highest enzyme activity at pH 9.5 with Mn2+, it could be activated by Ni2+ at 70°C and pH 6.5. Kinetic study showed that, compared with Mn2+-containing arginase, Ni2+-containing arginase had a higher substrate affinity and catalysis efficiency. Based on the properties of commercial Jack bean urease and recombinant arginase, both enzymes showed robust activity at pH 6.5 and 40–50°C. Using a coupled system involving arginase and urease for bioconversion, l-ornithine production of 37.8gl−1 was achieved with a 99.7% molar yield within 5h. Thus, this coupled system represents an applicable strategy for the biosynthesis of l-ornithine.

Determination of urea in canned foods by high performance liquid chromatography-fluorescence detection coupled with precolumn derivatization

A method for the determination of urea residue in canned foods by high performance liquid chromatography-fluorescence detection (HPLC-FLD) coupled with precolumn derivatization was established. The sample (5.0 g), including canned edible fungi, fruit, vegetable, fish, and meat was extracted with 20 mL 1% (v/v) acetic acid solution. The extract was centrifuged, filtrated, and then derivatized with xanthydrol. The analysis was completed with HPLC-FLD. A good linear relationship was obtained in the range of 0.1-500 mg/L with the correlation coefficients more than 0.9995. The average recoveries of urea spiked at 0.001-30 g/kg levels in five kinds of canned foods ranged from 80.2% to 109.7% with the RSDs of 2.05%-6.53%. The limit of detection (LOD) was 0.5 mg/kg, and the limit of quantitation (LOQ) was 1.0 mg/kg. The proposed procedure was then applied to the analysis of 168 real samples collected from Xiamen, Fujian Province, China. The existence of urea was found in three pork cans with contents of 10.6, 62.1 and 2.6 mg/kg, respectively. The method is stable, reliable, simple and suitable for the determination of urea in canned foods, and has great potential for routine analysis in foodstuffs.

Formation of the carboxamidine precursor of cyanuric acid from guanine oxidative lesion dehydro-guanidinohydantoin

DNA damage under oxidative stress leads to oxidation of guanine base. The identification of the resulting guanine lesions in cellular DNA is difficult due to the sensitivity of the primary oxidation products to hydrolysis and/or further oxidation. We isolated dehydroguanidino-hydantoin (DGh) (or oxidized guanidinohydantoin), a secondary oxidation product of guanine, and showed that this lesion reacts readily with nucleophiles such as asymmetric peroxides and transforms to 2,4,6-trioxo-1,3,5-triazinane-1-carboxamidine residue. Further hydrolysis of this intermediate leads to cyanuric acid and finally to urea residue. This work demonstrates a new possible pathway for the formation of the well-known carboxamidine precursor of cyanuric acid lesion.

Synthesis and folding propensity of aliphatic oligoureas containing repeats of proline-type units.

The synthesis and conformational analysis of aliphatic oligoureas containing multiple adjacent N-alkylated units derived from proline (i.e., Pro(u)) are reported. The insertion of trisubstituted ureas in the main chain of N,N'-linked oligourea foldamers locally impairs the characteristic three centered-hydrogen bonding pattern associated with the formation of 2.5-helical structures. Three series of oligomers have been studied: one series in which the Pro(u) repeat is flanked on both sides by canonical urea residues (e.g., oligomers 2-6), one series with canonical residues on either side of the Pro(u) repeat (oligomers 12 and 23), and one series consisting exclusively of Pro(u) residues (oligomers 25 and 26). Spectroscopic (NMR and electronic circular dichroism) and X-ray diffraction studies reveal that the 2.5-helix formed by oligomers of N,N'-disubstituted ureas is robust enough to accommodate short oligopyrrolidine segments (Pro(u))n (n < 7) that alone display no intrinsic folding propensity.

Validation of a LC–MS Method for the Determination of Urea Contamination in Market Teas

Tea is one of the most widely consumed beverages in the world preceded only by water. In some culture style of tea plant, urea fertilizer is sprayed on tea leaf in order to increase crop output; besides, in some processing method of green tea, urea is illegally added to maintain tea’s vivid color. The above-mentioned process may unavoidably cause urea residue, and prolonged or repeated exposure of body to urea may cause adverse effects. In this work, an easy and reliable hydrophilic interaction liquid chromatography/mass spectrometry analytical method for determination of urea in tea was firstly validated; the method exhibited a linear response from 4 to 60 μg mL−1 (R 2 > 0.9996), the limit of quantitation for urea is 4 μg mL−1, the mean recoveries of urea spiked at levels of 10 and 20 μg mL−1 were 95–110 %, and the relative standard deviations of intra- and inter-day measurements were less than 7.8 %. The method was later successfully applied to the analysis of urea residue in some market tea samples. The result showed that there is obvious urea contamination in some market teas, and the contamination percentage is especially high in green tea samples. Among the samples investigated, urea was detected at concentration ranges of 24.02–46.02 mg/kg. Some attention should be paid on the health effect resulting from such urea contamination in tea.

Selective dimerisation of tetraurea calix[4]arenes

The formation of hydrogen-bonded dimeric capsules from tetraurea calix[4]arenes is controlled by loops, connecting adjacent urea functions, and more or less bulky substituents. The dimerisation is only possible if loops are not overlapping and if the respective residues can pass the loops. A sorting scheme based on small and bulky residues and one to four loops allows reducing the number of possible dimers from 35 to 6 in a stoichiometric mixture of 11 ureas. With three different loop sizes (O–(CH2) n –O chains with n = 10, 14, 20 connecting adjacent phenylurea functions via their meta positions), it is possible to distinguish four urea residues of different sizes (small, medium, bulky and giant) ranging from tolyl to 4-[tris-(4-t-butylphenyl)methyl]-phenyl. While the smallest residue can pass all loops, the largest is excluded by all loops.

Fine-Tuning the Dimerization of Tetraureacalix[4]arenes

Calix[4]arenes substituted by four urea residues at their wide rim form hydrogen-bonded homo- and heterodimeric capsules in apolar solvents. If urea groups are covalently connected to loops or substituted by bulky residues, the dimerization may be restricted to those pairs in which the loops do not overlap and for which the residues are small enough to pass the loops. In the present study, we describe the dimerization properties of tetraureas with one, two (adjacent or opposite), three, or four loops and those bearing (additionally) up to four residues of different size: a = tolyl, b = 3,5-di-tert-butylphenyl, c = 4-propyloxy-3,5-di-(tert-butylphenyl)phenyl, and d = 4-[tris-(4-tert-butylphenyl)methyl]phenyl. For compounds with four loops of different size (-O-(CH2 )n-O-chains with n=10, 14, and 20 connecting the m-positions of the urea phenyl residues) a clear "stepwise" sorting scheme could be established, in which the bulkiest residue d is excluded by all tetraloop compounds and the smallest residue a can pass only the smallest loops (n=10). The medium-sized residues b or c are tolerated by n=14 and 20 or only by n=20. Selectivities can be built up also on geometrical factors. A trisloop compound, for instance, combines only with a tetraurea bearing a single bulky residue and tetraureas with two bulky substituents in adjacent or opposite position are distinguished by the bisloop derivatives with adjacent or opposite loops. The impossibility to form a homodimer of a monoloop compound containing two bulky residues leads to its selective heterodimerization with a derivative bearing three bulky groups. Subtle effects for "borderline" cases, in which the dimerization or reorganization takes a longer time, are also discussed.

Rotaxanes and Catenanes Derived from Tetra‐Urea Calix[4]arenes

AbstractSummary: Calix[4]arenes, substituted by four urea groups at their wide rim, form dimeric capsules in apolar solvents, which are held together by a seam of intermolecular hydrogen bonds. The heterodimerisation of tetra‐aryl and tetratosyl ureas was used to synthesize various derivatives, in which adjacent urea residues are connected to form two, three or four loops. The aliphatic connections were tied by olefin metathesis between adjacent alkenyl residues followed by hydrogenation. Heterodimers of tetra‐alkenyl substituted tetra‐ureas and bis‐ or tetraloop derivatives were converted analogously to multiple catenanes. Tetra[2]rotaxanes were obtained in a similar manner. In addition to the spectroscopic evidence (NMR, MS) several compounds were confirmed by crystal structures.

Photodegradation of DMMP and CEES on zirconium doped titania nanoparticles

The structure and photocatalytic activity of Zr doped TiO2 nanocrystallites with a varying Zr content between 0 and 15wt% prepared by an efficient and environmentally benign method has been studied by vibrational spectroscopy, TEM and XRD. It is shown that the presence of Zr4+ ions stabilizes the anatase structure and delays phase transformation to rutile upon annealing as well as retarding grain coarsening. All TiO2 samples up to 13wt% Zr doping concentration show better or similar photoreactivity compared to P25 (Degussa) for decomposition of adsorbed 2-chloroethyl ethyl sulphide (CEES) and dimethyl methylphosphonate (DMMP) in synthetic air at room temperature. The most efficient sample for photodegradation of both CEES and DMMP is shown to be titania doped with 6.8wt% Zr. The photodegradation of CEES is faster than DMMP under the same experimental conditions. On the undoped TiO2 sample urea residues are detected spectroscopically. Much less is detected on the Zr doped samples. Mode resolved in situ FTIR surface spectroscopy enables distinction of CEES or DMMP, decomposition products as well as the influence of residues from the particle synthesis. This facilitates extraction of intra-comparable reaction rates. Possible explanations for the improved reactivity of the Zr doped titania are discussed.

2-Aminobenzimidazoles as potent Aurora kinase inhibitors

This Letter describes the discovery and key structure–activity relationship (SAR) of a series of 2-aminobenzimidazoles as potent Aurora kinase inhibitors. 2-Aminobenzimidazole serves as a bioisostere of the biaryl urea residue of SNS-314 ( 1c), which is a potent Aurora kinase inhibitor and entered clinical testing in patients with solid tumors. Compared to SNS-314, this series of compounds offers better aqueous solubility while retaining comparable in vitro potency in biochemical and cell-based assays; in particular, 6m has also demonstrated a comparable mouse iv PK profile to SNS-314.

Tetra-urea calix[4]arenes 1,3-bridged at the narrow rim

The synthesis of special tetra-urea calix[4]arene derivatives is described. Two propyl ether groups in 1,3-position and a 5-iodo-isophthalamide bridge connecting two aminopropylether residues in 2,4-position at the narrow rim keep the molecule fixed in the cone conformation. The aryl urea residues are substituted by decyloxy groups in p-position to increase the solubility in apolar solvents, while the iodo substituent allows further functionalization. Two single crystal X-ray structures of 3 and 4 show a strongly pinched cone conformation in which the bridged phenol units are bent outwards, while the phenol units bearing the propyl ether groups are nearly parallel. The molecules are flexible enough, however, to form hydrogen bonded dimeric capsules in apolar solvents. Their (time averaged) D(2) conformation is confirmed by (1)H NMR spectroscopy.