Urea Loading Research Articles

Advancing H-Bonding Organocatalysis for Ring-Opening Polymerization: Intramolecular Activation of Initiator/Chain End.

Organocatalytic ring-opening polymerization (ROP) of lactones is a green method for accessing renewable and biodegradable polyesters. Developing new organocatalysts with high activity and controllability is a major and challenging research topic in this field. Here, we report a series of organocatalysts to achieve a fast and controlled ROP of lactones. These catalysts incorporate (thio)urea and alkoxide in one molecule and act as initiators in the ROP. Such catalysts enable an effective intramolecular activation of initiator/chain end, as revealed by computational studies, resulting in higher activity and fewer (thio)urea loads than existing (thio)urea/alkoxide binary systems. These organocatalysts exhibit ultrahigh activity comparable to metal complexes, i.e., turnover number up to 900 and turnover of frequency up to 4860 min-1, affording polyesters with tailor-made structure, predicted molecular weights, narrow dispersity, less epimerization, and minimal transesterification. The catalyst synthesis is simple and scalable, allowing widely tuned activities of the ROP.

Preparation and characterization of starch carbamate modified natural sodium alginate composite hydrogel blend formulation and its application for slow-release fertilizer

The exploration of environmentally friendly slow-release fertilizer (SRF) based on natural bio-polymers is of great importance in the development of modern agriculture and horticulture. Herein, a novel starch carbamate (SC) modified sodium alginate (SA) hydrogel (SC/SAH) was prepared utilizing as-synthesized SC and natural SA through the cationic ions crosslinking method and ultimately the corresponding slow-release fertilizer (SC/SAH-SRF) was successfully developed by immersing the dried SC/SAH matrix into saturated urea solution. Due to the low gelation temperature and high viscosity of the synthesized SC, the formed SC/SAH exhibits significantly enhanced properties including excellent water absorbency up to 8.02 g/g with considerable repeatability, abundant pore structure and high hydrophilicity compared with the neat SAH and natural starch based hydrogel (NS/SAH). Accordingly, the SC/SAH leads to higher urea loading amount ∼ 1.28 g/g. Importantly, the resultant SC/SAH-SRF also shows superior slow-release performance, yielding a cumulative urea release of only 61.6 % within 10 h and almost completely release >16 h in water, what's more, only 58.5 % of the urea releases within 25 days and exceeding 50 days for complete release in soil column assays. The slow-release of urea from SC/SAH-SRF well complies for the first-order kinetics and accomplishes via a non-Fickian diffusion process. Moreover, the pot experiment demonstrates that the SC/SAH-SRF has higher growth promotion role for the maize seedlings than those of others. Consequently, this work provides a novel strategy for preparing environmentally friendly SRF by blending modified starch and hydrogel.

Urea intercalated encapsulated microalgae composite hydrogels for slow-release fertilizers

In agriculture, hydrogels can be addressed for effective operation of water and controlled-release fertilizers. Hydrogels have a significant ability for retaining water and improving nutrient availability in soil, enhancing plant growth while reducing water and fertilizer usage. This work aimed to prepare a hydrogel composite based on microalgae and biopolymers including chitosan and starch for use as a soil conditioner. The hydrogel composite was characterized by FTIR, XRD, and SEM. All hydrogel properties were studied including swelling degree, biodegradability, water-holding capacity, water retention, and re-swelling capacity in soil and water. The urea fertilizer loading and releasing behavior of the prepared hydrogels were investigated. The results revealed that the range of the maximal urea loading was between 99 and 440%, and the kinetics of loading was fitted with Freundlich model. The urea release % exhibited 78–95%, after 30 days, and the kinetics of release was fitted with zero-order, Higuchi, and Korsmeyer–Peppas models. Furthermore, the prepared hydrogels obtained a significant water-holding capacity, after blending soil (50 g) with small amount of hydrogels (1 g), the capacity increased in the range of 99.4–101.5%. In sum, the prepared hydrogels have the potential to be applied as a soil conditioner.

The SLC6A18 Transporter Is Most Likely a Na-Dependent Glycine/Urea Antiporter Responsible for Urea Secretion in the Proximal Straight Tubule: Influence of This Urea Secretion on Glomerular Filtration Rate.

Urea is the major end-product of protein metabolism in mammals. In carnivores and omnivores, a large load of urea is excreted daily in urine, with a concentration that is 30-100 times above that in plasma. This is important for the sake of water economy. Too little attention has been given to the existence of energy-dependent urea transport that plays an important role in this concentrating activity. This review first presents functional evidence for an energy-dependent urea secretion that occurs exclusively in the straight part of the proximal tubule (PST). Second, it proposes a candidate transmembrane transporter responsible for this urea secretion in the PST. SLC6A18 is expressed exclusively in the PST and has been identified as a glycine transporter, based on findings in SLC6A18 knockout mice. We propose that it is actually a glycine/urea antiport, secreting urea into the lumen in exchange for glycine and Na. Glycine is most likely recycled back into the cell via a transporter located in the brush border. Urea secretion in the PST modifies the composition of the tubular fluid in the thick ascending limb and, thus, contributes, indirectly, to influence the "signal" at the macula densa that plays a crucial role in the regulation of the glomerular filtration rate (GFR) by the tubulo-glomerular feedback. Taking into account this secondary active secretion of urea in the mammalian kidney provides a new understanding of the influence of protein intake on GFR, of the regulation of urea excretion, and of the urine-concentrating mechanism.

Physiological Functions of Aquaporin-3 in Mediating Water and Solutes

Aquaporins (AQP), are a family of membrane channel proteins that facilitate the transmembrane diffusion of water and some small non-charged solutes such as glycerol and urea by osmosis or solute gradient. AQP3, an aquaglyceroporin, is expressed in the kidney, skin, and testes, etc. Mice lacking AQP3 have symptoms of diabetes insipidus. In addition, the absence of AQP3 leads to dry skin in mice. AQP4 is permeable to water only. To understand the specific function of the water permeability and small solute transport mediated by AQP3, we generated AQP3 knock-out (AQP3 KO) mice and AQP4 knock-in mice (AQP4 KI) with AQP4 replacing AQP3 in situ. In the basal condition, knock-out of AQP3 in mice led to increased urine volume, decreased urine osmolality and tubule dilation. Interestingly, in AQP4 KI mice, these phenomena were reversed, showing improved urine concentration and tubular morphology. However, there was no significant difference in non-urea solute concentrations between both genotypes. Subsequently, we conducted acute urea loading tests and high-protein diet experiments to further increase the production and excretion of urea in mice. The experimental results showed that both urea loading and high-protein diet had little impact on urine osmolality and urinary urea concentration in AQP3 KO mice. But the urine osmolality and urinary urea concentration in AQP4 KI mice were altered by exogenous administration of urea. Our data indicates that the absence of AQP3 prevents urea accumulation in the kidney, disrupting urine concentration mechanism. The knock-in of AQP4 can restore AQP3 mediated water channel function and help to regulate the urine concentration ability. The water permeability, other than solute transport, of AQP3 plays important role in urine concentrating mechanism. AQP3 KO mice exhibited significant epidermal thickening, excessive keratinization, decreased skin hydration and elasticity. The replacement of AQP4 in situ did not improve these phenomena, indicating that solute transport mediated by AQP3 may play a role in maintaining normal skin function. Therefore, we constructed a mouse model of psoriasis induced by imiquimod (IMQ). It was found that AQP3 expression was reduced in the lesional skin of wildtype (WT) mice, while AQP3 KO mice and AQP4 KI mice exhibited dry skin, excessive epidermal proliferation, and increased inflammatory response. Local treatment with urea (10%) could alleviate these symptoms. These experimental results confirmed the important role of AQP3 in the pathogenesis of psoriasis and the potential role of urea in the treatment of psoriasis. Our study suggests the diverse physiological functions of AQP3 in different tissues. This research was supported by Beijing Natural Science Foundation (7232249). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Influence of chitosan addition on the properties and characteristics of acrylic acid-chitosan based superabsorbent prepared through gamma irradiation technique and its application for urea loading

Influence of chitosan addition on the properties and characteristics of acrylic acid-chitosan based superabsorbent prepared through gamma irradiation technique and its application for urea loading

3D Porous Oxygen-Doped and Nitrogen-Doped Graphitic Carbons Derived from Metal Azolate Frameworks as Cathode and Anode Materials for High-Performance Dual-Carbon Sodium-Ion Hybrid Capacitors.

Sodium-ion hybrid capacitors (SIHCs) in principle can utilize the advantages of batteries and supercapacitors and satisfy the cost demand of large-scale energy storage systems, but the sluggish kinetics and low capacities of its anode and cathode are yet to be overcome. Here, a strategy is reported to realize high-performance dual-carbon SIHCs using 3D porous graphitic carbon cathode and anode materials derived from metal-azolate framework-6s (MAF-6s). First, MAF-6s, with or without urea loading, are pyrolyzed to synthesize MAF-derived carbons (MDCs). Then, cathode materials are synthesized via the controlled KOH-assisted pyrolysis of MDCs (K-MDCs). K-MDCs, 3D graphitic carbons, resulting in a record-high surface area (5214m2 g-1 ) being ≈four-fold higher than pristine MAF-6, oxygen-doped sites for high capacity, rich mesopores affording fast ion transport, and high capacity retention over 5000 charge/discharge cycles. Moreover, 3D porous MDC anode materials are synthesized from N-containing MAF-6 and exhibited to allow cycle stability over 5000 cycles. Furthermore, dual-carbon MDC//K-MDC SIHCs with different loadings (3 to 6mgcm-2 ) are demonstrated to achieve high energy densities exceeding those of sodium-ion batteries and supercapacitors. Additionally, it allows an ultrafast-chargeable high power density of 20000Wkg-1 and robust cycle stability overcoming those of a typical battery.

Clinico-Biological and Immuno-Virological Profile of People Living with HIV Non-Adhering to HAART at the Lerato Clinic, Bertha Qxowa Hospital, Germiston, South Africa

<i>Background and objectives</i>: Highly active antiretroviral therapy (HAART) is a mainstay in the management of PLWHIV, improving survival. However, since its advent and its side effects, the problem of adherence to this therapy arises... The objective of this study was to investigate the impact of non-adherence to HAART on clinical, biological, immunological and virological parameters. <i>Methods:</i> The investigator conducted a cross-sectional study at the Lerato Clinic at Bertha Qxowa Hospital in Germiston, Gauteng, South Africa, from September 2019 to December 2019. Included for participation were those over 18 years of age, on HAART for at least three months, consenting to participate, and attending the clinic during this period. Non-adherence was defined as taking their medication ≤ 95% of the time. A sample of 278 participants was selected. A non-adherence threshold of >5% was considered high, with P<0.05 statistical significance. <i>Results:</i> A sample of 278 participants was considered. Of these, 19% (n ꞊ 52) were non-adherent to HAART. Clinico-biologically and immunobiologically, this category had high averages of Systolic blood pressure, Waist circumference (WC), Hip circumference (HC), Creatinine, Urea, Uric acid, Blood glucose, Total cholesterol, LDL Cholesterol, Triglycerides (TG), CRP and Viral load. While the mean values for diatolic blood pressure (DBP), CD4 count and body mass index (BMI) were lower. <i>Conclusion:</i> Patients receiving HAART but not adhering to it have a higher risk of diabetes mellitus, cardiovascular disease, liver disease, chronic kidney disease and opportunistic infections. Regular monitoring of patients on HAART to avoid non-compliance is imperative to detect these risk factors and allow for early initiation of treatment.

Preparation and Properties of a Novel Biodegradable Composite Hydrogel Derived from Gelatin/Chitosan and Polylactic Acid as Slow-Release N Fertilizer

To improve the efficient use of nitrogen and decrease the environmental pollution of N losses, a novel and biodegradable composite hydrogel was prepared by chemical cross-linking synthesis using gelatin (Gel), chitosan (CS) and polylactic acid (PLA) as raw materials. Urea as the nitrogen source was loaded into this new biodegradable hydrogel using the solution immersion method. The chemical structures of the composite hydrogels were characterized and their properties were analyzed by XRD and XPS. The regulation of urea loading and the swelling behavior of the composite hydrogel under different temperature conditions were investigated; the release behavior and release model of the composite hydrogel in the aqueous phase was explored. The results show that the loading of urea is controllable in aqueous urea solution with different concentrations. In the water phase, it shows a three-stage sustained release behavior, that is, the initial release rate of urea is relatively fast, and the medium release rate of urea gradually slows down, and finally the nutrient release rate tends to be flat. The release behavior in the water phase fits to the Ritger-Peppas model. Within 10 min, 180 min and 900 min, the cumulative nutrient release rate of gelatin/chitosan/PLA-urea (GCPU) composite hydrogel is 20%, 70% and 86%, respectively. Compared with pure urea, The urea diffusion time of GCPU was extended by 1350-times. In addition, the GCPU also has good water absorption and water retention properties, in which average water content can reach as high as 4448%. All of the results in this work showed that GCPU hydrogel had good water absorption and retention and N slow-release properties, which are expected to be widely used in sustainable agriculture and forestry, especially in arid and degraded land.

Structurally stable polyvinyl alcohol/sodium alginate-based optimally designed electrospun mats as mechanistically robust controlled-urea-release-systems

The present study deals with the development of uniform, bead-free, and urea-loaded PVA/SA-based sustainable electrospun fibrous constructs as a controlled release fertilizer system. Taguchi L9 OA was used to predict the optimal level of control parameters i.e., urea loading (∼ 45 phr), flow rate (∼ 1 ml/h), polymeric concentration (∼ 8 wt%), and an applied voltage of ∼ 25 kV, to fabricate EMs with minimum fiber diameter (∼ 0.208 µm) and diametral variation (∼ 0.017 µm). Microstructural analysis confirmed the presence of hydrogen bonding interactions between urea and the polymer matrix, as well as successful ionic crosslinking. The contact angle and thermogravimetric analysis indicated an increase in hydrophobicity (from ∼ 30.64º to ∼ 74.13º) and thermal stability (from 164 ºC to ∼ 290 ºC) for PVA/SA-based EMs upon urea incorporation and post crosslinking, respectively. Further, the effect of urea loading and crosslinking on swelling and degradation behavior revealed a subsequent increase in water absorption capacity up to ∼ 296 % accompanied by a decrease in degradation rate up to ∼ 13%. The swelling behavior of EMs exhibited a desirably good level of pH level, salt/alkali solution sensitivity, and water retention potential lasting up to ∼16 days in soil. Spectroscopic analysis revealed a non-Fickian diffusion-induced sustained release of urea in water (> 21 days) and soil media (> 30 days). Soil burial studies of crosslinked urea-loaded EMs exhibited excellent biodegradability (> 80 % in 60 days) and structural stability (∼30 days). Thus, the study demonstrated the design of mechano-functionally engineered urea-loaded optimized PVA/SA-based EMs as potential controlled nutrient release substrates with improved and sustainable physicomechanical performance for agricultural practices.

Effects of urea loading on soil biodegradation properties of melt‐processed polycaprolactone‐based composites for potential application in agriculture

AbstractHerein, biodegradable composites of poly(ɛ‐caprolactone) (PCL)/hydroxyapatite (HAP)/urea, with potential application in agriculture, were developed. The concentration of HAP was fixed at 3 wt%, while urea concentration varied from 1 to 9 wt%. The effects of urea loading on the morphological, flow properties, and soil biodegradation of PCL/HAP composites were investigated. The morphological characterization showed well dispersion of HAP and urea particles in the PCL matrix. A decrease in viscosity of PCL was noticed upon the inclusion of urea at 1 wt%, indicating the plasticization effects of urea, whereas an increase in viscosity was observed with increasing the concentration. The morphological analysis after soil burial showed microbial adherence on the surface of the samples. In addition, the formation of cracks, holes, and uneven surfaces were noticed. The atomic force microscope analysis showed an increase in surface roughness due to surface degradation of the samples. On the other hand, two‐step degradation curves were noticed in the samples before soil degradation. In contrast, a single step degradation curve was observed after degradation, indicating the leaching of urea from the samples. Overall, PCL/HAP/urea composites with enhanced degradation rates were developed, and they can be applied in agriculture, where the materials can be buried after their end‐use.

Water resistance evaluation of a MFU resins with different molar ratio catalyzed with citric acid

Urea, in either solid form or in solution, is an additive commonly used to control the viscosity or act as a scavenger in MF (melamine-formaldehyde) and MUF (melamine-urea-formaldehyde) resins for particleboard production. The aim of this work was to evaluate the influence of adding urea to MF (melamine-formaldehyde) resin in terms of the water-resistance of the final particleboards. FTIR-ATR spectroscopy, adhesive bonding evaluation system (ABES) and gravimetric techniques were used. MF and MFU (melamine-formaldehyde-urea) resins were prepared. Urea was introduced as an additive, in different percentages (0, 10, 20, and 30% (on adhesive, dry basis), and citric acid was used as catalyst. Beech veneer strips were bonded together with these formulations and then tested in dry conditions and after immersion in water for 24 h. The effect of urea load on the resin curing reaction in dry and humid joints was studied. Particleboards were produced with MF and MFU (melamine formaldehyde urea) resins with different urea loads and using industrial recycled wood particles as raw material. Particleboard evaluation indicated that the water resistance of the final particleboards decreased linearly with urea addition.

Eco-friendly and biodegradable sodium alginate/quaternized chitosan hydrogel for controlled release of urea and its antimicrobial activity

Hydrogels could be employed in agriculture for efficient management of water and controlled-release urea (CRU). This study aimed to synthesize a superabsorbent hydrogel for CRU by cross-linking sodium alginate (Alg) and N-(2-hydroxy-3-trimethyl ammonium) propyl chitosan chloride (HTACC). The hydrogel structure was characterized by various techniques, and the urea loading and releasing behaviors of the synthetic hydrogels were investigated. The results revealed that the maximum urea loading ranged between 107 and 200%, and that the urea loading kinetics fitted with Langmuir model followed by the Freundlich model. The urea release behavior reached equilibrium after 30 days and urea releasing kinetics fitted with the zero-order and Higuchi models. The synthesized hydrogels exerted significant antimicrobial activities and molecular docking showed their binding affinity toward glucosamine-6-phosphate synthase, β-lactamase II, TraR binding site and nucleoside diphosphate kinase. In conclusion, these Alg/HTACC hydrogels showed swelling, urea release, and antimicrobial properties suitable to meet the plant requirements and produce economic and environmental benefits.

ACID-BASE STATE OF BLOOD AND MIXED SALIVA IN THE ORAL CAVITY IN PATIENTS WITH COMMUNITY-ACQUIRED PNEUMONIA AND THEIR SIGNIFICANCE IN DIAGNOSIS AND PREDICTION OF THE DISEASE

Acid-base imbalance is an indicator of many pathological changes, including community-acquired pneumonia. The aim of this work is to study the acid-base state of blood and mixed saliva in patients with community-acquired pneumonia during test loads and to determine the effectiveness of the load in diagnosis of the disease. Materials and methods. The study included 34 adult patients with community-acquired pneumonia, who took the treatment at the therapeutic department of the Municipal Clinical Hospital No. 25, Kharkiv. The diagnosis of community-acquired pneumonia was established based on epidemiological, clinical, laboratory, and radiological findings. All indicators obtained were compared with the findings taken from healthy individuals. A comparative study of the blood and saliva pH dynamics in patients with community-acquired pneumonia, as well as the concentration of calcium and inorganic phosphate in mixed saliva under test loads was carried out. A close interconnection in the dynamics between the studied parameters was revealed both under sugar and urea loading. Conclusion. The main diagnostic indicator of the acid-base balance disorders in the blood and saliva of patients with community-acquired pneumonia is pH and excess or deficiency of alkaline. Under a sugar load, patients with community-acquired pneumonia demonstrate an accumulation of acid equivalents, a decrease in the mixed saliva pH, the inorganic phosphate concentration and an increase in the calcium concentration. Under carbamide loading, the phosphate buffer system of saliva gets activated mainly to correct acid-basic status at pH values below 6.0. The results obtained will help to improve the diagnosis of community-acquired pneumonia.

Urine and fecal excretion patterns of dairy cows divergent for milk urea nitrogen breeding values consuming either a plantain or ryegrass diet

Environmental degradation has been attributed to inefficient nitrogen utilization from pastoral dairy production systems. This degradation has especially been associated with the urine patch, which has been identified as a key component of nitrate leaching to waterways. However, a lack of information exists regarding the pattern of urination events and individual urination characteristics across the day, which would help inform strategic management decisions. The aim of this study was therefore to evaluate and report the patterns and characteristics of fecal and urination events throughout the day for cows divergent for milk urea nitrogen breeding values (MUNBV) on either a plantain [Plantago lanceolata L. (PL)] or ryegrass [Lolium perenne L. (RG)] diet as ways to reduce environmental impact. Sixteen multiparous lactating Holstein Friesian × Jersey cows divergent for MUNBV were housed in metabolism crates for 72 h, with all excretion events captured and analyzed. Cows selected as low for MUNBV consistently had a 65.2-kg lower urinary urea nitrogen (UUN) load (kg/ha) than high MUNBV cows for all hours of the day when consuming RG. The association between lower urinary urea loading rates and less N leaching implies a reduced environmental impact from low MUNBV cows consuming RG. When cows consumed PL, regardless of MUNBV, they had on average a 137.5-kg (UUN/ha) lower loading rate compared with high MUNBV cows on RG and a 72.2-kg (UUN/ha) lower loading rate compared with low MUNBV cows consuming RG across the day. Cows on PL also exhibited a different diel pattern of UUN load compared with cows consuming RG. Differences in the diel pattern of N excreted in feces were also detected based on MUNBV and by diet, with low MUNBV cows excreting on average 3.06 g more N in feces per event for the majority of the day compared with high MUNBV cows when consuming RG. Lower UUN loading rates and more N excreted in feces indicate a potentially lower environmental impact from low MUNBV cows when consuming RG compared with high MUNBV cows. The use of the PL diet also resulted in lower UUN loading rates and greater levels of N excreted in feces compared with RG, therefore also indicating its ability to reduce environmental impact compared with RG.

Responses of coastal sediment phosphorus release to elevated urea loading

Increased urea is one of the common nitrogen forms polluting coastal waters and affecting nutrient dynamics. To investigate the effects of urea on sediment phosphorus (P) release, we carried out a 2-month mesocosm experiment with six targeted loadings of urea (0–0.6 mg N L−1 d−1). Results showed that: i) urea was rapidly transformed into ammonium and then nitrate (NO3−). ii) When nitrogen occurred as urea or ammonium, minor P release was observed. iii) After urea were mostly converted to NO3−, P release became clearer. iv) NO3− had a dual effect by promoting P release through decreasing sediment pH and increasing alkaline phosphatase activity or by inhibiting P release through improving sediment oxidation. v) The overall effects of urea on P release depended on the ultimate NO3− concentrations, being prominent when NO3− ≥ 11 mg N L−1. Our findings are of relevance when determining nitrogen reduction targets needed for combating eutrophication.

Optimization of mechanical strength of biocemented Martian regolith simulant soil columns

Biocemented Martian regolith simulant (MRS) columns were developed using a microalga, Thraustochytrium striatum. Response surface methodology was used to maximize the unconfined compressive strength (UCS) of biocemented MRS columns towards regolith particle size, cell biomass loading, and nutrient (CaCl2/urea) loading. Overall, the UCS increased with the increase of cell biomass loading while the MRS of medium particle size achieved the highest UCS. But the nutrient loading didn’t show a consistent effect. The maximum UCS reached 603.83 kPa with 0.25 ∼ 0.425 mm particle size, 3.8 g/100 mL cell biomass loading, 5.83 g/100 mL CaCl2 loading, and 14.18 g/100 mL urea loading.

Comment on “Synthesis and characterization of a novel nickel pillared–clay catalyst: In–situ carbon nanotube–clay hybrid nanofiller from Ni-PILC”, by M. Asgari, G. Vitale, U. Sundararaj [Applied Clay Science 205 (2021) 106064, doi:10.1016/j.clay.2021.106064

Kaolinite-urea intercalates were prepared by dry grinding kaolin KGa-1b with urea using a laboratory-scale planetary ball mill. The effect of milling conditions on the intercalation process was investigated over a wide range of urea content (25 m% - 80 m%) and milling times (up to 2 h). The purification of the complex obtained was carried out by repeated washings with isopropanol in order to remove the excess (non-intercalated) urea. For that purpose, the proportion of intercalated urea and non-intercalated urea crystals was quantified after each washing step by combining differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) results obtained simultaneously. The optimal conditions of the intercalation were realized at a 66 m% urea loading for which a relatively low-defect complex structure was obtained in a short milling time. One drawback with the use of a high urea content (> 25 m%) during grinding was the presence of a large proportion of excess urea crystals in the as ground sample. This required repeated washing with isopropanol to purify the complex. Furthermore, the results revealed that washing with water the kaolinite-urea intercalates led to the formation of 0.84 nm kaolin hydrates and that exfoliation/delamination of kaolinite was more efficient when a high concentration of urea was used in the milling process.

Influencing parameters of mechanochemical intercalation of kaolinite with urea

Kaolinite-urea intercalates were prepared by dry grinding kaolin KGa-1b with urea using a laboratory-scale planetary ball mill. The effect of milling conditions on the intercalation process was investigated over a wide range of urea content (25 m% - 80 m%) and milling times (up to 2 h). The purification of the complex obtained was carried out by repeated washings with isopropanol in order to remove the excess (non-intercalated) urea. For that purpose, the proportion of intercalated urea and non-intercalated urea crystals was quantified after each washing step by combining differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) results obtained simultaneously. The optimal conditions of the intercalation were realized at a 66 m% urea loading for which a relatively low-defect complex structure was obtained in a short milling time. One drawback with the use of a high urea content (> 25 m%) during grinding was the presence of a large proportion of excess urea crystals in the as ground sample. This required repeated washing with isopropanol to purify the complex. Furthermore, the results revealed that washing with water the kaolinite-urea intercalates led to the formation of 0.84 nm kaolin hydrates and that exfoliation/delamination of kaolinite was more efficient when a high concentration of urea was used in the milling process.

The urea transporter UT-A1 plays a predominant role in a urea-dependent urine-concentrating mechanism

Urea transporters are a family of urea-selective channel proteins expressed in multiple tissues that play an important role in the urine-concentrating mechanism of the mammalian kidney. Previous studies have shown that knockout of urea transporter (UT)-B, UT-A1/A3, or all UTs leads to urea-selective diuresis, indicating that urea transporters have important roles in urine concentration. Here, we sought to determine the role of UT-A1 in the urine-concentrating mechanism in a newly developed UT-A1-knockout mouse model. Phenotypically, daily urine output in UT-A1-knockout mice was nearly 3-fold that of WT mice and 82% of all-UT-knockout mice, and the UT-A1-knockout mice had significantly lower urine osmolality than WT mice. After 24-h water restriction, acute urea loading, or high-protein (40%) intake, UT-A1-knockout mice were unable to increase urine-concentrating ability. Compared with all-UT-knockout mice, the UT-A1-knockout mice exhibited similarly elevated daily urine output and decreased urine osmolality, indicating impaired urea-selective urine concentration. Our experimental findings reveal that UT-A1 has a predominant role in urea-dependent urine-concentrating mechanisms, suggesting that UT-A1 represents a promising diuretic target.