Narrow Results

Glucokinase (GK), an enzyme critical to glucose metabolism, exhibits thermal instability, which can affect its enzymatic activity under physiological and pathological conditions. This study aims to mathematically model the thermal denaturation kinetics of GK and empirically validate the model using experimental data. To establish a mathematical model on thermal denaturation of glucokinase (E.C.2.7.1.2) and its experimental validation, the enzyme glucokinase was investigated in a 0.075M Tris HCl buffer with pH 9.0 at 30^∘C and 0.6M MgCl₂. A first-order kinetic model was developed to describe the enzyme’s denaturation, incorporating temperature-dependent reaction rates based on the Arrehenius equation. Empirical data were collected through Spectrophotometer across a temperature range of 20^∘–60^∘C. Experimental validation revealed that GK undergoes irreversible denaturation above 60^∘ with a significant reduction as temperature increases. Moreover, the thermal denaturation of GK in the presence of osmolyte Urea is a critical process affecting enzyme stability and function. This study also aims to mathematically model and empirically validate the impact of Urea on GK’s thermal denaturation behavior. Results demonstrated that Urea significantly reduces the thermal stability of GK, lowering its denaturation temperature. The results are simulated graphically using the Wolfram MATHEMATICA software. The mathematical predictions closely matched experimental data, confirming the model’s accuracy.

The present paper attempts as how the pigments comprising of nano-sized hematite particles deposited on mica surfaces in optimum conditions offer an excellent pearlescent properties. To record the influencing parameters on the synthesis process, response surface methodology (RSM) technique was used where temperature of reaction, synthesis time and concentration of urea were selected as variable parameters. Taking into account colorimetric parameters, the whole process was then analyzed by "Design Expert" software that finally gave following optimum factors: reaction temperature=82.02°C, synthesis time=11.98 h, urea concentration=37.5 g/l. Once the above optimum parameters selected, seemingly, the spherical hematite particles of about 60 nm in diameter are deposited uniformly on mica surfaces.

Although biomass-derived metal-free electrocatalysts for oxygen reduction reaction (ORR) have garnered increasing attention, their ORR performance is lower than that of commercial 20% Pt/C. To improve their ORR performance, a series of porous carbons with high $N$ contents are prepared by pyrolyzing a mixture of spinach leaf powder and urea at different mass ratios (1:0, 1:5, 1:10, and 1:15) at a high temperature; the resultant materials are labeled as S-850, S-850-5, S-850-10, and S-850-15, respectively. The results indicate that the $N$ contents in the as-synthesized S-850, S-850-5, S-850-10, and S-850-15 products are 5.43, 5.74, 5.93, and 5.93 at%, respectively, which gradually increase with increasing urea contents, while the $P$ and $S$ contents (0.7 and 0.3 at%, respectively) show no change. Among all the as-synthesized products, the sample obtained by the addition of 10 wt.% urea (S-850-10) exhibits the best ORR catalytic performance in an O₂-saturated 0.1 M KOH solution with a half-potential of 0.748 V and a diffusion-limited current density of −4.76 mA cm${}^{-2}$ at 0.4 V. The half-potential and diffusion-limited current density of S-850-10 are improved by 0.53% and 8.61% compared to those of S-850 (0.744 V and −4.35 mA cm${}^{-2}$ at 0.4 V, respectively). These findings indicate that urea can be used as an $N$ resource to increase the $N$ content of biomass-derived metal-free porous carbon, enhancing its ORR performance.

In the International Space Station, urine is considered something to be treated. However, urine is mainly composed of water and urea, while they have been demonstrated as an excellent hydrogen carrier for sustainable energy supply. Through the simple chemical coprecipitation and hydrothermal reaction, the needle-like NiMoO₄ crystals were synthesized with the average width around 500nm and length up to 4$\mu$m. The resulted products were thoroughly characterized by scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction, Fourier-transform infrared spectroscopy and ultraviolet–visible spectrum. The needle-like NiMoO₄ crystals exhibited excellent electrocatalytic oxidation toward urea at anode in alkali solution, leading to the increased performance of hydrogen evolution reaction at cathode with the lower electrochemical potential and energy consumption required to drive the reaction. The high electrocatalysis of the needle-like NiMoO₄ crystals toward urea oxidation reveals their great potential for future application to clean the urine/urea-rich wastewater and to produce hydrogen in space station and environmental wastewater.

The amorphous nickel/carbon microspheres (Ni/C-MSs) were synthesized through dehydration and carbonization of glucose at high temperature and high pressure. The obtained Ni/C-MSs and the Ni/C-800-MSs (calcined at 800${}^{\circ }$C) were thoroughly characterized on morphology, composition and catalytic performance. It is found that the Ni/C-MSs showed good catalytic performance for hydrogen generation from aqueous H₃NBH₃ at room temperature. Urea was oxidized electrocatalytically by Ni/C-800-MSs in alkaline medium, indicating a viable method for wastewater remediation and simultaneous production of valuable hydrogen.

Microporous silica-alumina thin films were prepared by a simple and robust sol-gel method. Tetraethoxysilane was mixed with an acidic alumina hydrosol. Urea was added for the preparation of the alumina hydrosol, for controlling the polycondensation of the mixed oxide network and also as porogen agent. Thin films were deposited by dip-coating on dense substrates.

IR and ²⁷Al NMR spectroscopic analyses showed that for Si/Al molar ratios up to 6/1, a homogeneous mixed oxide is obtained with a random distribution of Al and Si atoms in the oxide lattice based on tetrahedral units. The deposited layers are crack-free as demonstrated by scanning electron microscopy (SEM) observations. Their microporosity was investigated using ellipsoporosimetry (EP) with films supported on flat substrates.

Incessant streak of unsuccessful attempts to synthesize low cost graphene with larger flake size and purity is frequently reported. Any reported methods that result in few layers of graphene with minimal contamination are definitive to exist. In this work, graphene was prepared economically from source of “paper” and detailed investigation was done on the effect of synthesizing parameters like paper source, temperature and amount of urea in the formation of graphene. This is a cost effective method, in which the paper that we use in our daily life was carbonized with the help of urea at a temperature of 850${}^{\circ }$C under N₂ atmosphere. The paper source was varied, shape of the paper was altered and the graphene paper with large surface area was synthesized without smudging and the prepared graphene paper was analyzed by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) for its structural, morphological investigation. To test the supercapacitance performance, electrochemical behavior was investigated in 6M KOH electrolyte. The specific capacitance of 1122F/g was obtained at 5mV/s scan rate. Chronopotentiometry curves showed an excellent cyclic stability with higher charge/discharge duration and hence could be used for electrochemical supercapacitor applications.

Photoluminescent graphene quantum dots (GQDs) have received tremendous attention due to their sui generis chemical, electronic and optical properties but fabricating the pristine quality of GQD is extremely challenging. Herein, we have reported the pyrolysis of citric acid which in the presence of different bases viz. triethylamine, ammonium hydroxide and urea, produced N-doped GQDs at different pH. The effect of different pH has been studied in detail to optimize the formation conditions of the GQD. Ultraviolet–visible (UV–Vis) spectroscopy and normalized fluorescence spectra were applied to analyze the optical properties of the GQD. The mean particle size was analyzed by a particle size analyzer (dynamic light dispersion).

The inhibition of the formation of J-aggregates of meso-tetra(4-sulfonatophenyl)-porphyrin (H₄TPPS) by urea is investigated spectroscopically by absorbance, fluorescence, and fluorescence lifetime techniques. In 8 M urea at pH 2 with 0.1 M NaCl, diacid TPPS (H₄TPPS) exists as a monomer up to 75 μM H₄TPPS where the absorbance is linearly dependent on porphyrin concentration. The extinction coefficient of monomeric H₄TPPS in 8 M urea at pH 2 with 0.1 M NaCl at 438 nm is 4.43 × 10⁵M^-1.cm^-1. No aggregation peaks at 491 nm and 708 nm are found in the 0.5-75 μM concentration range. Aggregated H₄TPPS (10 μM) molecules in pH 2 buffer dissociate to monomers when the temperature is raised to 65°C. In D₂O at pH 2, no aggregation is observed. These spectral observations suggest that the H₄TPPS aggregation involves intermolecular hydrogen bonding.

In this work, highly active graphitic carbon nitride composite photocatalysts with an isotype heterojunction semiconductor structure have been prepared through the molecular composite precursors consisting of urea and melamine. These photocatalysts were characterized by XRD, SEM, TEM, UV-Vis, BET and transient photocurrent responses. The photodegradation of dyes in aqueous solution under visible-light irradiation has been investigated over carbon nitride photocatalysts consisting of different urea/melamine mass ratios. Further studies by photocurrent indicate that the photosynergistic effect of isotype heterojunction can remarkably enhance the photoinduced interfacial charge transfer, thereby increasing the charge separation during the photocatalytic reaction.

Replacing the high theoretical potential of anodic water decomposition (oxygen evolution reaction) with the low theoretical potential of urea oxidation reaction (UOR) is an urgent need for hydrogen energy storage and conversion. Cobalt nitride nanoflakes, high-performance bifunctional catalysts supported on nickel foam (Co${}_{5.47}$N NF/NF), were synthesized by hydrothermal and calcination method. The morphology and composition of the catalyst were studied by XRD, XPS, SEM, TEM, HRTEM and elemental analysis. In order to conduct electrochemical performance and stability, a two-electrode electrolyzer composed of Co${}_{5.47}$N NF/NF as both anode and cathode materials is constructed (Co${}_{5.47}$N NF/$\mathrm{\text{NF}}||{\mathrm{\text{Co}}}_{5.47}$N NF/NF). Only a voltage of 1.687V is needed to complete 100$\mathrm{\text{mA}}\cdot {\mathrm{\text{cm}}}^{-2}$. It is much lower than the voltage of Pt/$\mathrm{\text{C}}||{\mathrm{\text{IrO}}}_2$ (1.816V), because of which it is believed that this work provides a valuable route for the design of inexpensive and efficient urea electrolysis-assisted hydrogen generation.

For the treatment of dye wastewater, it is of great significance to develop new adsorbents with high adsorption capacity and good separation effect. In this study, the Fe-Co magnetic activated carbon material (CN-Fe-Co-AC) was first prepared by high-temperature calcination. CN-Fe-Co-AC is physically characterized by various methods. CN-Fe-Co-AC can efficiently and quickly remove the organic dyes methylene blue (MB) and acid blue 80 (AB80). The adsorption of MB and acid blue based on CN-Fe-Co-AC adsorbent is mainly through the specific surface area and the functional groups on the surface. During this recovery process, the adsorption activity of CN-Fe-Co-AC for MB and AB80 decreased slightly. Kinetic data can be described using a Pseudo-second-order model and the data for adsorption equilibrium can be described using the Langmuir isotherm. The theoretical adsorption capacities of MB and AB80 are 104.82mg/g and 26.94mg/g, respectively. After repeated use of five times, the removal rate of MB exceeded 96%, and the removal rate of AB80 exceeded 75%. The excellent adsorption performance and recyclability of CN-Fe-Co-AC indicate that this material has certain potential application value.

The photocatalytic reduction of Cr(VI) to Cr(III) in aqueous solutions without or with urea (a model organic contaminant) using ZSM-5 zeolite as catalyst under UV illumination was studied. The used ZSM-5 zeolite has the characteristics of pure ZSM-5 zeolite crystalline structure, with the point of zero charge (pH_PZC) value of pH = 3.7–3.9. The effects of illumination time, mass content of ZSM-5 zeolite, urea concentrations, Cr(VI) initial concentrations and ionic strength on the photocatalytic reduction of Cr(VI) to Cr(III) were investigated. The results indicated that both the increase of urea concentration and the mass content of ZSM-5 zeolite can improve the photocatalytic reduction of Cr(VI) to Cr(III) under UV illumination. The results are important to understand the photocatalytic reduction of Cr(VI) to Cr(III) in natural environment with organic contaminant.

This study spotlights the fundamental insights about the systematic and comparative analysis of four famous hybrid classes of density functional theory (DFT) methods and their efficacy to calculate the linear and nonlinear optical (NLO) polarizabilities. For this study, urea and para-nitroaniline ($p$-NA) molecular geometries are used as prototypes to calculate their linear and NLO properties. For comparative purposes, these molecules are often used as reference organic molecules for determination of NLO response properties and there is a dire need for such a benchmark database to be utilized by the researchers. We report systematically a range of functionals including hybrid (B3LYP, PBE1PBE, BH and HLYP), meta-hybrid (M06, M06-2X, M06-HF, M06-L), long-range corrected (CAM-B3LYP, LC-BLYP, LC-B97D, LC-B97D3) and functional with dispersion correction ($\omega$B97, $\omega$B97X, $\omega$B97XD, HSEH1PBE). These groups are evaluated and their efficiency to calculate linear and NLO properties is graphically compared with each other. Overall, there are less deviations among different functionals for calculating dipole moments of $p$-NA and urea while these deviations enhance as one moves from dipole moment to linear polarizability and nonlinear hyperpolarizabilities. In general, if we look at the trends, the polarizability values of B3LYP, M06-L, CAM-B3LYP and HSEH1PBE are relatively large and can be compared with each other. The dispersion corrected and long-range corrected functionals show more systematic deviations. For instance, among dispersion corrected functionals, the amplitudes of dipole moments, linear polarizability and NLO polarizabilities show an increasing trend as $\omega \mathrm{\text{B}}97<\omega \mathrm{\text{B}}97\mathrm{\text{X}}<\omega \mathrm{\text{B}}97\mathrm{\text{XD}}<\mathrm{\text{HSEH1PBE}}$. It is also important to note that LC-B97D and LC-B97D3 of long-range corrected functional have observed exactly the same values of all the calculated parameters. A good agreement is being observed in static first and second hyperpolarizabilities of urea (B3LYP, M06-L, M06 and HSEH1PBE) and $p$-NA (B3LYP, M06, M06-L, CAM-B3LYP and HSEH1PBE). Thus, we believe that the current investigation will provide the benchmark data of reference NLO molecules at different methods for theoretical community and molecular level insights for experimental community to design better NLO materials for hi-tech NLO applications.

We have previously hypothesized that density-dependent natural selection is responsible for a genetic polymorphism in crowded cultures of Drosophila. This genetic polymorphism entails two alternative phenotypes for dealing with crowded Drosophila larval cultures. The first phenotype is associated with rapid development, fast larval feeding rates but reduced absolute viability, especially in the presence of nitrogenous wastes like ammonia. The second phenotype has associated with it the opposite set of traits, slow development, slow feeding rates and higher viability. We suggested that these traits are associated due to genetic correlations and that an important selective agent in crowded larval cultures was high levels of ammonia. To test this hypothesis we have examined viability and larval feeding rates in populations kept at low larval densities but selected directly for (i) rapid egg-to-adult development, (ii) tolerance of ammonia in the larval environment and (iii) tolerance of urea in the larval environment. Consistent with our hypothesis we found that (i) larvae selected for rapid development exhibited increased feeding rates, and decreased viability in food laced with ammonia or urea relative to controls, and (ii) larvae selected to tolerate either ammonia or urea in their larval environment show reduced feeding rates but elevated survival in toxin-laced food relative to controls. It would appear that development time and larval feeding rate are important characters for larvae adapting to crowded cultures. The correlated fitness effects of these characters provide important insights into the nature of density-dependent natural selection.