Enzyme activity was determined by immersing a plastic support coated with a known amount of enzyme-modified microspheres in the urea solution. Urea hydrolysis by the immobilized urease on the microspheres produced a change in pH, which caused the test solution to turn pink. Imatinib molecular weight The enzyme urease catalyzes the urea hydrolysis to change pH according to the following reaction:H2N?CO?NH2+3H2O��Urease2NH4++HCO3?+OH?The absorbance of the test solution was monitored for 30 min at a wavelength of 553 nm Inhibitors,Modulators,Libraries using the spectrophotometer.2.4. Enzyme Leaching Test and Effects of pH on Enzyme ImmobilizationTo determine the effects of pH on the immobilization of the enzyme, urease enzyme solutions were prepared using phosphate buffer at pHs of 6.5, 7.0, 7.5 and 8.0.
For the leaching test, a fixed amount of acrylic microspheres modified with immobilized urease were immersed in 0.05 M (pH 7.0) phosphate Inhibitors,Modulators,Libraries buffer solution, and 0.5 mL phosphate buffer solution was taken in every 10 min before mixing with 2.5 mL of urea solution Inhibitors,Modulators,Libraries (1.0 M) and phenolphthalein indicator. The mixture was monitored for 90 min, where the absorbance of that solution was periodically measured at a wavelength of 553 nm using the spectrophotometer.2.5. Determination of Urease ImmobilizedThe amount of urease immobilized onto the urea biosensor and the influence of various immobilization times (0.5 to 24 h) were quantified by Bradford reagent method [24] with bovine serum albumin (BSA) as a standard to quantify urease enzyme immobilization. Urease enzyme concentration for immobilisation studies was fixed at 2.0 mg mL?1.
The amount of immobilized enzyme was calculated according to the following Inhibitors,Modulators,Libraries equation:%?urease?immobilized=(A?B)/A��100%where A is the amount of urease used and B is the urease left after immobilisation.2.6. Construction and Evaluation of Urea Biosensor PerformanceA sample of 375.0 mg of dried acrylic microspheres, 300.0 ��L chromoionophore solution (0.1 mg mL?1 ethanol), 450.0 ��L ethanol and 125.0 ��L DMF were ultrasonically mixed for 3 min until homogene
Increasing fuel costs and the need to reduce CO2 emissions are the main drivers for the market penetration of fuel-efficient leanly operated internal combustion engines in the field of passenger cars. Due to their lean operation mode, NOx removal with a conventional three-way catalyst is not possible [1].
At the same time, the emission limits for NOx have been strongly tightened. Besides the ammonia-selective catalytic reduction process, in which NOx is selectively reduced Anacetrapib to nitrogen and water even under lean conditions [2], the NOx selleckchem storage catalyst (abbreviated NSR, also often denoted as lean NOx trap, abbreviated as LNT) has been developed [3], especially for direct injection gasoline engines that operate in the lean mode. During a lean phase, NOx is oxidized, absorbed, and stored in the form of nitrates.