Compounds with hydrated structures can degrade easily. Therefore, investigation of the degradation process of hydrated compounds is imperative from the viewpoint that the hydration status often contributes to the stability and even affects the spatial structure of compounds. Cefixime Trihydrate, a widely used antibiotic, is one of such typical examples, in which the hydrated water molecules have been revealed to contribute significantly to its crystallinity. Previous studies have shown that an over-drying process could cause the hydrolysis decomposition of Cefixime Trihydrate. However, no quantitative analysis has been reported. Herein, we report a systematic evaluation of the influence of over-drying on crystal condition. Analysis of the correlation between the water content and crystallinity indicated the importance of hydrated water molecules toward the stability of Cefixime. The Avrami equation was also employed to fit the correlation data between the increase of degradation ratio and the decrease of crystallinity. For the first time, the crystallinity was quantified to determine the stability of the crystal lattice, which depends on water content. It was confirmed that over-drying process could cause the destruction of the crystal lattice and lead to the acceleration of the degradation rate. We expect our results will deepen the comprehension of the relationships among the degradation rate, the hydration state, and the crystallinity, helping optimize the storage conditions of products in chemical plant scale manufacturing with more convenience.
Efficacious use of activated carbon beds (ACBs) as adsorbents for various types of organic vapors in respirator gas filters requires estimation of the breakthrough time. In this study, several types of activated carbon small beds acting as gas filters were preconditioned by equilibration at low relative humidity (RH=40%) and a constant temperature of 20°C. Then, we measured the breakthrough curves of 13 types of organic vapors through the beds under the same RH and temperature conditions as used for preconditioning and calculated their relative breakthrough time (RBT) with reference to cyclohexane. The ACBs comprised four types of activated carbon and had different weights (22.5–35 g), yet the measured RBTs showed good approximation to the reference data, with a small number of exceptions. We confirmed that RBT can be used as an effective index at RH=40% and 20°C.
Various solid oxide catalysts are active for the oxidative dehydrogenation of propane, but achieve yields of less than 2% when these were used for the oxidative dehydrogenation of isobutane to isobutene. An improved isobutene yield of 8% was obtained in the oxidative dehydrogenation of isobutane by using a folded-sheet mesoporous material (FSM-16) and mesoporous molecular sieve (MCM-41), with or without chromium via impregnation or template-ion exchange methods. Further activity enhancement, however, could not be attained. In the present study, chromium cations were introduced into the framework of SBA-15 using a direct synthesis method by mixing chromium nitrate with tetraethylorthosilicate in an aqueous solution with an initial pH of 1.5 and subsequent hydrothermal treatment. Loading the resultant catalyst, SBA-15, with a small amount of chromium (1.84 wt% Cr-SBA-15) increased the isobutene yield (15.4%) at 723 K, while a previous report showed that chromium oxide supported on SBA-15 (CrOx/SBA-15) prepared via incipient wetness impregnation had a lower isobutene yield (11%) at 813 K. To explain this improvement, the catalysts were characterized using X-ray diffraction, transmission electron microscopy, N2 adsorption–desorption, and NH3 temperature-programmed desorption. Cr-SBA-15 was found to have a large specific surface area (1,610 m2/g), although the structural and acidic nature of the catalyst was similar to the general properties of other mesoporous silicas. The conversion of Cr3+ species into Cr6+ on Cr-SBA-15 with the large specific surface area could affect the improvement of the oxidative dehydrogenation of isobutane to isobutene.
This paper proposes a new stiction compensation method that combines adaptive inverse model techniques and intelligent control theories to compensate for a process containing a sticky valve. This new method reduces the cycling caused by the nonlinear dynamic associated with stiction, while avoiding aggressive movements of the valve stem. The parameters of the compensator depend on both the type and degree of stiction, and their estimates are optimized using differential evolution. Both simulation and experimental results validate the approach. The compensation method demonstrates excellent performance in overcoming the effect of stiction and in reducing the oscillations with smooth valve stem movements.
We have developed an in vitro penetration cell for transcorneal iontophoretic delivery. The thickness of the diffusion boundary layer δ of this in vitro system was evaluated by benzoic acid dissolution experiments under several mixing conditions of receptor solution. The δ under the condition of magnetic stirrer at 300 rpm in the receptor solution for the present KK cell was 201.0±20.4 µm, which is thinner than that for a Franz diffusion cell (323 µm). Moreover, the mass transfer coefficient km (=D/δ) was calculated by Sh=2+3.45Re0.11Sc0.33; this equation gave the km and δ for the KK cell if the value of the diffusion coefficient D, viscosity μ, and density ρ of receptor solution were known. The penetration rate across cornea from pig in vitro was proportional to the voltage applied to the cornea during iontophoresis. The effect of iontophoresis on the penetration rate was quantitatively investigated after taking into consideration the hydrodynamic diffusion boundary layer.
A numerical simulation study was carried out to investigate the suspension of cell colonies in bioreactors of stirring and orbiting shaking tanks. The cell colonies in a culture liquid were modeled as rigid spherical solid particles. The shear stresses acting on these particles were analyzed. The simulation results have shown that the maximum shear stress acting on the particles in the stirring tank is higher than that on the particles in the orbital shaking tank. However, the average values of the shear stress on the particles in both tanks are comparable. The simulation results also show that more particles accumulate at the bottom of the orbital shaking tank in which the particle aggregation obeys the Einstein’s tea leaf paradox. The simulation results are evaluated based on the predicted shear stress profiles and tank configuration.
Poly-gamma-glutamic acid (γ-PGA) is a water-soluble, nontoxic biodegradable polymer. It is extensively utilized in medicines, foodstuffs, and cosmetics, as well as in water treatment. Highly pure γ-PGA is required for various purposes. In many cases, γ-PGA is produced by microbes of Bacillus sp. However, an increase in the viscosity of the culture broth is one of the major problems of γ-PGA production, as higher viscosity makes the separation and purification steps difficult. Herein, we propose a novel method to obtain pure γ-PGA using gemini quaternary ammonium salts (GQASs). The quaternary ammonium cation of GQASs binds to the carboxylic acid group of γ-PGA via an ionic bond, following which water-insoluble and antimicrobial complexes are formed. These complexes are obtained in the aqueous solution, which were resolved in ethanol solution. With an increase in the added amount of GQAS, the negative charge of the complex decreased in the aqueous solution. Subsequently, the GQAS within the complexes was dissociated by the addition of NaCl, affording pure γ-PGA in a high yield. Moreover, the complexes were shown to have antibacterial activity and adhered to glass, indicating that the complex itself has a utility value.
In this study, bovine bone biowaste was dissolved in an ionic liquid (1-ethyl-3-methyl bromide imidazole) to obtain hydroxyapatite (HAp) as a valuable product. The influence of solid–liquid ratio (mass ratios of bovine bone to ionic liquid of 1 : 10, 1 : 20, 1 : 30, 1 : 40, and 1 : 50), dissolution time (2, 3, 4, 5, and 6 h) and dissolution temperature (120, 140, 160, 180, 200, and 220°C) on the yield of HAp was examined. The optimal process parameters determined by an orthogonal test were a solid–liquid ratio of 1 : 25, a dissolution time of 3 h and a dissolution temperature of 220°C. HAp was obtained in a yield of 45%. The extracted HAp was characterized using Fourier transform infrared spectroscopy (FT-IR), X-rays diffraction (XRD), energy dispersive spectrometer (EDS), and scanning electron microscope (SEM). The FT-IR results showed peaks characteristic of HAp, which indicated that extracted HAp had similar components to natural bones. XRD showed that extracted HAp was crystallized. The EDS analysis showed a Ca/P ratio of 1.66 for extracted HAp. Furthermore, the biocompatibility of extracted HAp was assessed through acute toxicity, pyrogen, allergy, and hemolysis. The results showed that extracted HAp was pyrogen free and exhibited mild acute toxicity, slight hypersensitivity, no hemolysis phenomenon, and biocompatibility.
Curcumin holds promise as a therapeutic agent due to its capability of conferring several pharmacological activities. While curcumin shows efficacy in preclinical studies as an anti-cancer agent, its translation into the clinic as a drug has yet to be realized. One possible reason is its poor solubility and stability in water, which decreases the bioavailability. Here, we report the formation of biocompatible nanocomplexes (NCs) from caseinate (CS) and chitosan (CH) using an electrostatic interaction-based approach to stabilize and enhance water solubility of curcumin. The formation of CS–CH NCs (CCNCs) was studied as a function of CH concentration. We show that positively charged NCs, having size between approx. 250 nm with a narrow distribution was formed by adjusting CH concentration. CCNCs successfully entrapped curcumin with a high entrapment efficiency. Curcumin was possibly located in a hydrophobic region of CS as indicated by a blue-shift in the emission maxima of curcumin. Ultimately, the stability and water solubility of curcumin in CCNCs could be remarkably enhanced. These results suggest that CCNCs would be useful for increasing the potential of curcumin as a preventive or therapeutic agent.
Unseeded semi-batch cooling crystallization of potassium alum (AlK(SO4)2·12H2O) was carried out to obtain monodisperse crystal size distribution. A semi-batch cooling method was preferred to batch-wise cooling method for preventing from secondary nucleation because supersaturation was successfully controlled by the feed condition. Further, the semi-batch cooling method provided larger crystals than the batch-wise cooling method, and volume mean size linearly increased with feed rate. In crystallization processes of food and pharmaceuticals, unseeded conditions are occasionally preferred in view of crystal purity. Semi-batch cooling is a simple method to control supersaturation by feed conditions and modify crystal size distribution.
The cracking behavior in polystyrene (PS) nanocomposite thin films prepared by a solution casting method was investigated experimentally, and the formation mechanism of the cracks was clarified. A glass substrate was blade-coated with a toluene solution containing polystyrene and surface-modified nanoparticles prepared by the supercritical hydrothermal synthesis method; then, toluene was evaporated by a directional surrounding gas flow. In the case of nanocomposite thin films with oleic acid-modified nanoparticles, it was found that regularly spaced cracks were generated, and that the crack spacing was particularly affected by the partial vapor pressure of the solvent in the surrounding gas. On the other hand, there were no cracks in the thin films with decanoic acid-modified nanoparticles. In addition, the spatial structures of the thin films were observed by scanning electron microscopy and transmission electron microscopy. These observations revealed that a uniform layer of oleic acid-modified nanoparticles was formed at the surface of the thin film. Therefore, it was concluded that the cracks were formed by the tensile stresses due to the capillary force acting on the solvent meniscus between the nanoparticles in the surface layer during solvent evaporation.
Biomass pyrolysis experiments with iron oxide-based oxygen carrier for Biomass Direct Chemical Looping (BDCL) were carried out in order to understand pyrolysis behavior and oxygen carrier performance in a reducer. Biomass was used as feedstock in these experiments, and the effect of direct injection of feedstock to the reducer on oxygen carrier behavior associated with biomass pyrolysis was evaluated. In the experiments, the oxidizing and tar cracking abilities of different phases of iron oxide oxygen carrier were evaluated by measuring the produced gas composition and carbon deposition on the oxygen carrier. The volume and composition of produced gas varied according the iron oxide phases, and Fe2O3 composite showed the strongest oxidizing power, while FeO composite proved to have cracking ability of biomass tar components. Carbon deposit, on the other hand, was observed on the oxygen carrier, and increased in the order of FeO>Fe3O4>Fe2O3, regardless of the reaction temperature.