https://onlinelibrary.wiley.com/doi/pdf/10.1002/jps.22251

Solubilities of crystalline drugs in polymers: an improved analytical method and comparison of solubilities of indomethacin and nifedipine in PVP, PVP/VA, and PVAc.

Extracellular biosynthesis of silver nanoparticles using Rhizopus stolonifer.

Amorphous pharmaceuticals, a viable approach to enhancing bioavailability, must be stable against crystallization. An amorphous drug can be stabilized by dispersing it in a polymer matrix. To implement this approach, it is desirable to know the drug’s solubility in the chosen polymer, which defines the maximal drug loading without risk of crystallization. Measuring the solubility of a crystalline drug in a polymer is difficult because the high viscosity of polymers makes achieving solubility equilibrium difficult. Differential Scanning Calorimetry (DSC) was used to detect dissolution endpoints of solute/polymer mixtures prepared by cryomilling. This method was validated against other solubility-indicating methods. The solubilities of several small-molecule crystals in polymers were measured for the first time near the glass transition temperature, including d-mannitol (β polymorph) in PVP, indomethacin (γ polymorph) in PVP/VA, and nifedipine (α polymorph) in PVP/VA. A DSC method was developed for measuring the solubility of crystalline drugs in polymers. Cryomilling the components prior to DSC analysis improved the uniformity of the mixtures and facilitated the determination of dissolution endpoints. This method has the potential of providing useful data for designing physically stable formulations of amorphous drugs.

Solubility of Small-Molecule Crystals in Polymers: d-Mannitol in PVP, Indomethacin in PVP/VA, and Nifedipine in PVP/VA

Extensive and improper utilization of water from industrial, municipal, and agricultural activities generate 380 trillion L/y of wastewater worldwide. Wastewaters from different sources contain enormous amounts of nutrients such as carbon, nitrogen, and phosphorus. Thus, the recovery of these nutrients via appropriate sustainable process becomes a necessity. Among various processes microalgae-based technologies has attracted considerable attention and its strategies for sustainable and low-cost treatment of wastewater has allowed removal of over 70% nutrient loads from the wastewater. After the treatment of wastewater, the harvested microalgae biomass contains value-added biomolecules which can used for bioenergy production and nanoparticle synthesis. At present, high operational costs represent a major limitation for the development of microalgae-based biorefineries. Thus, the main aim of the review is to provide the knowledge about the potential of low-cost microalgae-based integrated biorefinery for wastewater treatments and resource recovery. Also, this review provides the insight of microalgae biomass-based bioenergy products, nanoparticles synthesis their application within the concept of circular bioeconomy. Furthermore, this review also provides information on different established industries which used microalgae for wastewater treatment.

Microalgae-based biorefineries for sustainable resource recovery from wastewater

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Separation Process Principles

Nanoparticles have large surface area, which gives them more pronounced effects. Silver nanoparticles, for example, have pronounced biocidal effects, since they can inactivate certain enzymes and alter the DNA synthesis of some microorganisms. In this context, the study of the synthesis and characterization of nanoparticles becomes potentially important. The aim of this work was to synthesize nanoparticles and to characterize them in order to contribute to the development of synthesis and characterization of nanomaterials. Several methods are used for the synthesis of silver nanoparticles; however, in this study we used the Turchevich method which makes use of a reduction reaction using sodium citrate as the reducing agent, and silver nitrate as starting material. After being synthesized, nanoparticles were analyzed with the technique of transmission electron microscopy (TEM). Also, a curve of the size distribution of the particles formed was obtained. This distribution was obtained through a nanoparticle filtration equipment connected to a particle counter-SMPS (Scanning Mobility Particle Sizer).

Synthesis and Characterization of Silver Nanoparticles

Protein crystallization is a subject in which the commonplace “more an art than a science” still survives, and in which crystallization and crystallography are still synonyms. One of the major hindrances has been the lack of thermodynamic and kinetic parameters required for efficient crystallization design. In this article, induction times for porcine insulin and hen egg-white lysozyme were measured by absorbance at 320 nm at different levels of supersaturation, pH, and temperature, allowing determination of nucleation kinetics and interfacial tension. These parameters can help in the design and control of crystallization systems. Moreover, nucleation is explained on the basis of electrostatic interactions, and interfacial tension is related to the zeta potential of protein particles.

Induction Time as an Instrument to Enhance Comprehension of Protein Crystallization

Crystallization is the second most important separation process in chemical industry after distillation. Crystallization consists of a solid disperse phase formation into a continuous medium, which usually is a liquid solution in industrial systems. This solid phase formation occurs in two main steps: the appearance of transition structures between solid and fluid phase, or nucleation; and the growth of these structures into solid particles, crystals. The solution concentration must be higher than the equilibrium concentration at that temperature (solubility) in order to nucleation and crystal growth occur. The difference between actual concentration and equilibrium concentration is called supersaturation and is the driving force of crystallization. Supersaturation can be generated in the system by cooling, solvent evaporation, or changing of medium – addition of an antisolvent which reduces the solute solubility in the resultant system, or changing the solute by chemical reaction producing another substance with much lower solubility. Frequently other secondary processes occur, as agglomeration and breakage of those particles, which affect the final product (crystal) size distribution.

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Crystallization by Antisolvent Addition and Cooling

The major bottleneck in industrial alcoholic fermentation is inhibition by the product, which limits the ethanol yield and productivity. An efficient way of overcoming this problem is to use gas stripping to remove the ethanol during the process. In this work, the production of ethanol from sugarcane using extractive continuous fermentation with CO2 stripping was modeled and simulated. The ethanol stripping performance was first evaluated experimentally, varying the specific CO2 flow rate (ϕCO2), the solution temperature (Tsol), and the initial ethanol concentration (CE0). The parameters ϕCO2 and Tsol showed positive influences on the stripping kinetics. The proposed CO2 stripping model considered the removal of ethanol and water, as well as changes in the solution volume, and was able to accurately describe the process. Modeling and simulation of the continuous fermentation were performed considering different conditions of feed substrate concentration and cell recycling. The results indicated that ethanol inhibition could be alleviated by CO2 stripping. In addition, the combined use of stripping and cell recycling enabled the use of feed musts containing up to 400 g L−1 of sucrose, with high substrate conversion, ethanol productivity of 10.79 g L−1 h−1, and total ethanol amount produced of 174.80 g L−1 (22.2°GL), which is about twice the value achieved in an industrial process without ethanol removal by CO2 stripping. This strategy is very promising, compared to traditional processes used in Brazilian distilleries, and has the potential to reduce the global process costs, since it decreases the energy consumed for product recovery and allows the use of smaller fermenters.

Modeling and simulation of continuous extractive fermentation with CO2 stripping for bioethanol production

The kinetics of crystallization – nucleation and crystal growth – was determined for a seeded batch cooling process. Several experiments were done utilizing always the same condition: initial concentration, seed mass and size distribution, and cooling rate. From one experiment to other the agitation speed was varied. As the utilized reactor is able to measure torque of the impeller, the power dissipated in agitation was monitored during the crystallization, as well as reactor temperature and turbidity of the suspension. Turbidity monitoring and the measurement of particle size distribution from seeds and final product allowed obtaining the evolution of the second moment of the particles during the crystallization. The crystallization process was modeled utilizing the Method of Moments and the nucleation and crystal growth kinetics were obtained from least-square minimization of calculated second moments of the crystals. A crystal growth kinetic was determined and the secondary nucleation rate was described as a function of dissipated power and as functions of impeller tip speed. Additional experiments were done, in which cooling rate, seed mass and seed size were varied. The calculated kinetics could satisfactorily describe the results of the additional experiments, corroborating the quality of the modeling.

André Bernardo

Papers

Synthesis and Characterization of Silver Nanoparticles

Induction Time as an Instrument to Enhance Comprehension of Protein Crystallization

Crystallization by Antisolvent Addition and Cooling

Modeling and simulation of continuous extractive fermentation with CO2 stripping for bioethanol production

Modeling of crystal growth and nucleation rates for pentaerythritol batch crystallization