Theory of Granulation
Dilip M. Parikh in Handbook of Pharmaceutical Granulation Technology, 2021
When considering a scale of scrutiny of the order of granules, we ask what controls the rate processes, as presented in detail in the previous sections. This key step links formulation or material variables to the process operating variables, and successful granulator design hinges on this understanding. Two key local variables of the volume element, A, include the local-bed moisture and the local level of shear (both shear rate and shear forces). These variables play an analogous role of species concentration and temperature in controlling kinetics in a chemical reaction, with the caveat that granulation mechanisms are primarily path functions in the thermodynamic sense, with work input as opposed to time controlling deformation mechanisms. In the case of chemical reaction, increased temperature or concentration of a feed species generally increases the reaction rate. For the case of granulation considered here, increases in shear rate and moisture result in increased granule/powder collisions in the presence of binding fluid, resulting in an increased frequency of successful growth events and increases in granule growth rate. Increases in shear forces also increase the granule consolidation rate and aid growth for deformable formulations. In the limit of very high shear (e.g., due to choppers), they promote wet and dry granule breakage or limit granule growth. In the case of simultaneous granulation and drying, bed and gas-phase moisture, temperature control, heat and mass transfer, and the impact of drying kinetics on currrent bed moisture should be considered.
Cell Biology
C.S. Sureka, C. Armpilia in Radiation Biology for Medical Physicists, 2017
Cells regulate their metabolic pathways in the following five basic ways:By controlling enzyme concentrations. Factors that affect the activity of the enzyme include (a) the temperature, (b) the pH of an enzyme, (c) the concentration/amount/volume of the enzyme, and (d) the concentration/amount/volume of the substrate. When these factors are increased, the reaction rate is also increased.By producing modulators that change reaction rates.By using two different enzymes to catalyze reversible reactions. Cells can use reversible reactions to regulate the rate and direction of metabolism.By compartmentalizing enzymes within intracellular organelles. Many enzymes of metabolism are only present in specific subcellular compartments. For example, enzymes of carbohydrate metabolism are dissolved only in the cytosol. This allows the cell to control metabolism by regulating the movement of the substrate from one cellular compartment to another.By maintaining an optimum ratio of ATP to ADP to regulate the energy status.
Simple Receptor-Ligand Interactions
John C. Matthews in Fundamentals of Receptor, Enzyme, and Transport Kinetics, 2017
Establishment of chemical equilibrium does not mean that the reaction has stopped. Every instant, molecules of R and L are combining to form RL and molecules of RL are dissociating to form R and L. At equilibrium these reactions have reached a balance such that for each RL that dissociates an R and an L combine to replace it. The change that has occurred in the system to allow it to reach equilibrium is in the relative concentrations of reactants and products. We can see from Figure 3 that as the reaction proceeds the concentrations of the reactants decrease and the steepness of the slope of the curve decreases. The rate constant (as the term would suggest) remains constant. Thus, the reaction rate decreases in direct proportion to the concentrations of the reactants. Similarly, the rate of the reverse reaction increases with time as the concentration of the reactant for the reaction in the reverse direction increases. Eventually the reaction reaches a state where the forward and reverse reaction rates are equal. This is equilibrium.
Silica nanoparticles on the oral delivery of insulin
Published in Expert Opinion on Drug Delivery, 2018
Xinyi Tan, Xiaolin Liu, Yan Zhang, Hongjuan Zhang, Xiaoyang Lin, Chenguang Pu, Jingxin Gou, Haibing He, Tian Yin, Yu Zhang, Xing Tang
As for hydrolysis, hydroxyl ions (OH−) and water molecules as nucleophilic reactants can attack the Si atom and trigger reactions in basic or acid condition respectively. When reaction medium is acidic, plentiful hydrogen ion (H+) as a catalyst has a promoting effect on the rate, of reaction. Condensation reactions are further conducted using hydrolyzed monomers above or condensed oligomers under basic or acidic condition. Negatively or positively charged monomers or oligomers as new nucleophilic reagents react with non-ionized monomers or unhydrolyzed precursors. As above, hydrolysis and condensation processes can be influenced by the pH value of the reaction medium. It has been noted the ideal pH value for condensation was 7.5 [27] or 8.4 [28], and the lowest rate happened on the pI of SNs. Besides, some factors like R-group and solvent also have effects on reaction equilibrium or intermediate stability, and thus influence continuing and reaction rate.
Therapeutic prospective of plant-induced silver nanoparticles: application as antimicrobial and anticancer agent
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2018
Krushna C. Hembram, Rahul Kumar, Laxman Kandha, Pankaj K. Parhi, Chanakya N. Kundu, Birendra K. Bindhani
Parameters that need to be considered while synthesizing AgNPs are pH, temperature, duration of reaction and the proportion of mixing biological extract to AgNO3. These parameters affect the overall outcome of the nanoparticle. Report suggests that adjustment of pH causes zeta potential of nanoparticles changes since the cationic nature of Ag+ ion tends to change due to change in ionic strength of solution. Likewise reaction rate increases by increasing the reaction temperature, which also affecting the thermo stability of reducing compound, thus affecting the yields. Along with the above two parameter time is directly proportional to the rate of reaction in most cases. Lastly, the size and shape of the nanoparticles depends upon the proportion of mixture in which the plant extract and AgNO3 were mixed [7,8].
Temperature compensation and entrainment in cyanobacteria circadian rhythm
Published in Chronobiology International, 2023
As an important signal of external environment, temperature plays essential roles in cyanobacteria circadian rhythm (Kim et al. 2020). However, to our knowledge, there is very little research work on it from the mathematical angle. In order to further understand the mechanism of cyanobacteria circadian rhythm, based on a known mathematical model (Kurosawa et al. 2006), we explore the effect of temperature and the combined effects of temperature and light. It is worth mentioning that a popular method is using Arrhenius equation to describe temperature dependence of reaction rate (Ruoff 1992; Ruoff and Rensing 1996; Ruoff et al. 2007). The Arrhenius equation characterizes a temperature-dependent reaction rate through the minimum amount of energy needed for a reaction to occur, called an activation energy. Specifically, for a given rate
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