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Introduction: Background Material
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
This is a stoichiometric equation, where stoichiometry is concerned with the relative quantities of reactants and products in a chemical reaction, and a stoichiometric equation shows the quantitative relationship between reactants and products. A proper stoichiometric equation must be balanced, that is, the number of atoms of any element must be the same on both sides of the equation in accordance with conservation of mass. Thus, in Equation 1.39, there are two atoms of oxygen and four atoms of hydrogen on either side. The number multiplying each species in the stoichiometric equation is the stoichiometric coefficient.
Evaluation of the Dermal Irritancy of Chemicals
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
Enzymes are protein catalysts of biological origin, a catalyst being defined as a substance which increases the rate of a particular chemical reaction without itself being consumed or permanently altered.71 Knowledge of enzymes and their actions goes back at least 150 years. Clinical enzymology, the application of the knowledge of enzymes to the diagnosis and treatment of disease processes, is a still rapidly developing field in contemporary clinical chemistry. Measurements of digestive enzyme activity in body fluid as an aid to diagnosis date back to the early 1900s. Measurement of enzyme activity in serum began in the 1920s and 1930s with studies on alkaline phosphatase in bone and liver diseases, and acid phosphatase in prostatic cancer. In 1943, Warburg and Christian observed increased activities of glycolytic enzymes in sera of tumor-bearing rats, and, in 1955, LaDue et al. reported a transitory rise of glutamic-oxaloacetic transaminase (SGOT; now called aspartate transaminase, AST) activity in serum following acute myocardial infarction.71
Small Molecules: Process Intensification and Continuous Synthesis
Published in Anthony J. Hickey, Sandro R.P. da Rocha, Pharmaceutical Inhalation Aerosol Technology, 2019
Chemical reactions to produce pharmaceuticals have significant diversity in terms of reaction type and mechanism. In addition, many of the processes are scaled up very quickly to pilot plant reactors before full chemistry characterization can take place. Understanding of reaction kinetic data is an important mechanism for interpreting reaction scalability and interaction with mass transfer processes, and therefore chemists should strive for early collection of kinetic data whenever possible. Fortunately, modern equipment such as controlled reactors and in-situ FTIR are reducing the barrier to gathering such information. An excellent introduction to in-situ monitoring as an enabling technique for gathering of reaction progress data has been outlined by Donna Blackmond.23 Blackmond has outlined that reaction progress kinetics can be conducted very simply if one has a method of in-situ analysis, as well as a curve-fitting software program. In-situ FTIR spectroscopy can be used to monitor the reaction concentration (or conversion) profile and converted to rate information via the integral method. The confidence of this data can be increased by using an orthogonal off-line analytical method such as HPCL or GC, which are routinely available during product development. In a follow-up paper, Blackmond outlined the use of both reaction calorimetry, as well as in-situ FTIR measurements to determine the mechanism of catalytic reactions, outlining how these two techniques can be used in a complementary fashion.24
Reducing free residual chlorine using four simple physical methods in drinking water: effect of different parameters, monitoring microbial regrowth of culturable heterotrophic bacteria, and kinetic and thermodynamic studies
Published in Toxin Reviews, 2021
Razieh Sheikhi, Amir Hossein Mahvi, Abbas Norouzian Baghani, Mahdi Hadi, Armin Sorooshian, Mahdieh Delikhoon, Somayeh Golbaz, Arash Dalvand, Fatemeh Johar, Mohammad Rezvani Ghalhari
As for the third method, it’s a well-known fact that heating accelerates chemical reactions and evaporation. Thus, in this study, the effect of heating on FRC concentration is associated with this fact. If there is potential of FRC taking part in chemical reactions, as mentioned above, heating will simply help by providing all or some of the activation energy needed for the reaction to be started. In the fourth method, incubator shaker accelerates FRC removal reactions and reduces FRC by a significant amount in less time than the SSA method (first method) and SSR with and without a lid (second method). As observed in this study, such different methods result in different fates of FRC. In fact, these findings can be concluded that each of these methods creates a unique situation in which FRC is reduced in a different way from another.
S-Carboxymethyl-l -cysteine: a multiple dosing study using pharmacokinetic modelling
Published in Xenobiotica, 2021
Glyn B. Steventon, Stephen C. Mitchell
Studies using cell-free systems assessed the scavenging activity of SCMC on reactive oxygen species generated from hypochlorous acid (HOCl), hydrogen peroxide (H2O2), peroxynitrite (ONOO–) and hydroxyl radicals (HO•; produced from H2O2/FeCl3) during incubation in phosphate buffer (Nogawa et al. 2009). Similar studies were reported for the SCMC-lysine salt (Brandolini et al. 2003). The drug was effective between concentrations of 0.179 μg/ml (against 54 μM NaOCl) and 179.2 μg/ml (against 1 μM ONOONa; 3 mM H2O2/FeCl3). However, these systems are purely chemical reactions and dependent upon the relative concentrations of reactants employed. Owing to its chemical structure, containing a sulphur moiety, the drug is able to scavenge reactive oxygen species. To have a direct biological meaning such experiments must be undertaken at concentrations of reactive oxygen species that actually occur within the living cell and even then, there are many confounding factors.
Neutralization of the eye and skin irritant benzalkonium chloride using UVC radiation
Published in Cutaneous and Ocular Toxicology, 2021
Manlong Xu, Jacob G. Sivak, David J. McCanna
The mechanism of the neutralization of BAK by UVC radiation remains unclear. It is possible that BAK absorbs the energy from UVC and undergoes a photochemical reaction that turns it into a non-toxic substance. Photochemical reactions are chemical reactions that initiated by the absorption of energy in the form of electromagnetic radiation and end with the formation of stable products that are different from the original chemicals. In such reactions, a molecule absorbs energy from electromagnetic radiation and is promoted to an exited electronic state, thereby initiating a sequence of events that continuously lower the energy of the excited molecule. These events can include a number of bond-breaking and/or bond-making processes. Because BAK contains a benzyl group and a long alkyl chain (ranging from 8 to 18 carbon atoms)27, several processes may occur upon its absorption of UV radiation: fragmentation of the long alkyl chain, cycloadditions of the unsaturated benzene ring, and substitution reactions of the benzyl group. In these processes, the excited BAK species can fall apart, change to new structures, combine with each other or other molecules, and hence result in the formation of new chemicals (stable final products). In the current study, the final products formed in the photochemical reaction were stable and non-toxic. Further studies are needed to analyse the final products and to understand the mechanisms involved in this neutralization effect.