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A Brief Background
Published in Nathan Keighley, Miraculous Medicines and the Chemistry of Drug Design, 2020
Organic reactions can be classified as either acid-base reactions or redox reactions. The transfer of a hydrogen ion (a proton) identifies an acid-base reaction, while a change in functional group from reactants to products shows reduction-oxidation reactions. Processes that involve homolytic bond cleavage are called radical reactions. Processes that involve heterolytic bond breaking are called polar reactions. Polar reactions are the most common type of reaction of organic molecules and involve reactions between polar molecules and/or ions. There are three main classes of polar reactions. An addition reaction involves the combining of two molecules to yield a single product, while in an elimination reaction, one reactant molecule is converted into two product molecules. In a substitution reaction, one functional group on the molecule is replaced by another.
Precipitation and Acid/Base Aqueous Reactions
Published in Patrick E. McMahon, Rosemary F. McMahon, Bohdan B. Khomtchouk, Survival Guide to General Chemistry, 2019
Patrick E. McMahon, Rosemary F. McMahon, Bohdan B. Khomtchouk
An acid/base reaction is the complete description of the transfer of one or more H+ ions from the acid to the base. An H+ ion does not have an independent existence. The reaction involves the exchange of one covalent bond involving the hydrogen on the acid for another covalent bond involving the hydrogen on the base. The hydrogen is transferred without its electron; thus, the species transferred is an H+ ion.
Skin Absorption Databases and Predictive Equations
Published in Richard H. Guy, Jonathan Hadgraft, Transdermal Drug Delivery, 2002
Brent E. Vecchia, Annette L. Bunge
These measurements are placed at pH = 4 in Fig. 10. Singh and Roberts (45) reported that their permeability coefficient measurements were determined at the pH at which fni = 0.5 (i.e., pH = pKa, if there is one dominant acid-base reaction). However, they did not list pH or pKa, values for any of the chemicals they studied. Lacking these values, pKa, values for each chemical were calculated using SPARC. Permeability coefficient values for compounds determined using a range of pH measurements (i.e., ethyl nicotinate, methyl nicotinate, and salicylic acid) were placed at the pH corresponding to the midpoint of the pH interval given in Table Al.
Modified self-healing cementitious materials based on epoxy and calcium nitrate microencapsulation
Published in Journal of Microencapsulation, 2021
Fahimeh Farshi Azhar, Aylin Ahmadinia, Alireza Mohammadjafari Sadeghi
At curing system of epoxy, the existence of calcium nitrate has a significant role on accelerating the reaction between epoxy and amine curing agents. Based on novel investigations (Mirmohseni Namin et al.2015, John 1992 , Whiter 2002), among inorganic salts, calcium nitrate was preferred to decrease the curing time of epoxy. The reaction of calcium nitrate and amine curing agent is controlled by three mechanisms: (1) poly-addition, (2) cationic polymerisation and (3) anionic polymerisation (scheme 2). Poly-addition reaction is based on the typical epoxy curing mechanism. Indeed, the reaction between amine curing agent and calcium nitrate acts as an acid–base reaction, which in it, calcium nitrate acts as an acid, and the amine curing agent has the alkaline role in the reaction. As it is known, the acid–base reaction increases the temperature of reaction so that the rate of reaction increases. Accordingly, the time of curing process will decrease. The produced nitrate ions from acid–base reaction steer the anionic polymerisation (Scheme 2(a)), and the protons trigger the cationic polymerisation (Scheme 2(b)). Three mentioned mechanisms lead the epoxy curing reaction with the aim of accelerating curing.
Studies of the early stages of the dynamic setting process of chemically activated restorative glass-ionomer cements
Published in Biomaterial Investigations in Dentistry, 2021
Fernanda M. Tsuzuki, Renata C. Pascotto, Luis C. Malacarne, Antonio C. Bento, Antonio Medina Neto, Lidiane Vizioli de Castro-Hoshino, Monique Souza, John W. Nicholson, Mauro L. Baesso
The initial reaction, after cement mixing, is an acid-base reaction between an aqueous polymeric acid solution and an ion-leachable basic glass powder [10,11]. When mixed with the liquid, the glass powder degrades so that Ca2+ or Sr2+ and Al3+ ions are released. These ions interact with carboxylate groups on the polymer chain, causing cross-linking and initial hardening. The setting reaction occurs rapidly, usually in the first minutes [12]. The final cement includes a substantial amount of unreacted glass particles acting as reinforcing fillers in the polymer matrix [10,13]. There is a further possibility for improving the properties of these materials to make them still more competitive compared with other restorative systems. Knowledge of the sequences of the setting reaction in dental cements is therefore crucial, as they will affect the handling and final physical properties of the cements [13].
Effect of fluoride varnish on glass ionomer microhardness changes in endogenous acid erosion challenge
Published in Biomaterial Investigations in Dentistry, 2021
Fatemeh Moharramkhani, Ladan Ranjbar Omrani, Mahdi Abbasi, Mohammad Javad Kharrazifard, Elham Ahmadi
In this study, exposure of RMGI to gastric acid significantly decreased its microhardness. However, gastric acid did not have a significant effect on the CGI samples. The reactive sites are evenly distributed in CGIs (unlike RMGIs); thus, the effect of acid on all areas would be the same upon acid attack. However, in RMGIs, the weakest area around glass particles is more severely affected by acid, leading to a selective destruction pattern, which further degrades the surface of RMGIs. This fact along with the presence of HEMA may explain the highest change in microhardness in the RMGIa subgroup. On the other hand, evidence shows that the equilibrium of acid-base reactions and the maximum polymerization of glass ionomers require 7 d to occur; thus, incubation at 37 °C for 7 d is often recommended [15]. However, we did not adhere to this protocol in our study, which might have further complicated the situation.