PKA of aminoglycosides by NMR
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Acid/Base and pH
Aminoglycosides: The term of acids was first reported to be used in Greece and was used to report substances that were sour; the word ‘acid’ was also derived from a Greek word, ‘Oxein’ (Reijenga et al., 2013, p.53). The term was later converted into Latin as ‘Actium’ to describe vinegar. Besides being sour acids were described to change the colour of litmus paper to red and corrode metals.
Their counterparts, the bases, were mainly defined to be the substances that counteract the acids. Later on the basis of their name, alkaline was derived from an Arabic word ‘roasting’ because of their discovery from the roasted ashes. Since then, both acids and bases have been defined in several ways by several scientists. Aminoglycosides.
One of the first clear definitions was given by Svante August Arrhenius; he defined acids to be the substances that give a hydrogen ion or proton in solutions and bases to be the substances that give hydroxyl ions in solution. These definitions were improved upon by a Danish chemist Johannes, who excluded the role of hydroxyl ions and described bases as the substances to be acceptors of protons while retaining the definition of acids.
Aminoglycosides: This definition was based on the behaviours of acids and bases in solutions. Thus, the definitions were further modified by Gilbert Lewis to be applicable in non-aqueous solutions and defined acids as the substances, which can receive electrons and bases as the substances, which can donate electrons (Lesney, 2003). All of the definitions given above are true and are still used in certain conditions however by the invention of pH scale, the decision of acidity and basicity is made based on the pH values of substances (LibreTexts, 2014).
pH and dissociation constants such as pKa are among one of the most frequently studied parameters and give a considerable amount of information about the physical and kinetic behaviour of chemical substances. pH, simply defined as the negative log of hydrogen ion concentration, is a measure of the potential hydrogen ions and the acidity and basicity of a solution.
The term was first coined by a Danish biochemist named, Soren Sorenson. He defined the p in pH to be the negative log. The letter ‘p’ is derived from the German word “potenz”, which stands for power or exponent of. The word pH was purported to mean Pondus Hydrogenii in Latin. The use of a logarithm in the formula entails that a change of one integer in the pH leads to a 10 fold change in hydrogen ion concentration.
With advancement in scientific knowledge, the definition has been modified to the negative log of the effective concentration of hydrogen ions which depends on a number of variables including concentration, because all of the hydrogen ions in a solution may not be available, for example in a concentrated acid solution (LibreTexts, 2014).
pH = −log [H+]
The main advantage of using pH instead of the actual concentration of hydrogen ion was convenience. By using the pH scale, one can denote a hydrogen ion concentration of 1.23×10-4 simply as 3.91. Due to the use of logarithmic scale, a very large range of concentrations is covered in a convenient manner. Use of this scale also has the advantage of converting very small values into easily tangible digits (LibreTexts, 2014).
The value of pH ranges from 0 to 14. Solutions having pH greater than 7 are basic and have more hydroxyl ions than hydrogen ions while acidic solutions have a pH lesser than 7 and have a greater concentration of hydrogen ions than hydroxyl ions. Solutions having a pH equal to 7 are neutral and an equal concentration of hydrogen and hydroxyl ions are present (LibreTexts, 2014).
The scale of pH usually ranges from 0-14 because most of the naturally occurring fluids have hydrogen ion concentration in this range. But values greater and lesser than….
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