Biological acid-base equilibria

The biological implication of this study is highly relevant to the fact that the enzyme s mechanism is pH-dependent and, in the case that a hydroxide is the fourth zinc ligand at pH 5, the deprotonation of the Zn—OH2 could not be simply described by the acid/base equilibrium with a pK, value close to 7.0. The combination of the Zn NMR spectroscopy data and ab initio structure calculations supports the existence of a hydroxide instead of... 

FIGURE 7.4 Of the 16 chemistry topics examined (1-16) on the final exam, overall the POGIL students had more correct responses to the same topics than their L-I counterparts. Some topics did not appear on all the POGIL exams. Asterisks indicate topics that were asked every semester and compared to the L-I group. The topics included a solution problem (1), Lewis structures (2), chiral center identification (3), salt dissociation (4), neutralization (5), acid-base equilibrium (6), radioactive half-life (7), isomerism (8), ionic compounds (9), biological condensation/hydrolysis (10), intermolecular forces (11), functional group identification (12), salt formation (13), biomolecule identification (14), LeChatelier s principle (15), and physical/chemical property (16). 

In many papers the term "superoxide" (HOO ) is used simultaneously with "superoxide anion radicals" (Oa )- However, this is under the physiological conditions incorrect The pKa value of this acid-base equilibrium is 4.8 [227] and, therefore, there is only a very small contribution of HOO at physiological pH (7.4). Therefore, the term "superoxide anion radical" should be exclusively used. The superoxide anion radical is both, a one-electron oxidant and a one-electron reductant. The reactions of O2 with many different biological substrates were studied in detail by the radiation chemists and a summary of the obtained second order rate constants is provided in [228]. However, not a single carbohydrate is mentioned in this comprehensive survey since no reaction could have been observed [229]. 

Acid-base chemistry is quite important in biological systems, and acid-base reactions drive many common processes. As for this chapter, one useful example of the acid-base equilibrium process is metabolic acidosis and metabolic... 

In Chapter 8, we learned the Arrhenius definition of acids and bases—that an acid is a snbstance that can increase the concentration of ions in water and a base is a snbstance that can increase the concentration of OH ions in water. In Chapter 18, we learned about equilibrium systems. This chapter extends both of these concepts in discussing acid-base equilibria in aqueous solutions, which are extremely important to biological as well as chemical processes. 

T he sea is a living system and, like other living systems, its properties are a complex fimction of many chemical and biological processes. Some of these involve, directly or indirectly, the protonation of basic species, and consequently the state of the seawater system— its equilibrium processes and the rate at which equilibrium is being approached —depends on pH. Interactions within the hydrosphere, in which carbonate, phosphate, and silicate play an important role, regulate the pH within rather narrow limits, as the acid-base balance of the human body controls the pH of human blood. 

The work described in the foregoing sections is of a preliminary nature. Nevertheless, it offers hope that experimental scales of free hydrogen ion concentration (pcn or pmn) in seawater may be feasible. One need not know pmn or pan to derive meaningful equilibrium data, such as acid-base ratios and solubilities, provided that suitable apparent equilibrium constants are chosen (7). In these cases, the unit selected for the acidity scale disappears by cancellation. Nevertheless, the acidity of seawater is a parameter of broader impact. It plays a role, for example, in the kinetics of organic oxidation-reduction reactions and in a variety of quasi-equilibrium processes of a biological nature. The concentration of free hydrogen ions is clearly understood, and its role in these complex interactions is more clearly defined than that of a quantity whose unit purports to involve the concept of a single-ion activity. 

Not all reactions attain equilibrium they may occur too slowly, or else products or reactants may be continually added or removed. Such is the case with most reactions in biological systems. On the other hand, some reactions, such as typical acid-base neutralizations, achieve equilibrium very rapidly. 

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