Intracellular pH and its Measurement

Arnost Kotyk,Jan Slavik

• Publisher: CRC Press
• Year: 2020
• ISBN:
  9781000141627
• Edition: 1
• Topic: Scienze biologiche
• Subtopic: Scienza generale

This volume introduces a summary of all the techniques used to estimate pH reliably. Emphasis is placed on the techniques that provide the most reliable and detailed data. The role of cell pH is explained with special emphasis on enzymology and membrane transport and bioenergetics. This book was written especially for molecular biologists, biochemists and biophysicists.

Chapter 1

THE CONCEPT OF pH, HYDROLYSIS, AND BUFFERS

Arnošt Kotyk

TABLE OF CONTENTS

I.	Definition of pH
II.	Ionization of Acids and Bases
III.	Hydrolysis of Salts
IV.	Buffering Power
V.	The Activity Coefficient
References

I. DEFINITION OF pH

Some 80 years ago, Sorensen introduced the symbol pH for the negative logarithm of concentration (moles or equivalents per cubic decimeter) of H⁺ ions.¹ The letter “p” derives either from the Latin pondus (weight or significance) or from potentia (might or potential) and has since been used to denote the negative logarithm of concentration of various other ions; e.g., log c_Na+ = −pNa, which is correct or at least consistent. It has also been used for the negative logarithms of various kinetic quantities having dimensions of concentration, such as the dissociation constant K_a, where −log K_a = pK_a, which is certainly incorrect in the original sense of “p” but is useful in cases where sums or differences, such as pK^a – pH, occur in formulae.

In Sörensen’s original version

${\text{pH = −log}}_{10}{c}_{{\text{H}}^{+}}$

(1)

but it is now defined in terms of activities a. Thus (with γ being the activity coefficient),

${\text{pH = −log}}_{10}(c_{\text{H}}+{\text{γ}}_{\text{H}}+)=-\log a_{{\text{H}}^{+}}$

(2)

which, particularly in more concentrated solutions, represents an appreciable difference, as will be seen below.

It should be observed that in rigorous derivations of these equations both c and a (and, hence, γ) are dimensionless quantities that can be understood as concentrations or activities relative to a unit reference. Their values are thus numerically identical with true concentrations or activities expressed in moles per cubic decimeter.

Water, which is the principal milieu of all subcellular and cellular systems, is an extremely weak electrolyte; but it is still dissociated into ions, accordin...