CHEMICAL PROPERTIES 



by the pH (see Eqs. 1-14-6 to 1-14-8). The variations of these species with 

 pH are shown in Fig. 1-1, and actual concentrations are given in Table 1-3 

 for malonate and succinate at a total concentration of 10 mM. In the 

 usual range of physiological pH, over 95% of these acids are in the form 

 of the completely dissociated doubly-charged anion; this is the active form 

 for the inhibition of succinate dehydrogenase. However, it is the concen- 

 trations of the other forms which are important in the rates and degrees 

 of penetration into cells, and these change appreciably with pH (e. g., 

 from pH 7.4 to 6.8 there is a 4-fold increase in the singly dissociated form 

 and a 16-fold increase in the undissociated form). 



pH 



Fig. 1-1. Concentrations of the various ionic species of malonic 



acid at different values of the pH expressed as per cent as of 



the total concentration. 



Das and Ives (1961) on the basis of thermodynamic evidence suggested 

 that an internal symmetrical hydrogen bond occurs in H-malonate~, and 

 that this would affect to some extent the piiC^ values and reduce hydration. 

 However, Lloyd and Prince (1961) examined the infrared spectra of malonic 

 acid and its ions in DgO, compared the data with those obtained with 

 fumaric acid (in which no hydrogen bonds could occur), and concluded that 

 if hydrogen bonding exists in H-malonate~, the bond is very weak and not 

 symmetrical. Eberson and Wadsd (1963) determined the ionization enthal- 

 pies in water and ethanol, and also concluded that hydrogen bonding is 

 not important in the dicarboxylates when zlpiiC^ is less than 4. It would 

 thus appear that intramolecular hydrogen bonding is not a significant 

 factor in stabilizing the H-malonate~ ion. 



