748 



7. MERCURIALS 



Table 7-6 

 Some Dissociation Constants for Simple Mercaptides' 



" The p/^i's for the mercaptides with seralbumin and hemoglobin have been recal- 

 culated (page 755), assuming pK„ for the SH groups to be 8.7 and the pK for complex- 

 ing with I to be 8.7. These values should not be considered as accurate because of 

 the assumptions involved. 



Table 7-7 



Dissociation Constants for Mercaptides with Hg++ Illustrating 

 THE Effects of pH and Temperature 



Cysteine 



Glutathione 

 12° 



42.29 

 43.54 

 43.47 



7.97 

 9.28 



25° 



40.96 



41.92 



41.58 



7.85 



9.15 



Thioglycolate 



12° 



45.66 

 45.85 

 45.52 



25° 



44.31 

 44.33 

 43.82 



" The constants are defined as follows: 



K^ 



(Hg++) (R)^ 

 (HgR2++) 



K,= 



(H+) (HgR,+ ) 

 (HgR,H++) ' 



(Hg++) (R) (R-) 

 (Hgi22+) 



(H+) (HgR,) 

 (HgR,H+) 



K. = 



(Hg++) (R-)^ 

 (HgR,) 



where R = +H3N — X — S~ and R~ = N2H — X — S for cysteine and glutathione, and 

 R = HOOC— X— S- and R- = "OOC— X— S" for thioglycolate. (From Stricks and 

 Kolthoff, 1953; Stricks et al, 1954.) 



