176 J. E. O'Hagan 



purposes which had not been subjected to the usual heat treatment to destroy 

 hepatitis virus. 



Imidazoles 



Caffeine B.P. and theophyUine B.P. were suppHed by Drug Houses of 

 AustraHa Ltd. They were recrystalhzed from water and used as saturated 

 aqueous solutions. 



Bujfer Solutions 



These were prepared with British Drug Houses A.R. grade chemicals from 

 tables calculated by George and Hanania (unpubhshed), and kindly supplied 

 by Professor P. George. The buffers were of constant ionic strength (I = 0.05) 

 and of the following composition: pH 2-0-3-8, HCl + KH phthalate; 

 pH 4-0-6-2, NaOH + KH phthalate + NaCl; pH 5-6-8-0, NaOH 

 + NaH2P04 + NaCl; pH 7- 5-9- 5 HCl + Na4Po04 + NaCl; pH 9-9-1 M, 

 NaOH + glycine + NaCl; pH 11-0-12-0, Na'gHPO^ + NaOH + NaCl; 

 pH 130, NaOH. 



Dithionite 



1 % w/v solutions were prepared immediately before use from sodium 

 hydrosulphite B.D.H., which was taken from a freshly opened ampoule 

 (repacked from a 500 g bottle). 



Standardization of Instruments 



The Hilger Uvispek Spectrophotometer, Beck Hartridge Reversion 

 Spectroscope and Jones Electronic pH Meter were standardized as previously 

 described (O'Hagan, 1960). All pH measurements were made with the 

 standard glass electrode, and, although corrections were applied, all readings 

 at high pH should not be regarded as exact. 



RESULTS 



Decrease in the Acid Strength of Haematin Propionate Groups on Reduction 

 to Haem 



It appeared possible that since substituents of R in RCH2CH2COOH 

 could alter the pAT value of the carboxyl by as much as 1-3 units (Edsall 

 and Wyman, 1958), a change in the electronic structure of the haem iron 

 atom producing alterations in the high resonance of the porphyrin ring 

 system might have the same effect as a substitution of R in simple com- 

 pounds, with subsequent change in the acid strength of the propionate 

 groups. To test this hypothesis two reactions known to involve the propionate 

 groups were investigated, those with human serum albumin, and with caffeine. 

 A new reaction with theophylline was found, and prehminary results obtained 

 supported those observed with caffeine. 



