THE EFFECT OF BETA RADIATION ON PORPHYRIN C:OMPOUNDS 



Irradiation — (/) 13 ml. portions of solution were irradiated with average 

 (i.e., per niillilitre) doses of 210 to 2500 rad. Dose rate (average) was 41 -7 

 rad/min. 



(//) 7 ml. portions of solution were irradiated with average doses of 1000 

 to 8000 rad. The average dose rate was 72-4 rad/min. 



Estimation of porphyrins — The solution was prepared by diluting 1 in 10 

 with water and was then read in the spectrophotometer at the wavelength 

 of maximum Soret absorption (401-404 m\i). 

 Irradiations and estimations were in duplicate. 



{b) Effect of dose rate 



Preparation of solution — 2-5 mg protoporphyrin were dissolved in 7 ml. 

 N NaHCOg and the volume made up to 80 ml. with plasma. 



Irradiation — Two batches of solution were irradiated with doses of 2000 

 and 750 rad respectively. Within each batch, the dose rate was varied by 

 adjusting the volume of solution. Dose rates of 36 to 108 rad/min were used. 



Estimation of porphyrins — As the position of the Soret bands in the previous 

 experiment had shown some tendency to fluctuate, the full extraction method 

 as described h\ Dresel and Falk^" was used. In this method, the porphyrins 

 are finally extracted with, and read in, 15 per cent w/v HCl. This has the 

 advantage of stabilizing the position of the absorption bands to a greater 

 extent than with the aqueous solution. 



Optical densities were measured at the wavelength of maximum Soret 

 absorption (410-411 m[j.) ; the extinction coefficient was that given by 

 Dresel and Falk^-"^. 



Changes in the porphyrin molecule 



(a) Protoporphyrin — 1-6 mg protoporphyrin were dissolved in 4 ml. n 

 NaHCOg and the volume made up to 40 ml. with water. 7 • 5 ml. of this 

 solution w'eie irradiated with a dose of 3000 rad, the dose rate being 72*4 

 rad/min. 



Solutions for spectrophotometric examination were prepared as follows: 



Protoporphyrin soln. 3-5 ml. 



IOn HCl 4-1 ml. 



Water to 10-0 ml. 



Irradiated and non-irradiated solutions, prepared as above, were examined 

 in a Gary Recording Spectrophotometer. The position and strength of the 

 bands were measured from the tracing. 



(b) Ferriprotoporphyrin — 4-8 mg ferriprotoporphyrin chloride (synonym 

 haemin) were dissolved in 2-5 ml. 0-1n NaOH and the volume made up 

 to 25 ml. with water. 7-5 ml. of this solution were irradiated with 3000 rad, 

 the dose rate being 72-4 rad/min. 



Solutions for spectrophotometric examination were prepared as follows: 



Ferriprotoporpliyrin soln. 0-5 ml. 



Water 5 • 5 ml. 



Pyridine 4-0 ml. 



A 'pinch' of sodium dithionite was added to each tube immediately prior 

 to spectrophotometric examination. 



96 



