; 



THE EFFECT OF BETA RADIATION' ()\ I'ORI'l I^'RIX C;OMPOUNDS 



DISCUSSION 



Dr. Duncan: From a theoretical point of view I should be very interested, Mr. Tirrell, 

 in whether vou have a comparison between the spectra of the haem and the por- 

 phyrin, particularly of the 'M)0 mix. downwards region, because one would have 

 expected the spectrum to show some of the iron bands in this region. I noticed you 

 used ferrous rather than ferric. I do not know whether there is a reason for this, 

 but the ferric would have been better from a theoretical point of view. 

 Mr. Tirrell: Yes, at ultra-violet range it probably would. However, for work with 

 the pyridine haemochrome, the ferric haemochromc bands are not particularly well 

 defined — and it is usual to reduce the haemochrome immediately before examination 

 with sodium dithionite, in which case the solution changes colour and the bands 

 sharpen quite markedly. 



Dr. Duncan: Is there any difierence between the haem (even in the ferrous state) 

 and the porphyrin? 



Mr. Tirrell: Yes, but it is difficult to compare the two, because normally you work 

 with pyridine for a haem and you look at protoporphyrin, for example, in strong acid 

 solution. When you look at them in, say, 0- In NaOH in both cases, the bands are 

 diffuse and they tend to wander over a range of a few millimicrons. 

 Dr. Gray: In regard to the dose-rate effect, these irradiations, as far as I could see 

 from your figures, were probably running for ten minutes up to sixty minutes. 



Mr. Tirrell: Yes, approximately. 



Dr. Gray: This seems to imply rather long-lived species, and I wondered if there 



could be any more stable species, and radicals which could produce your effect. 



For instance, if you irradiate the water or the medium and add the porphyrin, what, 



if any, effect do you get ? 



Mr. Tirrell: I have not tried that. 



Dr. Gr.\y: Something could be produced in the solution which then reacted with 



the porphyrin and this reaction rate was affecting your results. 



Mr. Tirrell: Yes, it is possible. I thought, of course, for some time of the possibility 



of peroxide formation because this seems to come up in the literature. However, 



both the work on lacto-peroxidase and also the work of Forssberg on catalase rather 



discredited the idea because in both cases the enzyme which was irradiated could 



react with any hydrogen peroxide formed. I had not thought of any other compound 



of a long-lived nature developing in the solution at all ; intuitively, I thought of the 



idea of resonance and the higher energy orbitals. I should imagine it could be quite 



easily checked by putting the porphyrin into the solution, after it had been irradiated. 



102 



