113 



centration of 2 X ^0"^ -^^ So our question is: can I" affect £* in 

 concentrations of the order of 10'* M? 



It has been shown earlier that iodide strongly quenches the 

 phosphorescence of riboflavine in 10"* M. It was also indicated as 

 probable that it stabilized the triplet of this vitamin and favored 

 the direct triplet excitation. All the same, its action, in vivo, can- 

 not be limited to riboflavine, since KI is not known to affect normal 

 metabolism and the effects of its medication (if any) are more 

 general. The experiment shows that it acts on the £* of a variety 

 of substances. For instance, KI strongly quenches the yellow phos- 

 phorescence of acridine in a frozen (saturated) watery solution at 

 10~* M. Its action on quinidine is more colorful, quinidine itself 

 having a colorful behavior. As mentioned before (Chapter 5), 

 10"^ M KI greatly favors the transitory yellow phosphorescence. At 

 the temperature of dry ice 10~* M renders the whitish blue phos- 

 phorescence deep blue. At this concentration it can also lengthen 

 the lifetime, making the excitation into a long-lived one, especially 

 if the solution of the alkaloid has been "washed out" with pure 

 N2. In the fast phosphoroscope a lengthening of the lifetime, that 

 is an increased luminosity, is still noticeable in presence of 10"^ 

 yVlKI. 



KI plays no major role as a therapeutic agent any more. What 

 still lends interest to its action on £* is the fact that hormones of 

 the thyroid are iodine compounds and they play a major role in 

 the regulation of the normal energy household of our body, as well 

 as in pathological processes. Since the disturbances caused in £* 

 by iodine are independent of the charge or mode of binding of 

 this atom, we can also expect that the thyroid hormones will be 

 equally capable of disturbing £* as free iodide is and do this /"« 

 vitro in the same concentration as the equimolar I'. This point was 

 tested by comparing KI, triiodothyronine, and thyroxine. They 

 were found to have a very similar action. Owing to their insolu- 

 bility the hormones could not be applied in higher concentrations, 

 but they lengthened lifetime in 5 X 10*^ ^^- Owing to their 



