94 



tion from the ground state into the triplet. While O2 seems to 

 make the triplet unstable and promotes tlie transition of electrons 

 from the triplet into the ground state, iodide seems to have the 

 opposite effect, making the triplet stable, abolishing light emis- 

 sions and increasing the probability of the transition G -^ Ti (Fig, 

 5). Iodide acts the strongest in 10"^ M. At higher concentrations 

 it begins to acts as a salt, disturbing the water structures, rendering 

 the triplet state unstable. 



These effects of iodine are independent of its charge or binding. 

 Bound iodine, as that in 3,5-diiodo-4-hydroxyben2oic acid, had 

 the same effect in isomolar concentrations. It abolished the light 

 emission and changed the color. Tliis indicates that iodine does 

 not produce these changes by a direct chemical interaction but by 

 electromagnetic coupling. 



Thyroxine and triiodothyronine were found to act as they were 

 expected to act being compounds of iodine: they suppress the light 

 emission of riboflavine in 10'* M concentration to a great extent. 

 Their insolubility renders it impossible to apply them in higher 

 concentration. So the two hormones can also be expected to un- 

 couple oxidative phosphorylation in mitochondria in 10"^ to 10"* 

 concentration, which, as is known from the work of Lipmann and 

 Martius and their associates, they actually do. 



The quenching or stabilizing action of iodide on riboflavine is 

 not specific. Iodide equally suppresses the phosphorescent light 

 emission of rhodamin B solutions (0.0001 M) at dry ice tem- 

 perature in 10"* M concentration. This is in agreement with the 

 assumption that iodide owes its activity to its being a rather big, 

 soft, and fat ion, by which is meant that it has a great number of 

 electrons which are capable of all sorts of transitions between 

 energy levels, enabling the molecule to resonate with other mole- 

 cules. Excited electrons coming close to its nucleus may also 

 reverse their spin, owing to the high atomic number of this ele- 

 ment and the correspondingly high positive nuclear charge. 



The assumption that iodide suppressed the phosphorescence of 



