(;. WEBER 



91 



state. The molecular deiormation caused by asymmetric vibrations 

 results in a (hange in the direction ol the oscillator of absorj)tion 

 as compared with the direction in a collection of molecules which 

 are in the zero vibrational level. In emission the two types of mole- 

 cules cannot be distinguished, since dining the lifetime of the ex- 

 citation, thermal equilibration has an ample chance of occurring so 

 that the emitting molecules are in l)oth cases a collection of mole- 

 cides predominantly in the zero level of the singlet excited state. 



Tryptophan, indole, and N-methyl indole show similar polariza- 

 tion spectra, with only minor differences between them. On the 

 other hand, N-glycyl tryptophan shows an extra polarization band 

 with a bandwidth of 10 nifx, and maximinii at 290 m^ (Fig- 7). The 



POLARIZATION SPECTRA OF N-GLYCYL TRYPTOPHAN at -70 C 

 26 



— • •propylene glycol /woter 



X X propylene glycol / 6M urea 



22 _ 



24 



20 



18 



Pl6 



14 



12 



lO 



8 



6 



4 



230 240 250 260 2X3 280 290 300 3IO 



lig. 7. Polarization spectra of N-glycyl tryptophan at — 70°C in different solvents. 



origin of this extra band is obscure. It is certain that it is not due 

 to an impinity, since it is also present in most of the tryptophan- 

 containing globular proteins so far examined. 



The variations of fluorescence polarization with concentration have 

 been studied in solutions of indole or phenol in propylene glycol 

 at — 70°C, examined in very thin layers (30 microns thickness) . 

 Examination of the concentrated solutions in these very thin layers 



