BENT LEY GLASS 837 



niediuin lias aijparenily (oiniiletely abolished the lolcled conforma- 

 tion ol the DPNH. 



The effects of striutmal analogues of DPNH arc illuminating. Re- 

 placement of the carboxamidc grouj) of the nicotinamide by an acetyl 

 group, to form an acetyl pyridine group (y\PNH) leaves the 260 m^u, 

 excitation band stronger than before. This observation, as Velick 

 suggests, seems to rule out participation of the amide group on the 

 carboxamide side-chain in the formation of the inner complex in- 

 volved in the energy transfer (but see below) . Desamino DPNH, in 

 which the amino group of adenine is replaced by — OH, shows a 

 weakening of the 260 m/x excitation band. Shifrin and Kaplan, in 

 their contribution to the Symposium, report the results of substitut- 

 ing a thioamide group for the carboxamide group. The absorption 

 maximum at 260 m^ is shifted and the 340 ni/i, band of S-DPNH is 

 similarly red-shifted. 40-50 ni/x toward the red in S-DPN. The new 

 thiocarbonyl absorption band, at 398 m/^, permits an examination of 

 the function of the carboxamide group in the intramoleculer energy 

 transfers. Shifrin and Kaplan j^ostulate H-bonding between the thione 

 S atom and the 6-amino group of adenine, as found to occur between 

 molecules of 2-mercaptothiazole. (S=i?-NH . . . S=i?-NH) . To 

 test this, a DPN analog was formed by attaching a — CHoCHoOH side- 

 chain to the adenine N adjacent to tlie adenine 6-amino group. It 

 proved unable to transfer absorbed energy at 260 m^i, to the dihydro- 

 nicotinamide moiety of the molecule. The thionicotinamide analog 

 of DPNH is very weakly fluorescent, but its absorption spectrum in 

 different solvents affords some information about the interacting 

 groups. A shoulder seen at 295 m^u, in water becomes a more pro- 

 nounced peak at 300 m^u, in propylene glycol. If, as seems probable, 

 the 300 m/x band results from an n -^ n* transition, then the postulated 

 hydrogen bond would require that a greater energy be expended in 

 the promotion of the ;? electron to the n* level. This would mean 

 a "blue shift" in the absorption band in hydroxylic solvents, exactly 

 as observed in the change from propylene glycol to water. 



When the thionicotinamide-DPNH is exposed to strong light, an 

 interesting reaction occurs. The 398 ni/x maximum absorption dis- 

 appears almost completely and a new maximum appears at 341 m^. 

 Also the 295-300 m/x absorption disappears, suggesting loss of the 

 postulated thione activity. The illumination product has no enzy- 

 matic activity, reverts to the original form in the dark, and its fluo- 



