350 400 450 WAVELENGTH (nm) Figure 1.M) in the presence of EDTA (0.01 M ) at pH 6.4. Traces 2 and 3 were recorded after 2 and 5 min of photolysis (total time); curves 4-9 were taken after an additional 0.1, 0.5, 1.5, 3.0, 5.0, and 8.0 hr of photolysis, respectively; curve 10 was traced after the admittance of air after prolonged photolysis. Initial sample contained in a 1-cm Thunberg cuvette was deoxygenated by alternatively evacuating and admitting V2+deoxygenated argon 20X. The photolysis was carried out with a No. 1 BBA floodlight at a distance of 6 in. The cuvette was kept at 25' in a water bath.Photolysis of I1 (8 X the characteristic spectra of a 4a Photolysis of I and I11 in the presence of EDTA (0.01 M , pH 6.1, V2'-scrubbed argon atmosphere) results in their direct conversion t o the corresponding 1,5-dihydroisoalloxazines without the appearance of intermediates. In Figure 1 is presented the spectral time course for the photolysis of I1 in the presence of EDTA. Examination of the figure reveals that initial photolysis is associated with fairly tight isosbestic points (395, 362, 325, and 283 nm) which then break upon further irradiation. Spectra taken at intermediate times during the photolysis, e.g., spectrum 5, show A, , , , at 376 and 307 nm, which is in agreement with that for other 4a adducts.bv6 Admittance of air at this point gave a 98 % return of II,, based on A, , , at 435 nm. This observation is noteworthy in that other 4a adducts have required illumination in the presence of O2 to restore oxidized flavines.; Prolonged photolysis, shown in spectra 6-9, resulted in a decrease in absorbance at 376 and 307 nm and the appearance of a shoulder at 288 nm, characteristic of 1,5-dihydroflavine. Admittance of air at this point gave a 89% return of II,, showing some irreversible photolysis of the isoalloxazine nucleus. These results are consistent with an A + B + C process. Much the same results were obtained when EDTA was replaced by phenylacetic acid which has previously been established to form 4a-addition products with flavines on photolysis.6 In this case tight isosbestic points were obtained initially at 386, 361, and 321 nm which broke away on continued photolysis to yield a spectrum consistent with the production of reduced flavine. However, admittance of air provided only a 58% return of II,,. The course of photolysis of IV in the presence of EDTA is shown in Figure 2. Examination of Figure 2 reveals that the spectrum of IV gives way to that anticipated of a 4a (7) (a)
