FLUORESCENCE OF CHLOROPHYLL in vitVO 1837 



chlorophyll h, by X 429 and 453 m/x, respectively. Chlorophyll a al)sorbs 

 fourteen times more quanta at 429 than at 453 m^; nevertheless, the in- 

 tensity ratio was only 1.7. Since the spectrum of fluorescence excited at 

 453 m/x indicates that only a minor part of it was due to the emission by 

 chlorophyll h (fig. 37C.23), the intensity measurements indicate that the 

 energy absorbed by chlorophyll h is made available for fluorescence of 

 chlorophyll a; the efficiency of this transfer could be estimated as 40-50%. 

 At lower concentrations (5 X 10^^ M, and 1.2 X lO"" M in each 

 component), the effectiveness of the transfer declined to 30-40% and 20%, 

 respectively. 



(/) Fluorescence of Colloidal Chlorophyll Solutions 



Table 37C.IIIB shows that Krasnovsky and Brin (1948), while con- 

 firming the nonfluorescence of most colloids and adsorbates of chlorophyll, 

 found some fluorescence in adsorbates on paraffin, palmitic acid and 

 magnesia, and strong fluorescence in colloidal solutions containing deter- 

 gents, whether prepared by dilution of alcoholic chlorophyll solutions with 

 aqueous detergents (2b), or by similar dilution of alcohofic solutions con- 

 taining alcohol-soluble proteins (3e), or by treatment of chloroplast or 

 grana suspensions wdth aqueous detergents (5d) (c/. pp. 775-777 for earlier 

 observations of weak fluorescence in some colloidal chlorophyll prepara- 

 tions). The non-fluorescence of microcrystalline chlorophyll suspensions 

 was noted above in section 3. 



(g) Fluorescence of Bacteriochlorophyll and Protochlorophyll 



The presence of two fluorescence bands, at 695 and 810 m/i, respectively, 

 in the fluorescence spectrum of bacteriochlorophyll, was noted in Part 1 of 

 Vol. II (p. 748, fig. 23.4). An interpretation of this phenomenon — if it 

 were real— could be sought in the theory of the tetraporphin spectrum 

 {cf. table 37C.I), according to which the "orange" absorption band of bac- 

 teriochlorophyll corresponds to a dipole oscillation parallel to the long axis 

 of the conjugated double bond system, while the red absorption band 

 corresponds to an oscillation perpendicular to this axis. Internal conver- 

 sion of the "parallel" into the "perpendicular" oscillation could be difficult; 

 the orange band of bacteriochlorophyll (in contrast to the blue-violet bands 

 of both chlorophyll and bacteriochlorophyll) could then have a fluorescence 

 band of its own associated ^\^th it. 



However, it seems more likely that the two-band fluorescence spectrum 

 in fig. 23.4 was obtained not with pure bacteriochlorophyll, but with a 

 mixture of bacteriochlorophyll and a green oxidation product (described 



