Ultraviolet reduction difference spectra

Fig. 10 (A) shows the 12 n -minus-IO ps, difference spectrum in the ultraviolet region for the [P680 O ] QA Fe -> [P680 O] QA Fe, or 0 Qa-> 0 Qa reaction. The wavelengths at which the reaction kinetics were measured for the onset of Qa reduction are marked in the figure. The onset kinetics determined from the amplitudes of absorbance changes at various times for three selected wavelengths are shown in Fig. 10 (B). At both 325 and 280 nm, arisetime of 300 100/ was obtained, in good agreement with the decay time of O in PS II particles in which Qa was originally in the oxidized state [Fig. 7 (C)].

Reduction of the porphyrin 7t-system results in a bathochromic shift and an enhancement of the extinction coefficient of the Q-band. There are characteristic differences between bacteriochlorins and isobacteriochlorins. An ultraviolet spectrum of a pyrrocorphin (15) has been described, proving earlier reports on a synthesis of this compound to be erroneous (85CC1604). 

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