Electronic action spectroscopy spectrum

Visible and UV light sources, which excite electronic transitions, can be used also for PD spectroscopy. By scanning the frequencies of the radiation emitted from the UV/vis light source and measuring PD or electron photodetachment as a function of excitation wavelength, an electronic action spectrum can be constructed in the same way as a vibrational action spectrum is constructed using an IR source. 

In modern work the combined information of the several spectroscopies are often stored numerically. For the response of electrons, the inaccessible parts of the spectrum as well as differences in the kinds of information given by the different forms of measurements can often be reconciled by "sum rules" that constrain the total action shown by all electrons.6... 

Difference spectroscopy showed that the extract contained the hemo-proteins P-450 and cytochrome 65. Of special interest is the inhibition of 6 -hydroxylase activity by CO and the reversal of this inhibition by light, suggesting that P-450 may be involved in the reaction. In a subsequent experiment, the 6,.3-hydroxylase activity was assayed in the presence and absence of CO, and under light of various wavelengths between 400-500 m//. Reactivation of the CO inhibited enzyme was maximum at 450 mix. An action spectrum obtained from these data exhibited a maximum at 450 mu and minima at 400 and 500 m//, closely resembling the absorption spectrum of the P-450 CO complex [Voigt (62)]. It thus appears that the 6j3-hydroxylase system, like several other steroid hydroxylases, requires the participation of microsomal electron transport with P-450 as the terminal oxidase. 

Fig. 1 Infrared photodissociation action spectra in the fingerprint infrared region Irom fairly early in the modem evolution of spectroscopy of biologically interesting complex ions. These spectra illustrate the use of electrospray ion production, ion trapping mass spectrometry (Fourier-transform ion cyclotron resonance in these examples) and the FELIX free electron laser light source. Lower spectrum originally derived from [10, 11] middle spectrum frran [12] upper spectrum from [13]. Figure reproduced with permission from [12]...

An illustration of the spectroscopic emergence of a strong isolated chromophore within the interior of a substantially large protein is given by this group s spectroscopy of the cytochrome-c system. The Soret band near 410 nm is nicely observed in the [M-6H] electron photodetachment action spectrum for cytochrome-c, containing the Fe(lll) heme chromophore [136] (Fig. 14). The gas-phase peak is very close to the position observed in solution, suggesting that the chromophore is well shielded from solvent interactions in solution. 

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